U.S. patent application number 11/265141 was filed with the patent office on 2006-03-16 for mapping electrophysiological data in a heart chamber.
This patent application is currently assigned to Endocardial Solutions, Inc.. Invention is credited to Graydon Ernest Beatty, Jeffrey Robert Budd, Jonathan Kagan.
Application Number | 20060058693 11/265141 |
Document ID | / |
Family ID | 27130293 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060058693 |
Kind Code |
A1 |
Beatty; Graydon Ernest ; et
al. |
March 16, 2006 |
Mapping electrophysiological data in a heart chamber
Abstract
A method of acquiring and mapping electrophysiological data in a
heart chamber includes inserting a catheter into the heart chamber.
Electrophysiological data in the heart chamber is acquired with the
catheter. The position of the catheter is determined by using an
electromagnetic field source external to the heart chamber, and the
location of the acquired electrophysiological data is determined
using the position of the catheter. Information related to the
three-dimensional geometry of at least a portion of the heart
chamber is received, and a continuous three-dimensional color-coded
map of the electrophysiological data is created and superimposed on
a geometrical representation of the three-dimensional geometry
information.
Inventors: |
Beatty; Graydon Ernest; (St.
Paul, MN) ; Kagan; Jonathan; (Minneapolis, MN)
; Budd; Jeffrey Robert; (St. Paul, MN) |
Correspondence
Address: |
STERNE, KESSLER, GOLDSTEIN & FOX PLLC
1100 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Endocardial Solutions, Inc.
St. Paul
MN
|
Family ID: |
27130293 |
Appl. No.: |
11/265141 |
Filed: |
November 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10375752 |
Feb 26, 2003 |
6978168 |
|
|
11265141 |
Nov 3, 2005 |
|
|
|
09588930 |
Jun 7, 2000 |
6603996 |
|
|
10375752 |
Feb 26, 2003 |
|
|
|
08387832 |
May 26, 1995 |
6240307 |
|
|
PCT/US93/09015 |
Sep 23, 1993 |
|
|
|
09588930 |
Jun 7, 2000 |
|
|
|
07950448 |
Sep 23, 1992 |
5297549 |
|
|
08387832 |
May 26, 1995 |
|
|
|
07949690 |
Sep 23, 1992 |
5311866 |
|
|
08387832 |
May 26, 1995 |
|
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Current U.S.
Class: |
600/508 |
Current CPC
Class: |
A61N 1/3702 20130101;
A61B 18/24 20130101; A61B 18/1492 20130101; A61B 2018/00267
20130101; A61B 2018/00214 20130101; A61B 5/287 20210101; A61B
2562/043 20130101; A61B 18/18 20130101; A61B 5/0538 20130101; A61B
5/6858 20130101; A61B 5/30 20210101; A61B 5/282 20210101; A61B
5/6853 20130101; A61B 2018/00839 20130101; A61B 5/1076 20130101;
A61B 18/1815 20130101; A61B 2560/045 20130101; A61B 5/283 20210101;
A61B 2562/046 20130101; A61N 1/3625 20130101; Y10T 29/49117
20150115 |
Class at
Publication: |
600/508 |
International
Class: |
A61B 5/02 20060101
A61B005/02 |
Claims
1. A method of acquiring and mapping electrophysiological data in a
heart chamber, comprising: a) inserting a catheter in the heart
chamber; b) acquiring electrophysiological data in the heart
chamber with the catheter; c) determining the position of the
catheter by using an electromagnetic field source external to the
heart chamber; d) determining the location of the acquired
electrophysiological data in step (b) using the position determined
in step (c); e) receiving information related to the
three-dimensional geometry of at least a portion of the heart
chamber from the position determined in step (c); and f) creating a
continuous three-dimensional, color-coded map of the
electrophysiological data superimposed on a geometrical
representation of the three-dimensional geometry information
received in step (e).
2. The method of claim 1, further comprising: calculating
potentials at locations on the heart chamber geometry utilizing the
acquired data and the determined position of the electrode; and
displaying data related to the calculated potentials as a portion
of the map.
3. The method of claim 1, wherein the heart chamber is a human
heart chamber.
4. The method of claim 1, wherein the map is an isopotential
map.
5. The method of claim 1, wherein the map is an isochronal map.
6. The method of claim 1, wherein the map is a local activation
time map.
7. The method of claim 1, wherein acquiring the
electrophysiological data in the heart chamber comprises acquiring
voltages, and the map displays data related to the acquired
voltages.
8. The method of claim 1, wherein the map displays electrical
propagation in the heart.
9. The method of claim 1, wherein the map is displayed in
real-time.
10. The method of claim 1 further comprising utilizing the map to
deliver ablation therapy.
11. The method of claim 1, further comprising displaying the
position of the catheter superimposed on the map.
12. The method of claim 1, further comprising: acquiring additional
data related to the electrophysiological data of at least a portion
of the heart chamber; updating the map to display the additional
data; and repeating the steps of acquiring additional data and
updating the map to display a visual representation of the changing
state of the heart chamber.
