U.S. patent application number 17/162857 was filed with the patent office on 2021-05-20 for patient self-monitoring of ivc volume for early heart failure warning signs.
The applicant listed for this patent is Foundry Innovation & Research 1, Ltd.. Invention is credited to Mark E. Deem, Hanson S. Gifford, III, Jeffry J. Grainger.
Application Number | 20210145405 17/162857 |
Document ID | / |
Family ID | 1000005371117 |
Filed Date | 2021-05-20 |
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United States Patent
Application |
20210145405 |
Kind Code |
A1 |
Gifford, III; Hanson S. ; et
al. |
May 20, 2021 |
Patient Self-Monitoring of IVC Volume for Early Heart Failure
Warning Signs
Abstract
Methods for patient self-monitoring of vascular lumen
dimensions, in particular in the inferior vena cava (IVC) for
determining heart failure status of a patient. Related therapy
systems as well as monitoring and therapy methods are also
disclosed.
Inventors: |
Gifford, III; Hanson S.;
(Woodside, CA) ; Deem; Mark E.; (Mountain View,
CA) ; Grainger; Jeffry J.; (Portola Valley,
CA) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Foundry Innovation & Research 1, Ltd. |
Dublin |
|
IE |
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Family ID: |
1000005371117 |
Appl. No.: |
17/162857 |
Filed: |
January 29, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15549042 |
Aug 4, 2017 |
10905393 |
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PCT/US16/17902 |
Feb 12, 2016 |
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17162857 |
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62172516 |
Jun 8, 2015 |
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62157331 |
May 5, 2015 |
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62115435 |
Feb 12, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/4836 20130101;
A61B 8/0891 20130101; A61B 5/1076 20130101; A61B 2090/3991
20160201; A61B 2090/3987 20160201; A61B 8/565 20130101; A61B 5/6882
20130101; A61F 2/01 20130101; A61B 90/39 20160201; A61B 5/4839
20130101; A61B 2090/3929 20160201; A61B 8/12 20130101 |
International
Class: |
A61B 8/08 20060101
A61B008/08; A61B 5/00 20060101 A61B005/00; A61B 5/107 20060101
A61B005/107; A61B 90/00 20060101 A61B090/00; A61B 8/12 20060101
A61B008/12; A61B 8/00 20060101 A61B008/00 |
Claims
1. A method for patient self-monitoring of fluid volume using
external ultrasound, comprising: storing a three-dimensional
ultrasound map of the patient in a detection system, said
three-dimensional map including a reference image slice
representing a monitoring location in the patient's IVC;
positioning an ultrasound probe of the detection system on the
patient, said positioning comprising-- generating a two-dimensional
image slice of the patient using the ultrasound probe, comparing
the generated two-dimensional image slice with the
three-dimensional ultrasound map; determining a position of the
generated two-dimensional slice within the three-dimensional
ultrasound map relative to the reference image slice based on said
comparing, and indicating to the patient at least one movement of
the ultrasound probe to position the ultrasound probe at the
monitoring location; and moving the ultrasound probe in accordance
with said at least one indicated movement to the monitoring
location; and measuring variation in IVC dimensions over time by
imaging opposed walls of the IVC at the monitoring location with
the ultrasound probe.
2. The method of claim 1, wherein said positioning further
comprises aligning the ultrasound probe with marks previously
placed on the patient's skin.
3. The method of claim 2, wherein said aligning comprises viewing
the marks through alignment windows on the ultrasound probe.
4. The method of claim 1, wherein the reference image slice
includes opposed walls of the IVC at the monitoring location.
5. The method of claim 1, further comprising the patient
self-securing the ultrasound probe to his/her body at the
monitoring location.
6. The method of claim 5, wherein said securing comprises attaching
the ultrasound probe to the patient with a strap around the
patient's body.
7. The method of claim 1, wherein said indicating to the patient
comprises wireless communication of the ultrasound probe with a
handheld device and delivery of directional prompts through a user
interface of the handheld device.
8. The method of claim 7, wherein the handheld device is a cell
phone.
9. A method for patient self-monitoring of fluid volume using
external ultrasound, comprising: marking a monitoring location on
the patient overlying the patient's IVC; patient self-positioning
an ultrasound emitter and receiver at the location marks;
generating, with an ultrasound system, an ultrasound image of the
patient including the IVC; automatically identifying the IVC within
the ultrasound image; automatically identifying anterior and
posterior walls of the IVC in the ultrasound image; and
continuously or periodically measuring variation in IVC dimension
over time.
10. The method for patient self-monitoring of claim 9, wherein said
patient self-positioning comprises the patient wearing a wearable
detection system.
11. The method for patient self-monitoring of claim 10, wherein the
patient self-positioning further comprises placing windows of the
wearable detection system over the location marks.
12. The method for patient self-monitoring of claim 9, further
comprising: storing a three-dimensional ultrasound map of the
patient in the ultrasound system, said three-dimensional map
including a reference image slice representing the monitoring
location in the IVC; comparing the generated ultrasound image with
the three-dimensional ultrasound map; and determine a position of
the generated ultrasound image within the three-dimensional
ultrasound map relative to the reference image slice.
13. The method for patient self-monitoring of claim 12, further
comprising: indicating to the patient at least one movement of the
ultrasound emitter and receiver to the monitoring location.
14. The method for patient self-monitoring of claim 10, further
comprising the patient self-securing the ultrasound probe to the
patient at the monitoring location.
15. A computer-based method for patient self-monitoring of fluid
volume using external ultrasound, comprising: storing a
three-dimensional ultrasound map of the patient in a monitoring
system memory, said three-dimensional map including a reference
image slice representing a monitoring location in the IVC;
self-positioning a monitoring system ultrasound probe on the
patient, said positioning comprising-- generating a two-dimensional
image slice of the patient with the ultrasound probe, comparing the
generated two-dimensional image slice with the three-dimensional
ultrasound map in a monitoring system processor communicating with
the monitoring system memory to determine a position of the
generated two-dimensional slice within the three-dimensional
ultrasound map relative to the reference image slice, indicating to
an operator through a user interface communicating with the
monitoring system processor at least one movement of the ultrasound
probe to align the generated two-dimensional image slice with the
reference image slice, and self-securing the ultrasound probe to
the patient at a monitoring position corresponding to the generated
two-dimensional image slice being aligned with the reference image
slice; and measuring variation in IVC dimensions over time by
imaging opposed walls of the IVC at the monitoring location with
the ultrasound probe while secured to the patient at the monitoring
position.
16. The method of claim 15, wherein said self-positioning further
comprises aligning the ultrasound probe with marks previously
placed on the patient's skin.
17. The method of claim 16, wherein said aligning comprises viewing
the marks through alignment windows on the ultrasound probe
housing.
18. The method of claim 15, wherein the reference image slice
includes opposed walls of the IVC at the monitoring location.
19. The method of claim 15, wherein said self-securing comprises
attaching the ultrasound probe to the patient with a strap around
the patient's body.
Description
RELATED APPLICATION DATA
[0001] This application is a continuation of U.S. Nonprovisional
patent application Ser. No. 15/549,042, filed Aug. 4, 2017, which
application is a U.S. national phase of International Patent
Application No. PCT/US16/17902, filed on Feb. 12, 2016, and titled
"Implantable Devices and Related Methods For Heart Failure
Monitoring." International Patent Application No. PCT/US16/17902
claims the benefit of priority of U.S. Provisional Patent
Application No. 62/172,516, filed Jun. 8, 2015, and titled "Methods
and Apparatus for Monitoring Patient Physiological Status Based On
Inferior Vena Cava Volume," claims the benefit of priority of U.S.
Provisional Patent Application Ser. No. 62/157,331, filed May 5,
2015, and titled "Heart Failure Monitoring System and Method," and
also claims the benefit of priority of U.S. Provisional Patent
Application Ser. No. 62/115,435, filed Feb. 12, 2015, and titled
"Implantable Device and Related Methods for Heart Failure
Monitoring." Each of these applications is incorporated by
reference herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
medical devices and methods for monitoring heart health. In
particular, the present invention is directed to methods for
patient self-monitoring of IVC volume for detecting early warning
signs of acutely decompensated heart failure.
BACKGROUND
[0003] Heart failure is one of the most significant chronic
conditions afflicting adult populations. In the United States, 5.7
million Americans have heart failure, with 870,000 new cases
annually. As the population ages, this population is growing, as
approximately 10% of the population over 80 suffers from heart
failure. It is estimated that by 2030 8 million Americans will have
heart failure. The costs of caring for heart failure are over
thirty billion dollars per year. Twenty billion of this cost is
direct medical costs. This expense is expected to more than double
over the next fifteen years.
[0004] In patients with chronic heart failure, a significant
portion of these costs is due to hospitalization to manage acutely
decompensated heart failure (ADHF). Each re-hospitalization can
last up to a week, and costs approximately $10,000. ADHF is very
often a result of some combination of a downturn in the heart's
performance and excessive intake of fluids and/or salt. This leads
to a buildup of fluid in the vascular system. Increased blood
volume in the left atrium at higher pressure means higher blood
pressure in the lungs, which eventually leads to fluid filling the
lungs and an inability to breathe. At this stage it is imperative
to hospitalize the patient to carefully manage them while drugs are
delivered to remove the excess fluids.
[0005] Managing these patients to prevent the need for
re-hospitalization is extremely challenging. Many non-invasive
approaches to monitoring patients have been tried, such as weighing
patients daily to detect fluid weight gain, having a nurse call
them daily to assess their health status, and so on. More recently,
various implantable monitoring devices have been tested. One
example is the "CardioMEMS" device of St. Jude Medical, Inc., which
is a wireless pressure monitor implanted in the pulmonary artery
(PA). An external power supply and receiver is placed on the
patient's chest to charge the implanted sensor and receive pressure
data measured by it. Other companies are developing their own
versions of such PA pressure monitors. The money saved by avoiding
re-hospitalization can more than pay for the cost of such
devices.
[0006] It is important to measure the onset of ADHF early enough to
give the patient and/or caregiver enough time to adjust their
behavior, medication, or other factors to prevent the patient from
ending up with frank congestion and the need for hospitalization.
FIG. 47, adapted from the CardioMEMS website, shows the timeline of
physiologic changes leading up to ADHF requiring hospitalization.
There is clinical evidence that IVC volume variation changes occur
up to several weeks prior to decompensation.
[0007] In addition to heart failure patients, hemodialysis patients
have a chronic need for careful volume management. Large volumes of
fluid are involved in the hemodialysis process, and managing
patients so that they don't end up hypovolemic or overloaded with
fluid requires careful management. A monitor which provided
immediate feedback on these patient's volume status before, during
and after hemodialysis would be very helpful.
[0008] There are other groups of patients who might benefit from
such a monitor. For example, patients in septic shock or occult
shock due to trauma are subject to hypoperfusion which can be
identified by measuring the degree of collapse of the IVC. While it
may or may not make sense to implant a device permanently to manage
these acute events, if the patient has recurrent episodes of these
events or already has such a monitor implanted for other reasons,
the IVC monitor may be helpful in managing these patients.
[0009] Congestive heart failure is so-named because additional
blood volume backing up into the lungs causes fluid to seep out of
the pulmonary circulation into the airway passages of the lungs,
causing congestion of the lungs. The patients become short of
breath, and typically need to be hospitalized and carefully managed
while the excess fluid is removed by a combination of fluid
management and aggressive use of diuretic medications.
[0010] This happens because the left ventricle is not able to pump
all of the volume of blood returning to the heart from the lungs.
Although measurement of left atrial pressure, typically by
measuring pulmonary artery wedge pressure, is commonly considered
the most direct way to measure congestion in heart failure, there
are other areas where congestion can be detected. When additional
blood volume is added to the circulatory system, the IVC is one of
the first places for that added volume to collect. To quote a
paper, "In patients with advanced heart failure, left ventricular
systolic dysfunction causes increased left atrial pressure. The
pressure is transmitted back through the pulmonary circulation to
cause pulmonary artery hypertension. The pulmonary artery
hypertension can worsen pre-existing right ventricular dysfunction
and exacerbate tricuspid valve regurgitation, leading to systemic
venous congestion. If venous congestion and elevated central venous
pressure are the hallmarks of heart failure, then distention of the
inferior vena cava [measured by echocardiography] may be a good
prognostic marker in patients with decompensated heart failure."
(Lee et al, "Prognostic significance of dilated inferior vena cava
in advanced decompensated heart failure," International Journal of
Cardiovascular Imaging (2014) 30:1289-1295).
[0011] The diameter of the IVC has also demonstrated correlation
with right atrial pressure, and it may correlate with renal
function and renal sodium retention, which are also very important
prognostic factors of heart failure. Therefore, increasing IVC
volume and/or pressure may be a very effective early indicator of
worsening heart failure condition.
[0012] However, recent studies have indicated that the variation in
IVC volume over the respiratory cycle is a more sensitive
measurement of fluid overload and/or heart failure than simple
measurement of average IVC volume, diameter, or pressure. During
inspiration, intrathoracic pressure decreases, thereby increasing
venous return and causing collapse of the IVC. During expiration,
intrathoracic pressure increases, decreasing venous return and
causing an increase in the volume of the IVC.
[0013] Since the IVC typically collapses in the anterior-posterior
direction, some studies have suggested that the most accurate
technique for measuring IVC volume changes with ultrasound is to
measure the distance from the anterior wall of the IVC to the
posterior wall.
[0014] In applying this measurement to heart failure, at least one
study has suggested that a variation of less than 15% (measured as
maximum anterior-posterior dimension minus minimum A-P dimension,
divided by the maximum A-P dimension) is indicative of impending or
present ADHF.
[0015] While vessel dimensions may be measurable using external
ultrasound, magnetic resonance imaging, computerized axial
tomography, or other technologies, these imaging procedures must be
administered in a hospital or other specialized facility, do not
permit continuous monitoring, and do not allow for monitoring of
the patient at their home or other remote location. As a result,
the condition of a heart failure patient can worsen into a critical
state before care providers become aware of it, dramatically
increasing the mortality risk and cost of treatment for the
patient.
[0016] Prior studies of IVC dimensions without implantable devices
have been conducted using ultrasound imaging. This typically
requires a highly trained physician or ultrasound technician to
manage the ultrasound machine, ensure an appropriate connection of
the transducer to the skin, position the ultrasound transducer in
the appropriate location, identify the IVC, and take accurate
measurements. This is not something that heart failure patients or
their caregivers could typically be trained to do predictably and
accurately with existing equipment. Moreover, these systems
typically include large, complex, and expensive pieces of equipment
which are not suitable for use outside of a specialized medical
facility.
[0017] As is understood in the art, there is a long history of
implantable vena cava filters to catch clots which embolize from
the leg veins, catching them and holding them in the vena cava
until they dissolve in the blood flowing past. The widespread
clinical use of such IVC filters demonstrates the safety and
feasibility of anchoring an implant in the IVC and provides useful
teachings as to how aggressively IVC anchors may be shaped, how
much radial force a device should exert, how strong the elements
should be, etc. However, in spite of the widespread use of IVC
filters over many years, heretofore it has not been suggested that
an implant in the IVC could be utilized for purposes of monitoring
fluid volume or IVC dimensions. Moreover, even if a suggestion were
made to equip an IVC filter with a sensor for monitoring vascular
dimensions, such filters would be unsuited to the purpose. The
anchoring structures used to secure IVC filters constrain the
vessel from natural size and shape changes in response to changes
in fluid volume and would thus limit the usefulness or accuracy of
such a device.
