U.S. patent application number 11/112473 was filed with the patent office on 2005-09-15 for system and method for passively reconstructing anatomical structure.
This patent application is currently assigned to SCIMED LIFE SYSTEMS, INC.. Invention is credited to Quarato, James A., Willis, N. Parker, Zeng, Jinglin.
Application Number | 20050203375 11/112473 |
Document ID | / |
Family ID | 22434674 |
Filed Date | 2005-09-15 |
United States Patent
Application |
20050203375 |
Kind Code |
A1 |
Willis, N. Parker ; et
al. |
September 15, 2005 |
System and method for passively reconstructing anatomical
structure
Abstract
The present invention is a system and method for graphically
displaying a three-dimensional model of a region located within a
living body. A three-dimensional model of a region of interest is
displayed on a graphical display. The location in three-dimensional
space of a physical characteristic (e.g. a structure, wall or
space) in the region of interest is determined using at least one
probe positioned within the living body. The graphical display of
the model is deformed to approximately reflect the determined
three-dimensional location of the physical characteristic.
Preferably, the probe or probes are moved throughout the region of
interest so as to gather multiple data points that can be used to
increase the conformity between the graphical display and the
actual region of interest within the patient.
Inventors: |
Willis, N. Parker;
(Atherton, CA) ; Zeng, Jinglin; (San Jose, CA)
; Quarato, James A.; (Sunnyvale, CA) |
Correspondence
Address: |
Bingham McCutchen, LLP
Suite 1800
Three Embarcadero
San Francisco
CA
94111-4067
US
|
Assignee: |
SCIMED LIFE SYSTEMS, INC.
Maple Grove
MN
|
Family ID: |
22434674 |
Appl. No.: |
11/112473 |
Filed: |
April 22, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11112473 |
Apr 22, 2005 |
|
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|
09128304 |
Aug 3, 1998 |
|
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Current U.S.
Class: |
600/407 |
Current CPC
Class: |
A61B 8/445 20130101;
Y10S 128/92 20130101; A61B 8/4245 20130101; A61B 2017/00243
20130101; A61B 6/541 20130101; A61B 2017/00053 20130101; A61B 8/12
20130101; Y10S 128/922 20130101; A61B 5/287 20210101; A61B 34/10
20160201 |
Class at
Publication: |
600/407 |
International
Class: |
A61B 005/05 |
Claims
1-58. (canceled)
59. A method of graphically reconstructing a region of interest of
a hollow anatomical structure having an interior surface and a
space therein, comprising: acquiring a plurality of anatomical
points within the anatomical space, each of the anatomical points
being automatically acquired at a specified time within a
respective periodic cycle; and generating a three-dimensional
graphical representation of the region of interest based on the
acquired anatomical points.
60. The method of claim 59, wherein the anatomical points comprise
interior points.
61. The method of claim 59, wherein the anatomical points comprise
surface points.
62. The method of claim 59, wherein the periodic cycle is a natural
biological cycle of the anatomical structure.
63. The method of claim 59, wherein generation of the graphical
representation comprises conforming the graphical representation to
the acquired anatomical points.
64. The method of claim 63, wherein conforming the graphical
representation comprises deforming a graphical model to incorporate
at least one of the anatomical points.
65. The method of claim 59, wherein the displayed graphical
representation is stationary.
66. The method of claim 59, further comprising moving a roving
probe within the anatomical space, wherein the anatomical points
are acquired by the roving probe as it is being moved within the
anatomical space.
67. The method of claim 59, wherein the anatomical structure is an
organ.
68. The method of claim 59, wherein the anatomical structure is a
heart, anatomical cavity is a chamber, the interior surface is an
endocardial surface, and the periodic cycle is a cardiac cycle.
69. A system for graphically reconstructing a region of interest on
a hollow anatomical structure having an interior surface and a
space therein, comprising: a roving probe configured for being
moved around within the anatomical space; at least one localization
processor configured for automatically acquiring three-dimensional
locations of at least a portion of the roving probe and deriving
anatomical points from the three-dimensional locations as the
roving probe is moved around within the anatomical space; and at
least one graphical processor configured for generating a
three-dimensional graphical representation of the region of
interest based on the acquired anatomical points.
70. The system of claim 69, wherein the anatomical points comprise
interior points.
71. The system of claim 69, wherein the at least one localization
processor is configured for acquiring each anatomical point at a
specified time within a respective periodic cycle.
72. The system of claim 71, wherein the periodic cycle is a natural
biological cycle of the anatomical structure.
73. The system of claim 71, wherein the at least one graphical
processor is configured for generated conforming the graphical
representation to the acquired anatomical points.
74. The system of claim 73, wherein the at least one graphical
processor is configured for conforming the graphical representation
by deforming a graphical model to incorporate at least one of the
anatomical points.
75. The system of claim 73, wherein the graphical representation is
stationary.
76. A method of graphically reconstructing a region of interest of
a hollow anatomical structure having an interior surface and a
space therein, comprising: acquiring a plurality of interior points
within the anatomical space; and conforming a three-dimensional
graphical representation of the region of interest to the acquired
interior points.
77. The method of claim 76, wherein conforming the graphical
representation comprises deforming a graphical model to incorporate
at least one of the interior points.
78. The method of claim 76, wherein the graphical representation is
only conformed to an outermost set of the interior points.
79. The method of claim 76, further comprising moving a roving
probe within the anatomical space, wherein the interior points are
acquired by the roving probe as it is being moved within the
anatomical space.
80. The method of claim 76, further comprising acquiring at least
one surface point coincident with the interior anatomical surface,
and conforming the graphical representation to the at least one
surface point.
81. The method of claim 76, wherein the anatomical structure is an
organ.
82. The method of claim 76, wherein the anatomical structure is a
heart, the anatomical cavity is a chamber, and the interior surface
is an endocardial surface.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a system for creating a
three-dimensional graphical model of a region within a living body
and for dynamically altering the graphical model to increase its
conformity with the actual region in the patient's body using
physical characteristics acquired from a medical device probing the
region of interest.
BACKGROUND OF THE INVENTION
[0002] For certain types of minimally invasive medical procedures,
endoscopic visualization of the treatment site within the body is
unavailable or does not assist the clinician in guiding the needed
medical devices to the treatment site.
[0003] Examples of such procedures are those used to diagnose and
treat supra-ventricular tachycardia (SVT), atrial fibrillation
(AF), atrial flutter (AFL) and ventricular tachycardia (VT). SVT,
AFL, AF and VT are conditions in the heart which cause abnormal
electrical signals to be generated in the endocardial tissue to
cause irregular beating of the heart.
[0004] A procedure for diagnosing and treating SVT or VT involves
measuring the electrical activity of the heart using an
electrophysiology catheter introduced into the heart via the
patient's vasculature. The catheter carries mapping electrodes
which are positioned within the heart and used to measure
electrical activity. The position of the catheter within the heart
is ascertained using fluoroscopic images. A map of the measured
activity is created based on the fluoroscopic images and is shown
on a graphical display. A physician uses the map to identify the
region of the endocardium which s/he believes to be the source of
the abnormal electrical activity. An ablation-catheter is then
inserted through the patient's vasculature and into the heart where
it is used to ablate the region identified by the physician.
[0005] To treat atrial fibrillation (AF), an ablation catheter is
maneuvered into the right or left atrium where it is used to create
elongated ablation lesions in the heart. These lesions are intended
to stop the irregular beating of the heart by creating
non-conductive barriers between regions of the atria. These
barriers halt passage through the heart of the abnormal electrical
activity generated by the endocardium. Following the ablation
procedure, a mapping catheter is positioned in the heart where it
is used to measure the electrical activity within the atria so that
the physician may evaluate whether additional lesions are needed to
form a sufficient line of block against passage of abnormal
currents. S/he may also attempt to induce atrial fibrillation using
a pacing electrode, and then further evaluate the line of block by
analyzing the time required for the induced electrical activity to
pass from one side of the block to the other.
[0006] The procedures used to diagnose and treat SVT, VT, AFL and
AF utilize catheters which are maneuvered within the heart under
fluoroscopy. Because the fluoroscopic image is in two-dimensions
and has fairly poor resolution, it may be difficult for the
physician to be certain of the catheter positions. Thus, for
example, once a physician has identified an area which is to be
ablated (using a map of the measured electrical activity of the
heart) it may be difficult to navigate an ablation catheter to the
appropriate location in order to accurately ablate the area of
concern. It is therefore desirable to provide a system by which the
positions of medical devices such as mapping and ablation catheters
may be accurately guided to selected regions of the body.
[0007] Co-pending U.S. application Ser. No. 08/905,090, filed Aug.
1, 1997, entitled SYSTEM FOR ELECTRODE LOCALIZATION USING
ULTRASOUND, assigned to Cardiac Pathways Corporation and
incorporated herein by reference, describes a device localization
system that uses one or more ultrasound reference catheters to
establish a fixed three-dimensional coordinate system within a
patient's heart, preferably using principles of triangulation. The
coordinate system is represented graphically in three-dimensions on
a video monitor and aids the clinician in guiding other medical
devices, which also carry ultrasound transducers, through the body
to locations at which they are needed to perform clinical
procedures.
[0008] The system is preferably used in the heart to help the
physician guide mapping catheters for measuring electrical
activity, and ablation catheters for ablating selected regions of
cardiac tissue, to desired locations within the heart.
[0009] Three-dimensional images are shown on a video display which
represent the three-dimensional positions and orientations of the
medical devices used with the system, such as the reference
catheters, and the electrodes of the mapping catheter and ablation
catheter. The video display may additionally include
representations (color differences, ispotential or isochronal maps,
symbols etc.) of the electrical activity measured by each mapping
electrode at its respective location on the three-dimensional
display. It may also represent ablation lesions formed within the
body at the appropriate three-dimensional locations, and/or certain
anatomic structures which may facilitate navigation of the medical
device(s) within the patient.
[0010] An enhancement to the three-dimensional localization system
described above has now been developed. The enhancement improves
the graphical display by showing medical devices positioned within
the living body superimposed with a three-dimensional graphical
representation of the region of interest within the patient's body.
The graphical representation of the region of interest is based
upon a model of the region of interest programmed into the system
software and dynamically updated to conform with the actual region
of interest as information concerning actual features of the region
of interest is gathered using a probe manipulated within the
patient's body.
SUMMARY OF THE INVENTION
[0011] The present invention is a system and method for graphically
displaying a three-dimensional model of a region located within a
living body. A three-dimensional model of a region of interest is
generated for display on a graphical display. The location in
three-dimensional space of a physical characteristic (e.g. a
structure, wall or space) in the region of interest is determined
using at least one probe positioned within the living body. The
model is deformed to approximately reflect the determined
three-dimensional location of the physical characteristic and the
model as deformed is displayed. Preferably, the probe or probes are
moved throughout the region of Interest so as to gather multiple
data points that can be used to increase the conformity between the
model and the actual region of interest within the patient.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a schematic representation of a model
transformation system according to the invention in combination
with a localization system useful in connection with the invention,
showing the major components of the systems.
[0013] FIGS. 2 through 36C illustrate features of a localization
system which may be used in connection with a model transformation
system according to the present invention, in which:
[0014] FIG. 2 is a schematic representation of a three-dimensional
coordinate system established using a reference catheter with the
localization system.
[0015] FIG. 3 is a side elevation view of a reference catheter for
use with the localization system.
[0016] FIG. 4 is a side elevation view of a first alternative
embodiment of a reference catheter for use with the localization
system, in which ultrasound transducers are included on a catheter
of a type conventionally used in the RV apex.
