U.S. patent application number 11/831643 was filed with the patent office on 2008-03-27 for cardiac rhythm management system with intramural myocardial pacing leads and electrodes.
This patent application is currently assigned to Richard C. Satterfield. Invention is credited to Jeanne M. Lesniak, William P. Santamore.
Application Number | 20080077217 11/831643 |
Document ID | / |
Family ID | 31188425 |
Filed Date | 2008-03-27 |
United States Patent
Application |
20080077217 |
Kind Code |
A1 |
Santamore; William P. ; et
al. |
March 27, 2008 |
CARDIAC RHYTHM MANAGEMENT SYSTEM WITH INTRAMURAL MYOCARDIAL PACING
LEADS AND ELECTRODES
Abstract
Medical devices and therapeutic methods for use in the field of
cardiology, cardiac rhythm management and interventional
cardiology, and more specifically to catheter-based systems for
implantation of pacing leads and electrodes, or intramural
myocardial reinforcement devices, within the myocardial wall of the
heart, such as the ventricles, to provide improved cardiac
function.
Inventors: |
Santamore; William P.;
(Medford, NJ) ; Lesniak; Jeanne M.; (Natick,
MA) |
Correspondence
Address: |
RISSMAN JOBSE HENDRICKS & OLIVERIO, LLP
100 Cambridge Street
Suite 2101
BOSTON
MA
02114
US
|
Assignee: |
Satterfield; Richard C.
Wellesley
MA
|
Family ID: |
31188425 |
Appl. No.: |
11/831643 |
Filed: |
July 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10626602 |
Jul 25, 2003 |
|
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|
11831643 |
Jul 31, 2007 |
|
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60398586 |
Jul 26, 2002 |
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Current U.S.
Class: |
607/120 ;
607/122 |
Current CPC
Class: |
A61N 1/056 20130101;
A61N 1/057 20130101; A61N 1/0568 20130101; A61N 1/0587
20130101 |
Class at
Publication: |
607/120 ;
607/122 |
International
Class: |
A61N 1/05 20060101
A61N001/05 |
Claims
1. A method for direct localized therapeutic treatment of
myocardial tissue in heart having a pathological condition
comprising the steps of: a. identifying a target region of the
myocardium having an epicardial region and an endocardial region
and an intramural space defined between; b. delivering a lead
having an electrode to said intramural space; wherein said
electrode is configured to be connected to a therapeutic or
diagnostic device, and wherein the mechanical properties of at
least a portion of the myocardial tissue of the target region
substantially identified in step (a) is physically modified.
2. The method of claim 1 wherein the modified mechanical properties
include an increase in systolic performance.
3. The method of claim 1 wherein the therapeutic or diagnostic
device is a pacemaker.
4. The method of claim 1 wherein the therapeutic or diagnostic
device is a cardioverter/defibrillator.
5. The method of claim 1 wherein the therapeutic or diagnostic
device is a cardiac resynchronization device.
6. The method of claim 2 wherein the modified mechanical properties
include substantially no decrease in diastolic performance.
7. The method of claim 1, wherein said target region includes a
myocardial infarct or ischemic zone.
8. The method of claim 7, wherein the lead includes an electro
active bridge for spanning said infarct or ischemic zone.
9. The method of claim 1, wherein said delivering step further
comprises delivering a substantially arcuately curved lead into the
intramural space.
10. The method of claim 9 wherein said delivering step further
comprises using a stylet.
11. The method of claim 9 wherein said delivering step further
comprises using a guidewire.
12. The method of claim 1, wherein said lead further comprises echo
features for aiding visualization.
13. The method of claim 1, wherein said lead further comprises
radiopaque features.
14. The method of claim 1, wherein said lead further comprises a
drug eluting surface.
Description
DESCRIPTION OF THE INVENTION
[0001] This application claims the benefit of U.S. Provisional
Application 60/398,586 filed on Jul. 26, 2002.
FIELD OF THE INVENTION
[0002] The invention relates generally to medical devices and
therapeutic methods for their use in the field of cardiology,
cardiac rhythm management and interventional cardiology, and more
specifically to catheter-based systems for implantation of pacing
leads and electrodes, or intramural myocardial reinforcement
devices, within the myocardial wall of the heart, such as the
ventricles, to provide improved cardiac function.
BACKGROUND OF THE INVENTION
[0003] In the normal heart, the electrical activity, which
initiates the subsequent mechanical contraction, is very organized.