13. Apparatus for acquiring and mapping electrophysiological data
in a heart chamber, comprising: a catheter having an electrode
positionable in the heart chamber to acquire electrophysiological
data; an antenna coupled to the catheter to detect an
electromagnetic field produced by an electromagnetic field source
external to the chamber in order to determine the position of the
catheter; an analog-to-digital converter coupled to the catheter to
process the catheter position information and the
electrophysiological data; and a computer coupled to the
analog-to-digital converter to determine the location of the
acquired electrophysiological data using the processed catheter
position information, the computer being adapted to receive
information related to the three-dimensional geometry of at least a
portion of the heart chamber from the catheter position information
and to create a continuous three-dimensional, color-coded map of
the electrophysiological data superimposed on a geometrical
representation of the received three-dimensional geometry
information.
14. The apparatus of claim 13, wherein: the computer is further
adapted to calculate potentials at locations on the heart chamber
geometry utilizing the acquired electrophysiological data and the
catheter position information; and the apparatus further comprises
a display adapted to display data related to the calculated
potentials as a portion of the map.
15. The apparatus of claim 13, wherein the map is an isopotential
map.
16. The apparatus of claim 13, wherein the map is an isochronal
map.
17. The apparatus of claim 13, wherein the map is a local
activation time map.
18. The apparatus of claim 13, wherein the map displays data
related to voltages processed by the analog-to-digital
converter.
19. The apparatus of claim 13, wherein the map displays electrical
propagation in the heart.
20. The apparatus of claim 13, wherein the map is displayed in
real-time.
21. The apparatus of claim 13, further comprising a catheter
adapted to deliver ablation therapy.
22. The apparatus of claim 13, wherein the catheter is a
multi-electrode catheter.
23. The apparatus of claim 13, wherein the catheter is an array
catheter.
24. A system for acquiring and mapping electrophysiological data in
a heart chamber, comprising: a catheter having an electrode
positionable in the heart chamber to acquire electrophysiological
data; an antenna coupled to the catheter to detect an
electromagnetic field produced by an electromagnetic field source
external to the chamber in order to determine information related
to the position of the catheter; an analog-to-digital converter
coupled to the catheter to process the catheter position
information and the electrophysiological data; and a computer
usable medium having computer readable program code to cause an
application program to execute on a computer to acquire and map the
electrophysiological data, comprising: code to determine the
location of the acquired electrophysiological data using the
processed catheter position information, code to process
information related to the three-dimensional geometry of at least a
portion of the heart chamber from the catheter position
information, and code to create a continuous three-dimensional,
color-coded map of the electrophysiological data superimposed on a
geometrical representation of the processed three-dimensional
geometry information.
25. The system of claim 24, further comprising: code to calculate
potentials at locations on the heart chamber geometry utilizing the
electrophysiological data and the catheter position information;
and display adapted to display data related to the calculated
potentials as a portion of the map.
26. The system of claim 24, wherein the map is an isopotential
map.
27. The system of claim 24, wherein the map is an isochronal
map.
28. The system of claim 24, wherein the map is a local activation
time map.
29. The system of claim 24, wherein the map displays data related
to voltages processed by the analog-to-digital converter.
30. The system of claim 24, wherein the map displays electrical
propagation in the heart.
31. The system of claim 24, wherein the map is displayed in
real-time.
32. The system of claim 24, further comprising a catheter adapted
to deliver ablation therapy.
33. The system of claim 24, wherein the catheter is a
multi-electrode catheter.
34. The system of claim 24, wherein the catheter is an array
catheter.
35. For use with a system that acquires and maps
electrophysiological data in a heart chamber, wherein the system
includes a catheter having an electrode positionable in the heart
chamber to acquire electrophysiological data, an antenna coupled to
the catheter to detect an electromagnetic field produced by an
electromagnetic field source external to the chamber in order to
determine information related to the position of the catheter, and
an analog-to-digital converter coupled to the catheter to process
the catheter position information and the electrophysiological
data, a computer usable medium having computer readable program
code to cause an application program to execute on a computer to
acquire and map the electrophysiological data, comprising: code to
determine the location of the acquired electrophysiological data
using the processed catheter position information; code to process
information related to the three-dimensional geometry of at least a
portion of the heart chamber from the catheter position
information; and code to create a continuous three-dimensional,
color-coded map of the electrophysiological data superimposed on a
geometrical representation of the processed three-dimensional
geometry information.
36. The computer usable medium of claim 35, further comprising code
to calculate potentials at locations on the heart chamber geometry
utilizing the electrophysiological data and the catheter position
information; wherein the system further comprises a display adapted
to display data related to the calculated potentials as a portion
of the map.
37. The computer usable medium of claim 35, wherein the map is an
isopotential map.
38. The computer usable medium of claim 35, wherein the map is an
isochronal map.
39. The computer usable medium of claim 35, wherein the map is a
local activation time map.
40. The computer usable medium of claim 35, wherein the map
displays data related to voltages processed by the
analog-to-digital converter.
41. The computer usable medium of claim 35, wherein the map
displays electrical propagation in the heart.
42. The computer usable medium of claim 35, wherein the map is
displayed in real-time.
43. The computer usable medium of claim 35, wherein the system
further comprises a catheter adapted to deliver ablation
therapy.
44. The computer usable medium of claim 35, wherein the catheter is
a multi-electrode catheter.
45. The computer usable medium of claim 35, wherein the catheter is
an array catheter.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/375,752, filed Feb. 26, 2003, which is a divisional of
U.S. patent application Ser. No. 09/588,930, filed Jun. 7, 2000,
now U.S. Pat. No. 6,603,996, which is a divisional of U.S. patent
application Ser. No. 08/387,832, filed May 26, 1995, now U.S. Pat.