SUMMARY OF DISCLOSURE
[0018] Embodiments disclosed herein include an implantable device
for monitoring vascular lumen diameter, comprising means for
detecting lumen diameter at a monitoring location; an anchor
element configured to securely anchor the device to the vascular
lumen at an anchoring location with the detecting means positioned
at the monitoring location; and an anchor isolation structure
extending between the detecting means and anchor element, the
anchor isolation structure having a shape and length specifically
configured to substantially isolate the detecting means at the
sensing location from distortions of the vessel caused by the
anchoring element at the anchoring location.
[0019] In one implementation, the present disclosure is directed to
a method for patient self-monitoring of fluid volume using external
ultrasound. The method includes storing a three-dimensional
ultrasound map of the patient in a detection system, the
three-dimensional map including a reference image slice
representing a monitoring location in the patient's IVC;
positioning an ultrasound probe of the detection system on the
patient, the positioning comprising generating a two-dimensional
image slice of the patient using the ultrasound probe, comparing
the generated two-dimensional image slice with the
three-dimensional ultrasound map; determining a position of the
generated two-dimensional slice within the three-dimensional
ultrasound map relative to the reference image slice based on the
comparing, and indicating to the patient at least one movement of
the ultrasound probe to position the ultrasound probe at the
monitoring location; and moving the ultrasound probe in accordance
with the at least one indicated movement to the monitoring
location; and measuring variation in IVC dimensions over time by
imaging opposed walls of the IVC at the monitoring location with
the ultrasound probe.
[0020] In another implementation, the present disclosure is
directed to a method for patient self-monitoring of fluid volume
using external ultrasound. The method includes marking a monitoring
location on the patient overlying the patient's IVC; patient
self-positioning an ultrasound emitter and receiver at the location
marks; generating, with an ultrasound system, an ultrasound image
of the patient including the IVC; automatically identifying the IVC
within the ultrasound image; automatically identifying anterior and
posterior walls of the IVC in the ultrasound image; and
continuously or periodically measuring variation in IVC dimension
over time.
[0021] In yet another implementation, the present disclosure is
directed to a computer-based method for patient self-monitoring of
fluid volume using external ultrasound. The method includes storing
a three-dimensional ultrasound map of the patient in a monitoring
system memory, the three-dimensional map including a reference
image slice representing a monitoring location in the IVC;
self-positioning a monitoring system ultrasound probe on the
patient, the positioning comprising generating a two-dimensional
image slice of the patient with the ultrasound probe, comparing the
generated two-dimensional image slice with the three-dimensional
ultrasound map in a monitoring system processor communicating with
the monitoring system memory to determine a position of the
generated two-dimensional slice within the three-dimensional
ultrasound map relative to the reference image slice, indicating to
an operator through a user interface communicating with the
monitoring system processor at least one movement of the ultrasound
probe to align the generated two-dimensional image slice with the
reference image slice, and self-securing the ultrasound probe to
the patient at a monitoring position corresponding to the generated
two-dimensional image slice being aligned with the reference image
slice; and measuring variation in IVC dimensions over time by
imaging opposed walls of the IVC at the monitoring location with
the ultrasound probe while secured to the patient at the monitoring
position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] For the purpose of illustrating and exemplifying the claimed
invention, the drawings show aspects of embodiments of the present
disclosure. However, it should be understood that the claimed
invention is not limited to the precise arrangements and
instrumentalities of the exemplifying embodiments shown in the
drawings, wherein:
[0023] FIG. 1 is a schematic illustration of one embodiment of an
implantable device deployed in the inferior vena cava (IVC) in
accordance with the present disclosure.
[0024] FIGS. 2A, 2B, 2C and 2D show schematic cross-sections of the
IVC and relative electrode positioning in embodiments described in
the present disclosure.
[0025] FIG. 3 is a schematic illustration of one disclosed
embodiment of an implantable device, showing its placement in the
vasculature.
[0026] FIG. 4 is a schematic illustration of another disclosed
embodiment of an implantable device, showing its placement in the
vasculature.
[0027] FIG. 5 is a perspective view of a further alternative
embodiment positioned in a partially cross-sectioned portion of the
IVC.
[0028] FIG. 6 is side view of the embodiment shown in FIG. 5 and
the partially cross-sectioned IVC.
[0029] FIG. 7 is an end view of the embodiment of FIG. 5 as viewed
in the IVC from the superior aspect.
[0030] FIG. 8 is an end view of the embodiment of FIG. 5 as viewed
in the IVC from the inferior aspect.
[0031] FIG. 9 is a detail of the anchor element of the embodiment
of FIG. 5 in a collapsed configuration.
[0032] FIG. 10 is a detail of the anchor element of the embodiment
of FIG. 5 in an expanded or deployed condition, shown outside the
IVC.
[0033] FIGS. 11 and 12 are perspective views illustrating a further
alternative embodiment of anchoring elements, in deployed and
collapsed configurations, respectively.
[0034] FIG. 13 is a perspective view illustrating the embodiment of
FIGS. 11 and 12 as it may appear deployed within the IVC (note that
for illustration purposes the orientation is not intended to be
anatomically accurate in this or similar figures).
[0035] FIGS. 14 and 15 are perspective views illustrating yet
another alternative embodiment of an anchor element, in the
collapsed and deployed configurations, respectively.
[0036] FIG. 16 is a perspective view illustrating the embodiment of
FIGS. 14 and 15 as it may appear deployed within the IVC.
[0037] FIG. 17 is a side view illustrating another alternative
embodiment of an implantable IVC monitor with a stent-like anchor
element and electronics capsule.
[0038] FIGS. 18 and 19 are perspective views illustrating a further
embodiment of an anchor element shown in the collapsed and
expanded/deployed configurations, respectively.
[0039] FIGS. 20 and 21 are perspective views illustrating the
embodiment of FIGS. 18 and 19 as it may appear deployed within in
IVCs of different dimensions.
[0040] FIG. 22 is a schematic illustration of a further embodiment
of implantable device positioned in the IVC according to the
present disclosure.
[0041] FIG. 23 is a schematic illustration of yet another
embodiment of implantable device positioned in the IVC according to
the present disclosure.
[0042] FIG. 24 is a schematic illustration of a further embodiment
of implantable device according to the present disclosure.
[0043] FIG. 25 is a schematic illustration of a further embodiment
of implantable device positioned in the IVC according to the
present disclosure.
[0044] FIG. 26 is a schematic illustration of another embodiment of
implantable device positioned in the IVC according to the present
disclosure.
[0045] FIGS. 27A and 27B are schematic illustrations of a further
embodiment of implantable device according to the present
disclosure.
[0046] FIGS. 28A, 28B and 28C are a series of schematic
illustrations showing delivery and placement of an embodiment of a
device configured for external placement on the IVC according to an
alternative of present disclosure.
[0047] FIG. 29 illustrates another alternative device embodiment
deployed in the IVC [1A-005].
[0048] FIG. 30 schematically depicts an alternative embodiment of a
system described in the present disclosure.
[0049] FIG. 31 schematically depicts an embodiment for detection of
markers in a deployed device using ultrasound.
[0050] FIG. 32 schematically depicts an arrangement of markers and
two sensors on a transverse cross-section of the body in a system
according to one disclosed embodiment.
[0051] FIG. 33 schematically depicts another alternative embodiment
of a system described in the present disclosure.
[0052] FIG. 34A illustrates placement or injection of a marker
between the medial and adventitial layers of the wall of the IVC
according to one exemplary embodiment disclosed herein.
[0053] FIG. 34B illustrates delivery and adherence of a marker to
the outer surface of the wall of the IVC in another exemplary
embodiment disclosed herein.
[0054] FIG. 35 illustrates another exemplary embodiment in which a
marker is deployed through a delivery catheter that holds the
marker between two jaws until it reaches the distal end of the
delivery catheter, at which point the jaws separate to release the
marker.
[0055] FIG. 36A illustrates an embodiment of a guidewire coil.
[0056] FIG. 36B illustrates a guidewire coil coated with a polymer
to permanently entrap air to provide echo-reflective
characteristics.
[0057] FIG. 36C is a close-up or enlarged view of a section of a
coiled ribbon marker with surface texture configured to increase
echo-reflectivity.
[0058] FIG. 36D illustrates another embodiment of a marker, which
may comprise a simple echo-reflective tube such as a sealed tube of
air.
[0059] FIG. 36E illustrates another embodiment of a marker, in this
case a tube of cast polymer such as silicone with echo-reflective
gas bubbles embedded in the tube wall.
[0060] FIGS. 37A, 37B and 37C illustrate various embodiments of
markers formed as particles in accordance with alternative
embodiments disclosed herein.
[0061] FIG. 38 is an enlarged view of a further exemplary
embodiment of a marker as disclosed herein comprising a gel mixed
with marker particles injected into the wall of the IVC.
[0062] FIG. 39A is a cross-sectional view of a particle/marker
containing patch endothelialized into the IVC wall.
[0063] FIG. 39B is a cross-sectional view of an alternative marker
patch utilizing a "Velcro-like" texture of microneedles or
microhooks to adhere to and embed into the IVC wall.
[0064] FIG. 40A illustrates balloon delivery of one or more markers
in accordance with a further alternative embodiment disclosed
herein.
[0065] FIG. 40B illustrates another alternative embodiment in which
a two-balloon catheter is used such that blood flow may be
maintained during marker delivery and placement.
[0066] FIG. 41 illustrates an exemplary embodiment of an external
transmitter/receiver configured to provide more consistent and
precise measurements of relative distance between IVC two markers
as described herein.
[0067] FIG. 42 schematically depicts another alternative system
employing communicating monitoring and therapeutic devices.
[0068] FIG. 43 schematically depicts a further alternative system
employing direct communication through the IVC wall.
[0069] FIG. 44 schematically depicts yet another alternative system
employing intravascular leads for direct communication.
[0070] FIG. 45 illustrates one exemplary embodiment of a pulmonary
artery sensor being implanted by a delivery catheter in the
pulmonary artery following implantation of an IVC monitoring device
in the IVC.
[0071] FIG. 46 is a block diagram illustrating embodiments for
communication and computerized implementation of various
embodiments described herein.
[0072] FIG. 47 illustrates a typical timeline of symptoms leading
to hospitalization for ADHF.
DISCLOSURE OF EMBODIMENTS
[0073] Various embodiments disclosed herein are intended to monitor
for and detect variations in volume and/or pressure of the inferior
vena cava (IVC) as an early warning signal of the acute severity of
heart failure. Implantable IVC monitors, markers and related
systems, devices and methods as described herein may enable the
patient and physician to take proactive steps in time to prevent
acute decompensation requiring hospitalization. Such devices and
methods also may be helpful in managing hemodialysis patients, in
whom volume management is a chronic challenge. The present
disclosure thus describes methods and devices for measuring IVC
volume and/or pressure more or less continuously, depending on
clinical need, using various forms of implantable devices.
[0074] In order to measure changes in IVC dimension or volume
accurately, the devices of the invention must be configured to be
secured at the desired location in or on the vessel without
affecting the natural dilation and constriction of the vessel, or
by affecting it in a way which is known and predictable so that it
can be accounted for. In many of the embodiments disclosed herein,
implantable monitoring devices include an anchoring member which
secures the device to the vessel and immobilizes the device both
longitudinally and rotationally, and a sensing or marking element
which responds to vessel expansion and contraction to allow
monitoring of changes in vessel dimension. It is critical in such
embodiments that the anchoring element not distort the vessel
dimensions being measured by the sensing/marking element. In
preferred embodiments, the sensing or marking element is isolated
from the anchoring member such that the vessel can naturally expand
and contract at the site of measurement without significant
constraint. In some embodiments, this isolation comprises a
longitudinal separation of the sensing/marking element from the
anchor member a distance sufficient to minimize the effects of the
anchor on the vessel motion at the measurement site. In such
embodiments the sensing/marking element will be coupled to the
anchor member by an elongated connecting element which has a length
and flexibility sufficient to provide the necessary isolation,
which has sufficient rigidity to maintain the position of the
sensing/marking element at the measurement site, and which, in many
embodiments, has the appropriate shape and resilience to bias the
sensing/marking element against the wall of the vessel as it moves
inward and outward. Such connecting elements will also have a
length selected to allow the anchor member to be implanted in the
desired location in the IVC, in preferred embodiments just inferior
to the hepatic veins, with the sensing/marking element positioned
in the IVC between the anchor member and the right atrium. In
certain exemplary embodiments, such connecting elements will have a
length in the range of 1 to 4 times the vessel diameter (e.g. 1-8
cm), more desirably 1 to 3 times the vessel diameter (e.g. 2-6 cm),
and preferably 1 to 2 times the vessel diameter (e.g. 2-4 cm). In
some embodiments it will be desirable to provide a longitudinal
separation between the anchor element and the marker elements of
about 3-5 cm. Also, it may be desirable to position the anchor
elements somewhat inferior to the renal arteries so that the marker
elements fall between the renal and hepatic veins. In one preferred
embodiment, the marker elements are positioned at a monitoring
location falling in a region from approximately 2 cm below the
hepatic veins down to, but not below the renal veins. In other
embodiments, instead or in addition to spatial separation of the
anchor and sensor/marker, isolation may be achieved by a mechanical
coupling between the anchor and the sensing/marking element which
mechanically isolates movement of the sensing/marking element from
the anchor, such as a spring, hinge, flexible link, or other type
of isolating coupling.
[0075] Because heart failure patients often receive catheters for
monitoring and treatment which are inserted through the IVC,
preferred embodiments of the invention will be configured to allow
the placement of catheters and other devices past the location of
the implanted monitoring device without risk of displacement or
compromising its function. In some embodiments, the devices of the
invention are configured to be anchored to the vessel wall without
jailing (i.e. extending across) or substantially occluding the
vessel lumen.
[0076] In certain embodiments described herein the monitoring
devices of the invention are configured to measure vascular
dimension in a predetermined direction or along a predetermined
axis. Such embodiments are configured to facilitate implantation
within the vessel in a position which enables such directional
measurement. In exemplary embodiments, the devices of the invention
are configured to measure IVC diameter in the anterior-posterior
direction. In such embodiments the devices are configured to
preferentially position and maintain the sensing or marking
elements against the posterior and/or anterior wall of the IVC
throughout the respiratory cycle. Exemplary embodiments may further
include anchoring elements that deploy in such a way as to
preferentially position the device in the desired rotational
position in the vessel. For example, such anchoring elements may
have a shape or include features which take advantage of the oval
cross-sectional shape of the IVC and naturally seat themselves in
the desired rotational orientation.