In general, once one cell is activated, the adjacent cells of the
heart will become activated to propagate the electrochemical
depolarization associated with systolic contraction of the heart
muscle. Unlike skeletal muscle, each heart muscle is electrically
connected to its neighbors. This activation usually starts in the
right atrium, in the sinoatrial node. From here, the electrical
activity spreads across the right and left atrium through either
special conduction (i.e., faster pathways) or through normal atrial
tissue. To electrically activate the main pumping chambers of the
heart, the left and right ventricles, the electrical activity
passes through the atrioventricular node. Within this node, the
spread of electrical activity is relatively slow. Mechanically,
this allows the atrium to contract and pump blood into the
ventricles before the ventricles contract.
[0004] Following this relatively slow spread of cardiac action
potential, the electrical activation travels rapidly down a special
conduction pathway, known as the bundle of His. The bundle of His
divides into right and left bundle branches; the left dividing in
turn into an anterior and posterior branch. This network consists
of high-speed conduction fibers, known as the Purkinje fibers. From
here, the remaining ventricular muscle cells are activated. This
high-speed network is essential for a synchronized contraction of
each ventricle relative to associated atria, and for efficient,
mechanical synchrony between the left and right ventricles.
[0005] Ischemic heart disease and other clinical problems
(fibrosis, etc.) can cause conduction delays and/or blockage in
this high-speed network. For example, a left bundle branch block
leads to late electrical activation of the left ventricular free
wall. These conduction problems change the QRS complex in the ECG
to a wide QRS complex greater than 120 ms. The corresponding
electrical conduction delays cause mechanical dysfunction,
decreased cardiac output, as well as valvular regurgitation.
Clinical studies have shown early septal circumferential
shortening, followed by late stretch as the left ventricular free
wall shortenings begins (Kawaguchi M, Murabayashi T, Fetics B J,
Nelson G S, Sarmejima H, Nevo E, Kass D A. Quantitation of basal
dyssynchrony and acute resynchronization from left or biventricular
pacing by novel-contrast variability imaging. Journal of the
American College of Cardiology 2002; 39:2052-8.). This
electrical-mechanical dyssynchrony decreases cardiac output and may
cause or exacerbate mitral regurgitation.
[0006] The electrical synchrony can be partially restored by
biventricular pacing. A pacemaker is implanted in the patient along
with a right atrial, right ventricular, and left ventricular lead.
The right atrial lead is used to sense the electrical activity in
the right atrium and/or to stimulate the right atrium. The
pacemaker senses this electrical activity and after a programmable
delay (i.e., the delay can be different for each ventricle)
electrically stimulates the right and left ventricles, thereby
re-establishing electrical synchrony. The leads can be either
bipolar or unipolar, and general consist of a coiled conductor,
which is electrically isolated from the surrounding tissue.
Numerous materials, such as platinum or tantalum coated MP35N alloy
wire, can be used for the conductor. At the distal end, the
conductor makes electrical contact with the tissue via an
electrode, commonly a ring electrode. The electrode can elude an
anti-inflammatory cortico-steroid, such as sodium dexamethasone, to
reduce irritation of tissue adjacent to the electrode. Insulation
materials such as polyurethane, silicone, and ethylene tetrafluor
ethylenefluoropolymer are used. The proximal end is directly
connected to the pacemaker through an IS-1 standard connector with
a sealing-ring (de Voogt W G, Pacemaker leads: Performance and
progress. American Journal of Cardiology 1999; 83:187 D-191D).
[0007] Initial clinical trials show that resynchronizaton therapy
increases exercise capacity and peak oxygen consumption, increases
left ventricular ejection fraction, and decreases left ventricular
end-diastolic size: all very positive changes for patients with
heart failure. These studies also indicate that left ventricular
pacing may be as effective as biventricular pacing (Abraham W T,
Fisher W G, Smith A L, Delurgio D B, Leon A R, Loh E, Kocovic D Z,
packer M, Clavell A L, Hayes D L, Ellestad M, Messenger J. Cardiac
resynchronization in chronic heart failure. New England Journal of
Medicine 2002; 346:1845-53).
[0008] A major technical and clinical challenge associated with
these applications concerns the issue of how to place a left
ventricular free wall electrode. A typical location for this left
ventricular lead is the lateral left ventricular free wall mid way
between the base and apex (Auicchio A, Klein H, Tockman B, Sack S,
Stellbrink C, Neuzner J, Kramer A, Ding J, Pochet T, Maarse A,
Spinelli J. Transvenous biventricular pacing for heart failure: can
the obstacles be overcome? American Journal of Cardiology 1999;
83:136 D-142D.). A specialized left ventricular lead is placed into
a distal cardiac vein by way of the coronary sinus through a
guiding catheter. For example, the EASYTRACK system (Guidant, St.