[0017] FIG. 5 is a side elevation view of a second alternative
embodiment of a reference catheter for use with the localization
system, in which ultrasound transducers are included on a catheter
of a type conventionally used in the coronary sinus.
[0018] FIG. 6 is a perspective view of a piezoelectric cylinder of
a type which may be used on catheters used in the localization
system, including those catheters shown in FIGS. 3-5.
[0019] FIG. 7 is a side elevation view of the piezoelectric
cylinder of FIG. 6 mounted on a catheter and modified to include a
divergent lens.
[0020] FIG. 8 is a perspective view of a mandrel having a polymer
piezoelectric wrapped around it for use with a reference catheter
in combination with the localization system.
[0021] FIG. 9 is a side elevation view of a catheter for use with
the localization system, which is provided with marking and
ablation capabilities.
[0022] FIG. 10 is a perspective view of a first alternative
embodiment of a catheter with marking and ablation capabilities for
use with the localization system.
[0023] FIGS. 11 and 12 are side section views of second and third
alternative embodiments of catheters having marking and ablation
capabilities for use with the localization system.
[0024] FIG. 13 is a side elevation view of a mapping catheter for
use with the localization system. As with all of the catheters
shown herein, the sizes of the electrodes and transducers are
exaggerated for purposes of illustration.
[0025] FIG. 14A is a front elevation view of the mapping catheter
of FIG. 13, showing the spacing of the basket arms.
[0026] FIG. 14B is a view similar to the view of FIG. 14A showing
alternate basket arm spacing.
[0027] FIG. 15 is a cross-section view of the mapping catheter
taken along the plane designated 15-15 in FIG. 13.
[0028] FIG. 16 is a plan view of an arm of the mapping catheter of
FIG. 13.
[0029] FIG. 17 is a cross-section view of the arm of FIG. 16, taken
along the plane designated 17-17.
[0030] FIG. 18 is a side elevation view of a linear lesion catheter
for use in the localization system.
[0031] FIG. 19 is a side section view of the linear lesion catheter
of FIG. 18.
[0032] FIG. 20 is a cross-section view taken along the plane
designated 20-20 in FIG. 19.
[0033] FIG. 21 is a cross-section view taken along the plane
designated 21-21 in FIG. 19.
[0034] FIG. 22 is a cross-section view taken along the plane
designated 22-22 in FIG. 19.
[0035] FIG. 23 is a side section view, similar to the view of FIG.
19, of an alternative embodiment of a linear lesion catheter for
use with the localization system.
[0036] FIG. 24 is a cross-section view taken along the plane
designated 24-24 in FIG. 23.
[0037] FIG. 25 is a side section view, similar to the view of FIG.
19, of an alternative embodiment of a linear lesion catheter for
use with the localization system.
[0038] FIG. 26 is a cross-section view taken along the plane
designated 26-26 in FIG. 25.
[0039] FIG. 27A is a schematic drawing showing ultrasound ranging
hardware and its interaction with the ultrasound hardware control
and timing systems.
[0040] FIG. 27B is a schematic diagram illustrating in greater
detail ultrasound ranging hardware and ultrasound hardware control
and timing systems of the type shown in FIG. 27A.
[0041] FIG. 28A is a plot of the voltage over time on an ultrasound
transmit line following initiation of a transmit pulse, and
illustrates the ringing which occurs on the transmit line following
the transmit pulse.
[0042] FIG. 28B is a plot of the voltage over time on an ultrasound
receive line which is located near the transmit line at the time
the transmit pulse of FIG. 28A is initiated. The figure shows the
ringing which results from the ringing on the transmit line, and
also shows a receive pulse following the ringing.
[0043] FIG. 28C is a plot of the voltage over time on an ultrasound
receive line which is located very close to a transmit wire at the
time the transmit pulse of FIG. 28A is instituted, and it
illustrates that the receive pulse may be lost in the ringing.
[0044] FIG. 28D is a plot of the voltage over time on an ultrasound
transmit line which is short circuited immediately following the
initiation of a transmit pulse.
[0045] FIG. 28E is a plot of the voltage over time on an ultrasound
receive line which is adjacent to the transmit line represented in
FIG. 28D. The figure shows that ringing is eliminated on the
receive line when the transmit line is short circuited just after
the transmit pulse is sent.
[0046] FIG. 29 is a schematic diagram illustrating a pulse
generator circuit which includes a switch for short circuiting the
transmit line just after the transmit pulse is sent.
[0047] FIG. 30A is a schematic illustration of the sample and hold
system used for gating position information to the cardiac
cycle.
[0048] FIG. 30B shows an EKG plot together with a plot of
transducer coordinates and illustrates a sample and hold sequence
which takes transducer coordinates at the end of diastole.
[0049] FIGS. 31 and 32 illustrate the graphical user interface of
the localization system. FIG. 31 illustrates display of anatomical
features, reference catheters, a linear lesion catheter, and burns
formed in the heart using the linear lesion catheter. FIG. 32
illustrates display of the reference catheters, anatomical
features, burns formed in the heart, and a basket catheter together
with its mapping electrode positions.
[0050] FIG. 33 is a flow diagram illustrating use of the catheters
of FIGS. 3, 9 and 13 to treat ventricular tachycardia.
[0051] FIGS. 34A-34C are a series of views of a heart illustrating
certain of the steps of FIG. 33: FIG. 34A is an anterior section
view of the heart showing placement of a reference catheter in the
right ventricle and a marking catheter in the left ventricle. FIG.
34B is a lateral view of the heart showing a reference catheter in
the coronary sinus. FIG. 34C is an anterior section view of the
heart showing a reference catheter in the right ventricle and a
mapping catheter in the left ventricle. FIG. 34D is a view similar
to the view of FIG. 34C showing introduction of an ablation
catheter into the mapping catheter.
[0052] FIG. 35 is a flow diagram illustrating use of the
localization system together with the catheters of FIGS. 3, 9, 13
and 18 to treat atrial fibrillation.
[0053] FIGS. 36A-36C are a series of views of a heart illustrating
certain of the steps of FIG. 35: FIG. 36A is an anterior section
view of the heart showing placement of a reference catheter in the
RV apex and a marking catheter in left atria; FIG. 36B is an
anterior section view of the heart showing a linear lesion ablation
catheter in the left atria; FIG. 36C is an anterior section view of
the heart showing a mapping catheter in the left atria.
[0054] FIGS. 37 through 42 illustrate a preferred embodiment of the
model transformation system and method according to the present
invention, in which:
[0055] FIG. 37 is a simplified block diagram illustrating the basic
components of the model transformation system according to the
preferred embodiment.
[0056] FIG. 38 is a simplified flow diagram illustrating basic
operation of the model transformation system according to the
preferred embodiment.
[0057] FIG. 39A is an example of a graphical display according to
the preferred embodiment showing a three-dimensional model of a
human heart prior to transformation of the model, superimposed with
a representation of a reference catheter positioned within the
heart.
[0058] FIG. 39B is an example of a graphical display similar to
FIG. 39A, showing a model of a human heart superimposed with a
representation of a reference catheter positioned within the heart.
The drawing shows the model after it has been transformed to
reflect information obtained using the reference catheter.
[0059] FIG. 40A is an example of a graphical display according to
the preferred embodiment showing a three-dimensional model of a
human heart prior to transformation of the model, superimposed with
a representation of a probe positioned within the left ventricle of
the heart.
[0060] FIG. 40B is an example of a graphical display similar to
FIG. 40A, showing the model of a human heart superimposed with the
representation of the probe positioned within the left ventricle.
The drawing shows the model after it has been transformed to
reflect Information obtained using the probe.
[0061] FIG. 40C is a schematic drawing illustrating transformation
of the model in response to input received by the system concerning
the location of the probe. The drawing shows an anterior section
view of a model of a human heart superimposed with a representation
of a probe positioned within the left ventricle of the heart.
Dashed lines and arrows illustrate the transformation that the
model will undergo as a result of information obtained by the probe
concerning the physical characteristics of the patient's heart.
[0062] FIG. 41A is an example of a graphical display according to a
preferred embodiment, showing a three-dimensional model of a human
heart superimposed with a representation of a probe positioned
within the left ventricle of the heart.
[0063] FIG. 41B is an example of a graphical display similar to
FIG. 41A, showing the model of a human heart superimposed with the
representation of the probe positioned within the left ventricle.
The drawing shows the model after it has been transformed to
reflect information obtained using the probe.
[0064] FIG. 41C is a schematic drawing illustrating transformation
of the model in response to input received by the system concerning
the location of the probe. The drawing shows an anterior section
view of a model of a human heart superimposed with a representation
of a probe positioned within the left ventricle of the heart.
Dashed lines and arrows illustrate the transformation that the
model will undergo as a result of information obtained by the probe
concerning the physical characteristics of the patient's heart.
[0065] FIG. 42 is a flow diagram illustrating a mode of operation
for the system of the preferred embodiment.
DETAILED DESCRIPTION
[0066] The model transformation system and method is designed for
use in combination with a localization system that permits
determination of the 3-D position of a medical device within a
body. From the determined 3-D position, the 3-D locations of
anatomical features in a region of interest may be derived and used
to deform a 3-D graphical model of the region of interest so as to
dynamically increase the conformity of the model with the actual
region of interest.
[0067] Various types of prior art localization systems may be used
in combination with the deformable model according to the present
invention. Once such localization system is described U.S. Pat.
Nos. 5,391,199, 5,443,489, 5,480,422, 5,546,951, 5,568,809,
5,694,945 and 5,713,946 (each to Ben-Haim) which are incorporated
herein by reference. That system utilizes antennas placed outside
the body and on catheters placed within the heart. Electromagnetic
fields are passed between the antennas and used to determine the
locations of the distal tips of the catheters.
[0068] Other localization systems that are useful for obtaining the
three-dimensional locations of catheters positioned within the body
and that are thus suitable for use with the system of the present
invention are described in U.S. Pat. No. 5,697,377 entitled
Catheter Mapping System and Method, Langbert et al, "The
Echo-Transponder Electrode Catheter: A New Method for Mapping the
Left Ventricle", Journal of the American College of Cardiology,
Vol. 12, No. 1 (1988), and R. R. Fenici and G. Melillo,
"Biomagnetically localizable multipurpose catheter and method for
MCG guided intracardiac electrophysiology, biopsy, and ablation of
cardiac arrhythmias", International Journal of Cardiac Imaging,
1991, Vol. 7, pp. 207-215, each of which is incorporated herein by
reference.
[0069] Another localization system useful in connection with the
present invention is an ultrasound localization system described in
U.S. application Ser. No. 08/905,090, filed Aug. 1, 1997, entitled
SYSTEM FOR ELECTRODE LOCALIZATION USING ULTRASOUND. A preferred
embodiment of the present invention will be described with
reference to this ultrasound localization system. It is important
to note, however, that the scope of the invention is not limited to
systems in which ultrasound localization is used.
[0070] For the purposes of this description, the term "physical
characteristics" will be used in a broad sense to describe not only
specific anatomical features within the body such as valves, organ
walls, and other structures, but also to describe spaces within the
body. The importance of such information will become clear as the
system is described in detail.
[0071] For purposes of clarity, the localization system will first
be described in connection with FIGS. 1 through 36C. Afterwards, a
preferred model transformation system and method according to the
present invention will be described in connection with FIGS. 37
through 42.
[0072] Localization System Overview
[0073] A localization system and procedure useful in combination
with the deformable model will first be described in general terms.