[0077] One type of device disclosed herein, as shown, for example,
by the embodiment in FIG. 1, may have flexible marker elements,
such as flexible electrodes, that lay unobtrusively against the
wall of the IVC. Various embodiments of this type of device are
described in more detail below. As the marker element positions
change relative to one another based on changes in shape/volume of
the IVC, the change may be determined through signals or feedback
exchanged between the marker elements. For example, as the IVC
decreases in volume, it may go from being fully inflated with a
round shape to a flatter shape. In a design with a number of marker
elements deployed circumferentially around a cross-section of the
IVC, this means that certain marker elements may become closer
together as the IVC collapses, and some may move farther apart.
FIGS. 2A, 2B, 2C and 2D schematically illustrate how this change
may occur. As is seen, the variation in proximity of the marker
elements with IVC collapse depends upon the orientation of the
device relative to the axis of collapse of the IVC. In FIGS. 2A and
2B, it is seen that marker elements a and c become closer as the
IVC collapses, while marker elements b and d move farther apart. In
FIGS. 2C and 2D, marker elements a and b and c and d become closer
as the IVC collapses. Alternatively, a single marker element may be
provided with a signal type that may be reflected off of the
opposite IVC wall. The same principals apply when a single marker
element is used with a signal reflected off the opposite IVC wall.
In one such example, the single marker element may be positioned at
location a in FIGS. 2A and 2B, with the reflected wall being
generally at location c, directly across from a.
[0078] In general, marker elements used in embodiments disclosed
herein may be active marker elements or passive elements. Examples
of active marker elements include ultrasound transducers,
electrodes and inductance coils. Passive marker elements are
generally signal reflective, such as echo-reflective, which can
reflect an ultrasound signal directed at the marker elements from
outside the body. In an embodiment where the market elements are
comprised of electrodes, it may be most effective to determine
which electrodes are positioned most directly on the anterior and
posterior walls, and to measure the variation in impedance between
those electrodes. Alternatively, the system could measure the
impedance from each electrode to each of the others, and to use the
variation in impedances to estimate the change in shape. Or it may
be equally effective to combine the impedances of all of the
opposing electrode pairs in parallel, and look at the variation in
that single overall impedance reading.
[0079] In certain situations it may alternatively or also be
effective to measure the longitudinal impedance along the length of
the IVC or the superior vena cava (SVC), or both. As the IVC and/or
SVC collapses, the cross-sectional area of the IVC and SVC
decreases, which may lead to a meaningful change in impedance along
its length. One exemplary embodiment employing this alternative is
illustrated in FIG. 35 as described below.
[0080] In addition to simply measuring impedance across the IVC by
use of implantable, flexible electrodes, there are a number of
other ways by which an implantable device may measure the variation
in shape of the IVC. Such further alternatives include elements
such as strain gauges or displacement sensors attached to a radial
or circumferential element of the device, proximity sensors, etc.
One exemplary embodiment in this regard is illustrated in FIG. 24
as described below.
[0081] Fluid pressure sensors may also be useful in measuring
variations in IVC status. Alternatively, the flow rate through the
IVC might be measured using a Doppler ultrasound sensor or other
sensor. As the volume and cross-sectional area of the IVC change,
the speed of blood flow through the IVC might change inversely and
proportionately, although blood volume and flow will also change
with changes in posture, exercise level, and so on. In this
approach, it might be helpful to measure heart rate as well as an
indicator of cardiac output, to normalize flow rates or to make
certain that measurements are only being taken when the patient is
at rest. Inertial sensors might also be included, to measure
posture and motion. MEMS inertial sensors have been developed which
are tiny and consume very little battery power. It might also be
helpful to implant a reference pressure sensor or inertial sensor
elsewhere in the body or vascular system, such as in the leg, to
detect posture changes and activity level.
[0082] A further alternative measurement means is to use
sonomicrometry. This involves tiny piezoelectric crystal sensors
which emit tiny sonic signals, which are then detected by other
sensors and converted to an electrical signal. By analyzing the
time between the transmission and reception of these signals, the
distance between the crystals can be accurately measured. A further
alternative measurement means is to transmit a sonic vibration into
the IVC, and by measuring the reflection or resonance of that
signal, the overall volume or dimensions of the IVC might be
determined.
[0083] The choice between these different methods will depend in
part on determining which ones measure the variation in IVC volume
and pressure most consistently and precisely. Minimizing energy
consumption is also an essential factor for implantable devices
which are intended to function for years, unless external power
sources are used to power or re-charge the device.
[0084] In alternative embodiments, one or more devices may be
implanted on an external surface of the IVC to detect changes in
vascular dimensions. For example, a single device having two
spaced-apart electrodes, or two separate devices each with its own
electrode, may be anchored to the outer IVC wall and used to
measure impedance between the electrodes. Alternatively, a device
having a strain gauge may be anchored to the outer wall to measure
stress, strain, or displacement between two points on the wall. In
another embodiment, a wire loop or band incorporating a force or
displacement sensor may be placed around the IVC to detect changes
in IVC circumference based upon the change in size or tension in
the loop or band. Such devices may be miniaturized so as to be
delivered using a large-bore needle or other low-profile delivery
instrument that can be placed through a small puncture in the
thoracic or abdominal wall and delivered to the desired location on
the IVC.
[0085] This monitoring may be performed continuously or
intermittently, depending upon the desired tradeoff between data
intensity and battery life. It might be most efficient to take
measurements only at night, when the patient is lying down and at
rest. It might be desirable to intermittently measure IVC
dimensions at random, or at specific time intervals. Although these
intermittent measurements might result in measuring the IVC
distention at random points in the cardiac and respiratory cycle,
over a period of minutes, hours, or days an effective picture of
the IVC variation may become clear. Alternatively, the device may
intermittently take continuous measurements over one or more entire
cardiac and/or respiratory cycles, to get an effective measurement
of the maximum and minimum IVC volumes. The difference between
those minimum and maximum volumes may be an important prognostic
indicator. If there is only a small variation between minimum and
maximum IVC volumes, that may be an indicator of congestion.
[0086] Exemplary embodiments shown in the figures will now be
described in more detail to further illustrate various
configurations and designs of the disclosure. As will be apparent
to persons of ordinary skill in the art based on the teachings
herein contained, different features of the various disclosed
embodiments may be employed with embodiments other than those with
which they are specifically shown in the drawings for purposes of
illustration. Given the number of possible combinations, it is not
possible within a concise disclosure to separately illustrate each
combination of features as would be understood by those skilled in
the art. As non-limiting examples, each of the different anchor
elements shown in FIGS. 5-21, and the marker elements shown in
FIGS. 1, 3-5, 22-30 may be used together in different combinations
or individually with each different implant herein.
[0087] As shown in FIG. 1, monitoring device 100 may have several
flexible, insulated arms 103 that lay passively against the wall W
of the IVC. Marker elements 106 (referred to hereinafter
generically as marker elements or by specific marker element type,
such as electrode, coil or ultrasound element, etc.) may be mounted
on arms 103, preferably at an end spaced from the body of device
100. In one exemplary embodiment, marker element 106 comprise
electrodes 106 mounted on arms 103, and the impedance between the
electrodes may be monitored via suitable monitoring devices and
means as described further below. There may be as few as two,
three, or four electrodes 106, or there may be many. There also may
be more than two arms 103. If there are just two arms 103, they may
generate the most effective measurements if positioned against the
anterior and posterior walls of the IVC. Electrodes 106, or other
marker element, may be arrayed circumferentially around the IVC at
one specific cross-section, or there may be electrodes at two or
more specific cross-sections, or they may be arranged over the
length of the IVC. Impedances may be measured in a matrix between
all of the different electrodes, or the system may focus on
measuring impedances just between electrodes on opposing walls, to
measure any collapse of the IVC most efficiently.
[0088] Alternatively, instead of measuring impedance between
electrodes, marker elements 106 may comprise inductance coils that
may be located at the ends of arms 103 of device 100 in FIG. 1. A
small current could be delivered to one coil, and the induced
current in the other coil could be measured to determine the
distance between the coils.
[0089] A further alternative embodiment comprises positioning two
ultrasound crystals as marker elements 106 on opposing arms 103 of
device 100. An ultrasonic signal from one crystal could then be
detected by the opposing crystal, and the diameter of the IVC could
then be determined by measuring the time-of-travel between the two
crystals. Alternatively, and as described further below, a single
ultrasound crystal could be positioned on a single arm of the
device with the crystal acting as both emitter and receiver of an
ultrasound signal such that vessel diameter could be determined by
reflecting a signal against the opposing wall of the vessel and
measuring time of travel back and forth from the crystal.
[0090] Device 100 may be located entirely within the IVC as shown
in FIG. 1. In this exemplary embodiment, device 100 is held in
place by anchor element 109, comprising a radially expanding stent,
which has hooks 112 that engage the IVC wall W. Multiple arms 103
extend superiorly along the IVC, and are biased gently outwards to
hold themselves against the IVC wall W. At the end of arms 103 are
marker elements 106, which may be electrodes as described above.
Device 100 senses changes in impedance between the marker element
electrodes to measure the degree of distention or collapse of the
IVC. Alternatively or in addition, device 100 may also include arms
103 extending inferiorly, holding another set of marker elements
106 against the IVC wall W in a more inferior position, which can
also be used to determine the variation in IVC size. Anchor element
109, such as the illustrated radially expanding stent, may be made
gentle enough so as to not prevent the distention or collapse of
the IVC. In that case, marker elements 106 (here illustrated as
electrodes) may be mounted directly on the anchoring element
itself. Various similar embodiments disclosed herein, may be
important to encapsulate the structure and arms of the device in an
electrically insulative material, so that it doesn't prevent the
measurement of IVC cross-section via impedance measurements.
[0091] In a further alternative, anchor element 109 (such as, for
example, the stent shown in FIG. 1 or in FIG. 23) and/or arms 103
may be made of a bioerodable material which softens over time, to
minimize any effect the structure might have on the natural motion
of the IVC. The structure of arms 103 (or anchor element 109) may
also be designed to aggressively heal into the walls of the IVC, to
minimize the risk of migration or embolization over time. Such
alternatives may also be combined, for example, by making the
anchor element or arms out of a bioerodable material such as
poly-1-lactide (PLLA) and covering the struts of the device with a
woven or braided polyester sleeve or open-cell expanded
polytetrafluorethylene (ePTFE). As the struts erode over time, they
will stimulate a somewhat inflammatory response which will
encourage the fabric to heal into the wall, so that by the time the
PLLA structure is gone, the device will be well-healed into the
wall.
[0092] The IVC is large enough that a low-profile electronics
control housing, such as capsule 118 in FIG. 1, can be located on
an implantable device such as device 100 without meaningfully
occluding blood flow through the IVC. Such an electronics capsule
also may be configured and dimensioned to be entirely positioned
against the walls of the IVC, so that the central channel of the
IVC remains open and unimpeded for the introduction of any other
catheter in the future. Electronics capsule 118 may have either a
battery or inductive coil or both to power the device.
Alternatively, or additionally, the device may be designed to
harvest energy from local environmental sources by including, for
example, a piezoelectric generator to produce power from the
pulsation of the heart. In addition, the electronics capsule will
have connections to the marker elements and a telemetry circuit to
communicate information to a controller unit (not shown) outside
the patient's body. Preferably the device includes a wireless
transmitter to transmit sensor data to an external receiver and
controller. The device may be configured to transmit continuously
or at programmed intervals, or to transmit data upon interrogation
by an external device. It may also have a memory circuit to store
historical sensor measurements, and a calculation circuit to
convert the various sensor measurements to an estimate of IVC
distention or collapse. Additionally or alternatively, the device
may be configured to communicate with a wireless-enabled cellular
device such as a smartphone, which may include software to transmit
data via cellular or wireless network to a remote computer. In this
way, the measured IVC parameters may be automatically transmitted
to healthcare providers to allow monitoring of the patient's
condition. More details of related control and networking
embodiments are discussed below.
[0093] Device 100, as illustrated in FIG. 1, is shown positioned
largely superior to the renal veins within the IVC. However,
implantable devices as disclosed herein also may be positioned
partially or entirely inferior to the renal veins, or even within
the right atrium or the superior vena cava (SVC). Alternatively the
devices may have multiple components implantable in different
locations, such as one component in the IVC, and a second component
in the SVC or elsewhere.
[0094] In an alternative embodiment, device 300 may have a
secondary element 321 that deploys portions of the device within
the vascular system much closer to a point of insertion, or at
another location more easily accessed (for physical access or
energy transfer), as shown in FIG. 3. In this embodiment, device
300 includes IVC sensing unit 323 (which may be generally
configured including anchor element(s) and marker element(s) as
described with respect to other embodiments disclosed herein), with
secondary element 321 located remotely from the sensing unit 323,
and lead 329 connecting and providing communication between the two
units. For example, an antenna element for telemetry and/or an
inductive coil may be placed in secondary unit 321 in the
subclavian vein or jugular vein. This would make it much easier to
accurately position an external power source and/or controller
antenna 332 close to the antenna or inductive coil contained within
secondary unit 321. The secondary unit 321 may be held in place,
for example, using a self-expanding stent or other intraluminal
anchor element as described herein.
[0095] Alternatively, an implantable device according to the
present disclosure may have an implantable battery and circuitry
that can be implanted within the body, but outside of the vascular
system as shown in FIG. 4. Device 400 comprises IVC sensing unit
423 (which also may be generally configured as described with
respect to other embodiments disclosed herein) and implantable
controller/battery unit 426 connected to sensing unit 423 by lead
429 providing communication there between. There are similarities
between placement of device 400 and the common placement of
pacemakers and defibrillators in an infra-clavicular pocket.
However, unlike those common devices, lead 429 between the IVC
sensing unit 423 and placement location of controller/battery unit
426 would not need to traverse any heart valves, which may make it
a relatively safe and simple connection. Alternatively, IVC sensor
423 may be adapted to connect to a pacemaker or defibrillator,
including additional leads providing sensing and stimulation of the
heart, for example, as described below in connection with the
embodiment of FIG. 45.
[0096] A further exemplary embodiment is shown in FIGS. 5-10. As
shown therein, device 500 comprises three major components or
assemblies, electronics capsule 503, anchor element 506 and anchor
isolation structure 507 connecting the electronics capsule and
anchor element. Electronics capsule 503 comprises a sealed housing
509 for containing control, power and other alternative functional
modules as elsewhere described herein to provide a self-contained,
sealed device. Capsule 503 also provides support for marker element
512, which in the case of device 500 is a single ultrasound marker
element positioned at the inferior end of the device. Such a marker
element may utilize one or more ultrasound crystals to measure IVC
diameter by emitting an ultrasound pulse, and then detecting the
reflection of that pulse from the opposing wall of the IVC. Other
modes of detection with ultrasound receivers and/or other marker
element types as described herein may be alternatively employed by
persons of ordinary skill without departing from the teachings of
this disclosure. Electronics capsule 503 generally will be provided
with the lowest possible profile so as to minimize obstruction of
the lumen when positioned in the IVC.