Paul, Minn.) is a transvenous, coronary venous, unipolar pace/sense
lead for left ventricular stimulation. [Purerfellner H, Nesser H J,
Winter S, Schwierz T, Hornell H, Maertens S. Transvenous left
ventricular lead implantation with the EASYTRACK lead system: The
European experience. Am J Cardiol 2000; 86 (suppl): 157K-164K.] The
lead is delivered through a guiding catheter with a specific design
to facilitate access to the ostium of the coronary sinus. This
catheter provides pushability by incorporating an internal
braided-wire design. The distal end of the catheter features a soft
tip to prevent damaging of the right atrium or the coronary sinus.
The EASYTRACK lead has a 6 Fr. outer diameter and an open-lumen
inner conductor coil that tracks over a standard 0.014-inch
percutaneous transluminal coronary angioplasty guidewire. The
distal end of the electrode consists of a flexible silicone rubber
tip designed to be atraumatic to vessels during lead
advancement.
[0009] In many patients (i.e., at least 10%), either the lead
cannot be placed or complications (e.g., dissection or perforation
of the coronary sinus or cardiac vein, complete heart block,
hemopericardium, and cardiac arrest) occur (Abraham 2002). Because
of these difficulties, the left ventricular lead is sometimes
placed through a small thoracotomy (Auricchio A, Stellbrink C, Sack
S, Block M, Vogt J, Bakker P, Huth C, Schondube F, Wolfhard U,
Bocker D, Krahnefeld O, Kirkels H. Long-term clinical effect of
hemodynamically optimized cardiac resynchronization therapy in
patients with heart failure and ventricular conduction delay.
Journal of the American College of Cardiology 2002;
39:2026-33.).
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, devices and
methods are provided for an effective intervention, which
contemplates the implantation of intramural, myocardial pacing
leads and electrodes, as well as implants for localized
reinforcement of infarcted myocardial tissue, by delivery from the
right ventricle directly into the left ventricular free wall.
[0011] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate one (several)
embodiment(s) of the invention, and together with the specification
serve to explain the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1a is a cross-sectional, planar view of the left and
right ventricles with the distal end of a guide catheter wedged
into the junction of the right ventricular free wall and the
interventricular septum, to facilitate introduction and implanting
of a pacing lead within the intramural myocardial tissue of the
heart.
[0013] FIG. 1b depicts an intramural pacing lead with multiple
electrode sites for pacing.
[0014] FIG. 1c illustrates multiple, intramural pacing leads
implanted within the left ventricular myocardium.
[0015] FIG. 2 illustrates an implantable, intramural pacing lead
which is introduced along a curved trajectory to simplify
introduction.
[0016] FIGS. 3a-3c illustrate several examples of pacing lead tips
which enhance echo-based imaging to facilitate placement.
[0017] FIG. 4a illustrates the resistance forces associated with
the endocardial or epicardial surfaces during lead/electrode
introduction.
[0018] FIG. 4b illustrates an exemplary pacing lead with a
spherical shaped tip to enhance echo-based imaging and minimize
likelihood of lead introduction inadvertently piercing the
epicardial tissue during introduction.
[0019] FIG. 4c depicts an exemplary pacing lead having a shaped tip
and deflectable shaft to minimize forces exerted against the
epicardial surface during lead introduction.
[0020] FIGS. 5a-5d illustrate several exemplary anchoring elements
for the intramural pacing lead/electrode system.
[0021] FIG. 6a illustrates shaft designs for the intramural
lead/electrode systems.
[0022] FIG. 6b illustrates an exemplary, reduced-profile lead
design.
[0023] FIG. 6c illustrates an exemplary design providing for an
external coiled wire around the intramural lead.
[0024] FIG. 6d illustrates an external coiled wire incorporated
into the outer insulator of an exemplary intramural lead.
[0025] FIG. 7 illustrates exemplary designs for a tapered pacing
lead, including a distal feature to provide enhanced echo-based
imaging and tracking.
[0026] FIG. 8 depicts two pacing leads, placed circumferentially
and spaced-apart vertically, to enable a uniform current
distribution throughout the myocardium.
[0027] FIGS. 9a and 9b depict placement of a coil electrode segment
of the left ventricular lead located in the lateral wall close to
the base of the heart, and a coil electrode segment of the right
ventricular lead placed by the apex of the heart.
[0028] FIG. 10 illustrates one possible configuration for the left
ventricular lead.