Specific examples of procedures which may be carried out using the
system will be described in the Operation section of this
description. The system is described primarily with respect to
catheters in the heart, but it should be understood that the system
is intended for use with other medical devices and in other regions
of the body as well.
[0074] Referring to FIG. 1, the localization system 100 uses one or
more ultrasound reference catheters 10 to establish a
three-dimensional coordinate system within a patient's heart. The
system allows the positions of one or more additional catheters 12,
14, 16, to be represented graphically on a graphical user interface
124 relative to a coordinate system. This aids the clinician in
guiding the additional catheter(s) 12, 14, 16 through the heart to
locations at which they are needed to perform clinical
procedures.
[0075] In one embodiment of such a localization system, the
additional catheters include mapping catheters 14 for measuring
electrical activity within the heart and ablation catheters 12, 16
for ablating selected regions of cardiac tissue. These catheters
12-16 may also be described as "electrophysiology catheters" or "EP
catheters."
[0076] Each of the reference catheters 10 carries a plurality of
ultrasound transducers, with there being a total of at least four
such transducers employed during use of the system. The reference
catheter transducers can function as ultrasound receivers by
converting acoustic pressure to voltage, and as ultrasound
transmitters by converting voltage to acoustic pressure. Each of
the additional catheters 12, 14, 16 carries at least one ultrasound
transducer which preferably functions as an ultrasound receiver but
which may also function as a transmitter or a
transmitter/receiver.
[0077] Using known techniques, the distance between each transducer
and other ones of the transducers may be computed by measuring the
respective time for an ultrasound pulse to travel from a
transmitting transducer to each receiving transducer. These
distance measurements are preferably carried out in parallel. In
other words, when an ultrasound pulse is emitted by a reference
catheter transducer, the system simultaneously measures the
respective times it takes for the pulse to reach each of the other
transducers being used in the system.
[0078] The velocity of an acoustic signal in the heart is
approximately 1570-1580 mm/msec, with very small variations caused
by blood and tissue. The time for an acoustic pulse to travel from
one transducer to another may therefore be converted to the
distance between the transducers by multiplying the time of flight
by the velocity of an acoustic pulse in the heart (i.e. by
1570-1580 mm/msec). As detailed below, the localization system 100
uses this "time of flight" principal in combination with the
geometric principal of triangulation to establish a
three-dimensional coordinate system using the reference transducers
on the reference catheter 10, and to then use the additional
catheter transducers to track the location of an additional
catheter 12, 14, 16, relative to the coordinate system.
[0079] During use of the localization system 100, one or more of
the reference catheters 10 is introduced into the heart or the
surrounding vasculature (or even into other areas such as the
esophagus) and is left in place for the duration of the procedure.
Once reference catheter(s) 10 are positioned within or near a
patient's heart, the system first measures the distances between
each of the reference catheter transducers using the "time of
flight" principal. It then uses these distances to establish the
relative positions of the reference transducers and therefore to
establish a three-dimensional coordinate system.
[0080] Referring to FIG. 2, establishing the coordinate system
requires placement of the reference catheter(s) 10 such that at
least four reference transducers, designated T.sub.REF1 through
T.sub.REF4 in FIG. 2, are available to define a 3-dimensional
coordinate system as follows: T.sub.REF1 through T.sub.REF3, define
the plane P at z=0; one reference transducer T.sub.REF1 defines the
origin of the coordinate system; a line between T.sub.REF1 and
T.sub.REF2 defines the x-axis of the system; and T.sub.REF3 lies in
the plane z=0. The fourth reference transducer, T.sub.REF4, lies on
one side of the plane P, at z>0. Given these constraints, the
coordinates of the reference transducers can be computed using the
law of cosines. See, for example, Advanced Mathematics, A
preparation for calculus, 2nd Ed., Coxford, A. F., Payne J. N.,
Harcort Brace Jovanovich, New York, 1978, p. 160.
[0081] Each of the reference transducers T.sub.REF1 through
T.sub.REF4 must be capable of both receiving and transmitting
ultrasound pulses. As discussed, each reference transducer is
separately made to emit acoustic pulses that are received by each
of the other reference transducers so that the distances d1 through
d6 shown in FIG. 2 are calculated using the respective times it
takes for an acoustic pulse to travel between each pair of the
reference transducers. These distances are triangulated to
establish the positions of the reference transducers relative to
each other, and therefore to establish a three-dimensional
coordinate system.
[0082] Once a 3-dimensional coordinate system is established in the
manner described, the three-dimensional location of an additional
catheter transducer placed near or within the heart (such as a
transducer on a mapping or ablation catheter 12, 14, or 16) can be
calculated as follows. First, using the "time of flight" method,
the distances between each of the reference transducers T.sub.REF1
through T.sub.REF4 and the additional catheter transducer
(designated T.sub.CATH in FIG. 2) are established, in parallel. In
practice, these distances are preferably also performed in parallel
with the distance measurements that are made to establish the
coordinate system. Next, using basic algebra and the law of cosines
(see, e.g., the Advanced Mathematics text cited above), the
coordinates of T.sub.CATH relative to the reference transducers are
calculated using the measured distances from T.sub.REF1 through
T.sub.REF4 to T.sub.CATH. This process is referred to as
triangulation.
[0083] The locations of all or portions of the reference catheters
may be displayed as well. The system is preferably programmed to
extrapolate catheter position from the coordinates of the
transducer locations based on models of the various catheters
pre-programmed into the system, and to display each catheter's
position and orientation on a graphical user display (see display
124 in FIG. 1). The locations of all or portions of the additional
catheters (such as, for example, their distal tips, their
electrodes or ablation sections, if any, or other sections which
may be of interest) are displayed.
[0084] The reference catheter(s) 10 thereby establish an internal
coordinate system by which the relative positions of EP catheter
transducers in the heart may be calculated using triangulation and
shown in real-time on a three dimensional display.
[0085] Ultrasound Catheters
[0086] Catheters of the type which may be used with the
localization system 100 are shown in FIGS. 3, 9, 13 and 18. These
include a reference catheter 10 (FIG. 2), a marking and ablation
catheter 12 (FIG. 9), a basket-type mapping catheter 14 (FIG. 13),
and a linear lesion ablation catheter 16 (FIG. 18).
[0087] Reference Catheters
[0088] Referring to FIG. 3, a reference catheter 10 which may be
used with the localization system 100 is an elongate catheter
having a plurality of ultrasound transducers 18 positioned at its
distal end. The transducers 18 are piezoelectric transducers
capable of transmitting and receiving ultrasound signals.
[0089] The reference catheters can be integrated with typical EP
catheters by providing the ultrasound transducers described above.
This allows the system to utilize the localization function using
catheters which are already needed for the EP procedure. Thus, use
of the system does not require the physician to use more catheters
than would be used had the EP procedure been carried out without
the localization function.
[0090] For example, referring to FIG. 4, the reference catheter 10a
may be an RV apex catheter having a distal pair of EP electrodes
30, an ultrasound transducer 18a at the distal tip, and additional
ultrasound transducers 18 proximally of the distal tip. It may also
be a coronary sinus reference catheter 10b (FIG. 5) having at least
three bipole pairs of EP electrodes 30 distributed over the section
of the catheter that is positioned in the coronary sinus, and
having at least three ultrasound transducers also distributed over
the section of the catheter that is in the coronary sinus.
[0091] Referring to FIG. 6, a preferred transducer 18 is a
piezoelectric cylindrical tube having inner and outer surfaces. The
cylindrical transducer may be made of PZT-5H, PZT-5A, PMN (lead
metaniobate or lead magnesium niobate) or other piezoelectric
ceramic materials.
[0092] Electrodes 20 are positioned on the inner and outer surfaces
of the transducer. The electrodes are metal surfaces not limited to
materials such as sputtered chrome and gold, electroless nickel, or
fired silver. The piezoelectric ceramic is polarized in the
thickness mode, i.e., between the two electrodes 20.
[0093] The cylinder includes an outside diameter (designated "OD"
in FIG. 6) of approximately 0.040 to 0.250 inches, and preferably
approximately 0.060 to 0.090 inches. The cylinder has a length L of
approximately 0.020 to 0.125 inches and preferably approximately
0.030 to 0.060 inches. Wall thickness W is approximately 0.004 to
0.030 inches and preferably approximately 0.006 inches to 0.015
inches. The transducers 18 are spaced from one another along the
catheter 20 (FIG. 3) by a distance of approximately 0.5-10 cm, and
most preferably 1-3 cm.
[0094] Preferably, the localization system is operated using the
same operating frequencies for all transducers. The optimal
operating frequency for the system is determined by considering the
resonant frequencies of the ultrasound transducers used for the
catheters in the system. It has been found that, given the
dimensions and thus the resonances of the preferred transducers
being used in the system, the transducers are most preferably
operated at a frequency of approximately 1.0-3.0 MHz, which in the
case of the transducer 18 is the transducer resonance in the length
mode. Transducer 18 further has a beam width of approximately
114.degree., where the beam width is defined as the angle over
which the signal amplitude does not drop below 6 dB from the peak
amplitude. If desired, a diverging lens 22 (FIG. 7), in the form of
a spherical bead of epoxy or other material may be formed over the
ceramic cylinder to make the signal strength more uniform over the
beam width.
[0095] Referring to FIG. 8, the reference catheter transducers 18b
may alternatively be formed of piezoelectric polymer films of
copolymers such as PVDF. Such films would have thicknesses of
approximately 0.005-1.0 mm, and preferably approximately
0.007-0.100 mm, and would preferably include gold film electrodes
on the inner and outer surfaces. As shown in FIG. 8, the polymer
film would be wrapped around a mandrel 24 (which may be part of the
catheter shaft 10c itself or a separate polymer plug inside the
catheter 10). A transducer configuration of this type operates with
a very large band width and does not have a specific resonance due
to the polymer piezoelectric.
[0096] Electrode leads (not shown) are attached to the inner and
outer transducer electrodes (such as electrodes 20 of FIG. 6). If
piezoelectric ceramics are used as in FIGS. 6 and 7, leads may be
attached using low temperature solders which typically contain
large proportions of indium metal. Leads may alternatively be
attached with silver epoxy. It is important that the leads be
attached using a minimum amount of material to minimize distortion
of the acoustic field. In the case of the polymer transducers of
FIG. 8, photo lithographic techniques are typically used to create
electrodes and their associated lead tabs. In this manner, the one
side electroded polymer at the tab site does not contribute to the
acoustic field. Leads are typically attached to these tabs with
either low temperature indium based solders or with silver epoxy.
Therefore, for these polymer transducers, the amount of material on
the connection tab does not affect the acoustic field.
[0097] The reference catheter preferably includes at least four
such transducers so that a three-dimensional coordinate system can
be established using a single catheter. If desired, the reference
catheter may have more transducers or it may have fewer transducers
if more than one reference catheter is to be used to establish the
three-dimensional coordinate system. Using more than four reference
transducers is advantageous in that it adds redundancy to the
system and thus enhances the accuracy of the system. When more than
four reference transducers are used, the problem of determining the
location of catheter transducers is over determined. The additional
redundancy may provide greater accuracy if the measured distances
between the reference transducers and catheter transducers are
noisy. The overdetermined problem can be solved using
multi-dimensional scaling as described in "Use of Sonomicrometry
and Multidimensional Scaling to Determine 3D Coordinates of
Multiple Cardiac Locations: feasibility and implementation",
Ratciffle et. al, IEEE Transactions Biomedical Engineering, Vol.
42, no. 6, June 1995.
[0098] Referring again to FIG. 3, a connector 32 enables the
catheter 10 to be electrically coupled to the ultrasound ranging
hardware 116 (described below and shown in FIG. 1).