No. 6,240,307, which is a national stage application of
PCT/US93/09015, filed Sep. 23, 1993, which in turn claims priority
to U.S. patent application Ser. No. 07/950,448, filed Sep. 23,
1992, now U.S. Pat. No. 5,297,549 and U.S. patent application Ser.
No. 07/949,690, filed Sep. 23, 1992, now U.S. Pat. No. 5,311,866,
each of which is incorporated by reference herein in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The invention discloses the apparatus and technique for
forming a three-dimensional electrical map of the interior of a
heart chamber, and a related technique for forming a
two-dimensional subsurface map at a particular location in the
endocardial wall.
[0004] 2. Background Art
[0005] It is common to measure the electrical potentials present on
the interior surface of the heart as a part of an
electrophysiologic study of a patient's heart. Typically such
measurements are used to form a two-dimensional map of the
electrical activity of the heart muscle. An electrophysiologist
will use the map to locate centers of ectopic electrical activity
occurring within the cardiac tissues. One traditional mapping
technique involves a sequence of electrical measurements taken from
mobile electrodes inserted into the heart chamber and placed in
contact with the surface of the heart. An alternative mapping
technique takes essentially simultaneous measurements from a
floating electrode array to generate a two-dimensional map of
electrical potentials.
[0006] The two-dimensional maps of the electrical potentials at the
endocardial surface generated by these traditional processes suffer
many defects. Traditional systems have been limited in resolution
by the number of electrodes used. The number of electrodes dictated
the number of points for which the electrical activity of the
endocardial surface could be mapped. Therefore, progress in
endocardial mapping has involved either the introduction of
progressively more electrodes on the mapping catheter or improved
flexibility for moving a small mapping probe with electrodes from
place to place on the endocardial surface. Direct contact with
electrically active tissue is required by most systems in the prior
art in order to obtain well conditioned electrical signals. An
exception is a non-contact approach with spot electrodes. These
spot electrodes spatially average the electrical signal through
their conical view of the blood media. This approach therefore also
produces one signal for each electrode. The small number of signals
from the endocardial wall will result in the inability to
accurately resolve the location of ectopic tissue masses. In the
prior art, iso-potentials are interpolated and plotted on a
rectilinear map which can only crudely represent the unfolded
interior surface of the heart. Such two-dimensional maps are
generated by interpolation processes which "fill in" contours based
upon a limited set of measurements. Such interpolated
two-dimensional maps have significant deficiencies. First, if a
localized ectopic focus is between two electrode views such a map
will at best show the ectopic focus overlaying both electrodes and
all points in between and at worst will not see it at all. Second,
the two dimensional map, since it contains no chamber geometry
information, cannot indicate precisely where in the three
dimensional volume of the heart chamber an electrical signal is
located. The inability to accurately characterize the size and
location of ectopic tissue frustrates the delivery of certain
therapies such as "ablation".
BRIEF SUMMARY OF THE INVENTION
[0007] In general the present invention provides a method for
producing a high-resolution, three-dimensional map of electrical
activity of the inside surface of a heart chamber.
[0008] The invention uses a specialized catheter system to obtain
the information necessary to generate such a map.
[0009] In general the invention provides a system and method which
permits the location of catheter electrodes to be visualized in the
three-dimensional map.
[0010] The invention may also be used to provide a two-dimensional
map of electrical potential at or below the myocardial tissue
surface.
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
[0011] Additional features of the invention will appear from the
following description in which the illustrative embodiment is set
forth in detail in conjunction with the accompanying drawings. It
should be understood that many modifications to the invention, and
in particular to the preferred embodiment illustrated in these
drawings, may be made without departing from the scope of the
invention.
[0012] FIG. 1 is a schematic view of the system.
[0013] FIG. 2 is a view of the catheter assembly placed in an
endocardial cavity.
[0014] FIG. 3 is a schematic view of the catheter assembly.
[0015] FIG. 4 is a view of the mapping catheter with the deformable
lead body in the collapsed position.
[0016] FIG. 5 is a view of the mapping catheter with the deformable
lead body in the expanded position.
[0017] FIG. 6 is a view of the reference catheter.
[0018] FIG. 7 is a schematic view representing the display of the
three-dimensional map.
[0019] FIG. 8 is a side view of an alternate reference
catheter.
[0020] FIG. 9 is a side view of an alternate reference
catheter.
[0021] FIG. 10 is a perspective view of an alternate distal
tip.
[0022] FIG. 11 is a schematic view representing the display of the
subsurface two-dimensional map.
[0023] FIG. 12 is a schematic flow chart of the steps in the
method.
DETAILED DESCRIPTION OF THE INVENTION
[0024] In general, the system of the present invention is used for
mapping the electrical activity of the interior surface of a heart
chamber 80. The mapping catheter assembly 14 includes a flexible
lead body 72 connected to a deformable distal lead body 74. The
deformable distal lead body 74 can be formed into a stable space
filling geometric shape after introduction into the heart cavity
80. This deformable distal lead body 74 includes an electrode array
19 defining a number of electrode sites. The mapping catheter
assembly 14 also includes a reference electrode preferably placed
on a reference catheter 16 which passes through a central lumen 82
formed in the flexible lead body 72 and the distal lead body 74.