[0029] FIG. 11 depicts an exemplary myocardial reinforcement device
implanted within an anterior wall infarct with the proximal end of
the device connected to a lead.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0030] Reference will now be made in detail to exemplary
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts.
[0031] Introduction and placement of appropriate ventricular pacing
leads and electrodes are the subject of this application, as well
as improved methods for introducing myocardial tissue reinforcement
devices within the intramural space. It is believed that several
problems associated with traditional introduction and placement of
left ventricular pacing leads can be circumvented according to the
present invention, which provides for placement of the lead
directly into the intramural space of the left ventricular
myocardium via right ventricular catheter introduction.
[0032] FIG. 1 depicts a cross-sectional, planar, short-axis view of
the left and right ventricles. Using a novel technique, a guide
catheter is first introduced via a vein (e.g., right external
jugular vein) and advanced into the right ventricle. The distal end
of the guide catheter is wedged into the junction of the right
ventricular free wall and the interventricular septum. X-ray or
echo-based imaging facilitates this catheter positioning. In this
example, the guide catheter is placed by the anterior surface, but
the guide catheter can also be placed by the posterior surface. A
straight pacing lead is pushed from the guide catheter directly
into the intramural tissues of the myocardium. The pacing lead and
electrode system is advanced well into the left ventricular free
wall comprising the intramural tissues. In this example, an
imaginary position designated in FIG. 1, indicated at a 0 degree
position, representing the ideal ventricular lead placement. The
right ventricular free walls intercept the left ventricle at
approximately 120 and 240 degrees. It is understood that most
straight pacing leads are capable of reaching locations
approximately 30 degrees away from the 0 degree position. In many
patients, the conduction delays are not symmetrical between the
anterior and posterior wall. If the posterior wall were activated
first, then the pacing lead position, as depicted in FIG. 1a, is
ideal.
[0033] FIG. 1b illustrates an exemplary pacing lead providing
multiple sites for intramural pacing. In between these pacing
spots, the lead is electrically isolated for the myocardium. At the
pacing sites, the lead can be provided with appropriately
spaced-apart electrodes along its distal shaft which establish a
direct electrical contact with the myocardium at desired locations.
All the sites or selected sites can be used to re-establish
electrical synchrony.
[0034] FIG. 1c illustrates an exemplary anterior pacing lead within
the myocardium. The guide catheter has been removed, and the lead
has been connected to the stimulator. A second pacing lead can be
similarly placed. The guide catheter is repositioned by the
posterior junction of the septum and the right ventricular free
wall. A straight pacing lead is advanced from the guide catheter
into the posterior left ventricular free wall.
[0035] FIG. 2 illustrates a cross-sectional, planar, short-axis
view of the left and right ventricles with the distal end of the
guide catheter wedged into the junction of the right ventricular
free wall and the interventricular septum. In this example with a
simple curve, the pacing lead is advanced well into the left
ventricular free wall, well beyond the 0 degree point. Thus with a
simple curve, in this case similar to the curvature of the left
ventricular epicardial surface, the pacing lead is placed well into
the left ventricular free wall.
[0036] Numerous methods are available to achieve a curved pacing
lead. For example, if the distal portion of the pacing lead is
straight, a curved stylet inserted along its length can induce a
curve in the distal portion of the lead. The curvature of the
stylet can be selected to match the corresponding curvature of the
heart. Guide wires have been developed with a preferred shape or
are steerable. U.S. Pat. No. 5,769,796 issued to Palermo, for
example, describes a super-elastic composite guidewire. This is a
composite guidewire for use in a catheter and is used for accessing
a targeted site in a patient's body. The guidewire core or
guidewire section may be of a stainless steel or a high elasticity
metal alloy, preferably a nitinol-type of super-elastic alloy, also
preferably having specified physical parameters. The composite
guidewire assembly is especially useful for accessing peripheral or
soft tissue targets. Variations include multi-section guidewire
assemblies having, in part, super-elastic distal portions and
super-elastic braided reinforcements along the mid or distal
sections. U.S. Pat. No. 5,480,382 issued to Hammerslag and U.S.
Pat. No. 6,165,139 issued to Damadian, for example, describe
steerable guidewires. In certain cases, a movable pull wire extends
through the guide wire to its tip. Pulling on this wire causes the
tip of the guide wire to bend. Similar approaches can be employed
to steer a pacing lead.