[0099] Four twisted pairs 26 of Teflon coated forty-two gauge
copper wire (one pair can be seen in the cutout section shown in
FIG. 3) extend from connector 32 through the catheter 10. Each
twisted pair 26 is electrically coupled to a corresponding one of
the ultrasound transducers 18, with one wire from each pair 26
coupled to one of the transducer electrodes 20 (FIG. 6). When a
transducer is to act as an ultrasound transmitter, a high voltage
pulse (i.e, approximately 10-200V) is applied across the
corresponding twisted pair 21 and causes the transducer 18 to
generate an ultrasound pulse. When a transducer is to act as an
ultrasound receiver, the ultrasound ranging hardware 116 (FIGS.
27A-27B, described below) awaits receive pulses of approximately
0.01-100 mV across the twisted pairs corresponding to receiving
transducers. Additional leads (not shown) couple the EP electrodes
30 to the EP hardware 114 (FIG. 1).
[0100] To facilitate manipulation of the reference catheter through
a patient's vessels and into the heart, the reference catheter 10
may have a pre-shaped (e.g. curved) distal end.
[0101] Marking/Ablation Catheter
[0102] Referring to FIG. 9, the localization system 100 preferably
utilizes a catheter 12 to identify the locations of anatomical
landmarks (such as the septal wall) relative to the coordinate
system so that the landmarks may be included on the
three-dimensional display. Showing anatomical landmarks on the
display correlates the three-dimensional coordinate system to
discrete anatomical locations and thereby assists the physician in
navigating EP catheters to the desired locations within the
heart.
[0103] The marking catheter 12 is preferably a 7 French steerable
catheter having one or more ultrasound transducer(s) 34 mounted at
or near its distal tip. Preferably, the catheter 12 includes one
transducer at or near its distal tip and a second transducer spaced
from the distal tip by approximately 0.5-4.0 cm. The marking
catheter 12 need not be one which is limited to use in marking
anatomical sites. It can be a catheter useful for other purposes as
well; the term "marking catheter" is being used in this description
as a matter of convenience. Catheter 12 may also include an
ablation electrode 36 at its distal tip, so that it may also be
used to ablate tissue while the position of the ablation electrode
36 is tracked using the localization system 100. It may also
include other electrophysiology electrodes 38 which may be used for
pacing and/or mapping as desired by the user.
[0104] The transducers 34 may be similar to the reference catheter
transducers 18. While the outer diameter and wall thickness of the
transducers 34 may differ from that of transducer 18 to accommodate
mounting requirements, the length of the transducers 34 is
preferably the same as that of the transducers 18 to assure a
common operating frequency of approximately 1.0-3.0 MHZ.
[0105] Alternatively, the more distal transducer might be packaged
differently than the reference catheter transducers. For example,
referring to FIG. 10, the transducer 34 may be mounted just
proximal of the distal ablation tip 36. Alternatively, a
cylindrical transducer 34a or a plate transducer 34b may be
positioned inside the distal ablation tip, in FIGS. 11 and 12,
respectively. An internal piezoelectric transducer would be
embedded in a bead of epoxy 40 positioned in the catheter tip. This
bead would preferably have a spherical contour across the distal
end so that it would act as a divergent lens for the ultrasound
energy. The metal forming the ablation tip 36 must be very thin
(i.e., less than a small fraction of a wavelength) to facilitate
the transmission of acoustic energy to and from an internal
transducer.
[0106] The marking catheter 12 may additionally be provided with EP
electrodes 38. As shown in FIG. 9, a handle 42 and a knob 44 for
actuating a pull wire (not shown) allow the marking catheter 12 to
be maneuvered through a patient's vessels and heart using
conventional steering mechanisms. A connector 46 enables the
catheter 12 to be electrically coupled to the EP hardware 114 and
the ultrasound ranging hardware 116 (described below, see FIG.
1).
[0107] Mapping Catheter
[0108] FIG. 13 shows a first embodiment of a mapping catheter 14
for use with the localization system 100. The catheter 14 is of the
type known in the art as a "basket" catheter. It includes an
elongate shaft 48 carrying a mapping basket 50 at its distal end.
The basket 50 is formed of preferably eight arms 52. Arms 52 are
constructed of ribbons of a shape memory material such as Nitinol.
The shape memory material is treated such that the ribbons assume
the basket structure shown in FIG. 13 when in an unstressed
condition.
[0109] The arms 52 may be concentrated at one section of the basket
(FIG. 14A) so that during use mapping may be concentrated in one
area of a cardiac chamber. The arms may alternatively be uniformly
spaced as shown in FIG. 14B. Basket catheters of these types are
shown and described in U.S. Pat. No. 5,156,151, the disclosure of
which is incorporated herein by reference.
[0110] A sheath 54 is disposed around shaft 48. Sheath 54 is
longitudinally slidable between the proximal position in FIG. 13
and a distal position in which the basket 50 is compressed within
it. During use the sheath 54 is moved to the distal position to
compress the basket before the catheter 14 is inserted into the
patient, so that the basket can be easily moved through the
patient's vessels and into the patient's heart. Once the basket is
within the desired chamber of the patient's heart, the sheath is
withdrawn, the basket is opened into its expanded condition,
(either by spring action of the arms 52 or by a separate actuator)
and the arms to map electrical activity of the chamber wall.
[0111] Each arm 52 of the basket catheter 14 carries a plurality of
EP mapping electrodes 56 designed to detect the electrical activity
of underlying cardiac tissue. A plurality of ultrasound receiving
transducers 58 are also mounted to each arm 52. Preferably, the
mapping electrodes 56 and the ultrasound transducers 58 alternate
with each other along the length of each arm 52, although there
need not be one-to-one correspondence between the transducers and
electrodes.
[0112] FIG. 16 is a plan view of one arm 52 of basket catheter 14,
and FIG. 17 is a side section view of the arm of FIG. 16. As shown,
the mapping electrodes 56 and ultrasound transducers 58 are
preferably formed on a flex circuit 60 which is attached to the arm
52. Copper leads 62 are formed on the flex circuit and each lead is
electrically connected to one of the EP electrodes 56 and one of
the ultrasound transducers 58, and to the EP and localization
hardware 110 (FIG. 1). Each arm 52, including its associated flex
circuit 60, is covered in polyethylene shrink tubing 64, with only
the electrodes 56 being exposed through the shrink tubing 64.
[0113] Referring to FIG. 16, a preferred piezoelectric transducer
for the mapping catheter comprises a flat piezoelectric ceramic
plate 66. The plate 66 may be made of PZT-5H, PZT-5A, PMN (lead
metaniobate or lead magnesium niobate) or other piezoelectric
materials.
[0114] The transducer includes a depth D and length L, each of
approximately 0.010 to 0.060 inches, and preferably approximately
0.025 to 0.040 inches. The transducer has a wall thickness W of
approximately 0.004 to 0.030 inches and preferably approximately
0.006 to 0.015 inches. The length and depth resonances of the
transducer fall in the range from 1.0 MHz to 3 MHz and thus
contribute to the overall performance of the system. The beam width
considerations are the same as those described above for the
reference catheter transducers 18 (FIG. 6).
[0115] Electrodes 68a, 68b are positioned on the upper and lower
flat surfaces of the plate. The electrodes are metal surfaces not
limited to materials such as sputtered chrome and gold, electroless
nickel, or fired silver. The piezoelectric ceramic is polarized in
the thickness mode, i.e., between the two electrodes.
[0116] The mapping catheter transducers 58 may alternatively be
formed of piezoelectric polymer films of copolymers such as PVDF.
Such films would have thicknesses of approximately 0.005-1.0 mm,
and preferably approximately 0.007-0.100 mm, and would preferably
include gold film electrodes on the inner and outer surfaces. The
polymer film would preferably be taped to the printed wiring board
of the basket arm, and leads attached to the top electrodes in a
manner similar to that mentioned above for the reference catheter
transducers. Alternatively, the polymer film could be used to form
the entire flex circuit.
[0117] Lead wires 70a, 70b extend between the copper leads 62 and
the electrodes 68a, 68b. It is important to note that each of the
leads 62 electrically connects both an ultrasound transducer 58 and
an EP electrode 56 to the EP and localization hardware 110. Each
lead 62 therefore carries electrical activity measured by EP
electrodes 56 as well as receive signals from the ultrasound
transducers 58 to the hardware 110. It is possible to do this
because EP signals have a lower frequency (i.e., on the order of 1
Hz-3 kHz) than the ultrasonic signals, which have frequencies of
approximately 500 kHz-30 MHz. Thus, the EP signals can be removed
from the recorded signal using low-pass filtering while the
ultrasound signal can be removed using high pass filtering.
[0118] Combining EP and ultrasound signals on the same lead 62 has
the advantage of reducing the total number of conductors in the
catheter 14. While this is advantageous, it is not a requirement
for functionality of the system. Naturally, the system may also be
provided using separate leads for the EP and ultrasound
signals.
[0119] For both piezoelectric ceramic and polymer transducers, one
lead 70b will most typically be attached by bonding the bottom
electrode 68b of the piezoelectric (e.g., plate 66) with silver
epoxy to the printed circuit of the basket arm. Leads 70a may be
attached to the top electrodes 68a in a manner similar to that set
forth with respect to the reference catheter transducers. For the
piezoelectric ceramics 66, the top lead 70a may be attached with
low temperature solders which typically contain large proportions
of indium metal. It is important that the leads be attached using a
minimum amount of material to minimize distortion of the acoustic
field. Top leads 70a may also be attached with silver epoxy. In the
case of the polymer piezoelectrics, metallization of the electrodes
and leads is typically achieved using photo lithographic
techniques. In this manner, the one side electroded polymer at the
lead site does not contribute to the acoustic field as discussed
previously for the polymer transducer of the reference
catheter.
[0120] Acoustic wave propagation does not occur across a vacuum or
air gap, consequently it is necessary to provide a rubber path or a
path through an insulating polymer in order to fill air gaps around
the transducers. For example, after the top lead 70a has been
attached, the entire top surface and surrounding areas including
the inner surface of the shrink tubing is coated with a rubber
primer. Subsequently, the area between and around the top surface
of the piezoelectric and the shrink tubing is filled with a
silicone rubber material.
[0121] Alternatively, the top surface of the piezoelectric and the
electrical lead may be coated with an insulating polymer. After the
heat shrink tubing is attached to the basket strut, a small area
over and around the top electrode of the ceramic may be cut out of
the shrink tubing to provide an unobstructed exposure of the
transducer to the blood field.
[0122] The EP electrodes 56 are preferably platinum black
electrodes having a size of approximately 0.009.times.0.030 inches.
For these small electrodes, platinum black is used for low
impedance, i.e., approximately less than 5.0 k Ohms over the
frequency range (approximately 1 Hz-3 kHz) of interest for EP
signals. This is important in that it prevents the impedance of the
ultrasound transducers from loading the output of the EP
electrodes.
[0123] FIG. 15 is a cross-section view of the portion of the
catheter 14 which is proximal of the basket 50. The catheter shaft
48 is formed of an inner shaft 72 and an outer, braided shaft 74
preferably made from stainless steel braid of a type conventionally
known in the art. The inclusion of the braid improves the torque
characteristics of the shaft 48 and thus makes the shaft 48 easier
to maneuver through patient's vessels and heart.
[0124] Inner shaft 72 includes a center lumen 76 through which
ribbon cables 78 extend. Leads (not shown) are formed on the ribbon
cables 78 and function to carry signals corresponding to signals
received by the ultrasound transducers 58 and by the
electrophysiology electrodes 56 to the system hardware 110 (FIG.