The reference catheter assembly 16 has a distal tip electrode
assembly 24 which may be used to probe the heart wall. This distal
contact electrode assembly 24 provides a surface electrical
reference for calibration. The physical length of the reference
catheter 16 taken with the position of the electrode array 19
together provide a reference which may be used to calibrate the
electrode array 19. The reference catheter 16 also stabilizes the
position of the electrode array 19 which is desirable.
[0025] These structural elements provide a mapping catheter
assembly which can be readily positioned within the heart and used
to acquire highly accurate information concerning the electrical
activity of the heart from a first set of preferably non-contact
electrode sites and a second set of in-contact electrode sites.
[0026] The mapping catheter assembly 14 is coupled to interface
apparatus 22 which contains a signal generator 32, and voltage
acquisition apparatus 30. Preferably, in use, the signal generator
32 is used to measure the volumetric shape of the heart chamber
through impedance plethysmography. This signal generator is also
used to determine the position of the reference electrode within
the heart chamber. Other techniques for characterizing the shape of
the heart chamber may be substituted.
[0027] Next, the signals from all the electrode sites on the
electrode array 19 are presented to the voltage acquisition
apparatus 30 to derive a three-dimensional, instantaneous high
resolution map of the electrical activity of the entire heart
chamber volume. This map is calibrated by the use of a surface
electrode 24. The calibration is both electrical and dimensional.
Lastly this three-dimensional map, along with the signal from an
intramural electrode 26 preferably at the tip of the reference
catheter 16, is used to compute a two-dimensional map of the
intramural electrical activity within the heart wall. The
two-dimensional map is a slice of the heart wall and represents the
subsurface electrical activity in the heart wall itself.
[0028] Both of these "maps" can be followed over time which is
desirable. The true three-dimensional map also avoids the problem
of spatial averaging and generates an instantaneous, high
resolution map of the electrical activity of the entire volume of
the heart chamber and the endocardial surface. This
three-dimensional map is an order of magnitude more accurate and
precise than previously obtained interpolation maps. The
two-dimensional map of the intramural slice is unavailable using
prior techniques.
Hardware Description
[0029] FIG. 1 shows the mapping system 10 coupled to a patient's
heart 12. The mapping catheter assembly 14 is inserted into a heart
chamber and the reference electrode 24 touches the endocardial
surface 18.
[0030] The preferred array catheter 20 carries at least twenty-four
individual electrode sites which are coupled to the interface
apparatus 22. The preferred reference catheter 16 is a coaxial
extension of the array catheter 20.
[0031] This reference catheter 16 includes a surface electrode site
24 and a subsurface electrode site 26 both of which are coupled to
the interface apparatus 22.
[0032] It should be understood that the electrode site 24 can be
located directly on the array catheter. The array catheter 20 may
be expanded into a known geometric shape, preferably spherical.
Resolution is enhanced by the use of larger sized spherical shapes.
A balloon 77 or the like should be incorporated under the electrode
array 19 to exclude blood from the interior of the electrode array
19. The spherical shape and exclusion of blood are not required for
operability but they materially reduce the complexity of the
calculations required to generate the map displays.
[0033] The reference electrode 24 and/or the reference catheter 16
serves several purposes. First they stabilize and maintain the
array 19 at a known distance from a reference point on the
endocardial surface 18 for calibration of the shape and volume
calculations. Secondly, the surface electrode 24 is used to
calibrate the electrical activity measurements of the endocardial
surface 18 provided by the electrode array 19.
[0034] The interface apparatus 22 includes a switching assembly 28
which is a multiplexor to sequentially couple the various electrode
sites to the voltage acquisition apparatus 30, and the signal
generator apparatus 32. These devices are under the control of a
computer 34. The voltage acquisition apparatus 30 is preferably a
12 bit A to D convertor. A signal generator 32 is also supplied to
generate low current pulses for determining the volume and shape of
the endocardial chamber using impedance plethysmography, and for
determining the location of the reference catheter.
[0035] The computer 34 is preferably of the "workstation" class to
provide sufficient processing power to operate in essentially real
time. This computer operates under the control of software set
forth in the flow charts of FIGS. 12A and 12B.
Catheter Description
[0036] FIG. 2 shows a portion of the mapping catheter assembly 14
placed into a heart chamber 80. The mapping catheter assembly 14
includes a reference catheter 16 and an array catheter 20. In FIG.
2 the array catheter 20 has been expanded through the use of a
stylet 92 to place the electrode array 19 into a stable and
reproducible geometric shape. The reference catheter 16 has been
passed through the lumen 82 of the array catheter 20 to place a
distal tip electrode assembly 24 into position against an
endocardial surface. In use, the reference catheter 16 provides a
mechanical location reference for the position of the electrode
array 19, and the tip electrode assembly 24 provides an electrical
potential reference at or in the heart wall for the mapping
process.
[0037] Although the structures of FIG. 1 are preferred there are
several alternatives within the scope of the invention. The
principle objective of the preferred form of the catheter system is
to reliably place a known collection of electrode sites away from
the endocardial surface, and one or more electrode sites into
contact with the endocardium. The array catheter is an illustrative
structure for placing at least some of the electrode sites away
from the endocardial surface. The array catheter itself can be
designed to mechanically position one or more electrode sites on
the endocardial surface. The reference catheter is a preferred
structure for carrying one or more electrode sites and may be used
to place these electrode sites into direct contact with the
endocardial surface.