[0037] Several imaging techniques are available (e.g., X-ray, MRI,
echocardiography) to follow or track pacing lead placement. In
cardiac catheterization laboratories, for example, X-ray imaging is
often used to position catheters within the right ventricular
chamber. The same equipment and imaging can be used in the
positioning of the pacing lead within the intramural space of the
myocardium. For example, once the pacing lead is within the
myocardial tissue, the relative circumferential or base-to-apex
direction of the guidewire advance can be easily observed. The
relative endo-to-epicardial positioning is somewhat more difficult
to ascertain, but it can be inferentially or relatively determined
in response to the movement of the pacing lead in relationship to
the left ventricular cavity.
[0038] The positioning of the pacing lead into the left ventricular
myocardium can also be guided by echocardiography. Ultrasound
imaging, echocardiography, is widely available and provides
excellent visualization of cardiac structures. Echocardiographic
guidance can facilitate placing the lead. The echo images can help
with the positioning of pacing lead within the myocardium. In real
time, the echo images provide the exact positioning of these leads
within the myocardium. This real time imaging makes placement of
these leads easier. Transthoracic and transesophageal
echocardiographic views can also be used.
[0039] The lead itself is made more visible under echo by having
multiple surface features to reflect the echo sound. A simple
example of this surface is the commonly used clinical braided or
coiled guide wire. One potential difficulty with using echo
guidance is to follow the tip of the pacing lead. The rest of the
pacing lead must follow the tip, so knowledge of tip position is
critical. A two-dimensional echo view takes a thin slice, in
effect, across the left ventricle. With this thin slice, the tip of
the pacing lead may move out of the field of view, and thus may not
be easily recognized. FIG. 3a, for example, depicts a
uniformly-shaped tip for a pacing lead. This shaped tip may be hard
to follow accurately under echo. Simple variations of this design
are depicted in FIGS. 3b-3c, to facilitate tracking. By having a
known, different shape at the tip of the pacing lead, the exact
position of the tip can be easily followed.
[0040] The pacing lead itself can be modified or altered to
increases its visualization under echo. As described in U.S. Pat.
No. 6,053,870, transverse notches in the lead increase the echo
reflecting area, thus enhancing the ultrasound image. As described
in U.S. Pat. No. 6,106,473, the lead can be coated with material to
enhance its echogenicity. The lead can also generate sound waves as
described in U.S. Pat. No. 5,967,991. A piezo-driver assembly is
coupled to the lead, causing the tip to vibrate. These vibrations
can be matched to the frequency of the echocardiographic
transducer. (Armstrong G, Cardon L, Vilkomerson D, Lipson D, Wong
J, Rodriguez L L, Thomas J D, Griffin B P. Localization of needle
tip with color doppler during pericardiocentesis: In vitro
validation and initial clinical application. J Am Soc Echocardiogr
2001 January; 14(1):29-37).
[0041] During placement, it is also possible to ascertain the
relative position of the pacing lead within the myocardium, based
upon the inherent tissue property differences of the intramural
space and boundary tissues of the epicardium. The actual resistance
to pushing the pacing lead is very different on the surfaces versus
the interior of the myocardium, and the tactile feedback of the
user will likely suffice to confirm the relative position is being
maintained within the intramural space. FIG. 4a illustrates these
differences, and it can be appreciated that piercing or exiting the
endocardial or epicardial surface requires more force than pushing
the pacing lead through the interior myocardium. Consequently,
these physical characteristics of the heart can be used to keep the
pacing lead within the myocardium. FIG. 4b illustrates a
cross-sectional view of the left ventricle, including a pacing lead
with a spherical shaped tip introduced into the left ventricular
free wall. The tip is being pushed against the epicardial surface.
The angle at which the tip is being pushed against the epicardium
and the spherical shape of the tip create a very high force, which
opposes the pacing lead from being pushed through the epicardium.
The force or resistance deflects the tip and keeps the pacing lead
within the myocardium as the lead is advanced, as shown in FIG. 4c.
The pacing lead thus remains just below the epicardial surface as
it is pushed around the left ventricular free wall.
[0042] Adjusting the strength or stiffness of the pacing lead can
also assist this restraining force. To accomplish this purpose, the
ideal lead would incorporates two extreme functions, namely, being
relatively stiff to provide column strength along its length for
pushing the lead into the myocardial tissue, while offering a
relatively flexible or floppy distal segment to avoid trauma to the
epicardial surface and provide the desired steering
characteristics. By selecting the appropriate balance of structural
features and flexibility, the pacing lead can be advanced into the
myocardium with relatively modest prospect of inadvertently exiting
through the epicardium or endocardium. The pacing leads will thus
preferably have variable flexibility along the length of the lead.