1). An ablation catheter lumen 80 extends through the shaft 48 and
allows an ablation catheter such as catheter 12 to be introduced
through the shaft 48 and into contact with tissue surrounding the
basket 50.
[0125] Inner shaft 72 further includes a deflection lumen 82. A
pull wire (not shown) extends through the deflection lumen 82 and
facilitates steering of the basket using means that are
conventional in the art.
[0126] Linear Lesion Ablation Catheter
[0127] FIGS. 18 through 26 show a linear lesion ablation catheter
16 for use with the localization system 100. Catheter 16 is an
elongate shaft preferably constructed of a thermoplastic polymer,
polyamid ether, polyurethane or other material having similar
properties. An ablation section 84, the section of the catheter 16
at which ablation is carried out, is located at the distal end of
the shaft.
[0128] As shown in FIG. 18, an elongate window 86 is formed in the
wall of the ablation section 84. The window 86 may be made from
heat shrink polyethylene, silicone, or other polymeric material
having a plurality of small holes or perforations formed in it. It
may alternatively be formed of the same material as the remainder
of the shaft and simply include a plurality of holes formed through
it.
[0129] Referring to FIG. 19, a foam block 88 is disposed within the
catheter, next to the window 86. The foam block 88 is formed of
open cell polyurethane, cotton-like material, open-cell sponge,
hydrogels, or other foam-like materials or materials that are
permeable by conductive fluids. A plurality of RF ablation
electrodes 90 line the edge of the foam block 88 such that the foam
block lies between the electrodes 90 and the window 86.
[0130] Ultrasound transducers 92 are positioned at the distal and
proximal ends of the foam block 88. The transducers 92 are
preferably formed of piezoelectric ceramic rings having electrodes
bonded to their inner and outer surfaces, although the transducers
may also be formed in a variety of alternative shapes.
[0131] Referring to FIGS. 20-22, several lumen extend through the
catheter 16. The first is a fluid lumen 94 that extends the length
of the catheter 16 and is fluidly coupled to a fluid port 96 (FIG.
18) at the proximal end of the catheter. It should be noted, with
reference to FIG. 20, that the walls of the fluid lumen are cut
away at the ablation section 84 to accommodate placement of the
foam block 88 and the RF electrodes 90 within the catheter.
[0132] A pair of lead lumen 98 house lead wires 100 that carry RF
energy to the electrodes 90 and lead wires 102 that carry voltage
signals from the transducers 92. A fourth lumen 104 houses a
Nitinol core wire 106 which provides rigidity to the catheter.
[0133] Because breaks in a linear lesion can reduce the success of
an ablation procedure by leaving a path through which current may
travel during atrial fibrillation episodes, the fluid lumen, foam,
and window are provided to improve the coupling of the RF energy to
the cardiac tissue to minimize the likelihood of breaks in the
lesion.
[0134] Specifically, during use, the window 86 of ablation section
84 of the apparatus is positioned adjacent to the body tissue that
is to be ablated. RF energy is delivered to the electrodes 90 while
saline or other conductive fluid is simultaneously delivered
through the fluid lumen 94. The conductive fluid passes out of the
fluid lumen 94 and into the foam 88, and contacts the electrodes
90. The fluid also flows through the window 86 into contact with
the body tissue, thereby improving the coupling of the RF energy
from the electrodes 90 to the tissue and improving the efficiency
of the ablation of the tissue.
[0135] Using a conductive liquid dispersed over the desired area as
a mechanism for coupling RF energy to the tissue produces lesions
having greater continuity (and thus fewer breaks through which
current can pass during atrial fibrillation episodes) than lesions
formed by apparatuses that rely solely on direct contact between
the electrodes and the body tissues, decreasing the likelihood of
thrombus formation on the electrodes and thus decreasing the chance
of an embolism. The foam and the window improve ablation in that
the conductive liquid is uniformly dispersed within the foam and
then is focused onto the body tissue as it passes through the holes
or pores in the window. This concept, and several alternate ways of
configuring linear lesion catheters that may be adapted to include
ultrasound transducers and used in the localization system 100, are
described in published International Application PCT/US96/17536,
the disclosure of which is incorporated herein by reference.
[0136] FIGS. 23 and 24 show a first alternative embodiment of a
linear lesion catheter for use with the localization system 100.
The first alternative embodiment 16a differs from the embodiment of
FIG. 19 primarily in the shape and placement of the transducers.
Transducers 92a of the first alternative embodiment are
piezoelectric chips embedded within the foam block 88. Each
transducer 92a includes a pair of electrodes on its opposite faces
and is encapsulated in an insulating cocoon 108 of epoxy, acrylic,
or silicone rubber which prevents the fluid in the foam from
creating a short circuit between the electrodes.
[0137] A second alternative embodiment of a linear lesion catheter
is shown in FIGS. 25 and 26. The second alternative embodiment also
differs from the preferred embodiment only in the form and
placement of the transducers. Each transducer 92b and its leads
102b is inside an epoxy capsule 109 embedded in the foam block 88.
It should be noted, then, that only the RF electrode leads 100
extend through the lumen 98. The leads 102b of the second
alternative embodiment extend through fluid lumen 94 as shown.
[0138] System Components
[0139] Referring to FIG. 1, the system 100 generally includes
amplification and localization hardware 110, catheters 10, 12, 14
and 16, and a microprocessor workstation 112.
[0140] Hardware 110 includes conventional signal amplifiers 114 of
the type used for electrophysiology procedures (for example, the
Model 8100/8300 Arrhythmia Mapping System available from Cardiac
Pathways Corporation, Sunnyvale, Calif.). It also includes
ultrasound ranging hardware 116 and an ultrasound hardware control
and timing component 118 which together initiate, detect, and
measure the time of flight of ultrasound pulses emitted and
received from the ultrasound transducers on the reference and EP
catheters 10-16.
[0141] Signal amplifiers 114 and the ranging hardware 116 and
controller 118 are electronically coupled to a microprocessor
workstation 112. The microprocessor work station 112 is designed to
control the system hardware and the data processing for both the EP
and ultrasound functions of the system, and to generate a visual
display of EP and catheter position data for use by the
clinician.
[0142] For EP functions, the microprocessor 112 includes an
amplifier controller 120 that delivers mapping, and/or pacing
commands to the EP signal amplifiers 114. Signal processors 122
receive data corresponding to electrical activity measured by the
mapping catheters 14, 16 and generate graphical representations of
the measured data for display on graphical interface display 124.
The mapping signals shown on the graphical display can represent
any number of parameters or characteristics, such as measured
signal values or impedance values, indicators of electrode contact,
or indicators of the probability that there is an arrhythmogenic
site in the area, etc.
[0143] Ultrasound hardware controller 118 and a triangulation
processor 126 control the catheter localization functions and data
processing. During use, controller 118 directs the ultrasound
ranging hardware 116 to initiate an ultrasound pulse from a
selected transmitting transducer. It further directs the hardware
116 to (1) detect, in parallel, voltages corresponding to reception
of the ultrasound pulse by the receiving transducers, and (2)
measure the elapsed time (time of flight) between transmission of
the ultrasound pulse and its detection by the selected receiving
transducers. Triangulation processor 126 receives data
corresponding to these time of flight measurements from the ranging
hardware 116 and uses it to calculate the locations of the EP
catheter transducers relative to the reference transducers (see
Localization System Overview). Data corresponding to catheter
position, as calculated from transducer locations, and measured EP
signals is shown in graphical form on graphical user interface
display 124.
[0144] The ultrasound ranging hardware 116 may be configured to
detect an acoustic pulse received by a receiving transducer in a
number of ways. For example, if the transmitting transducer is made
to generate a short burst of high frequency ultrasound energy, the
hardware 116 may be configured to detect the first signal excursion
above or below a predetermined maximum and minimum voltage
threshold, or the peak of a received signal. Alternatively, the
transducer may be made to generate a continuous wave of low
frequency ultrasound, in which case the hardware 116 would be
configured to measure the difference in phase between the standing
wave as generated by the transmitting transducer and as detected by
the receiving transducer.
[0145] Referring to FIG. 27A, the ultrasound ranging hardware 116
includes a plurality of channels 128a, 128b, each of which is
electronically coupled to one of the ultrasound transducers in the
system. Depending on whether a transducer is intended to transmit
and receive ultrasound signals (as in the case of a reference
catheter transducer 18) or to receive ultrasound signals only (as
in the case of an additional catheter transducer 34, 58 or 92), a
transducer's corresponding channel circuitry may be configured to
permit transmission and receipt of ultrasound signals by the
transducer, or it may be configured only to allow receipt of
signals by the transducer. Accordingly, transmit/receive channels
128a are each connected to a corresponding one of the reference
catheter transducers 18 (FIG. 3), and receive channels 128b are
each connected to a catheter transducer 34, 58, 92 (e.g., FIGS. 9,
13 and 19).
[0146] Referring to FIG. 27B, the circuitry of each of the channels
128a, 128b generates digital data corresponding to the time of
flight of an ultrasound transmit pulse from a transmitting
transducer to the transducers corresponding to each of the channels
128a, 128b. Each channel 128a, 128b includes an amplifier 130 which
amplifies voltage signals generated by the ultrasound transducers
in response to receive pulses. The transmit/receive channels 128a
additionally include transmitters 132 which, in response to signals
from transmit and receive controller 142 (discussed below), apply
voltages across the reference transducers 18 to trigger ultrasound
pulses.
[0147] Each channel 128a, 128b further includes a threshold
detector 134 which triggers a latch 136 once a received signal
exceeds a threshold level. Latch 136 is coupled to distance
register 138 which is in turn coupled to place distance output data
onto data bus 140 upon activation of the latch 136.
[0148] Ultrasound hardware control and timing component 118
includes transmit and receive controller 142. Controller 142 is
electronically coupled to a system clock 141 that drives a distance
counter 144, and to a threshold amplitude generator 146 which
provides the threshold reference input for threshold detectors
134.
[0149] As will be discussed in greater detail, count values from
the distance counter 144 are used by the system 100 to calculate
the distances between transmitting transducers and receiving
transducers. Because system clock 141 drives the distance counter
144, it is the frequency of the system clock that determines the
resolution of measured distances between transducers. The higher
the frequency of the clock, the greater the resolution of the
distance measured. Clock 141 is therefore a high frequency counter
which preferably operates at least approximately 5-50 MHz, which is
equivalent to a resolution of approximately 0.3-0.03 mm.
[0150] The threshold amplitude generator 146 produces time varying
positive and negative thresholds that are used as inputs to the
threshold detectors 134 of each channel 128a, 128b. Preferably, one
threshold amplitude generator 146 is used for the entire system in
order to minimize the amount of hardware in the system. However,
the system may alternatively use a separate threshold amplitude
generator for each channel, or separate threshold amplitude
generators for different groups of channels. For example, different
threshold amplitude generators may be used for different types of
receiving transducers, since some produce weaker signals and
therefore require lower thresholds. As another alternative, a fixed
threshold may be used together with a variable gain amplifier in
place of amplifier 130.
[0151] The threshold amplitudes are preferably varied by the
threshold amplitude generator 146 so that they are large at the
time a transmit pulse is initiated and so that they decrease as
time passes following transmission of a pulse. Using a variable
threshold rather than a fixed one is beneficial because the dynamic
range (i.e., the ratio of the largest signal to be detected to the
smallest signal to be detected) is quite large, and may even be as
high as 70 dB due to factors such as anisotropy of the transit and
receive beam profiles, signal decay due to ultrasound wave
propagation, and attenuation of the signal caused by blood and
tissue. Because transducer receiving wires for a catheter based
system must be closely spaced, a fixed dynamic range of this
magnitude could lead to erroneous data, because cross-talk between
the closely spaced receiving wires could be interpreted by the
system to be actual receive signals.