[0097] Electronics capsule 503 is connected to anchor element 506
at the superior end of the capsule. Anchor element 506 as depicted
in this embodiment includes a single anchor wire 515 configured in
a generally figure-eight or double helix shape. Alternatively, the
same configuration can be provided with two or more wires. Anchor
wire 515 is pinned to telescoping deployment member 518 at both its
inferior end 521 and superior end 524. Telescoping deployment
member 518 includes inner member 527, which is secured to
electronics capsule 503, through anchor isolation structure 507 and
outer member 530. Relative motion between inner member 527 and
outer member 530 moves anchor wire 515 from a collapsed position,
shown in FIG. 9, to a deployed or anchoring position, shown in FIG.
10.
[0098] Various actuation mechanisms may be utilized for deploying
and securing anchor element 506. In one alternative, anchor wire
515 is resilient, with shape-memory properties configured to
provide a rest state in the deployed configuration. In this
alternative, device 500 may be delivered to the desired location in
the IVC via a conventional guide catheter or other suitable sheath
type delivery device. When position is confirmed as described
below, device 500 is ejected from the delivery catheter or sheath
with anchor element 506 self-deploying upon ejection.
[0099] In another alternative deployment mechanism, an actuating
wire (not shown) is removably connected to deployment member 518 at
superior end 524 using a mechanical release mechanism, for example
a screw threaded connection, spring release, hooks or other such
means known in the art. The actuating wire may be a single or
double wire, which may be coaxial or parallel, depending on the
mode of actuation. In this alternative, movement of the actuating
wire effects relative movement of the inner and outer deployment
members 527, 530 to deploy anchor wire 515 from the collapsed
configuration to the expanded, deployed configuration as explained
above. After deployment of the anchor element, the actuating wire
is released from device 500 according to its mode of connection and
released to leave the device secured in the IVC via anchor element
506.
[0100] As mentioned above, a further feature of this and other
embodiments disclosed herein is the spacing between the marker
element position relative to the anchor element, provided by anchor
isolation structure 507. In general, it is preferred if the anchor
element is positioned sufficiently distant from the marker elements
so as to not have an effect upon the IVC size or shape at or close
to the location of measurement due to the anchoring force imparted
to the IVC wall. Anchor isolation structure 507 ensures the desired
positioning, which may be approximately 1 to 4 times the IVC
diameter as indicated above. In general, the IVC has a somewhat
oval cross section with a minor axis of the oval extending in the
anterior-posterior direction and a major axis extending in the
lateral-medial direction. It is thus desirable to minimize any
effect of the device on this natural oval shape at or close to the
point of measurement.
[0101] The shape of the IVC and possible effect of the anchor
element on the IVC shape is illustrated, in one possible
configuration, in FIGS. 5-8. As shown therein, at the more inferior
portion of the IVC, proximate marker element 512, the IVC assumes
its more natural oval shape as best seen in FIG. 7. However, at the
superior portion where subjected to the force of anchor wire 515 of
anchor element 506, the IVC is forced into a more circular shape as
best seen in FIG. 8. Thus, not only does the anchor element
potentially distort the shape of the IVC, it may also stiffen the
IVC so as not to be as responsive to varying fluid volumes which
may indicate heart failure risk. Anchor isolation structure reduces
or eliminates such problems as might otherwise be associated within
sensing devices positioned in the IVC.
[0102] In order to achieve accurate measurement with marker element
512 using an anchor configuration of the type shown in FIGS. 5-10,
the entire device, from deployment member 518 through anchor
isolation structure 507 into electronics capsule 503 should be
provided with a stiffness sufficient to maintain the electronics
capsule (and marker element) against the wall of the IVC at one
side and yet provide sufficient flexibility (and smoothness) to
avoid damage or erosion of the IVC wall by contact with device 500
over the remaining lifetime of the patient.
[0103] As also shown in FIGS. 5-8, it may be most advantageous if
the device, such as device 500, or other device disclosed herein,
is positioned with the electronics capsule 503, and more
specifically the active marker element (e.g., ultrasound marker
element 512), against the posterior wall of the IVC so as to
measure the distance to the anterior wall. This arrangement may
offer advantages in accuracy and sensitivity in measurements by
measuring along the minor anterior-posterior axis of the oval IVC
shape, and by measuring from the posterior wall, bony structures
lying behind the posterior wall, which may create artifacts or
other interference with ultrasound measurements may be avoided.
Such positioning may provide for the greatest accuracy in
measurement of diameter over the respiratory cycle (e.g.,
measurement of diameter variability vs. static measurement). While
a single ultrasound marker element 512 is shown for device 500, a
similar device with more than one ultrasound crystal may be
positioned elsewhere in the IVC, for example in the center of the
IVC, with two crystals measuring the distance to the anterior and
posterior walls simultaneously. Specific requirements for
positioning and measurements may be clinically determined based on
patient anatomy as determined by the procedure provider, and the
device to be implanted may be modified according to the teachings
contained herein to suit those specific patient requirements.
[0104] In general, devices as disclosed herein may be positioned at
any suitable position in the IVC based on clinical assessment. In
one example, the marker element of the device, such as an
ultrasound crystal, may be disposed at the cranial end of the
device, with the cranial end then positioned in the IVC between the
renal veins and the hepatic veins. In this case, the anchor element
may be disposed at the opposite, caudal end of the devices and thus
positioned in the IVC inferior to the renal veins. Also, when
positioning the device on the posterior wall of the IVC, it may be
desirable to ensure that the device is centrally located on the
posterior wall and oriented at least substantially straight across
the minor axis for most accurate measurements. Positioning of the
device in the IVC may be controlled using convention
catheterization techniques with observation under fluoroscopy.
However, in a device such as device 500, marker element 512 may be
used to assist in confirming placement by slightly rotating
electronics capsule 503 so as to effectively scan the opposite IVC
walls with the ultrasound sensor to detect placement position
relative to the oval IVC cross-sectional shape.
[0105] In a further alternative embodiment in FIG. 5, additional
anchor elements may be provided on electronics capsule 503, such as
barbs 533. It is to be noted, however, that while barbs 533 are
shown in FIG. 5, they are an optional feature. Basic operation of
anchor element 506 is described above. As anchor element 506 opens,
it shortens and tends to pull back on electronics capsule 503.
Through a linkage between barbs 533 and deployment member 518, the
relative movement of those two parts during deployment of anchor
element 506 may be used to deploy barbs 533 from the back of
electronics capsule 503. Anchor element 506 and barbs 533 may be
positioned to engage the IVC wall in opposition to one another to
reinforce the anchoring force and security. However, as previously
indicated, substantially the same device may be alternatively
provided without anchor barbs 533, held in place only by the
collapsible/expandable double helix anchor wire 515 of anchor
element 506. These anchor structures, as well as further
alternative anchor structures described below, are configured to
achieve secure fixation against both longitudinal and rotational
movement while preferentially maintaining at least the marker
element in the posterior aspect of the IVC, most preferably against
the posterior IVC wall. The anchor elements described also can be
deployed and redeployed multiple times during a placement procedure
in order to ensure the most optimum placement of the device. The
shape or configuration of the anchoring wire also may be adapted
for IVC size and shape using different anchor element
configurations as exemplified by the following additional
alternatives.
[0106] The anchoring elements exemplified herein may take a wide
variety of alternative shapes, as shown generally in FIGS. 11-21.
Such alternatives may or may not utilize one or more aspects of the
"double helix" anchor wire design discussed above
[0107] Alternative anchor element 1100 is shown in FIGS. 11 and 12.
Anchor element 1100 includes two separate wire loops 1103 and 1106
secured to deployment member 1109, which is comprised of an inner
member 1112 and concentric telescoping members 1115 and 1118, which
are in turn covered by outer telescoping member 1121. Wire loop
1103 is secured to inner member 1112 and covered directly by inner
concentric telescoping member 115. Second wire loop 1106 is also
secured to inner member 1112, either by access through an opening
in the concentric telescoping members or by an attachment wire that
extends along the inside of telescoping member 1118 and is secured
at the remote end to inner member 1112. Alternatively, second wire
loop 1106 may be secured directly to the second concentric
telescoping member 1118. In the collapsed configuration each wire
loop is covered at least in part by one of the telescoping members.
To deploy the anchor element, the telescoping members are pulled
back, either by self-deployment forces generated by the wire loops
or by actuation with external means as previously described. FIG.
12 shows anchor element 1100 in its fully collapsed state with the
anchor wires and concentric telescoping members 1115, 1118 covered
by outer telescoping member 1121. Also shown in FIGS. 11 and 12 is
a further alternative electronics capsule 1124, which is joined to
anchor element 1100 by anchor isolation structure 1127.
[0108] FIG. 13 illustrates anchor element 1100 and electronics
capsule 1124 as it may appear when deployed within the IVC. Anchor
wire loops 1103 and 1106 are released to extend outwardly to
contact the IVC wall while leaving the central portion of the IVC
unobstructed to allow access for other procedures and to minimize
restriction of blood flow.
[0109] FIGS. 14-16 illustrate another alternative anchor element
1400. In this embodiment, mesh sleeve 1403, secured at one end to
anchor wire 1405 is deployed over inner member 1408 to which anchor
wire 1405 is secured. Once again, relative movement between inner
member 1408 and mesh sleeve 1403 controls deployment or collapse of
the anchor wire 1405. Anchor element 1400 is depicted in FIG. 16 as
deployed within the IVC with wire anchor 1405 engaging the IVC
wall.
[0110] FIG. 17 illustrates a collapsible, tubular, stent-like
alternative anchor element 1700. Anchor element 1700 may be formed
of braided wires, welded wires, spiral wound wire, or laser-cut
tube, and is preferably a resilient self-expanding metal or
polymer. Electronics capsule 1701 is depicted as attached to one
end of the anchor element. Weld or cold bond 1703 with
biocompatible materials may be used to attach the electronics
capsule to the anchor element. Anchor element 1700 may be deployed
through a guide catheter in a manner similar to conventional stent
deployment. Advantageously, such a tubular anchor element provides
secure anchoring in the vessel while leaving the vessel lumen
patient to allow introduction of catheters and other devices
without disruption of the monitoring device.
[0111] FIGS. 18-21 illustrate yet another alternative anchor
element 1800 coupled with electronics capsule 1801. In this
embodiment, anchor wire loops 1803 and 1806 in this embodiment are
secured at opposite ends to inner member 1809 and outer member
1812. In this manner, relative movement between inner member 1809
and outer member 1812 permits deployment of the anchor wires
without a covering sheath. The anchor wires may be again collapsed
by an opposite relative movement between the inner member and outer
member. FIGS. 20 and 21 show how anchor element 1800 may be
deployed in different sized IVCs. In this embodiment, anchor wire
loops 1803 and 1806 are relatively longer such that they may cross
multiple times when less than fully expanded to accommodate smaller
size IVCs, as is apparent from a comparison of FIGS. 20 and 21.
[0112] As should be apparent to those of ordinary skill in the art,
each of the anchor element configurations described above includes
common features of secure anchoring with a virtually unobstructed
IVC, even when the anchor elements are fully deployed. By
minimizing or eliminating obstruction of the IVC, combined with
positioning of the anchor elements remote from sensing elements and
location, embodiments of the present disclosure may remain
positioned in the IVC over longer periods of time without affecting
the natural tendency of the IVC to collapse or expand when venous
pressure or volume is changed.
[0113] While it is anticipated that in most cases it will be
desirable to maintain an unobstructed pathway through the IVC as
provided by exemplary anchor elements described above, in some
cases it may be desirable to integrate a monitoring device as
described herein with an IVC filter, as shown for example in FIG.
22. In addition to monitoring IVC distention, device 2200 would
trap any clots embolizing from the legs and prevent them from
reaching the lungs as is understood with respect to IVC filters as
stand-alone devices. Device 2200 includes electronic capsule 2203
with battery, connections to the sensor, memory, telemetry, etc.,
stent-like anchor element 2206 with anchor members 2209, and
flexible arms 2212 supporting marker element 2215. In this
embodiment, marker element 2215 are depicted as electrodes, which
may be substantially the same as the electrodes described above in
connection with the embodiment of FIG. 1. In addition, arms 2218 at
the superior end of device 2200 extend across the lumen of the IVC
and intersect to form a basket to retain any clots which embolize
from the legs.
[0114] FIGS. 23 and 24 show devices 2300 and 2400, respectively,
configured to measure the longitudinal impedance along the length
of the IVC or the superior vena cava (SVC), or both. Device 2300
includes anchors 2303 to engage the IVC and secure electronics
capsule 2306. One electrode 2309 is provided relatively closer to
electronics capsule 2306, and an insulated straight or spiral wire
2312, which lays against the IVC wall, leads to second electrode
2315 located more superiorly in the IVC, right atrium, or SVC.
Rather than applying a simple direct current voltage between these
two electrodes to measure the impedance, it may be more effective
to apply a particular alternating-current frequency that exhibits a
lower impedance through blood and a higher impedance across the IVC
wall and through other tissues. This would allow such a device to
measure the variation in IVC volume even more effectively.
Alternatively, a device may measure a combination of the change in
both longitudinal and radial impedance, to gather an even more
effective measurement of the change in IVC volume.
[0115] FIG. 24 further shows device 2400, shaped similarly to a
standard IVC filter, which uses the variation in bending of struts
2403 to apply pressure to pressure sensors 2406 on central body
2409 of the device. Struts 2403 extend radially outward from body
2409 and have distal tips 2412 configured to engage and anchor to
the wall of the IVC. Struts 2403 have flexibility and resilience so
as to move with the wall as the vessel contracts and expands,
thereby changing the forces exerted by the struts on sensors 2406.
Electronics capsule 2415 is contained within body 2409 providing
power, control and communication for sensors 2406.
[0116] FIG. 25 shows another embodiment, device 2500, configured
similarly to an IVC filter. However, in this embodiment, device
2500 is provided with lateral struts 2503, which are intended to
anchor the device in the IVC, and anterior-posterior struts 2506,
which are intended to flex with the movement of the anterior and
posterior walls of the IVC. Therefore, the distance between marker
elements 2509, such as sensors or electrodes, on the anterior and
posterior struts can be measured. As with other embodiments, device
2500 includes electronics capsule 2512, which provides structural
support for the struts and contains necessary power and control
functions as elsewhere described.
[0117] FIG. 26 shows a further alternative embodiment in which
device 2600 is comprised as a stent 2603 on which marker element
2606 are disposed at two different cross-sections (lateral-medial
and anterior-posterior) of the IVC. Stent 2603 has a resilient,
self-expanding configuration which will expand and contract with
the IVC. Stent 2603 may be a mesh or woven structure, a simple
wire-form having a zig-zag or sinusoid shape, or a series of closed
or open cells cut from a tube. Power and control may be provided by
integrated power and data transmission components in an electronics
capsule as previously described, or marker element sensors directly
powered via external energy delivery means, and transmitting
information directly to an external module may be provided.
[0118] FIGS. 27A and 27B show another embodiment in which device
2700 is provided with two pairs of arms 2703 held in place by a
stent structure 2706. Marker element 2709 (such as electrodes,
ultra sound crystals or other sensors as previously described) are
positioned at the apex of each pair of arms. These may be oriented
in the patient such that one side of each pair extends from the
anterior wall of the IVC, and one from the posterior wall. As the
IVC collapses as shown in FIG. 27B, the arms tend to scissor
together and the apices holding marker elements 2709 move closer
together. This change in position may be detected. Alternatively,
strain gage type sensors or other angle detection may be used to
detect the change in angle from compression alone or in combination
with the change in distance sensors. Embodiments such as device
2700 can be configured such that the sensors move relative to each
other a distance greater than the actual movement of the IVC wall,
thereby magnifying the change in the distance from the anterior to
posterior walls.