U.S. Pat. No. 6,146,339 issued to Biagtan, for example, describes a
guide wire with operator controllable tip stiffness. Many different
approaches are available to vary the stiffness of the pacing leads.
For example, U.S. Pat. No. 5,957,903 issued to Mirzaee describes a
guidewire whose stiffness is adjusted by advancing or retracting a
movable core within the guidewire.
[0043] The anchoring element comprises another important component
of the lead system. Once the pacing lead is properly positioned,
the anchoring element is deployed to maintain the pacing lead in
this position. FIGS. 5a-5d illustrate several exemplary anchoring
elements for the intramural pacing lead/electrode system. FIG. 5d,
for example, provides an anchoring element serving dual functions,
namely, preventing the pacing lead from exiting the epicardium and
keeping the lead in its proper position within the intramural space
of the myocardium.
[0044] FIGS. 6a and 6b illustrate alternative body designs for the
leads. FIG. 6a depicts a traditional design for a bipolar lead. An
electrical insulator separates two conductors, and both conductors
are enclosed within an outer insulator. The conducting wire is not
insulated. FIG. 6b depicts shows a design where both conducting
wires are insulated and enclosed within an outer insulator, which
offers a reduced profile design. As described above, however, these
standard designs may be less suitable for the right ventricular
placement of the left ventricular pacing lead, since their
relatively smooth surfaces will not likely image well under echo
techniques. Without distinctive features, it is believed that the
distal end of the lead would be hard to follow during placement
with echo guidance. More importantly, the stiffness characteristics
of these standard leads are not suitable to provide the column
strength necessary to advance the leads through myocardial tissues.
As these leads are pushed through the tissue, resistance to further
insertion increases until one portion of the lead buckles. At this
point, the lead cannot be further advanced. Since these traditional
leads are not currently designed for applications of this type,
modifications are believed necessary to minimize tissue irritation
and the build-up of scar tissue by the electrodes.
[0045] Therefore, a new lead design is required for the right
ventricular introduction and placement of the left ventricular lead
within the intramural space of the myocardium. As described in U.S.
Pat. No. 6,106,473, the outer insulator of the lead is coated with
material to enhance its tracking characteristics and echogenicity.
FIGS. 6c and 6d show additional surface features to increase the
echogenicity of the lead. In FIG. 6c, an external coiled wire is
wrapped around the lead, which provides a lead that is more visible
under echo (by having an echogenic coating and including multiple
surface features to reflect the echo sound). In FIG. 6d, an
external coiled wire is incorporated into the outer insulator of
the lead. The outer insulator of the lead is coated with material
to enhance its echogenicity. This lead is more visible under echo
by having the multiple surface features to reflect the echo sound
and by the surface coating.
[0046] In connection to the leads described in FIGS. 6c and 6d,
FIG. 7 illustrates a relatively extended distal section of the
lead. The distal end of the lead has a distinctive feature, which
facilitates echo tracking. In this example, the tip has a spherical
shape. This shape can be solid or a wire mess to reduce tissue
trauma. In other designs, additional imaging-enhancing features can
be employed, including the ring electrode itself. Since the smooth
metal surface of the electrode may offer reduced echo visibility, a
contrast can be incorporated in the design which better
distinguishes the echogenic wire wrap part of the lead versus the
echolucent electrode associated with the tip of the lead.
[0047] By selecting the appropriate lead strength or stiffness, the
lead is able to be easily introduced into the intramural space,
while posing a reduced likelihood of inadvertently piercing
epicardial or endocardial surfaces. As shown in FIG. 7, for
example, the thickness and relative stiffness of the leads
desirably varies along the length of the electrode to support
steering through the myocardial tissue and provide conformity with
the curved, ventricular free walls. The flexibility of the tip
minimizes long-term trauma with the surrounding tissue, resulting
in decreased scar formation by the electrodes, and thus providing
better long-term electrical pacing characteristics.
[0048] Other components of the pacing leads are constructed by
standard techniques known to those familiar with the arts. Numerous
materials, such as platinum or tantalum coated MP35N alloy wire,
can be used for the conductor. At the distal end, the conductor
makes electrical contact with the tissue via an electrode, commonly
a ring electrode. The electrode can elude an anti-inflammatory
cortico-steroid such as sodium dexamethasone to reduce irritation
of tissue adjacent to the electrode. Insulation materials such as
polyurethane, silicone, and ethylene tetra
fluorethylenefluoropolymer are used. The proximal end is directly
connected to the pacemaker through an IS-1 standard connector with
a sealing-ring.