[0038] It should be understood that the reference catheter could be
replaced with a fixed extension of the array catheter and used to
push a segment of the array onto the endocardial surface. In this
alternate embodiment the geometric shape of the spherical array
maintains the other electrodes out of contact with the endocardial
surface.
[0039] FIG. 3 shows the preferred construction of the mapping
catheter assembly 14 in exaggerated scale to clarify details of
construction. In general, the array catheter 20 includes a flexible
lead body 72 coupled to a deformable lead body 74. The deformable
lead body 74 is preferably a braid 75 of insulated wires, several
of which are shown as wire 93, wire 94, wire 95 and wire 96. An
individual wire such as 93 may be traced in the figure from the
electrical connection 79 at the proximal end 81 of the flexible
lead body 72 through the flexible lead body 72 to the distal braid
ring 83 located on the deformable lead body 74. At a predetermined
location in the deformable lead body 74 the insulation has been
selectively removed from this wire 93 to form a representative
electrode site 84. Each of the several wires in the braid 75 may
potentially be used to form an electrode site. Preferably all of
the typically twenty-four to one-hundred-twenty-eight wires in the
braid 75 are used to form electrode sites. Wires not used as
electrode sites provide mechanical support for the electrode array
19. In general, the electrode sites will be located equidistant
from a center defined at the center of the spherical array. Other
geometrical shapes are usable including ellipsoidal and the
like.
[0040] The proximal end 81 of the mapping catheter assembly 14 has
suitable electrical connection 79 for the individual wires
connected to the various electrode sites. Similarly the proximal
connector 79 can have a suitable electrical connection for the
distal tip electrode assembly 24 of the reference catheter 16 or
the reference catheter 16 can use a separate connector. The
distance 90 between the electrode array 19 and the distal tip
assembly 24 electrode can preferentially be varied by sliding the
reference catheter through the lumen 82, as shown by motion arrow
85. This distance 90 may be "read" at the proximal end 81 by noting
the relative position of the end of the lead body 72 and the
proximal end of the reference catheter 16.
[0041] FIG. 4 is a view of the mapping catheter with the deformable
lead body 74 in the collapsed position.
[0042] FIG. 5 shows that the wire stylet 92 is attached to the
distal braid ring 83 and positioned in the lumen 82. Traction
applied to the distal braid ring 83 by relative motion of the
stylet 92 with respect to the lead body 72 causes the braid 75 to
change shape. In general, traction causes the braid 75 to move from
a generally cylindrical form seen in FIG. 4 to a generally
spherical form seen best in FIG. 2 and FIG. 5.
[0043] The preferred technique is to provide a stylet 92 which can
be used to pull the braid 75 which will deploy the electrode array
19. However, other techniques may be used as well including an
optional balloon 77 shown as in FIG. 3; which could be inflated
under the electrode array 19 thereby causing the spherical
deployment of the array 19. Modification of the braid 75 can be
used to control the final shape of the array 19. For example an
asymmetrical braid pattern using differing diameter wires within
the braid can preferentially alter the shape of the array. The most
important property of the geometric shape is that it spaces the
electrode sites relatively far apart and that the shape be
predictable with a high degree of accuracy.
[0044] FIG. 6 shows a first embodiment of the reference catheter 16
where the distal electrode assembly 24 is blunt and may be used to
make a surface measurement against the endocardial surface. In this
version of the catheter assembly the wire 97 (FIG. 2) communicates
to the distal tip electrode and this wire may be terminated in the
connector 79.
[0045] FIG. 8 shows an alternate reference catheter 98 which is
preferred if both surface and/or subsurface measurements of the
potential proximate the endocardial surface are desired. This
catheter 98 includes both a reference electrode 24 and an
extendable intramural electrode body 100.
[0046] FIG. 9 illustrates the preferred use of an intramural
electrode stylet 101 to retract the sharp intramural electrode body
100 into the reference catheter lead body 102. Motion of the
intramural electrode body 100 into the lead body 102 is shown by
arrow 103.
[0047] FIG. 10 shows the location of the intramural electrode site
26 on the electrode body 100. It is desirable to use a relatively
small electrode site to permit localization of the intramural
electrical activity.
[0048] The array catheter 20 may be made by any of a variety of
techniques. In one method of manufacture, the braid 75 of insulated
wires 93, 94, 95, 96 can be encapsulated into a plastic material to
form the flexible lead body 72. This plastic material can be any of
various biocompatible compounds with polyurethane being preferred.
The encapsulation material for the flexible lead body 72 is
selected in part for its ability to be selectively removed to
expose the insulated braid 75 to form the deformable lead body 74.
The use of a braid 75 rather than a spiral wrap, axial wrap, or
other configuration inherently strengthens and supports the
electrodes due to the interlocking nature of the braid. This
interlocking braid 75 also insures that, as the electrode array 19
deploys, it does so with predictable dimensional control. This
braid 75 structure also supports the array catheter 20 and provides
for the structural integrity of the array catheter 20 where the
encapsulating material has been removed.