[0119] Device embodiments as described herein may be delivered into
the IVC from a variety of locations. The subclavian or cephalic
vein is the normal route of introduction of pacemaker and
defibrillator leads, so that these leads can be attached to the
pacemaker itself, which is placed in an infra-clavicular pocket
just below the subclavian vein. Embodiments disclosed herein may be
similarly delivered from the subclavian vein, cephalic vein or the
jugular vein, or the femoral vein. Other access points to the
venous circulation may also be used.
[0120] One exemplary delivery method for certain embodiments
disclosed herein is to have the device to be delivered compressed
into a catheter, with a cover sleeve over the device. A guidewire
lumen within the catheter would allow a guidewire to be positioned
under fluoroscopy or ultrasound guidance into the IVC, and then the
delivery catheter would be advanced over that guidewire into the
appropriate location. Once appropriate location is confirmed, the
cover sleeve would be retracted, allowing the device to self-expand
against the walls of the IVC. Under appropriate clinical
indications, disclosed devices may be delivered at the bedside
under ultrasound imaging guidance, without the need for
fluoroscopy.
[0121] If the device has an electronic lead, the lead may take
advantage of all of the designs, materials, and techniques that
have been used to optimize pacemaker leads. This lead may extend to
a secondary fixation element within the circulatory system, as
shown in FIG. 3, or it may extend out of the circulatory system to
an implantable element as shown in FIG. 4.
[0122] As a source of power, embodiments described herein may
include an inductance coil to power the sensors on the device using
a power source from outside the body. Externally powered devices
may also include a small battery or capacitor to maintain steady
power to the sensors. An external power source could be in the form
of a pendant which hangs from a necklace around the patient's neck,
or a module which is kept in a shirt pocket, strapped around the
patient's chest or abdomen, clipped to the patient's belt, or other
locations proximate to the implanted device. It could also be kept
at the patient's bedside or under their mattress or pillow, so it
can deliver power, take measurements, download data, etc. each
evening while the patient is sleeping.
[0123] Given the available cross-sectional area of the IVC and the
low power requirements of current implantable device circuitry,
embodiments of devices described herein, including a long-term
battery and circuitry, may be safely implanted in the IVC without
disrupting blood flow. The diameter of the delivery catheter for
such a device may be as large as 24-30 French size (8-10 mm) if
delivered via the femoral vein. The overall implanted device or
structural elements also may be used as an antenna to enhance
transmission of this data outside of the body, especially, for
example, if the device has a stent-like body or multiple metal
arms.
[0124] In yet another alternative embodiment, a sensing device may
be implanted on the outside of the IVC as shown, for example, in
FIGS. 28A-C. In this embodiment, device 2800 is configured to be
implanted around the outside of the IVC and thus includes two
resilient arms 2803 extending from electronics capsule 2806. Marker
elements 2809 are disposed at the ends or elsewhere along resilient
arms 2803. Arms 2803 may be, for example, a coated, resilient
flexible material or a tubular insulator with a wire inside. Device
2800 may be placed via an otherwise conventional laparoscopic
procedure. A right posterolateral access to the abdomen, just
inferior and/or posterior to the liver, should allow the surgeon to
advance to the IVC. In this manner a resilient loop device such as
device 2800 could be wrapped around the IVC, as shown in FIG. 28B.
FIG. 28C shows one embodiment of delivery device 2815 containing
straightened device 2800. Delivery device 2815 may comprise a
tubular member such as a catheter or trocar with a pushing element
for delivery and position of device 2800 around the IVC.
[0125] In a further alternative embodiment, a marker element as
elsewhere described herein may be implanted against one side of the
external wall of the IVC, held in place by sutures, clips,
adhesives, or other mechanical attachment means. Such an external
sensor type element could measure IVC cross-sectional area via
mechanical, sonic, impedance, or other means.
Marker Element Embodiments with External Activation
[0126] Embodiments described above focus on implantable systems
with electronics to measure IVC dimensions as well as other
physiologically important data, and then transmit that information
to a receiver located outside the patient's body. Embodiments
described hereinafter include devices, systems, and methods for
measuring the IVC employing external instruments to measure IVC
dimensions in communication with implanted marker devices,
potentially without a need for more complex implants, or implanted
active measurement devices and/or the need to transmit measurement
data out of the body. Such devices, systems and methods may include
passive elements, which are used in conjunction with external
instruments for calculating and communicating IVC dimensions. More
specifically, disclosed systems may have one, two or more markers
that would allow an instrument outside the body to easily measure
IVC dimensions without the need for sophisticated training or human
analysis. Such systems may use portable, and relatively inexpensive
instruments to take the measurements.
[0127] In one disclosed embodiment, shown in FIG. 29, device 2900,
including two or more passive elements 2903, is configured to be
implanted in the IVC. Passive elements 2903 are themselves
configured to reflect a signal directed towards them from outside
the body. Such passive element reflectors may be made of a metal
such as Nitinol, or they may be made from any other echoreflective
material (or other suitable biocompatible material reflective of
the signal employed). Passive elements 2903 are connected by anchor
isolation structures 2906 to anchor structure 2909, exemplified
here as a stent-like structure, which may be made of Nitinol or
other resilient material biased into engagement with the IVC wall.
Other anchor elements as described herein may be alternatively
employed.
[0128] It will be appreciated by persons skilled in the art that
the depiction in FIG. 29, as in other figures presented in this
disclosure, is not at a particular scale. Connecting elements 2906
may be suitably elongated to allow the anchoring structure to be
placed in a position spaced upstream or downstream from the
location of the markers so that the anchoring structure does not
affect the natural geometry and movement of the IVC where it is
measured by the passive elements as previously described. Passive
elements 2903 may be gently biased outwardly against the anterior
and posterior walls of the IVC to maintain contact therewith.
[0129] In other embodiments employing passive marker elements, the
passive elements may be mounted directly to an anchoring structure
such as a stent, and not separated therefrom by connecting
elements. Alternatively the marker elements may be stapled,
screwed, sutured, or otherwise fastened to the IVC wall. Passive
elements such as shown in FIG. 29 may be fenestrated, including
grooves, channels, holes, depressions or the like to accelerate the
ingrowth of IVC wall tissue over them. The passive elements may
also have a surface texture or coating to enhance reflection of the
signals. For example, the surface may have a series of grooves or
depressions whose walls were at right angles or other selected
angles relative to each other to more effectively reflect those
signals. Alternatively, such grooves, channels or other features
may be arranged on each passive element in unique patterns which
make them more clearly identifiable and differentiable from each
other and from surrounding structures by an external detection
instrument. In other embodiments, the passive elements may be of
known size, but oriented at different known angles relative to each
other, such as in orthogonal directions (e.g. at least one in
circumferential direction and one in the axial direction), so
calculating the length and orientation of the reflected signal can
determine the location of each passive element in three
dimensions.
[0130] It is anticipated that within a few months of their
implantation, the passive elements as of the types described herein
would be fully healed into the IVC wall. The posterior passive
element may be somewhat larger than or offset from the anterior
passive element, so that one does not shield the other regardless
of where the reading/detecting instrument is held against the
anterior abdomen.
[0131] A reading instrument for use with passive elements as
described above may comprise a generally conventional ultrasound
signal generator and receiver which would be held against the
anterior abdomen or thorax outside the body to detect the device in
the IVC, as schematically depicted in FIGS. 30 and 31. In this
exemplary embodiment, ultrasound system 3000 includes handheld
probe 3003 connected to table top control console 3006 and display
3009. Advantageously, ultrasound system 3000 would not need to
image the IVC, although optionally may do so. Thus, ultrasound
probe 3003 could be provided as a single crystal, intermittently
delivering a pulse and measuring the time-of-travel until the
reflected echo is detected by the same crystal. Ultrasound probe
3003 transmits a sonic signal, as shown, for example, in FIG. 31,
through the body wall BW and the receiver records the reflection of
that signal from the two passive elements 2903 elements on device
2900 implanted within the IVC. System 3000 may differentiate the
two passive elements in any of various ways, including through
differences in their relative distance away, size, shape, patterns
of fenestrations, echo-reflective coatings or other features. By a
time-of-travel calculation, for example, the relative spacing of
the two passive elements could be calculated. By measuring this
distance many times per second, an accurate assessment of the
variation in IVC dimensions could be made.
[0132] System 3000 may be programmed to look for the appropriate
number of signals from the passive elements within the appropriate
time period after it transmits a signal. This would minimize the
risk of it tracking inappropriate signal reflections from other
sources or anatomical structures such as the spine. In use, probe
3003 is held against the anterior abdomen and gently reoriented
until it receives an effective echo from all of the passive
elements. At this point system 3000 emits an audible signal, shows
a green light, or uses other indicator means to confirm to the
patient that the instrument is appropriately positioned. System
3000 may also include a strap around the patient's body that could
be tightened to hold the device in place, or the patient could hold
it in place manually, or use tape, adhesive, or other means to hold
it in place while readings are taken.
[0133] In further alternative embodiments, instead of or
accompanying passive elements, more active elements may be included
with an implantable device such as device 2900. Such more active
elements may comprise piezoelectric or other crystals which absorb
incoming sonic signals and re-transmit these signals back to the
receiver. Such embodiments may further comprise active elements
powered by an externally delivered magnetic, electrical, or
ultrasonic field. In such active embodiments, active marker
elements, which may be also be schematically depicted by elements
2903 in FIG. 29, could then emit a signal that allows the external
instrument to determine position more exactly. In further examples,
each active marker element may include an inductance coil or other
means to gather energy from a variable external electric or
magnetic field; a capacitor or other means to store that energy;
and then a piezoelectric crystal to emit an ultrasound signal,
along with the appropriate circuitry to manage these elements. Such
externally powered active marker elements need not be overly
complex, firing an ultrasound signal whenever they are sufficiently
charged or excited. Alternatively, the external system may send a
triggering signal to tell each marker element when to fire, or to
make them all fire simultaneously.
[0134] In embodiments employing active, ultrasound-emitting marker
elements, one or more external ultrasound receivers may be arrayed
on the body surface to detect the emitted signals. Again using
time-of-travel calculations as will be appreciated by persons
skilled in the art, the precise location of the active marker
elements within the body could be determined. If the active marker
elements fired simultaneously, then one ultrasound receiver located
on the anterior abdominal wall could be enough to accurately
measure the anterior-posterior dimension of the IVC. If they did
not fire simultaneously, then more than one receiver may be
necessary. The external sensors may be arrayed in a way that
maximizes the precision of the anterior-posterior measurement. FIG.
32 shows a transverse cross-section of the body, and one
arrangement of two external sensors 3203. The distance from
implanted active marker elements 2903, within the IVC, to sensor
3203A on the patient's anterior abdomen will vary directly as the
anterior-posterior (A-P) IVC dimensions change, while the distance
from implanted active marker elements 2903 to sensor 3203B on the
patient's side will change little. By analyzing the difference in
the time it takes for ultrasound signal from each active marker
element to reach sensor A versus sensor B, the A-P dimensions of
the IVC can be calculated. As long as at least two sensors are used
(for example, one on the anterior wall of the IVC and one on the
posterior wall), their relative motion could be measured quite
accurately, cancelling out other motions such as the rise and fall
of the abdominal wall during respiration. Note that elements 2903
may also be implanted on an external surface of the IVC as depicted
in the embodiment of FIGS. 28A-C, or may be passive elements if
transducers are used instead of sensors 3203.
[0135] Other methods of determining position from passive or active
marker elements also may be employed. For example, in one
embodiment, the marker elements may comprise one or more small
magnets implanted against the IVC wall using device embodiments
described herein above, and a sensitive magnetometer could be used
to detect the position and motion of the magnet(s). A SQUID
magnetometer (Superconducting Quantum Interference Device) could be
used to very sensitively measure the variation in location of an
implanted magnet, although this device may require a cooling
apparatus to bring even a high-temperature SQUID to a temperature
where it becomes superconducting. Other types of magnetometers
could also be used.
[0136] A further alternative embodiment may comprise the
implantation of marker elements, such as containing ultrasound
crystals, that show up very brightly on an ultrasound image.
Automated image analysis software within the ultrasound system can
then automatically detect marker element positions and record them.
One embodiment of this approach would be to implant a stent with
Nitinol arms that can be easily identified by an ultrasound imaging
system using automated software. An implanted device similar to
that shown in FIG. 29 could include a stent implanted caudal to the
renal veins, and two or more metal arms that extend cranial to the
renal veins. For example, one arm could be positioned along the
anterior wall of the IVC and another along the posterior wall. A
transverse cross-sectional ultrasound image of the IVC cranial to
the renal veins will cross these arms, and they will show up as
clear marks on the ultrasound image. Image-analysis software could
then identify those marks, track them, and measure the variation in
IVC dimensions automatically. To make these measurements
consistent, the patient or caregiver could be trained to hold an
ultrasound imaging transducer on the patient's abdomen in a
specific location. Tattoos or other markings on the skin could be
used to identify a consistent location from which measurements are
to be taken. In one embodiment, as shown in FIG. 33, a wearable
detection system 3300 includes ultrasound probe 3303 that may be
fastened in place on the patient via strap 3306 and buckle 3309.
Ultrasound probe 3303 may also include windows 3312 mounted on body
contacting tabs 3315, or other indicators, that would be placed
over or adjacent the location mark on the body to ensure proper
location of probe 3303. Ultrasound probe 3303 may communicate
wirelessly with an external device 3318, such as a cell phone,
which controls the probe, displays the measured data, and transmits
it to other systems or cell phones. Alternatively the ultrasound
transducer could be shaped so that the transducer is reliably
positioned a certain distance from various anatomical points, such
as a distance from the bottom of the rib cage.
[0137] A further embodiment is a system that monitors IVC
dimensions without implanted elements. For example, a portable,
external ultrasound system could comprise a processor and software
that analyzes a reasonably consistent ultrasound image of the
abdomen to automatically identify the IVC. This software then
automatically identifies the anterior and posterior walls of the
IVC within that image, and continuously or periodically measures
and records the variation in IVC dimensions over time. In such an
embodiment, the system would include an emitter and receiver that
can be secured to the patient, or that can be positioned at one or
more marked locations on the patient's skin, so that measurements
are taken from a consistent location. Preferably such a system is
contained in a lightweight, compact housing, battery-powered, and
small enough to be worn by the patient or easily held by the
patient during measurements. System 3300 as shown in FIG. 33 may
also be used in this embodiment.
[0138] As a further method of simplifying the identification of the
IVC and appropriate positioning of the probe, a three-dimensional
ultrasound map of most of the patient's abdomen can be stored in
the ultrasound system's memory when the patient first begins using
the system. From that point, optimal positioning of the probe and
its two-dimensional slice within that three-dimensional volume can
be defined. Then, when the patient is imaged in a subsequent
measurement, the ultrasound system can compare the image to the
three-dimensional map, determine where the image is relative to the
desired slice, and indicate to the person doing the image to move
the probe cranially, caudally, medially, or laterally to reach the
optimal position.