[0152] It should be noted that both positive and negative
thresholds are used so as to increase the accuracy of the detection
time, since a negative oscillation of a transmit pulse may reach
the detection threshold before a positive oscillation. Latch 136
will therefore be triggered by whichever of the positive or
negative thresholds is achieved first.
[0153] When a transmit pulse T (FIG. 28A) is being sent to a
transducer, oscillation, or "ringing", designated "R.sub.T", can
occur on the corresponding twisted pair 26 (FIG. 3). The ringing in
the transmit line is not problematic in and of itself. However, in
catheters such as the reference catheter 10 which includes
transducers which can both transmit and receive ultrasound signals,
the close proximity of the transmitting and receiving lines can
cause the ringing to cross over to the receiving line. This problem
arises most frequently when the system is computing the relative
orientations of the reference transducers 18 (FIG. 3) in order to
establish the three-dimensional coordinate system, since that
procedure requires measuring the time it takes for a pulse emitted
by one of the reference transducers 18 to be received by the other
reference transducers 18 on the same catheter. The ringing (which
is designated "RR" in FIGS. 28B and 28C) can be of similar
magnitude to a receive signal "S" and can therefore make it
difficult to determine whether a receive signal has been
detected.
[0154] If the transmitting and receiving transducers are far apart,
a receive signal on a receiving line (such as twisted pair 26) will
be measured by the ultrasound system circuitry despite the ringing,
because transmission of the receive signal on the receiving line
will happen only after the ringing has diminished. See FIG. 28B.
However, if the transmitting and receiving transducers are close
together (i.e., separated by less than approximately 2 cm), the
receive pulse will be lost in the ringing on the receive line,
because the receive pulse will reach the receiving line while the
ringing is still occurring. See FIG. 28C.
[0155] It has been found that this problem may be avoided by
including circuitry which will short the conductors of the transmit
line immediately after the transmit pulse is sent. An example of
such circuitry is shown in FIG. 29. The circuit includes the pulse
generator 148 and center tapped transformer 150 which comprise
basic pulse generating circuitry, plus a switch 152 which is closed
immediately after a transmit pulse in order to short the ringing to
ground. A small impedance 154 is placed in series with the switch
in order to dampen the ringing through the short circuit. As
illustrated in FIGS. 28D and 28E, by eliminating the ringing from
the transmitting line, the switch eliminates the ringing from the
receiving line as well.
[0156] Referring again to FIG. 27B, during use of the system, each
transmit/receive channel 128a is sequentially selected for
transmission of a transmit pulse, and all channels 128a, 128b are
simultaneously selected for parallel reception of distance data.
Transmit and receive controller 142 selects which of the
transmit/receive channel 128a will initiate an ultrasound pulse,
and cycles through each transmit/receive channel, causing
sequential transmission of pulses by the reference transducers 18
(FIG. 3). It uses the system clock 141 to generate a lower
frequency transmit clock, which in turn controls how often
ultrasound pulses are transmitted.
[0157] Each time a transmit pulse is to be initiated, the transmit
and receive controller 142 performs the following sequence of
steps. The distance counter 144 is first reset to zero, and the
threshold amplitude generator 146 is reset. A detection hold off
and reset signal is next sent by controller 142 to all channels
128a, 128b. This resets the latch 136 for each channel and prevents
it from latching for a specified time period to prevent detection
due to electromagnetic coupling of ringing after transmission of a
transmit pulse. This "hold off" period is determined by the
smallest distance within the patient that is to be measured, and is
calculated according to the following equation:
hold off period=smallest distance*1/(velocity of transmit
signal).
[0158] Thus, if the smallest distance to be measured is 10 mm, the
"hold off period" is: 1 10 mm * 1 1.5 mm sec = 6.66 sec
[0159] After the hold off and reset signals, a transmit control
signal is sent to a selected one of the transmit/receive channels
128a, causing it to initiate a transmit pulse. Shortly afterwards,
a signal is sent to the same transmitter to initiate damping in
order to prevent/reduce ringing as described above.
[0160] When a transmit pulse is initiated, the distance counter 144
is simultaneously activated. After a transmit pulse is triggered,
each channel 128a, 128b "listens for" a receive pulse. When the
threshold detector 134 for a particular channel detects a receive
pulse that exceeds the threshold set by the threshold amplitude
generator 146, the latch 136 for that channel is activated. Once
the latch 136 is activated, a load data command is sent to the
associated distance register 138 and the current contents of the
distance counter 144 are loaded into the distance register 138 for
that channel. This data is subsequently placed on the distance data
bus 140 along with data indicating which channel transmitted the
pulse. Thus, the data bus receives a number of distance values
which correspond to the number of transmit/receive and receive only
channels. These distance values are then used by the triangulation
processor 126 (FIG. 1) to determine the relative positions of the
ultrasound transducers, and the microprocessor 112 uses the
position data to create a three-dimensional display of the
catheters.
[0161] Graphical Display Features
[0162] As described, the three-dimensional positions of the
integrated ultrasound transducers (such as those on catheters 10,
12, 14 and 16) may be continuously displayed in real-time on the
graphical user interface display 124 (FIG. 1). The
three-dimensional positions of the catheters (10, 12, 14 and 16),
or portions thereof, may also or alternatively be continuously
displayed based on the position of the transducers by extrapolating
the catheter position using a known model of the catheter
programmed into the system. The three-dimensional positions of the
transducers and/or catheters may also be stored in the system's
memory and selectively displayed on the graphical display user
interface display 124 as required during a procedure.
[0163] For example, data corresponding to electrode locations on a
mapping basket 14 may be saved in the system memory, together with
data representing EP measurements taken by EP electrodes
corresponding to the transducer locations. If, after the mapping
basket 14 has been removed from the patient, the user wishes to
guide an ablation catheter to a location corresponding to one of
the basket electrodes, s/he may elect to display the saved location
information for the basket simultaneously with the real time
position of the ablation catheter.
[0164] The graphical user interface is further provided with
several additional functions that improve the accuracy and
usefulness of the system.
[0165] For example, the microprocessor 112 includes software which
enhances the accuracy of the system by "gating out" the effects of
cardiac motion on the position data calculated for the transducers
and/or catheters. Because a beating heart contracts and expands
with each beat, the catheter will move with the heart throughout
the cardiac cycle even when a catheter is at a mechanically stable
location within the heart. Thus, a real time display of the
catheter (or transducer) position would show the catheter or
transducer moving on the display because of the cardiac
movement.
[0166] Such movement of the catheter/transducer on the display does
not present problems in and of itself. However, if the user elects
to save in the system memory the position of the catheter so that
it may be used later during the procedure (such as to indicate
anatomical landmarks, ablation locations, mapping locations, etc.),
the effects of the movement on the saved locations can lead to
inaccuracies if the user attempts to navigate a catheter (shown in
real time on the display) with respect to the representation on the
graphical display of the previous catheter position data.
[0167] To eliminate this problem, the patient's electrocardiogram
(EKG) is monitored during use of the system, and the EKG is used to
synchronize the acquisition of position data so that all position
data is acquired at the same point in the cardiac cycle. Thus, for
example, when EP signals are recorded from catheters having
Integrated locelizatlon transducers, the relative positlon/locatIon
information for the EP electrodes is accurate when displayed
because all of the location information will have been collected
during the same phase of the cardiac cycle. Gating is similarly
carried out for the ablation and marking catheters, by collecting
the appropriate position/location data for such catheters and the
anatomical landmarks during the same phase of the cardiac
cycle.
[0168] FIG. 30B shows an EKG signal along with corresponding
electrode position data recorded over the cardiac cycle. It has
been found that the end of diastole, at the Q-R wave of the EKG
signal, is a convenient point for gating the position measurements.
FIG. 30A schematically shows a gating system in which a patient's
EKG signal is passed through an amplifier 302 and a detector 304
which initiates a sample and hold sequence 306 of position data
when the initiation of a Q-R wave is detected.
[0169] The user preferably has the option of showing the gated
position, or the actual (moving) position, or both on the real time
display. The actual position of a catheter may be useful for
assessing whether a catheter is in firm contact with the wall of
the heart, because if the catheter is spaced away from the wall it
will not move with the wall. A display of actual position may also
be helpful during steering of a catheter because it provides more
rapid feedback of a catheter's position and orientation.
[0170] It should be emphasized, however, that gated position
information is essential during navigation of a catheter to a
location which has been saved in the three-dimensional display,
because unless the catheter position and the stored location are
gated to the same point in the cardiac cycle, the user cannot be
certain that the catheter has been navigated to the proper
location.
[0171] Similarly, if EP signals are to be displayed in the form of
an isochronal map on the three-dimensional display, the position
used in the isochronal map to display an activation time for that
location should be an EKG gated location.
[0172] Similar gating may also be provided to eliminate
inaccuracies in location information due to the rising and falling
of the chest during respiration. For respiratory gating, chest
movement would be monitored using a bellows or other device and the
sample and hold sequence would be triggered at a desired portion of
the respiratory cycle.
[0173] Referring to FIG. 31, the gated positions of lesions and
anatomical landmarks may be stored in the system software and added
and deleted from the display as needed by the user by manipulating
a cursor using a mouse or other user input device to the
appropriate item in marker box 156.
[0174] The microprocessor 112 is preferably further provided with
software which allows the physician to manipulate the display in
many ways so that the maximum benefit may be obtained from the
system. For example, referring again to FIG. 31, the user can
rotate the display in three-dimensions by guiding the cursor to the
appropriate icon in manipulation box 158. The user may likewise
"zoom" towards or away from the image in the same manner. S/he may
also elect which of the catheters 10, 10a, 12, 16 to display in
real time using real time box 156.
[0175] The system further allows the user to select one of the
standard orientations used in fluoroscopy such as
anterior-posterior ("AP"), lateral, right anterior oblique ("RAO")
or left anterior oblique ("LAO") by selecting the appropriate icon
in orientation box 160. In the RAO view, the plane formed by the
aortic-valve ring ("AV ring") is approximately perpendicular to the
plane of the display, with the end of the coronary sinus pointing
to approximately the 2-3 o'clock position on the AV ring. In the
LAO view, the apex of the heart is oriented such that it "points"
towards a user viewing the display.
[0176] When the system 100 is used is a preferred mode, the
transducers of a reference catheter positioned in the coronary
sinus ("CS reference catheter") define the AV ring, and the distal
tip of a second reference catheter is positioned in the RV apex
("RV apex catheter"). The system can orient the display to an RAO
orientation by deriving the location of the AV ring from the
location of the transducers on the CS reference catheter, and
re-orienting the display until the AV ring is perpendicular to the
display and until the distal tip of the CS reference catheter
points towards the 2 o'clock position.
[0177] With the AV ring perpendicular to the display, the system
may also display straight anterior, posterior, left lateral, and
right lateral views by orienting the CS catheter distal tip at the
12 o'clock, 6 o'clock, 3 o'clock, and 9 o'clock positions,
respectively.
[0178] Similarly, the system can orient the display to an LAO
orientation by deriving the location of the RV apex from the
locations of the transducers on the RV apex catheter, and by
orienting the display so that the RV apex points out of the
display.