[0049] To form the deformable lead body 74 at the distal end of the
array catheter 20, the encapsulating material can be removed by
known techniques. In a preferred embodiment this removal is
accomplished by mechanical removal of the encapsulating material by
grinding or the like. It is also possible to remove the material
with a solvent. If the encapsulating material is polyurethane,
tetrahydrofuran or cyclohexanone can be used as a solvent. In some
embodiments the encapsulating material is not removed from the
extreme distal tip to provide enhanced mechanical integrity forming
a distal braid ring 83.
[0050] With the insulated braid 75 exposed, to form the deformable
lead body 74 the electrodes sites can be formed by removing the
insulation over the conductor in selected areas. Known techniques
would involve mechanical, thermal or chemical removal of the
insulation followed by identification of the appropriate conducting
wire at the proximal connector 79. This method makes it difficult
to have the orientation of the proximal conductors in a predictable
repeatable manner. Color coding of the insulation to enable
selection of the conductor/electrode is possible but is also
difficult when large numbers of electrodes are required. Therefore
it is preferred to select and form the electrode array through the
use of high voltage electricity. By applying high voltage
electricity (typically 1-3 KV) to the proximal end of the conductor
and detecting this energy through the insulation it is possible to
facilitate the creation of the electrode on a known conductor at a
desired location. After localization, the electrode site can be
created by removing insulation using standard means or by applying
a higher voltage (e.g. 5 KV) to break through the insulation.
[0051] Modifications can be made to this mapping catheter assembly
without departing from the teachings of the present invention.
Accordingly the scope of the invention is only to be limited only
by the accompanying claims.
Software Description
[0052] The illustrative method may be partitioned into nine steps
as shown in FIG. 12. The partitioning of the step-wise sequence is
done as an aid to explaining the invention and other equivalent
partitioning can be readily substituted without departing from the
scope of the invention.
[0053] At step 41 the process begins. The illustrative process
assumes that the electrode array assumes a known spherical shape
within the heart chamber, and that there are at least twenty-four
electrodes on the electrode array 19. This preferred method can be
readily modified to accommodate unknown and non-reproducible,
non-spherical shaped arrays. The location of each of these
electrode sites on the array surface is known from the mechanical
configuration of the displayed array. A method of determining the
location of the electrode array 19 and the location of the heart
chamber walls (cardiac geometry) must be available. This geometry
measurement (options include ultrasound or impedance
plethysmography) is performed in step 41. If the reference catheter
16 is extended to the chamber wall 18 then its length can be used
to calibrate the geometry measurements since the calculated
distance can be compared to the reference catheter length. The
geometry calculations are forced to converge on the known spacing
represented by the physical dimensions of the catheters. In an
alternative embodiment reference electrode 24 is positioned on
array catheter 20 and therefore its position would be known.
[0054] In step 42 the signals from all the electrode sites in the
electrode array 19 are sampled by the A to D converter in the
voltage acquisition apparatus 30. These measurements are stored in
a digital file for later use in following steps. At this point
(step 43) the known locations of all the electrodes on the
electrode array 19 and the measured potentials at each electrode
are used to create the intermediate parameters of the
three-dimensional electrical activity map. This step uses field
theory calculations presented in greater detail below. The
components which are created in this step (.PHI..sub.lm) are stored
in a digital file for later use in following steps.
[0055] At the next stage the question is asked whether the
reference catheter 16 is in a calibrating position. In the
calibrating position, the reference catheter 16 projects directly
out of the array catheter 20 establishing a length from the
electrode array 19 which is a known distance from the wall 18 of
the heart chamber. This calibration position may be confirmed using
fluoroscopy. If the catheter is not in position then the process
moves to step 45, 46 or 47.
[0056] If the reference catheter 16 is in the calibrating position
then in step 44 the exact position of the reference catheter 16 is
determined using the distance and orientation data from step 41.
The available information includes position in space of the
reference catheter 16 on the chamber wall 18 and the intermediate
electrical activity map parameters of the three-dimensional map.
Using these two sets of information the expected electrical
activity at the reference catheter surface electrode site 24 is
determined. The actual potential at this site 24 is measured from
the reference catheter by the A to D converter in the voltage
acquisition apparatus 30. Finally, a scale factor is adjusted which
modifies the map calculations to achieve calibrated results. This
adjustment factor is used in all subsequent calculations of
electrical activity.
[0057] At step 47 the system polls the user to display a
three-dimensional map. If such a map is desired then a method of
displaying the electrical activity is first determined. Second an
area, or volume is defined for which the electrical activity is to
be viewed. Third a level of resolution is defined for this view of
the electrical activity. Finally the electrical activity at all of
the points defined by the display option, volume and resolution are
computed using the field theory calculations and the adjustment
factor mentioned above. These calculated values are then used to
display the data on computer 34.
[0058] FIG. 7 is a representative display 71 of the output of
process 47. In the preferred presentation the heart is displayed as
a wire grid 36. The iso-potential map for example is overlaid on
the wire grid 36 and several iso-potential lines such as
iso-potential or isochrone line 38 are shown on the drawing.
Typically the color of the wire grid 36 and the iso-potential or
isochrone lines will be different to aid interpretation. The
potentials may preferably be presented by a continuously filled
color-scale rather than iso-potential or isochrone lines. The
tightly closed iso-potential or isochrone line 39 may arise from an
ectopic focus present this location in the heart. In the
representative display 71 of process 47 the mapping catheter
assembly will not be shown.