[0139] In all of the above-mentioned marker element-based
embodiments, external components of such systems are preferably
configured to report the IVC dimensions to the patient, as well as
wirelessly transmit that information to the patient's doctor or
other people monitoring the patient's health. Since they are
external to the body, size is less critical, and such components
could have more significant batteries to allow communication with
the physician or other monitors via a Bluetooth.RTM., WiFi.RTM.,
cellphone, or other communications modality as described in more
detail later in this disclosure. The ultrasound
receiving/transmitting element of any of these less-invasive IVC
monitoring systems could be configured to be worn continuously by
the patient, or it could be used for a period of minutes once or
more per day. All of the external components may be contained in a
single housing, or could be broken up into two or more separate
units. For example, in system 3000, shown in FIG. 30, ultrasound
receiver/transmitter probe 3003 may be connected either wirelessly
or by cable to console 3006 adapted to provide user control
functions, perform calculations, store and display information, and
communicate with cell phones or the Internet via wireless networks.
Console 3006 may include a CPU, memory device, and other components
for input, communication and storage as described in further detail
below in connection with FIG. 46. In this way, a
transmitter/receiver probe may be compact, lightweight and wearable
(as in FIG. 33), while the control console could be a larger
tabletop unit.
Injectable and Other Passive Marker Embodiments
[0140] Embodiments discussed above primarily encompass active
marker element-based embodiments and more passive marker elements
that may be fastened to the IVC wall by various embodiments of
anchor elements or other similar suitable means. In further
alternative embodiments, as described herein below, marker elements
are placed or injected into or within the IVC wall. In some
clinical situations, instead of a marker element that is fastened
to the inner or outer wall of the IVC, such placement may be easier
or preferable.
[0141] In one such injectable-type embodiment, as shown in FIGS.
34A and 34B, a relatively small guiding catheter 3403 may be
introduced into the IVC, and through that catheter a needle or
blade 3406 may be introduced. Under ultrasound or fluoroscopic
guidance, needle 3406 may be directed towards the appropriate wall
of the IVC, and inserted into the wall. Needle/blade/catheter 3406
may have a shoulder or hilt a selected distance from its distal tip
to engage the wall surface so as to limit the depth of penetration
of the needle or blade. The needle or blade 3406 may be configured
to create a pocket or flap in the IVC wall into which biocompatible
or resorbable substance 3409 containing marker elements 3412 may be
placed or injected. System 3400 may be further configured to
deliver marker elements 3412 into the middle of the IVC wall, such
as between the medial and adventitial layers of the IVC, or between
the intimal and medial layers. System 3400 may also be configured
to deliver marker elements 3412 through the thickness of the IVC
wall to the exterior so that marker elements 3412 would adhere
against the outer surface of the IVC as shown, for example, in FIG.
34B.
[0142] Injectable marker elements may be, for example, a flexible
wire, ribbon, or guidewire segment, which could be advanced easily
through a catheter or needle into or against the IVC wall. Such a
marker element could be attached to a delivery wire or catheter,
and removed or repositioned as needed. The marker element would
only be detached from the delivery system once appropriate
positioning had been confirmed. System 3500, shown in FIG. 35, uses
coiled wire marker element 3503, which is deployed using delivery
catheter 3506. Delivery catheter 3506 holds marker element 3503
with two jaws 3509 until the marker element reaches the distal end
of the delivery catheter 3506, at which point the jaws separate to
release the marker element. Marker element 3503 also may be
released via a threaded connection, an interlocking mechanism, an
electrolytic or other soluble connection, or other such release
mechanisms as are known in the art.
[0143] Examples of embodiments of guidewire segments for use in
such injectable marker element embodiments are shown in FIGS.
36A-E. Such segments may have a surface texture optimized to
reflect the ultrasound or other signal and may be metallic, such as
platinum, titanium, gold, or other material, or it may be a
polymer. A polymer embodiment may be molded with appropriate
echo-reflective surfaces and radiopaque markings. Alternatively,
such a guidewire marker element may comprise a section of hollow
wire, sealed on each end and filled with air or echo-reflective
fluid. A wire or ribbon may include barbs, scales, or other
features to inhibit it from backing out of the IVC wall or
migrating completely through the IVC wall. FIG. 36A shows a simple
guidewire coil 3603. FIG. 36B shows a guidewire coil 3606 coated
with polymer 3607 to permanently entrap air creating a highly
echo-reflective marker. FIG. 36C shows a close-up of a coiled
ribbon marker element 3609 with surface texture 3612 to enhance its
echo-reflectivity. FIG. 36D shows marker element 3615 formed as a
sealed tube of air. FIG. 36E shows marker element 3618, formed as a
tube of cast polymer such as silicone which has been emulsified
prior to curing, entrapping many tiny echo-reflective gas bubbles
3621. Gas bubbles 3621 can be of a particular gas to minimize any
absorption through the walls of the polymer over time. Tubular or
coil devices delivered through a catheter may be provided with a
selectively releasable retention mechanism such that placement may
first be confirmed before the device is released from the catheter.
One such mechanism is illustrated in FIG. 36E, which includes
threaded connector 3624 at one end, configured to cooperate with a
threaded release mechanism in the delivery catheter. Once
appropriate positioning has been confirmed, the delivery catheter
may be unscrewed, leaving the polymer tube permanently in
place.
[0144] Alternatively, injectable marker elements may comprise a
number of small echo-reflective beads or particles, as shown in
FIGS. 37A-C, which may be injected into the wall of the IVC or into
the peri-adventitial space against the outside of the IVC. Such
injectable marker particles may comprise spheres of gas similar to
commonly used air bubbles for temporary ultrasound imaging, except
they would be encased in surrounding shells of a permanent or
semi-permanent material such as silicone or other polymers. These
bubbles form spherical reflectors for ultrasound signals. The
injectable marker particles may alternatively be shaped with
pyramidal indentations with 90 degree angles which will reflect
signals very effectively, similar to radar reflectors used on
sailboats. Injectable marker particles may be metallic, such as
titanium, or they could be a polymer such as PEEK
(polyetheretherketone).
[0145] FIG. 37A shows injectable marker particles 3703 with random
jagged echo-reflective shapes. FIG. 37B shows hollow spherical
injectable particles 3706. FIG. 37C shows alternative injectable
marker particles 3709 with molded or shaped configurations having
echo-reflective indentations 3712. Such injectable marker particles
may be of any size from a few microns, to hundreds of microns, or
the maximum size which will pass through the delivery catheter. The
size might be particularly selected to maximize the reflection of
signals of specific frequencies. Nanoparticle-based technologies
also may be employed to provide such particles.
[0146] During delivery, injectable marker particles as described
above may be suspended in a fluid such as saline, or a gel such as
certain formulations of polyethylene glycol (PEG). PEG is already
used in vessel walls for vascular closure applications, such as the
MYNX.TM. device from Access Closure. Depending upon their
formulation, materials such as PEG can be resorbed over the course
of weeks or months, leaving the marker particles permanently in
place. Alternatively, a permanent polymer could be injected which
can be injected as a liquid, but then hardens in place. This
polymer may have marker particles suspended within it, or the
polymer itself could be the marker. One example of a biocompatible
polymer which could be used for this is urethane methacrylate. FIG.
38 shows a close-up of a urethane methacrylate gel 3803 mixed with
marker particles 3806 injected into the wall W of the IVC.
[0147] Another alternative embodiment may comprise securing or
sticking marker particles 3903 to the inner walls of the IVC with a
material 3906 or texture that encourages the marker elements to
grow into the IVC wall as shown, for example in FIGS. 39A and 39B.
Fibrin is one example of a biocompatible material that is known to
adhere to blood vessel walls, and to endothelialize in place. Other
biocompatible, bioabsorbable adhesives could be used. Marker
particles 3903 may be mixed into a fibrin patch and placed as
desired in or against the IVC wall. After the patch is
endothelialized and the fibrin absorbed, the marker particles
remain in the vessel wall. FIG. 39A shows a cross-sectional view of
patch 3906, containing marker particles 3903, which has
endothelialized into the vessel wall, but patch 3906 itself has not
yet been resorbed. Alternatively, a marker patch could be designed
with a "Velcro-like" texture of microneedles or microhooks 3909 as
shown in FIG. 39B, which embed into the IVC wall and may remain in
place permanently.
[0148] Marker elements 4003 designed to be applied to an inner
surface of the IVC wall may be delivered to the IVC wall by
mounting them on the outside of an inflatable balloon 4006,
introducing that balloon into the IVC, and inflating it to press
the marker elements against the IVC wall as shown in FIG. 40A.
Marker elements 4003 may be relatively long and slender, to
minimize the overall diameter of the combined marker elements and
delivery system. Various marker elements described herein for
adherence to or embedding in the IVC wall may be applied using this
technique, such as, e.g., as shown in FIG. 39A or 39B. Before or
during delivery, it will be important to confirm that marker
elements 4003 are aligned with the anterior and posterior walls of
the IVC, which may be accomplished, for example, by using
radiopaque markers and fluoroscopy. Delivery balloon 4006 may have
wings 4009 to cover marker elements 4003 during delivery, but which
unfold or retract to expose the marker elements as the balloon is
inflated. Alternatively, a cover sheath may be provided over the
markers to hold them in place on the balloon during introduction.
This cover sheath would then be withdrawn shortly before expansion
of the balloon to deploy the markers. In a further alternative,
two-balloon catheter 4012 may be used as shown in FIG. 40B, to
permit blood flow through space 4015 so that blood flow would not
be interrupted during the delivery process.
[0149] Sensing and position/measurement detection using
injectable-type marker elements as described in the embodiments
above may be accomplished by a variety of means or systems. For
example, injectable marker elements may be designed to reflect
ultrasound energy. Since the ultrasound signal is being used to
measure distance rather than imaging, the signal may be provided at
a relatively low power. Since the IVC is located deep in the
abdomen, and higher-frequency signals attenuate rapidly in human
tissue, it may be preferable to use a relatively low frequency,
perhaps in the range of 200 KHz-2 MHz, although the frequency might
be higher or lower in practice. The anterior-posterior dimension of
the IVC could be measured simply by measuring the additional time
it takes the signal to reflect off the posterior marker element and
return to the system monitor, compared to the time it takes to
reflect off the anterior marker element. Since the speed of sound
in human soft tissue is approximately 1540 meters/second, if the
A-P dimension of the IVC is approximately 20 mm in an average human
patient, the posterior reflection will return to the monitor
approximately 26 microseconds after the anterior reflection. Each
additional millimeter of dimension will add approximately 1.3
microseconds to the differential.
[0150] It should be noted that one important measurement may be the
percentage variation in that anterior-posterior dimension. Even if
the absolute dimensional measurement is not accurate, the
percentage variation should still be accurate. For example, if the
monitor is 15 degrees to one side of the anterior-posterior
alignment of the marker elements, the maximum measured absolute A-P
dimension may be reduced by [one minus the cosine of 15 degrees],
or 3.4%. But the minimum measured A-P dimension should be similarly
reduced, so the overall percentage change should be minimal.
Similarly, any movement of the abdominal wall, for instance with
respiration, should not affect the differential in the time it
takes for the two reflected signals to return to the system
monitor.
[0151] Given the relatively low power needed for such a simple
distance measurement, the monitor device may be of simple design
and obtain a good signal even with a very low-power signal, which
should maximize both the safety and battery life of the device.
However, if more accurate distance measurements are desired, an
external transmitter/receiver can be configured to provide
consistent, precise measurement of the relative distance of the two
marker elements. In one exemplary embodiment, shown in FIG. 41,
external handset 4103 comprises two emitter/receiver pairs 4106
mounted a fixed distance apart on handle 4109. Each
emitter/receiver pair 4106 is mounted on a contact pad 4712
configured to engage the patient's skin. Each emitter transmits a
signal toward the implanted IVC markers, which reflect the signals
back toward the handset for reception by the receivers. In this way
the distance to each IVC marker may be calculated by triangulation
to obtain a very precise measurement. Optionally, the two emitters
can transmit signals at different frequencies to eliminate
interference.
Multi-Sensor Monitoring Systems
[0152] While pulmonary artery (PA) pressure measurement mentioned
in the Background above holds some promise as an approach to heart
failure monitoring, it is believed that IVC volume measurement may
present a more accurate and early indication of heart failure.
However, the combination of IVC volume measurement with PA pressure
monitoring may provide an even more comprehensive picture of
disease progression.
[0153] The systems of the present disclosure may therefore include
both an IVC volume monitor along with a PA pressure monitor, and/or
other sensors for measuring symptoms related to heart failure. The
multiple monitors/sensors may be coupled together by either a wired
or wireless connections to allow data transmission between them, or
they could operate completely independently. In preferred
embodiments, the IVC monitor and the PA monitor will both
communicate with a single data receiver outside the patient's body.
Alternatively one of the monitors could transmit data to the other,
from which it could be transmitted to an external receiver.
Additionally, a power supply integrated into one of the two
monitors could deliver power to the other of the monitors, or a
separately implanted power supply could be connected to each
monitor. The system could also include a controller/data analyzer
that analyzed the data received from each monitor and used the
combined data to determine the extent of or change in the patient's
disease, and whether to set off an alarm or transmit a notification
to the patient or health professional.
[0154] One exemplary embodiment of such a system is system 4200,
shown in FIG. 42. System 4200 may include a first delivery catheter
(not shown) for implanting IVC volume monitoring device 4203 in the
IVC, and second delivery catheter 4206 for implanting pressure
sensor 4209 in the pulmonary artery. Each of these catheters could
be introduced through a single introducer 4212 positioned in a
peripheral vein such as a femoral or iliac vein. Alternatively,
system 4200 may utilize a single delivery catheter carrying both
IVC monitor 4203 and PA pressure monitor 4209. A single catheter
arrangement allows monitoring of implants to be delivered serially
(either PA first or IVC first) from a single catheter in a single
intervention. Other sensors that could be included in a
multi-sensor system such as system 4200, to provide additional data
related to heart failure include a respiratory rate monitor,
cardiac rhythm monitor, arterial or venous blood pressure monitor,
blood oxygen saturation sensor, or cardiac output monitor.
Closed-Loop Therapy System Embodiments
[0155] This disclosure has heretofore described various
embodiments, devices and methods for using the size, relative size,
and variation in size of the IVC to detect the early onset of acute
decompensation in heart failure. With the information provided by
these devices and methods, various actions may be taken by
patients, caregivers and physicians to diagnose or treat the
disease. In still further embodiments, the IVC monitoring system
may be expanded to provide for closed-loop control of a number of
different therapeutic interventional systems. By sensing the onset
of an event of acute heart failure decompensation and then
triggering an intervention that may reverse, minimize or eliminate
the episode of decompensation, significant suffering or death of
the patient potentially may be avoided, and the health care system
will save significant financial and human resources.