[0179] Operation
[0180] Two examples of procedures which may be carried out using
the localization system 100 will next be described. It should be
appreciated, however, that the system 100 may be utilized in any
procedure in which three-dimensional navigation of devices relative
to one another is required.
[0181] FIG. 33 is a flow diagram giving a sample methodology for
using the localization system 100 for diagnosis and treatment of
ventricular tachycardia. The steps shown in the flow diagram will
be discussed with reference to the illustrations of the heart shown
in FIGS. 34A through 34D.
[0182] First, step 200, a reference catheter 10 is introduced into
the inferior vena cava and is passed under fluoroscopy into the
right ventricle (designated RV). The catheter is positioned with
its distal tip at the apex (A). A second reference catheter 10a is
introduced via the superior vena cava into the coronary sinus (a
vein, shown and designated CS in FIG. 34B, that extends around the
edge of the AV ring separating the left atrium and the left
ventricle). The reference catheters may be positioned elsewhere
without departing from the scope of the invention. However, the RV
and CS are suitable locations because they allow the catheters to
remain mechanically stable within the heart. Moreover, these
reference catheters will include the EP electrodes equivalent to
those already used on CS and RV apex catheters, i.e. they will
replace conventional CS and RV apex catheters. Placement of the
reference catheters using these approaches therefore does not
require introduction of additional introducer sheaths or catheters
into the patient.
[0183] Throughout the procedure, the system calculates the relative
positions of the ultrasound reference transducers 18 (FIG. 3) using
time-of-flight measurements and triangulation, establishes the
three-dimensional coordinate system, and displays at least a
portion of the reference catheter on the graphical interface
124.
[0184] Next, referring again to FIG. 34A, marking catheter 12 is
preferably (but optionally) introduced into the left ventricle.
Catheter 12 is guided under fluoroscopy to sequentially position
its distal tip against various anatomical landmarks, such as the
apex, septal wall, lateral wall, etc. The location of each
transducer 34 (FIG. 9) relative to the reference catheters is
calculated again using time-of-flight measurements and
triangulation. The location of the catheter distal tip and thus the
location of the anatomical site is extrapolated from the transducer
location using a model of the catheter 12 pre-programmed into the
system, and it may be subsequently displayed on the graphical
display. Once the desired landmarks are identified and displayed,
the marking catheter 12 is removed from the heart. Steps
202-208.
[0185] Referring to FIG. 34C, basket catheter 14 (FIG. 13) is next
introduced under fluoroscopy into the left ventricle (LV), at a
location at which the clinician suspects there may be
arrhythmogenic tissue. Step 210. Because the basket arms 52 include
ultrasound transducers 58 as well as mapping electrodes 56, the
locations of the mapping electrodes can be determined relative to
the reference catheters and displayed on the graphical display
based on a model of the basket 50 programmed into the system. Step
212.
[0186] Electrical activity within the heart is recorded from the
mapping electrodes 56 and mapping data derived from the recorded
activity is displayed on the graphical display. The EP signal
display may be displayed separately from the three-dimensional
display, such as in the signal display window 162 shown in FIG. 32.
Each graph in the signal display window 162 represents the voltage
data over time, as measured by one of the EP electrodes 56 on the
basket catheter 14.
[0187] The EP signals may alternatively be displayed in the form of
an isochronal map on the three-dimensional display. A display of
this type would be generated by first placing an activation time on
each signal, where an activation time is the time at which the
tissue under a mapping electrode 56 activates. The activation times
can be either placed automatically using an algorithm or manually
by the user. The map is generated by showing a color on the
three-dimensional display that represents an activation time at a
location corresponding to the location of the electrodes that
measured the signal. It may be in the form of discrete color dots
or an interpolated color surface or sheet which passes through the
locations of the EP electrodes.
[0188] The EP display may alternatively take the form of an
isopotential display on the three-dimensional display. An
isopotential map is similar to an isochronal map except that it is
a time varying color display that is proportional to signal
amplitude rather than a static display of activation time.
[0189] Other mapping data derived from the EP signals may also be
shown on the display. For example, data indicating the adequacy of
contact between the electrodes and the tissue, or indicating the
probability that there is an arrhythmogenic site at the mapped
location may be represented on the display. The physician may
induce electrical activity for subsequent measurement by pacing the
heart from the basket electrodes 56. Step 214.
[0190] If an arrhythmogenic region is identified by the clinician
on the visual display, a marking and ablation catheter 12 (FIG. 9)
is inserted into the center lumen 80 of mapping catheter 14 (FIG.
15) and is guided into the left ventricle. The three-dimensional
position of the ablation electrode 36 is displayed (using
ultrasound receiving transducer 18 to track its position) in real
time to aid the physician in guiding the electrode 36 to the
arrhythmogenic region of the endocardium. FIG. 34D and step 216.
Once the ablation electrode is positioned at the arrhythmogenic
region, ablation is carried out by supplying RF energy to the
electrode 36.
[0191] The clinician next attempts to induce ventricular
tachycardia by pacing the site from the basket catheter electrodes
56 or from electrodes on another catheter. Step 220. If VT cannot
be induced, the procedure is considered successful and the
catheters 10, 14 are removed. Step 222. If VT is induced,
additional mapping and ablation steps are formed until the VT
appears to be eradicated.
[0192] It should be noted that if mapping is carried out using a
basket catheter that is not provided with a center lumen 39, the
basket catheter may be removed after its electrode positions and
corresponding mapping signals (which may include a visual
identification of the arrhythmogenic region) are saved in the
system memory, and a separate ablation catheter may be introduced
into the heart and guided to the arrhythmogenic region identified
on a visual display of the gated positions of the mapping
electrodes.
[0193] FIG. 35 is a flow diagram illustrating use of the
localization system 100 with a linear lesion catheter of the type
shown in FIGS. 18-26 to treat atrial fibrillation. The steps shown
in the flow diagram will be discussed with reference to the
illustrations of the heart shown in FIGS. 36A-36C and the examples
of the graphical user interface shown in FIGS. 31 and 32.
[0194] First, reference catheters 10, 10a are placed in the
coronary sinus and RV apex as illustrated in FIGS. 34A and 34B. The
reference catheters 10, 10a are preferably represented on the
graphical display as shown in FIG. 31. Step 300. Although only the
reference transducer positions are precisely known, the catheter
locations can be estimated using the transducer positions, the
known spacing of the transducers along the catheter bodies, and a
known model of the catheter.
[0195] Next, referring to FIG. 36A, marking catheter 12 (FIG. 9) is
positioned in the left atrium, preferably by inserting it through a
transeptal sheath passed from the right atrium, through the septum
and into the left atrium. Steps 302-304. Marking catheter 12 is
sequentially positioned with its distal tip at anatomical
landmarks, such as the pulmonary veins, septal wall, mitral valve,
etc.
[0196] The location of each ultrasound transducer 34 on the marking
catheter 12 relative to the 3-D coordinate system is calculated
using time-of-flight measurements and triangulation. The position
of the distal tip is extrapolated from the transducer using a model
of the catheter pre-programmed into the system, and is subsequently
displayed on the graphical display when the distal tip is
positioned at a desired anatomical site (as verified using
fluoroscopy), the user adds an appropriate indicator to the display
at the distal tip location by entering the necessary input at
marker box 156 (FIG. 31). For example, see FIG. 31 in which the
left superior pulmonary vein and left inferior pulmonary vein are
identified as "LS" and "LI". After the appropriate landmarks are
added to the 3-D display, the marking catheter 12 is removed from
the heart.
[0197] Next, using a mouse or other user input device, lines
representing target locations for linear lesions are added to the
display. Step 312. These lines are identified by the dashed lines
on FIG. 31. The linear lesion catheter 16 (FIG. 8) is next inserted
into the left atrium, preferably via the transeptal sheath 87 shown
in FIG. 36A. During placement of the linear lesion catheter, the
position of ablation window 86 (FIG. 19) is tracked in real time by
tracking the positions of the transducers 92 using the localization
system 100 and by deriving the window location from the transducer
location. An arrow A1 or other icon representing the length of the
catheter 16 lying between the transducers 92 is shown on the
display as shown in FIG. 31.
[0198] Referring to FIG. 36B, lesion catheter 16b (shown in FIG.
36B to have an ablation section slidable on a looped baffle wire as
described in PCT/US96/17536), is guided using the localization
system 100 to a first one of the desired ablation locations marked
onto the display by the physician. By manipulating the catheter 16
such that the display shows arrow A1 lying over the area marked as
a target location, the physician can ensure that the window 86
through which ablation will occur is at the correct location. If a
different type of ablation catheter is used, including one which
does not involve the use of an electrolytic fluid, the physician
may use a similar procedure to align the ablation section (which
may be an electrode, an electrode array, or another region of the
ablation catheter at which ablation will be carried out) with the
target location.
[0199] RF energy is supplied to the RF electrodes 90 (FIG. 19)
while a conductive fluid is supplied to the fluid port 96 (FIG.
18), to create a linear lesion in the target tissue. Step 318.
Arrows A2 or other icons representing the window 86 positions
during each ablation are added to the display to indicate the
location of a linear lesion. These arrows may be coded by color or
other means to indicate characteristics of the lesion, such as the
wattage used to create the lesion or the impedance during the
ablation. The linear lesion catheter is then repositioned for
additional ablation steps until all of the desired ablation
locations have been treated.
[0200] Next, the linear lesion catheter is removed, and mapping
basket 50 is inserted into the left atrium as shown in FIG. 36C.
Steps 322, 324. The positions of basket electrodes and arms are
determined using the ultrasound localization system and are
displayed on the 3-D display in the manner described above. FIG. 32
illustrates the positions of the arms 52 with solid lines and the
position of the recording electrodes 56 with stars. Pacing and
mapping is carried out using the electrodes 56 in a conventional
manner to determine whether the linear lesions have blocked
transmission of the electrical currents that traverse the left
atrium during an atrial fibrillation episode. The electrical
activity measured by the mapping electrodes 56 is shown in the form
of an isochronal map over the lesion locations A2 on the
three-dimensional display. Steps 328-330. If the linear lesions are
found to be successful, the basket catheter is removed and the
procedure ended. If additional lesions are necessary, the locating,
the ablating, pacing and mapping steps are repeated.
[0201] Three-Dimensional Deformable Model
[0202] The present invention provides a three-dimensional graphical
model of a region of interest within the body (e.g. the heart,
abdominal cavity etc.) which may be used together with the visual
display generated by the localization system so as to give the
physician additional anatomical context as s/he manipulates medical
devices within the body. The model is dynamically deformable so
that, as information concerning the three-dimensional location of
actual physical characteristics in the relevant region is obtained,
the model as displayed on the graphical display is changed to more
closely resemble the actual region of interest in the patient's
body.
[0203] The deformable model will be described with reference to the
heart, although it is equally suitable for other regions of
interest within the body including other organs or cavities.
[0204] The deformable model system 124a may be programmed into the
localization system microprocessor 112 (FIG. 1). Referring to FIG.
37, the system 124a includes a model generation component 125a
which generates and displays a "basic" model of a human heart on
the graphical display 124 (FIG. 1). The basic model is preferably
preprogrammed into the system based on the size and proportions of
an average healthy human heart. The model preferably includes basic
anatomical features, which for the heart may include four chambers
with their associated boundaries, valves, major vessels and their
orifices, electro-anatomical structures such as the sinus node, AV
node, HIS bundle, ETC., and major anatomical structures such as
papillary muscles, chordae, etc.