[0059] In step 45 a subthreshold pulse is supplied to the surface
electrode 24 of the reference catheter 16 by the signal generator
32. In step 54 the voltages are measured at all of the electrode
sites on the electrode array 19 by the voltage acquisition
apparatus 30. One problem in locating the position of the
subthreshold pulse is that other electrical activity may render it
difficult to detect. To counteract this problem step 55 starts by
subtracting the electrical activity which was just measured in step
44 from the measurements in step 54. The location of the tip of the
reference catheter 16 (i.e. surface electrode 24), is found by
first performing the same field theory calculations of step 45 on
this derived electrode data. Next, four positions in space are
defined which are positioned near the heart chamber walls. The
potentials at these sites are calculated using the
three-dimensional electrical activity map. These potentials are
then used to triangulate, and thus determine, the position of the
subthreshold pulse at the surface electrode 24 of the reference
catheter 16. If more accurate localization is desired then four
more points which are much closer to the surface electrode 24 can
be defined and the triangulation can be performed again. This
procedure for locating the tip of the reference catheter 16 can be
performed whether the surface electrode 24 is touching the surface
or is located in the blood volume and is not in contact with the
endocardial surface.
[0060] At step 48 the reference catheter's position in space can be
displayed by superimposing it on the map of electrical activity
created in step 47. An example of such a display 71 is presented in
FIG. 7.
[0061] When step 46 is reached the surface electrode 24 is in a
known position on the endocardial surface 18 of the heart chamber
which is proper for determining the electrical activity of the
tissue at that site. If the intramural or subsurface extension 100
which preferentially extends from the tip of the reference catheter
102 is not inserted into the tissue then the user of the system
extends the subsurface electrode 26 into the wall 18. The
potentials from the surface electrode 24 and from the intramural
subsurface 26 electrode are measured by voltage acquisition
apparatus 30. Next a line 21 along the heart chamber wall which has
the surface electrode 24 at its center is defined by the user of
the system. The three-dimensional map parameters from step 43 are
then used to compute a number of points along this line including
the site of the reference catheter surface electrode 24. These
calculations are adjusted to conform to the measured value at the
reference catheter surface electrode 24. Next a slice of tissue is
defined and bounded by this line 21 (FIG. 7) and the location of
the intramural subsurface electrode 26 (FIG. 11) and computed
positions such as 23 and 25. Subsequently a two-dimensional map 27
of the electrical activity of this slice of tissue is computed
using the center of gravity calculations detailed below in the
section on algorithm descriptions. Points outside of the boundary
of the slice cannot be computed accurately. In step 49 this map 27
of electrical activity within the two-dimensional slice is
displayed as illustrated in FIG. 11. In this instance the
iso-potential line 17 indicates the location within the wall 18 of
the ectopic focus.
Description of the Preferred Computing Algorithms
[0062] Two different algorithms are suitable for implementing
different stages of the present invention.
[0063] The algorithm used to derive the map of the electrical
activity of the heart chamber employs electrostatic
volume-conductor field theory to derive a high resolution map of
the chamber volume. The second algorithm is able to estimate
intramural electrical activity by interpolating between points on
the endocardial surface and an intramural measurement using center
of gravity calculations.
[0064] In use, the preliminary process steps identify the position
of the electrode array 19 consequently the field theory algorithm
can be initialized with both contact and non-contact type data.
This is one difference from the traditional prior art techniques
which require either contact or non-contact for accurate results,
but cannot accommodate both. This also permits the system to
discern the difference between small regions of electrical activity
close to the electrode array 19 from large regions of electrical
activity further away from the electrode array 19.
[0065] In the first algorithm, from electrostatic volume-conductor
field theory it follows that all the electrodes within the solid
angle view of every locus of electrical activity on the endocardial
surface are integrated together to reconstruct the electrical
activity at any given locus throughout the entire volume and upon
the endocardium. Thus as best shown in FIG. 7 the signals from the
electrode array 19 on the catheter 20 produce a continuous map of
the whole endocardium. This is another difference between the
present method and the traditional prior art approach which use the
electrode with the lowest potential as the indicator of cardiac
abnormality. By using the complete information in the algorithm,
the resolution of the map shown in FIG. 7 is improved by at least a
factor of ten over prior methods. Other improvements include: the
ability to find the optimal global minimum instead of sub-optimal
local minima; the elimination of blind spots between electrodes;
the ability to detect abnormalities caused by multiple ectopic
foci; the ability to distinguish between a localized focus of
electrical activity at the endocardial surface and a distributed
path of electrical activity in the more distant myocardium; and the
ability to detect other types of electrical abnormalities including
detection of ischemic or infarcted tissue.
[0066] The algorithm for creating the 3D map of the cardiac volume
takes advantage of the fact that myocardial electrical activity
instantaneously creates potential fields by electrotonic
conduction. Since action potentials propagate several orders of
magnitude slower than the speed of electrotonic conduction, the
potential field is quasi-static. Since there are no significant
charge sources in the blood volume, Laplace's Equation for
potential completely describes the potential field in the blood
volume: v.sup.2.phi.=0
[0067] LaPlace's equation can be solved numerically or
analytically. Such numerical techniques include boundary element
analysis and other interactive approaches comprised of estimating
sums of nonlinear coefficients.
[0068] Specific analytical approaches can be developed based on the
shape of the probe (i.e. spherical, prolate spherical or
cylindrical). From electrostatic field theory, the general
spherical harmonic series solution for potential is: .PHI.