[0156] It is common practice to use intravenous (IV) diuretics to
increase fluid output for patients who are admitted to the hospital
for acute heart failure decompensation. Many patients in heart
failure take oral diuretics, but as their heart failure status
deteriorates, diuretics can become less and less effective when
delivered orally. Intravenous or intramuscular diuretic delivery
remains more effective in these situations. The output from the
sensor/monitor contemplated herein could be coupled with IV pumps,
for example, to control the dosage of IV diuretics in the
in-patient setting. In this example, the sensor/monitor would
communicate to an external module, increasing or decreasing dosage
of the IV diuretics as necessary to maintain a desired IVC status.
The external communication module could be a separate module, which
in turn communicates to the IV pump, or it could be incorporated
into the IV pump directly. Even if the physician preferred to
manually set the initial infusion rate for the drug, the feedback
system here could serve as an additional safety shut-off,
interrupting delivery of diuretics once the IVC status reaches the
appropriate level.
[0157] Also in clinical practice or in development are wearable or
fully implantable pumps that can deliver IV or subcutaneous
diuretics. To date these have been open-loop or uncontrolled
systems. For example, Zatarain-Nicolas et al. reported a series of
patients who were implanted with simple, passive constant-flow
elastomeric subcutaneous pumps to deliver furosemide (a common
diuretic) over time. The sensors discussed herein could be
configured to communicate with a valved version of this type of
pump to create a simple closed-loop system and to deliver
subcutaneous diuretics.
[0158] Alternatively, fully implantable, refillable drug pumps, for
example the Medtronic SynchroMed pump, are currently used to
deliver pain medications. A fully implantable pump could be
configured to communicate with the IVC sensors and deliver IV or
subcutaneous diuretics. In one configuration, an implantable pump
could be implanted in an infraclavicular pouch and the IVC sensor
could be introduced into the IVC from the subclavian vein adjacent
to the pouch. A lead could connect the two elements of the system,
so that the pump uses the data from the IVC sensor to help
determine whether to infuse the drug, and how much drug to deliver.
The pump could deliver the drug into the infraclavicular pouch,
into nearby muscle tissue, or it could deliver the drug directly
into the vascular system. If it were delivering the drug directly
into the vascular system, the infusion lumen from the pump to the
vascular system might be integral with the lead from the IVC
sensor, or it might be introduced parallel to it. The infusion
lumen might be designed with a valve at the distal tip, to minimize
the incidence of clotting or clogging that might block drug
delivery.
[0159] Another class of drugs commonly used to treat heart failure
are inotropes. Inotropes change the force of muscular contractions.
In each of the embodiments described herein, diuretics could be
exchanged for, or used in conjunction with, inotropic drugs. For
example, dual chamber drug pumps configured to deliver both
diuretic drugs and inotropic drugs could be configured to act upon
the data generated by and communicated from the sensors described
herein.
[0160] In addition to directly administering diuretics to the body,
drug pumps and electrical neuromodulation systems have been
contemplated for the control of heart failure by directly
modulating the activity of the renal nerves. The renal nerves
directly influence the renin angiotensin system and modulate fluid
retention or excretion. The IVC sensors herein could be configured
to communicate with drug pumps or neuromodulation systems to up- or
down-regulate the activity of the renal nerves, thus increasing or
decreasing the actions of the renin angiotensin system.
[0161] It should be noted that the renin angiotensin system also
has regulatory effects on other aspects of heart failure
decompensation. Notably, the peripheral vascular system,
specifically vascular tone, is involved in heart failure status.
The modulatory effects of the closed-loop systems described herein
may also act directly on the systems that control vascular tone,
such as the renin angiotensin system.
[0162] It was described above that the IVC sensor could be
configured to communicate with an external IV pump. Similarly, the
sensor data can be used to control other external devices to effect
a therapeutic outcome. For example, the external data collection
systems described in earlier open-loop IVC sensor systems could be
configured to contain as part of that external system an automatic
drug injection device similar to an EpiPen. In one embodiment the
external data reader can be held in contact with the body while the
data from the IVC sensor is transmitted. If the data shows that an
intervention is required, the external system containing one or
more automatic injection systems could deploy as a result of the
collected data, injecting for example subcutaneous furosemide.
[0163] FIG. 43 presents a high-level schematic of such closed-loop
system embodiments, which may include an IVC monitoring device
(passive or active as described above) and at least one
interventional treatment device, wherein the devices are configured
to communicate with one another. The IVC monitor and the
therapeutic device may communicate as necessary to coordinate
sensed physiologic data and required intervention in a number of
ways. Any of the typically used communication protocols may be
used, including but not limited to Bluetooth protocol, RF
communication link, microwave communication link, ultrasound
communication or the like as further described below.
[0164] In one embodiment, a direct communication can be made
through the wall of the IVC proximate to, or posterior to the main
body of the IVC sensor as shown in FIG. 44. This direct
communication through the wall of the IVC may, for example, take
the form of a mechanical grommet 4403 extending laterally from a
side wall of anchor element 4406 of monitoring device 4409. Grommet
4404 is configured to pass through a penetration in the IVC wall.
The grommet attachment can serve a dual purpose of helping anchor
the sensor to the IVC and providing a wired communication port to
the therapeutic device 4412. Grommet 4403 may be configured to seal
with the IVC wall around its periphery, either mechanically and/or
via an induced healing response, and may include a flange on its
outer end to seal against the exterior surface of the IVC.
Alternatively, a purse-string suture can be used to seal the vessel
wall around the leads. A further alternative would be to locate the
IVC sensor(s) on the outside of the IVC, for example as in the
embodiment shown in FIG. 28B. If the therapeutic device is also
outside the vascular system, then no transmural link is necessary.
Note that monitoring device 4409 utilizes marker elements 4415
connected to anchor element 4406 via anchor isolation structure
4418.
[0165] In another alternative, exemplified by the embodiment shown
in FIG. 45, wired communication occurs via leads which run
intravascularly to allow the IVC sensor to connect directly to the
therapeutic device. For example, leads 4503 from IVC monitor 4506
can connect directly to dedicated ports 4509 of the therapeutic
device 4512 (for example a pacing device such as a biventricular
pacemaker). Inputs from IVC monitor 4506 can be programmed into the
algorithm of the therapeutic device. For example, the inputs can be
programmed into the biventricular pacing algorithm of a
biventricular pacemaker to fine tune the coordination of the pacing
of the heart. Since biventricular pacers are typically placed in an
infraclavicular pouch with pacing leads 4515 introduced into the
subclavian vein and advanced into the heart, the IVC monitor(s)
could also be introduced into the subclavian vein on a delivery
catheter and advanced into the IVC using techniques described
above. This example could be incorporated to modulate the action of
any of the therapeutic devices described below.
[0166] As an alternative to working directly with the therapeutic
device by feeding the IVC sensor data into the device to modify a
treatment algorithm, a separate lead (or a wireless signal)
emanating from the sensor to modify the actions of a therapeutic
device may be used. For example, the leads emanating from an IVC
sensor could be placed in a position in which the signal from the
sensor device can interact with the signal of a therapeutic device
such that the signal from the sensor modifies the action of the
therapeutic device. More specifically, a lead from a sensor can be
placed in proximity to a lead from a pacing device such that a
signal from the sensor causes a signal to emit from the sensor
leads to interfere with or to augment the signal from the
therapeutic device.
[0167] Embodiments of the interference mode of action described
above may include placing a lead from the sensor alongside a lead
from a pacemaker or biventricular pacemaker such that the signal
from the sensor cancels out the signal from the pacer, or
conversely augments the signal from the pacer to modify or modulate
the therapy delivered. This example could be incorporated to
modulate the action of any of the therapeutic devices described
below. The integration of sensor data into a closed-loop system may
be accomplished with many different therapeutic devices and methods
currently marketed or in development for the treatment of heart
failure and its associated comorbidities.
Closed-Loop Systems with Spinal Cord Stimulation
[0168] Spinal Cord Stimulation (SCS) has been tested to treat heart
failure by modulating the balance of sympathetic and
parasympathetic activity in the body. This typically involves the
surgical implantation of an implantable pulse generator (IPG) or
neurostimulator, with electrodes which are placed near the spinal
cord to deliver a series of low-energy electrical impulses. The IPG
is typically implanted in the abdomen near the spine.
[0169] It may be appropriate to adjust the delivery, frequency, or
intensity of these electrical impulses to match the severity of the
patient's heart failure status. Therefore, it may be appropriate to
link the IVC monitor and the SCS into a closed-loop system. Since
the IPG is very close to the IVC near the posterior wall of the
abdomen, it may be appropriate to surgically implant sensors in the
IVC which are connected via leads directly to the IPG.
Alternatively, wireless markers could be implanted in the IVC and
the IPG could wirelessly sense the distance of the markers to
determine the volume status of the patient, similar to the
previously described external monitoring device.
[0170] The healthcare provider could then program this closed-loop
system based on an algorithm which might have the SCS impulses
turned down or completely off when the patient's status is
relatively healthy, with increasing intensity of SCS impulses if
the patient's condition deteriorated. This system could also
integrate additional physiologic information such as heart rate,
respiration rate, physical activity, etc. into its calculations. It
could also wirelessly communicate with external devices, which
communicate the patient's and system's status to the patient, a
physician, or other caregiver.
[0171] One exemplary application of this device would be to monitor
the heart failure status of patients with chronic heart failure. It
may very sensitively measure a patient's trend toward fluid
overload, and may do so well in advance of an episode of acute
decompensated heart failure. This would give the patient,
physician, nurse, or other caregiver time to adjust fluid intake,
increase diuretic medications or take other steps to reduce the
patient's fluid status. The external module might include an alarm
which tells the patient to get out of bed and sleep more upright or
to go directly to the hospital, if the perceived risk of fluid
overload is extremely high.
[0172] Another exemplary application of disclosed devices is to
manage a patient during an episode of hospitalization for acute
decompensated heart failure. Even though a patient may spend
several days in the hospital receiving intravenous diuretics,
reduced fluid intake, and even aquapheresis (dialysis to reduce
fluid volume), it is quite possible that the patient leaves the
hospital with excess fluid. In these situations, embodiments
described may be usefully applied to titrate the diuresis process
and to assess when the patient should be discharged. Further, as
this new parameter of IVC distention and variability is studied
more extensively based on the teachings of the present disclosure,
it may prove to be an important prognostic indicator for a number
of other conditions and situations other than management of heart
failure, dialysis, and patients in shock.
[0173] As noted in connection with various embodiments described
herein, one or more aspects and embodiments may be conveniently
implemented using one or more machines (e.g., one or more computing
devices that are utilized as a user computing device for electronic
medical information or documents, one or more server devices, etc.)
programmed according to the teachings of the present disclosure, as
will be apparent to those of ordinary skill in the art.
[0174] This device may have electronic circuitry that stores data
which may then be communicated to an outside monitor via a
telemetry system. This information could then be further processed
for presentation to the patient, giving a simple indication of
their risk level or recommended level of drug intake, or diet and
activity recommendations. This information could also be forwarded
to the patient's physician, so that they can monitor the patient's
condition and communicate with the patient as appropriate.
[0175] This information could also be forwarded via the internet or
other means to the company which manufactures or sells the device,
so that the company can continue to optimize the algorithms which
use the raw data to determine the patient's risk level. It may be
most effective to have the external monitor forward all of the raw
data to the company, since the company will have the most
up-to-date and optimized algorithms for analyzing data, and then
send the processed information back to the patient and their
physician. The company might also have the most secure data storage
means for storing all historical information for each specific
patient, so that the data analysis algorithm can be further
optimized for each specific patient.
[0176] Embodiments disclosed herein may also be used for measuring
dimensions of other body elements besides the IVC. Sensors could be
placed in the heart, for example placing them in the left ventricle
via catheter-based delivery. They could also be placed on the
surface of the heart, within the pericardium via a subxyphoid
access. These sensors could be used to directly monitor the heart's
activity. As another example, sensors could be placed on or in the
bladder to monitor bladder conditions. In patients who need to
self-catheterize to drain their bladders, it may be useful to have
an automated warning of when the bladder was full.
[0177] For all of the above-mentioned embodiments that have markers
or sensors implanted into the IVC, these markers or sensors may
heal into the IVC wall over time. Therefore, the stent, anchor, or
other elements that hold the markers in place may not need to be
permanent. Therefore, it may be desirable to make the stent or
anchor bioerodable, so that after a period of time, there is no
longer a stent in the IVC. The specific duration of the anchoring
elements can be varied from weeks to years through material
selection, formulation, and processing. This would eliminate a
foreign body, and it would also render the IVC more flexible,
allowing it to more naturally collapse or expand. Other
bioabsorbable vascular elements have already been made from
materials such as Poly-L-Lactide. These materials have less
springiness than Nitinol, so the stent design may need to be
modified. For example, the stent could be made with circumferential
elements that ratchet open to apply pressure to the IVC to hold the
stent in place. The delivery catheter for this bioabsorbable stent
might include a balloon to actively expand the stent against the
IVC.
[0178] Embodiments described in this disclosure so far have focused
primarily on volume changes in the IVC. As the patient inhales,
thoracic pressure drops slightly, increasing the flow of blood from
the IVC into the right atrium (RA). As the patient exhales,
thoracic pressure increases slightly, decreasing the flow of blood
into the right atrium. This leads to a variation in blood volume in
the IVC over the respiratory cycle. This variation in blood volume
is necessarily correlated with a slight variation in the relative
pressure between the IVC and the RA. As an alternative or adjunct
to IVC volume measurement, a measurement of the relative variation
in fluid pressure between the IVC and right atrium may provide a
useful indication of blood volume. An implant with two pressure
sensors arrayed along a single lead could be implanted from the
femoral vein, jugular vein, or subclavian vein and anchored in
position so that one pressure sensor is in the RA and one in the
IVC. Embodiments described above having different configurations
for IVC monitors (wireless, externally powered, powered by
electronics deployed within the IVC or RA, powered from an
infraclavicular implant, etc.) may alternatively or additionally
employ such a measurement of relative variation in fluid
pressure.
System and, Control and Communication Hardware and Software Aspects
of Disclosed Embodiments
[0179] Appropriate software coding can readily be prepared by
skilled programmers based on the teachings of the present
disclosure, as will be apparent to those of ordinary skill in the
software arts. Aspects and implementations discussed above
employing software and/or software modules may also include
appropriate hardware for assisting in the implementation of the
machine executable instructions of the software and/or software
module.
[0180] Such software may be a computer program product that employs
a machine-readable storage medium. A machine-readable storage
medium may be any medium that is capable of storing and/or encoding
a sequence of instructions for execution by a machine (e.g., a
computing device) and that causes the machine to perform any one of
the methodologies and/or embodiments described herein. Examples of
a machine-readable storage medium include, but are not limited to,
a magnetic disk, an optical disc (e.g., CD, CD-R, DVD, DVD-R,
etc.), a magneto-optical disk, a read-only memory "ROM" device, a
random access memory "RAM" device, a magnetic card, an optical
card, a solid-state memory device, an EPROM, an EEPROM, and any
combinations thereof. A machine-readable medium, as used herein, is
intended to include a single medium as well as a collection of
physically separate media, such as, for example, a collection of
compact discs or one or more hard disk drives in combination with a
computer memory. As used herein, a machine-readable storage medium
does not include transitory forms of signal transmission.