[0049] In addition to the use of the above-described use of the
present invention for support of cardiac resynchronization
therapies, further adaptations of the present invention are
contemplated for management of other electrical stimulation
therapies of heart tissue, such as cardiac contractility modulating
signals. Prolonging membrane depolarization by voltage-clamp
techniques applied to isolated cardiac muscle increases
trans-sarcolemmal calcium entry into the cell and thus enhance
contractility (Wood E H, Heppner R L, Weidmann S. Inotropic effects
of electric currents. I. Positive and negative effects of constant
electric currents or current pulses applied during cardiac action
potentials. II. Hypotheses: calcium movements,
excitation-contraction coupling and inotropic effects. Circulation
Research 1969; 24:409-445.). Extracellularly applied electrical
signals have a similar effect as voltage clamping in muscles
isolated from normal animals and failing human hearts. When applied
regionally, electrical currents enhance contractility of normal and
failing hearts in-vivo (Mohrl S, He K L, Dickstein M, Mika Y,
Shimizu J, Shemer I, Yi G H, Wang J, Ben-Haim S, Burkhoff D.
Cardiac contractility modulation by electric currents applied
during the refractory period. American Journal of Physiology 2002;
282:H1642-H1647.).
[0050] While this concept of altering regional contractility has
many potential advantages, there are currently several limitations
presented when considering traditional leads and electrode
placement techniques. If the leads use ring-type electrodes, for
example, the leads are in-effect only point sources of the current,
and only small regions of the myocardial will experience the
positive contractility effects. Better results could be obtained by
creating a larger electrical field, which generally requires an
electrode with a longer length. In addition to the electrodes
themselves, placement can be a problem. For most patients, however,
left ventricular dysfunction or failure is the main problem. Thus,
the leads need to be positioned within the left ventricle. A
catheter-based introduction approach (i.e., an intracardiac lead
introduced from the left ventricular cavity into the adjacent wall)
can deliver these pacing electrode leads within the left
ventricular cavity, which is believed to present a huge risk for
thrombus formations and embolic clots. For external placement, a
thoracotomy is required.
[0051] The same approaches described above can be employed to place
leads in the left ventricular free wall or septum via a catheter
and without touching the left ventricular endocardial surface. FIG.
8 shows a view of the left ventricular free wall. Embedded within
the left ventricular myocardium are two pacing leads, which are
placed circumferentially, as previously described. In this
illustration, one lead is placed closer to the base, while the
other lead is placed closer the left ventricular apex. The leads
have either continuous or intermittent connection to the
myocardium. In this example, the leads are placed around the entire
left ventricular free wall. Partial coverage of the left
ventricular free wall is also possible. By covering a broad area,
the leads enable a uniform current distribution over a larger
portion of the left ventricle. The leads may optionally include
intramural, myocardial electrode implants that align with
identified areas of myocardial tissue requiring resynchronization
or adjunctive pacing.
[0052] Ventricular fibrillation, chaotic electrical activity of the
ventricular myocardium, is a life-threatening event, if not treated
quickly. Implantable defibrillators sense the heart's electrical
activity and defibrillate the heart when needed. Since the initial
concept, the size and functionality of the implantable
defibrillators have improved. Two defibrillator issues still need
to be resolved, namely, the size of the defibrillators and the
generated electrical field for defibrillation. While these issues
may seem different, the issues are tied together. The magnitude of
the energy required to successfully defibrillate the heart with a
safety margin is a primary determinant of the implantable
defibrillators size. The leads used to distribute the
defibrillation shock determine, in part, how much current will be
needed.
[0053] Initially, pacing leads were placed external to the heart.
Modern pacing systems favor intracardiac leads, which are often
transvascular, venous implants. In one approach, the lead is placed
in the right ventricle adjacent the endocardium, and the
defibrillator itself constitutes the other lead electrode. The
stimulator or pacing current is spread between these two leads,
such that it flows from the right ventricular lead to the
implantable defibrillator, which is often located in the pectoral
region. A disadvantage of this approach is the low current density
delivered to the left ventricular apical region. Another approach,
shown in U.S. Pat. No. 6,370,427 uses leads in both the left and
right ventricular chambers. The shock current can be distributed
between the right and left ventricular leads or between the leads
and the implantable defibrillator. Unfortunately, this approach
fails to provide an even current distribution, and also presents
additional concerns relating to potential lead thrombogenicity when
placed directly within the left ventricular cavity.