.function. ( x , .theta. , .phi. ) = .infin. l = 0 .times. m = - l
l .times. .times. { A l .times. r l + B l .times. r - ( l - 1 }
.times. .PHI. lm .times. Y lm .function. ( .theta. , .phi. )
##EQU1##
[0069] In spherical harmonics, Y.sub.lm (.theta., .phi.) is the
spherical harmonic series made up of Legendre Polynomials.
.PHI..sub.lm is the lm.sup.th component of potential and is defined
as:
.phi..sub.lm=.intg.V(.theta.,.phi.)Y.sub.lm(.theta.,.phi.)d.OMEGA.
where V(.theta., .phi.) is the measured potential over the probe
radius R and d.OMEGA. is the differential solid angle and, in
spherical coordinates, is defined as:
d.OMEGA.=sin.theta.d.theta.d.phi.
[0070] During the first step in the algorithmic determination of
the 3D map of the electrical activity each .PHI..sub.lm component
is determined by integrating the potential at a given point with
the spherical harmonic at that point with respect to the solid
angle element subtended from the origin to that point. This is an
important aspect of the 3D map; its accuracy in creating the 3D map
is increased with increased numbers of electrodes in the array and
with increased size of the spherical array. In practice it is
necessary to compute the .PHI..sub.lm components with the subscript
1 set to 4 or greater. These .PHI..sub.lm components are stored in
an 1 by m array for later determination of potentials anywhere in
the volume within the endocardial walls.
[0071] The bracketed expression of equation 1 (in terms of A.sub.1,
B.sub.1, and r) simply contains the extrapolation coefficients that
weight the measured probe components to obtain the potential
components anywhere in the cavity. Once again, the weighted
components are summed to obtain the actual potentials. Given that
the potential is known on the probe boundary, and given that the
probe boundary is non-conductive, we can determine the coefficients
A.sub.1 and B.sub.1, yielding the following final solution for
potential at any point within the boundaries of the cavity, using a
spherical probe of radius R: .PHI. .function. ( r , .theta. , .phi.
) = l = 0 .infin. .times. .times. m = - l l .times. .times. [ ( l +
1 2 .times. l + 1 ) .times. ( r R ) l + ( l 2 .times. l + 1 )
.times. ( r R ) - l - 1 ] .times. .PHI. lm .times. Y lm .function.
( .theta. , .phi. ) ##EQU2##
[0072] One exemplary method for evaluating the integral for
.PHI..sub.lm is the technique of Filon integration with an
estimating sum, discretized by p latitudinal rows and q
longitudinal columns of electrodes on the spherical probe. .PHI. lm
.gtoreq. 4 .times. .pi. pq .times. i = 1 p .times. .times. j = 1 q
.times. .times. V .function. ( .theta. i , .phi. j ) .times. Y lm
.function. ( .theta. i , .phi. j ) ##EQU3## Note that p times q
equals the total number of electrodes on the spherical probe array.
The angle .theta. ranges from zero to .pi. radians and .phi. ranges
from zero to 2.pi. radians.
[0073] At this point the determination of the geometry of the
endocardial walls enters into the algorithm. The potential of each
point on the endocardial wall can now be computed by defining them
as r, .theta., and .phi.. During the activation sequence the
graphical representation of the electrical activity on the
endocardial surface can be slowed down by 30 to 40 times to present
a picture of the ventricular cavity within a time frame useful for
human viewing.
[0074] A geometric description of the heart structure is required
in order for the algorithm to account for the inherent effect of
spatial averaging within the medium (blood). Spatial averaging is a
function of both the conductive nature of the medium as well as the
physical dimensions of the medium.
[0075] Given the above computed three-dimensional endocardial
potential map, the intramural activation map of FIG. 11 is
estimated by interpolating between the accurately computed
endocardial potentials at locations 23 and 25 (FIG. 7), and actual
recorded endocardial value at the surface electrode 24 and an
actual recorded intramural value at the subsurface electrode 26
site. This first-order estimation of the myocardial activation map
assumes that the medium is homogeneous and that the medium contains
no charge sources. This myocardial activation estimation is limited
by the fact that the myocardial medium is not homogeneous and that
there are charge sources contained within the myocardial medium. If
more than one intramural point was sampled the underlying map of
intramural electrical activity could be improved by interpolating
between the endocardial surface values and all the sample
intramural values. The center-of-gravity calculations can be
summarized by the equation: V .function. ( I x _ ) = i = 1 n
.times. .times. V i .function. ( I nx _ - I i _ - k ) i = 1 n
.times. .times. I x _ - I i _ ##EQU4## where, V(.sub.x) represents
the potential at any desired point defined by the three-dimensional
vector .sub.x and, V.sub.i represents each of n known potentials at
a point defined by the three-dimensional vector .sub.i and, k is an
exponent that matches the physical behavior of the tissue
medium.
[0076] From the foregoing description, it will be apparent that the
method for determining a continuous map of the electrical activity
of the endocardial surface of the present invention has a number of
advantages, some of which have been described above and others of
which are inherent in the invention. Also modifications can be made
to the mapping probe without departing from the teachings of the
present invention. Accordingly the scope of the invention is only
to be limited as necessitated by the accompanying claims.
* * * * *