[0181] Such software may also include information (e.g., data)
carried as a data signal on a data carrier, such as a carrier wave.
For example, machine-executable information may be included as a
data-carrying signal embodied in a data carrier in which the signal
encodes a sequence of instruction, or portion thereof, for
execution by a machine (e.g., a computing device) and any related
information (e.g., data structures and data) that causes the
machine to perform any one of the methodologies and/or embodiments
described herein.
[0182] Examples of a computing device include, but are not limited
to, an electronic book reading device, a computer workstation, a
terminal computer, a server computer, a handheld device (e.g., a
tablet computer, a smartphone, etc.), a web appliance, a network
router, a network switch, a network bridge, any machine capable of
executing a sequence of instructions that specify an action to be
taken by that machine, and any combinations thereof. In one
example, a computing device may include and/or be included in a
kiosk.
[0183] FIG. 46 shows a diagrammatic representation of one
embodiment of a computing device in the exemplary form of a
computer system 4600 within which a set of instructions for causing
a control system to perform any one or more of the aspects and/or
methodologies of the present disclosure may be executed, such as a
control system that may be embodied by or implemented in accordance
with one or more components of: any one or more of the IVC sensors
and/or monitors and/or associated components disclosed herein;
electronics capsule 118 of FIG. 1; electronics capsule 503 of FIG.
5; electronics capsule 1124 of FIG. 11; electronics capsule 1701 of
FIG. 17; electronics capsule 1801 of FIG. 18; electronics capsule
2306 of FIG. 23; electronics capsule 2512 of FIG. 25; electronics
capsule 2806 of FIG. 28A-C; console 3006 and/or ultrasound
receiver/transmitter probe 3003 of FIG. 30; wearable detection
system 3300 and/or external device 3318 of FIG. 33; external
handset 4103 of FIG. 41; system 4200 of FIG. 42; one or more
components of the systems of FIGS. 43 and/or 44; and/or IVC monitor
4506 of FIG. 45, among others. It is also contemplated that
multiple computing devices may be utilized to implement a specially
configured set of instructions for causing one or more of the
devices to perform any one or more of the aspects and/or
methodologies of the present disclosure. Computer system 4600
includes a processor 4604 and a memory 4608 that communicate with
each other, and with other components, via a bus 4612. Bus 4612 may
include any of several types of bus structures including, but not
limited to, a memory bus, a memory controller, a peripheral bus, a
local bus, and any combinations thereof, using any of a variety of
bus architectures.
[0184] Memory 4608 may include various components (e.g.,
machine-readable media) including, but not limited to, a random
access memory component, a read only component, and any
combinations thereof. In one example, a basic input/output system
4616 (BIOS), including basic routines that help to transfer
information between elements within computer system 4600, such as
during start-up, may be stored in memory 4608. Memory 4608 may also
include (e.g., stored on one or more machine-readable media)
instructions (e.g., software) 4620 embodying any one or more of the
aspects and/or methodologies of the present disclosure. In another
example, memory 4608 may further include any number of program
modules including, but not limited to, an operating system, one or
more application programs, other program modules, program data, and
any combinations thereof.
[0185] Computer system 4600 may also include a storage device 4624.
Examples of a storage device (e.g., storage device 4624) include,
but are not limited to, a hard disk drive, a magnetic disk drive,
an optical disc drive in combination with an optical medium, a
solid-state memory device, and any combinations thereof. Storage
device 4624 may be connected to bus 4612 by an appropriate
interface (not shown). Example interfaces include, but are not
limited to, SCSI, advanced technology attachment (ATA), serial ATA,
universal serial bus (USB), IEEE 1394 (FIREWIRE), and any
combinations thereof. In one example, storage device 4624 (or one
or more components thereof) may be removably interfaced with
computer system 4600 (e.g., via an external port connector (not
shown)). Particularly, storage device 4624 and an associated
machine-readable medium 4628 may provide nonvolatile and/or
volatile storage of machine-readable instructions, data structures,
program modules, and/or other data for computer system 4600. In one
example, software 4620 may reside, completely or partially, within
machine-readable medium 4628. In another example, software 4620 may
reside, completely or partially, within processor 4604.
[0186] Computer system 4600 may also include an input device 4632.
In one example, a user of computer system 4600 may enter commands
and/or other information into computer system 4600 via input device
4632. Examples of an input device 4632 include, but are not limited
to, an alpha-numeric input device (e.g., a keyboard), a pointing
device, a joystick, a gamepad, an audio input device (e.g., a
microphone, a voice response system, etc.), a cursor control device
(e.g., a mouse), a touchpad, an optical scanner, a video capture
device (e.g., a still camera, a video camera), a touchscreen, and
any combinations thereof. Input device 4632 may be interfaced to
bus 4612 via any of a variety of interfaces (not shown) including,
but not limited to, a serial interface, a parallel interface, a
game port, a USB interface, a FIREWIRE interface, a direct
interface to bus 4612, and any combinations thereof. Input device
4632 may include a touch screen interface that may be a part of or
separate from display 4636, discussed further below. Input device
4632 may be utilized as a user selection device for selecting one
or more graphical representations in a graphical interface as
described above.
[0187] A user may also input commands and/or other information to
computer system 4600 via storage device 4624 (e.g., a removable
disk drive, a flash drive, etc.) and/or network interface device
4640. A network interface device, such as network interface device
4640, may be utilized for connecting computer system 4600 to one or
more of a variety of networks, such as network 4644, and one or
more remote devices 4648 connected thereto. Examples of a network
interface device include, but are not limited to, a network
interface card (e.g., a mobile network interface card, a LAN card),
a modem, and any combination thereof. Examples of a network
include, but are not limited to, a wide area network (e.g., the
Internet, an enterprise network), a local area network (e.g., a
network associated with an office, a building, a campus or other
relatively small geographic space), a telephone network, a data
network associated with a telephone/voice provider (e.g., a mobile
communications provider data and/or voice network), a direct
connection between two computing devices, and any combinations
thereof. A network, such as network 4644, may employ a wired and/or
a wireless mode of communication. In general, any network topology
may be used. Information (e.g., data, software 4620, etc.) may be
communicated to and/or from computer system 4600 via network
interface device 4640. In some embodiments, one or more cloud
computing services, "software as a service" services, "storage as a
service" services, and/or distributed networks or components, among
others, may be used to receive, store, and/or provide data and/or
execute software in accordance with aspects of the present
disclosure, as will be understood by those of ordinary skill in the
relevant art after reading this disclosure in its entirety.
[0188] Computer system 4600 may further include a video display
adapter 4652 for communicating a displayable image to a display
device, such as display device 4636. Examples of a display device
include, but are not limited to, a liquid crystal display (LCD), a
cathode ray tube (CRT), a plasma display, a light emitting diode
(LED) display, and any combinations thereof. Display adapter 4652
and display device 4636 may be utilized in combination with
processor 4604 to provide graphical representations of aspects of
the present disclosure. In addition to a display device, computer
system 4600 may include one or more other peripheral output devices
including, but not limited to, an audio speaker, a printer, and any
combinations thereof. Such peripheral output devices may be
connected to bus 4612 via a peripheral interface 4656. Examples of
a peripheral interface include, but are not limited to, a serial
port, a USB connection, a FIREWIRE connection, a parallel
connection, and any combinations thereof.
[0189] Device embodiments disclosed herein also may measure other
physiologic data, and integrate that data in its reporting and
analysis. It might be used at different times to treat different
conditions. For example, the IVC diameter and its variation will be
significantly different while the patient is standing in comparison
to when the patient is sitting, prone, or supine. Therefore, the
IVC monitor can also be used to track patient activity. Also,
electrodes can be placed on the IVC element itself and/or on the
leads leading to the device, in order to monitor, record, and
communicate the heart's electrical activity.
[0190] Although a primary indication described for embodiments
disclosed herein is the management of heart failure, embodiments
and information collected thereby may be used for management of
other conditions as well. For example, it could also be
simultaneously used to manage blood volume in patients undergoing
dialysis, providing direct feedback to dialysis machines to
modulate total fluid volume delivered or removed. It could
similarly be used to communicate with IV pumps to manage
re-hydration for patients who have acute episodes of shock.
[0191] As described above, embodiments may be connected to a drug
pump or stimulator to modulate the renal nerves, due to the
multiple indirect effects the renal nerves have on heart failure.
If a device of such embodiments is also monitoring heart rhythm
status as well and detected an episode of atrial fibrillation, it
could be programmed to modulate the renal nerves in that situation
as well. Afferent renal nerves are known to increase systemic
sympathetic tone, and increased systemic sympathetic tone increases
the risk of atrial fibrillation, so temporary denervation of the
renal nerves might cause the episode of atrial fibrillation to
terminate.
Use of IVC Volume Measurement in Dialysis Patients
[0192] Volume management in dialysis patients can be particularly
challenging, since the kidneys are not providing normal volume
homeostasis. Dialysis patients typically increase their fluid
volume between dialysis sessions. Since the kidneys are not making
urine, excess volume needs to be removed during dialysis, along
with the other waste products which dialysis filters out. However,
most of the excess volume is in the cells and interstitial volume,
not in the circulatory system. It takes time, typically more than
an hour, for that volume to re-enter the circulatory system as
other fluid is removed from the blood. The excess volume should not
be removed too quickly, as that would lead to excessive
hemoconcentration and potentially dangerously low blood pressure.
Excessive hemoconcentration can cause myocardial stunning and other
significant dangers. Moreover, it may be difficult and impractical
for the care provider managing the dialysis process to track the
patient's blood volume continuously during the dialysis session.
Therefore, excess fluid is typically removed very gradually over
the course of a dialysis session. This reduces the rate at which
intracellular and extracellular fluid returns to the vascular
system, and makes the overall dialysis session less efficient. An
efficient and effective method to measure circulating blood volume
real-time during dialysis is needed.
[0193] Secondly, it is important to remove as much volume as is
safely possible over the course of the complete dialysis session.
As mentioned, fluid volume builds up in patients between dialysis
sessions. This leads to many potential clinical issues, including
high blood pressure, fluid in the lungs, fibrosis, and heart
failure. If the patients leave each dialysis session with a minimum
of fluid in their systems, that increases the chances that they
will not be overloaded with fluid by the time they return for their
next session. However, determining whether the patient is euvolemic
(has the right fluid volume) or is hyper- or hypo-volemic is
challenging with current techniques. An effective method to measure
final blood volume in dialysis patients at the end of dialysis
sessions is therefore also an important need.
[0194] At present, blood concentration during dialysis is often
measured using devices such as Fresenius' Critline or Intelomedics'
CVinsight. These systems measure the patient's hematocrit and blood
oxygenation to calculate the fluid volume removed from the patient.
Assessing euvolemia at the end of dialysis may be done using
`BioImpedance measurement`, which gives an indication of
extracellular and intracellular fluid volume in the patient. These
measurements are imperfect, but are the best available at this
time.
[0195] Measurement of a dialysis patient's volume status using
ultrasound imaging of the IVC has been studied. It gives an
important physiologic reading of the patient's volume status, one
which relates directly to whether the patient is truly euvolemic.
However, it is user-dependent, technology-sensitive, and difficult.
It also gives only a single-point measurement, and is completely
impractical as a method of continuously measuring volume
status.
[0196] For all of these reasons, IVC volume measurement systems
embodied in the present disclosure provide an improved method of
managing the dialysis patient's volume status. Described systems
provide for continuous monitoring and give a true measurement of
whether the patient is hyper-, hypo-, or euvolemic, and can be used
to guide therapy. The IVC markers described herein, when implanted
on or in the IVC wall, allow a patient's fluid volume to be
monitored before, during or after a dialysis session. Because
dialysis is typically conducted in a specialized facility staffed
by healthcare providers, readings could be taken by trained
professionals to ensure accuracy. In addition, with the patient
being immobile in a chair or bed during dialysis, an ultrasound
probe may be attached to the patient's skin to provide continuous
monitoring of the IVC markers during the dialysis session. The IVC
volume monitor may be connected directly to the dialysis machine,
for closed-loop volume management. For example, an appropriate
minimum blood volume may be established by the healthcare provider;
for example, as an average 40% variation in IVC dimension over the
respiratory cycle. The dialysis machine could then be programmed to
reduce the blood volume at a measured, but relatively rapid pace
until that volume is reached, and then to maintain that volume over
the rest of the dialysis session. This approach would maximize the
intracellular and extracellular fluid that is removed from the
patient, while preventing the patient from risk of myocardial
stunning, lightheadedness, or the other dangers of hypovolemia. It
may be possible to shorten the dialysis session slightly as a
result. At the end of the dialysis session, the IVC monitor would
reconfirm that the patient was appropriately euvolemic before
ending the session.
[0197] All of this discussion of volume management in dialysis
patients applies equally to the management of heart failure
patients who are having volume removed using an aquapheresis system
such as the CHF Solutions Aquadex, or when using aggressive
diuretics. It is desirable to remove the excess volume as quickly
as possible, but also to allow time for the excess volume in tissue
to gradually return to the bloodstream, so that overall blood
volume does not drop too low, nor the blood become too
concentrated.
Measurement of Volume Status in Other Vessels Besides the IVC
[0198] The discussion of the various alternative embodiments above
is generally made in the context of measurement of volume in the
IVC. However, these embodiments also apply to and may be used for
similar measurements in the superior vena cava (SVC), right atrium,
or other vessels. The variation in IVC volume over the respiratory
cycle has been well documented in studies using ultrasound imaging.
The mild valsalva effect of respiration causes a slight variation
in thoracic pressure, which modulates the flow of blood from the
IVC (in the abdomen) into the right atrium (in the thorax).
Therefore, this variation may be more pronounced in the IVC than in
other vessels. IVC variation may also be more sensitive to
variations in right atrial pressure, which may vary less in
patients with marked volume overload causing tricuspid
regurgitation or reduced right ventricular filling volume. However,
very sensitive measurement systems might measure similar variations
in vessels that are more accessible for the placement of markers
and/or for placement of a measurement device. The subclavian veins,
jugular veins, and femoral veins, among others, are all potential
vessels for measurement of volume and volume variation that could
provide similar information about a patient's blood volume and/or
heart failure status. However, the teachings of this disclosure are
not so limited and may be applied by persons of ordinary skill to
any vein in the body, using the sensitive measurement techniques
described herein. Further features, considerations and embodiments
are described below, which may be incorporated singly or multiply
into one or more embodiments described above. For example,
discussed above is the use of the sensor/monitor input to modify
the action of cardiac pacemakers to better control the heart and
circulatory system. Another embodiment or method of treating heart
failure, and more specifically the fluid overload associated with
heart failure, is through chemical, neural, hormonal, or electrical
manipulation of the renin-angiotensin system and the degree to
which the kidneys excrete or retain water.
[0199] Exemplary embodiments have been disclosed above and
illustrated in the accompanying drawings. It will be understood by
those skilled in the art that various changes, omissions and
additions may be made to that which is specifically disclosed
herein without departing from the spirit and scope of the present
disclosure.
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