[0205] System 124a further includes a transformation component 125b
that deforms the model based on input 127a from the localization
system concerning the 3-D locations of physical characteristics of
the heart and displays the model (as so deformed) on the graphical
display 124 (FIG. 1). This input is generated by the localization
system using time-of-flight data received from one or more probes
positioned within or near the heart. User input 127b, such as an
identification of the chamber in which the probe is positioned, is
also received by the transformation software and used to deform the
model, as described in further detail below.
[0206] FIG. 38 is a flow diagram illustrating the basic operation
of the system. In step 400, a model of the region of interest is
provided by the system. Preferably, a model is stored in the system
software and used to generate the basic model image on the
graphical display. The basic model may be displayed on the
graphical display 124 (FIG. 1), or the system may instead delay
display of the model until after one or more of the transformations
have been carried out. The system may be provided with multiple
basic models, each having different characteristics relating to
particular classes of patients (e.g. enlarged hearts, hearts having
common forms of aneurysms etc.) from which the user can choose for
a particular application. The system may further enable the user to
add aneurysms, infarct scars, and other conditions to the graphical
display of the model by dragging the structures onto the model from
a toolbar on the graphical display or by electronically drawing
such structures onto the model using a computer mouse.
[0207] In step 402, the localization system is used together with
one or more probes positioned within the heart to obtain
information concerning physical characteristics of the heart. If
the system is used with the ultrasound localization system
described above, each probe includes one or more ultrasound
transducers at or near its distal tip. As a probe is manipulated
within the heart, the location of its distal tip and thus the
location of an adjacent anatomical structure is derived from the
location of the transducer using the triangulation algorithm
discussed earlier.
[0208] Although the ultrasound localization system is preferred for
use in connection with the deformable model of the invention, the
probe may be any kind of probe or medical device that can provide
input to the transformation system regarding the physical
characteristics of the region of interest.
[0209] Locations of physical characteristics derived by the
localization system are delivered to the transformation software
and used in Step 404 to alter the model to more closely conform to
the physical characteristics of the actual heart. A "physical
characteristic" can be any feature within the region of interest,
ranging from information that a particular x,y,z coordinate is
simply part of a space within a chamber, to information that a
certain coordinate is an endocardial surface, to more specific
information concerning an actual structure such as a valve or
vessel. Information of the type obtained using the localization
system can be classified into three general categories: anatomical
points, interior points, and surface points.
[0210] Anatomical points are the three-dimensional positions of
specific anatomical structures (or portions thereof) within the
heart. These points are highly useful to the transformation
software to update the model because they serve to tie down a
particular anatomical structure to a particular three dimensional
position on the model. To obtain an anatomical point, the user will
steer a probe to a known structure using fluoroscopy or other
visualization techniques. S/he will then position an identifiable
portion of the probe (e.g. the distal tip) at the structure, for
example the orifice of the right superior (RS) pulmonary vein. Once
the probe is positioned at the known structure the user provides
input identifying the structure at which the probe is positioned
using an input device such as a keyboard or mouse. The localization
system then determines the three-dimensional location of the
anatomical structure and the model transformation software, at Step
404, alters the model so that the RS pulmonary vein on the model
coincides with the determined location of that structure in the
patient. This anatomical feature will serve as a "hard tack point"
for the pulmonary vein, and so further transformations of the model
will not move the pulmonary vein from this three-dimensional
location.
[0211] Additional anatomical point information may be provided to
the system by positioning reference catheters such as catheter 10,
FIG. 3, at known locations in the region of interest, such as in
the coronary sinus ("CS") and right ventricular apex ("RV apex") as
described with respect to use of the localization system. FIG. 39A
illustrates the way the three-dimensional graphical display might
appear if the basic model 600 is displayed after a reference
catheter 10 has been placed in the RV apex but before the model has
been transformed. It is evident from the visual representation of
the catheter 10, which extends beyond the lower walls of the
graphical image of the heart, that the model 600 of the heart
differs greatly from the actual patient's heart.
[0212] Once the catheter 10 is in place, the user enters input into
the system indicating that a catheter is positioned in the RV apex.
The localization system at step 402 calculates the
three-dimensional location of the reference catheter. The
transformation software at Step 404 deforms the model so that the
RV apex of the model conforms with the actual determined location
of the RV apex. The model (as seen in FIG. 39B) is then shown in
its deformed state on the graphical display. A similar procedure is
preferably also carried out using a coronary sinus catheter. In
this manner, the system uses the RV apex and CS catheters to
"initialize" the model by defining the gross translation, rotation
and scale of the heart and to deform the model to reflect the
appropriate translation, rotation and scale.
[0213] The second type of information obtained at Step 402, FIG.
38, concerning the physical characteristics of the heart is
interior point information. Referring to FIG. 40A, during the
procedure the user positions the distal portion of the probe (e.g.
catheter 12) within a chamber of the heart such as the left
ventricle. In the example shown in FIG. 40A, the graphical
representation of the catheter 12 extends beyond the graphical
image of the wall of the left ventricle of the model 600.
[0214] The user provides input to the transformation system
indicating that the probe is within a specified chamber, e.g. the
left ventricle. The localization system determines the
three-dimensional location of the distal portion of the catheter 12
and provides that information to the transformation system. Once it
has been informed the distal portion of the probe is within the
specified chamber, the transformation software can use the
determined three-dimensional location to further update the model
in accordance with Step 404. The model as further updated in this
manner is shown in FIG. 40B. It should be noted that while it is
useful for the system to receive user input concerning the chamber
in which the probe is positioned, this input is not required. The
system may determine which chamber the probe is in based on the
relative positions of the reference catheters in the RV apex and
coronary sinus.
[0215] FIG. 40C illustrates the transformation undertaken at Step
404 for this particular example. The left ventricular wall of the
model prior to transformation is shown in solid lines, and the
dashed lines illustrate the transformed state of the model. Arrows
illustrate the transformation process.
[0216] As the probe is steered from place to place within the
chamber additional points are gathered and used to update the
model. It can thus be seen that the interior point information
allows the system to identify multiple points that are known to lie
within the specified chamber and to thus approximately conform the
size and shape of the chamber on the model to the size and shape of
the corresponding chamber in the patient's heart.
[0217] A third type of information, surface point information, is
obtained by steering the probe into a known chamber of the heart
and into contact with the endocardial surface within the chamber.
FIG. 41A illustrates the three-dimensional graphical display of the
model 600 together with a catheter 12 positioned in contact with
the endocardial wall in the left ventricle. Because the model has
not yet been deformed to reflect the proper location of the
endocardial wall, the catheter is shown as being inside the chamber
but spaced from the wall.
[0218] After confirming that the catheter is in contact with the
wall, the user provides input to the system indicating that the
catheter is in contact with the wall of a specified chamber. The
operator can use a variety of methods to determine whether the
probe is in contact with the endocardial surface. One such method
involves observing the probe on the fluoroscope (or viewing an
un-gated representation of the probe on the localization system
display), simultaneously observing the patient's EKG, and
determining whether the probe is pulsing with the patient's EKG.
The user may also evaluate contact between the probe and the
endocardial surface by feeling mechanical resistance as the
catheter is advanced. Alternatively, if the probe is provided with
mapping electrodes, contact with the endocardial surface may also
be confirmed by monitoring EP signals from the mapping
electrode(s). Rapid deflection of the EP signals indicates contact
between the electrode and the endocardium. The EP signals may be
monitored visually on an EP display or automatically by the system
as set forth in detail in co-pending application Ser. No.
08/732,511, filed Oct. 15, 1996, entitled APPARATUS AND METHOD FOR
AIDING IN THE POSITIONING OF A CATHETER. If the monitoring is
automatic, the EP system may automatically send a signal to the
transformation system that the catheter is in contact with the
chamber wall.
[0219] The transformation software receives as input the
three-dimensional locations of points on the endocardial wall which
have been derived by the localization system based on the catheter
position. The model 600 is then deformed as indicated schematicaly
by arrows in FIG. 41C to bring it into closer conformity with the
actual heart. It should be noted that deformations made based on
interior point and surface point information do not change the
positions of the anatomical points ("tack points") that have been
added to the model as described above. The three-dimensional visual
display of the model after transformation is illustrated in FIG.
41B.
[0220] FIG. 42 is a flow diagram illustrating a preferred mode of
using the model transformation system. First, at step 500, a model
of the heart is generated and may be shown on the graphical
display, although in the preferred embodiment the model is not
visually displayed until after the first transformation has been
performed. Features including disease conditions such as aneurysms,
infarct scars, etc. may be added to the model at any time as
described above.
[0221] At step 502, the user positions ultrasound reference
catheters in the coronary sinus and RV apex and provides input to
the system indicating that RV apex and CS catheters have been
placed. At step 506 the localization system determines the
three-dimensional locations of the transducers on the CS and RV
apex catheters and provides that information as input to the
transformation software. The transformation software compares the
coordinates of the CS and RV apex catheter transducers with
corresponding points on the models, and uses that information to
scale and orient the model. Step 506. This transformation step is
preferably carried out using the procrustean rigid body
transformation techniques as described in I. Borg & J. Lingoes,
Multidimensional Similarity, Structure Analysis, Chapter 19
Procrustes Procedures, New York: Springer Verlay, 1987. See Section
19.4. The model as transformed is shown on the graphical display.
Step 507.
[0222] At step 508, a probe which may be a 7 Fr catheter such as
catheter 12, is positioned in the heart, and the user preferably
may provide input to the system indicating the general location of
the probe. Step 509. For example, the user may indicate which
chamber the probe is in. If the probe is placed in contact with the
endocardial surface, or at a known anatomical point, that
information is preferably input into the system by the user at step
509.
[0223] At step 510, the localization system calculates the
three-dimensional position of the physical characteristic
identified by the probe and delivers that information to the
transformation system. The transformation further deforms the model
to incorporate the physical characteristics into the model,
preferably using the vector field interpolation method described by
D. Ruprecht et al, Spatial Free-Form Deformation With Scattered
Data Interpolation Methods, Computers & Graphics, Vol. 1, No.
1, pp. 63-71, 1995, which is incorporated herein by reference. See
in particular equations (1) and (2).
[0224] Additional physical characteristics are obtained by
repositioning the probe(s) and repeating steps 510 and 512 as
desired by the user to increase the conformity between the model
and the actual heart. Afterwards, the user may conduct mapping
and/or ablation procedures such as those described with respect to
FIGS. 33 and 35, with the catheters used for those procedures being
shown within the deformed model of the heart. The model may be
further deformed by following steps 508-516 if the user chooses to
do so at any time during the ablation/mapping procedure.
[0225] Certain features added to the graphical display during the
course of the mapping and/or ablation procedures are added to the
endocardial surfaces of the model. For example, maps, including
isochronal or isopotential maps, generated during mapping
procedures are preferably shown on the endocardial walls of the
model appearing on the graphical display. Likewise, lesions formed
during the ablation procedure are also shown on the "walls" of the
model.
[0226] As with the localization system, the user may manipulate the
model on the graphical display to rotate or change the orientation
of the model. The system also allows the user to take
three-dimensional cut-outs through the model across one or more
section planes specified by the user using a mouse or other input
device. This would result in a three-dimensional section view of
the heart and its associated structures.
[0227] One embodiment of the system according to the present
invention has been described, and it has been described primarily
with respect to an ultrasound localization system, EP catheters,
and cardiovascular procedures. It should be appreciated, however,
that the system and its components may be used in a variety of
medical contexts in which three-dimensional representation of
structures and surfaces is needed. Thus, the present invention is
not to be limited by the specific embodiments and procedures
described herein, but should be defined only in terms of the
following claims.
* * * * *