[0054] By placing a lead within the left ventricular lateral wall
close to the base of the left ventricle, and positioning the other
lead in the apical right ventricle, a better current distribution
can be achieved. In this example, both ventricular regions will
receive appropriate cardioversion and defibrillator shock. FIGS. 9a
and 9b, for example, show desired lead positions. The coil
electrode segment of the left ventricular lead is placed in the
lateral wall close to the base. Placing the left ventricular lead
within the myocardium further reduces the magnitude of current
needed to successfully defibrillate the heart. The coil electrode
segment of the right ventricular lead is desirably placed within
the right ventricular cavity by the apex. As described above, the
left ventricular lead is positioned just below the epicardial
surface. This placement of the left and right ventricular leads
provides an improved and more predictable current distribution
across both ventricles.
[0055] This left ventricular lead can be placed from the right
ventricle as described for the resynchronization therapy, and can
be used in combination with resynchronization therapy in an
adjunctive manner. FIG. 10 shows one possible configuration for the
lead within the left ventricular myocardium. By selecting the
appropriate lead strength or stiffness, the lead can be advanced
into the myocardium with little chance of exiting through the
epicardium or endocardium. The thickness and stiffness
characteristics of the leads preferably vary along the length of
the electrode. The flexibility of the tip prevents the lead from
penetrating the epicardium or the endocardium. The flexible tip
also minimizes long-term trauma with the surrounding tissues, and
tends to decrease scar formation by the electrodes, thereby
ensuring better long-term electrical characteristics. The stiffer
body component of the proximal portion of the lead enhances
introduction into the myocardium.
[0056] The coil-shaped electrode can be made from a single wire,
but multi-filament wire is preferred. The coil-shape provides a
large surface area to reduce electrical resistance, and more
effectively distributes current density along the desired
myocardial regions of the heart. Platinum clad titanium, platinum
clad tantalum, or platinum coated MP35N wire can be used for the
coil. The coil-shaped electrode portion of the lead makes the
distal end of the lead echogenic, thus making echo tracking during
positioning easier. The electrode is connected to a coil conductor,
which carries the current from the connector pin to the electrode.
Insulation materials such as polyurethane, silicone, and ethylene
tetrafluor ethylenefluoropolymer can be used along the length of
the lead. A conventional connector pin is used to attach the lead
to the implantable defibrillator.
[0057] It is also recognized that the above-described technique for
lead introduction can be practiced to introduce discreet,
implantable devices within the myocardial wall to provide acute
reinforcement of localized ventricular regions damaged by a recent
myocardial infarction. These reinforcement devices can be placed
into the anterior and posterior left ventricular wall, as well as
the septum from a right ventricle, using the approaches described
in this application for placement of LV pacing leads and intramural
pacing electrodes. Again, the steerable catheter is placed into the
right ventricle rather than the left ventricle. The catheter is
positioned against the septum and the guidewire is advanced into
the septum as far as desired into the left ventricular free wall.
The remaining deployment of these reinforcement devices follows the
same steps as generally described above.
[0058] As shown in FIG. 11, the intramural reinforcement can also
be used as an electrical bridge across the infarct region. In this
example, the implantable device is placed across an anterior wall
infarct. The end of the MyoMend device embedded in the normal
lateral wall is in electrical contact with the surrounding tissue.
The body of the device is encapsulated with an insulator. The other
end of the device is connected to a lead, which in turn connects to
a pacemaker. If electrical synchronization therapy is needed, the
left ventricular lateral wall can be stimulated through the
lead/electrode system.
[0059] It is also recognized that the above-described technique for
introducing intramural pacing leads could be accomplished with the
combination of two devices. A novel intramural guidewire and a
separate intramural pacing lead can be used. The guidewire would
possess the features described above and would be optimized for
intramural navigation. The guidewire would include all of the novel
features for pacing and intramural anchoring described in sections
above. The guidewire would be introduced to the target intramural
tissue first and the pacing lead would be introduced second. The
pacing lead and/or guidewire could be of a solid or hollow
design.
[0060] It is also recognized that a device similar to that shown in
FIG. 11 could be fabricated that would be an electro-active bridge.
The device would be placed across the infarct region in a manner
described above. The device would use the heart's systole
deformation to store strain energy and then convert this energy
into electrical energy to be discharged back to the distal end of
the device at the next systolic cycle. This discharge would allow
depolarization to spread to the opposite side of the infarct region
that would otherwise be blocked. The device could also have an
electrical sensing circuit/system and logic within to better time
the exact point of discharge.
[0061] Other embodiments of the invention will be apparent to those
of skill in the art from consideration of the specification and
practice of the inventions disclosed herein. It is intended that
the specification and examples be considered as exemplary only.
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