U.S. patent application number 09/783778 was filed with the patent office on 2001-08-30 for systems and methods for examining the electrical characteristic of cardiac tissue.
This patent application is currently assigned to EP Technologies. Invention is credited to Foster, Kenneth R., Mirotznik, Mark S., Panescu, Dorin, Schwartzman, David S., Swanson, David K..
Application Number | 20010018608 09/783778 |
Document ID | / |
Family ID | 22692363 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018608 |
Kind Code |
A1 |
Panescu, Dorin ; et
al. |
August 30, 2001 |
Systems and methods for examining the electrical characteristic of
cardiac tissue
Abstract
Systems and methods examine heart tissue morphology using three
or more spaced apart electrodes, at least two of which are located
within the heart in contact with endocardial tissue. The systems
and methods transmit electrical current through a region of heart
tissue lying between selected pairs of the electrodes, at least one
of the electrodes in each pair being located within the heart. The
systems and methods derive the electrical characteristic of tissue
lying between the electrode pairs based, at least in part, upon
sensing tissue impedances. The systems and methods make possible
the use of multiple endocardial electrodes for taking multiple
measurements of the electrical characteristics of heart tissue.
Multiplexing can be used to facilitate data processing. The systems
and methods also make possible the identification of regions of low
relative electrical characteristics, indicative of infarcted
tissue, without invasive surgical techniques.
Inventors: |
Panescu, Dorin; (Sunnyvale,
CA) ; Swanson, David K.; (Mountain View, CA) ;
Mirotznik, Mark S.; (Silver Spring, MD) ;
Schwartzman, David S.; (Philadelphia, PA) ; Foster,
Kenneth R.; (Haverford, PA) |
Correspondence
Address: |
LYON & LYON LLP
SUITE 4700
633 WEST FIFTH STREET
LOS ANGELES
CA
90071-2066
US
|
Assignee: |
EP Technologies
|
Family ID: |
22692363 |
Appl. No.: |
09/783778 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09783778 |
Feb 14, 2001 |
|
|
|
08888456 |
Jul 7, 1997 |
|
|
|
08888456 |
Jul 7, 1997 |
|
|
|
08558044 |
Nov 13, 1995 |
|
|
|
08558044 |
Nov 13, 1995 |
|
|
|
08188247 |
Jan 28, 1994 |
|
|
|
Current U.S.
Class: |
607/122 ;
600/547 |
Current CPC
Class: |
A61B 5/287 20210101;
A61B 2562/043 20130101; A61B 5/6855 20130101; A61B 5/053 20130101;
A61B 5/05 20130101; A61B 5/6858 20130101; A61B 18/00 20130101; A61B
5/0538 20130101; A61N 1/056 20130101 |
Class at
Publication: |
607/122 ;
600/547 |
International
Class: |
A61N 001/00 |
Claims
We claim:
1. A system for examining tissue within the heart comprising at
least three spaced apart electrodes, means for locating at least
two of the electrodes within the heart for contact with endocardial
tissue, generator means operable in one mode for transmitting
electrical current in a first path through a region of heart tissue
between a first pair of the electrodes, at least one of which is
within the heart, the generator means being operable in another
mode for transmitting electrical current in a second path through
heart tissue in the region between a second pair of the electrodes,
at least one of which is within the heart, without substantially
altering position of first pair of electrodes, and processing means
for deriving a tissue electrical characteristic based, at least in
part, upon sensing the impedances of the tissue lying in the first
and second paths.
2. A system according to claim 1 wherein the processing means
compares the derived electrical characteristic of the tissue lying
in first path with the derived electrical characteristic of the
tissue lying second path.
3. A system according to claim 2 wherein the processing means
generates an output based upon the comparison of derived electrical
characteristics.
4. A system according to claim 1 wherein the processing means
derives the electrical characteristic by measuring the voltages in
the first and second paths and dividing the measured voltages by
the measured currents transmitted through the paths to derive the
tissue impedances.
5. A system according to claim 4 wherein the processing means
compares the derived impedance of the tissue lying in the first
path with the derived impedance of the tissue lying in the second
path.
6. A system according to claim 5 wherein the processing means
generates an output based upon the comparison of the derived tissue
impedances.
7. A system according to claim 1 wherein the processing means
derives the resistivities of the tissue lying in the first and
second paths.
8. A system according to claim 7 wherein the processing means
compares the derived resistivity of the tissue lying in first path
with the derived resistivity of the tissue lying second path.
9. A system according to claim 8 wherein the processing means
generates an output based upon the comparison of the derived tissue
resistivities.
10. A system according to claim 1 wherein the locating means
establishes substantially simultaneous, constant contact between at
least two of the electrodes and endocardial tissue.
11. A system according to claim 1 and wherein the locating means
establishes substantially simultaneous, constant contact between at
least two of the electrodes and endocardial tissue, and wherein at
least one of the remaining electrodes comprises an electrode
located outside the heart.
12. A system according to claim 1 wherein the locating means
establishes substantially simultaneous, constant contact between
all the electrodes and endocardial tissue.
13. A system according to claim 1 wherein the locating means
includes a catheter tube having a distal end that carries at least
two of the electrodes.
14. A system according to claim 13 wherein the generator means and
processing means includes a multiplexer/demultiplexer element at
least a portion of which is carried by the catheter tube.
15. A system according to claim 1 and further including means for
emitting energy to ablate myocardial tissue within the heart.
16. A system for examining tissue within the heart comprising a
three dimensional array of spaced apart electrodes for contacting
endocardial tissue in a selected position, means for transmitting
electrical current from the spaced apart electrodes in multiple
paths through a region of heart tissue without altering the
position of the array, and processing means for deriving an
electrical characteristic of tissue lying in the multiple paths
based, at least in part, by sensing tissue impedances in the
multiple paths.
17. A system according to claim 16 wherein the processing means
compares the electrical characteristic derived for tissue lying in
one of the multiple paths with the electrical characteristic
derived for tissue lying an another one of the multiple paths.
18. A system according to claim 17 wherein the processing means
generates an output based upon the comparison of the derived
electrical characteristics.
19. A system according to claim 16 wherein the processing means
derives the electrical characteristic for each of the multiple
paths by measuring the voltages in each path and dividing the
measured voltage by the measured current transmitted through the
path to derive the tissue impedance in the path.
20. A system according to claim 16 wherein the processing means
compares the derived tissue impedances of the multiple paths.
21. A system according to claim 20 wherein the processing means
generates an output based upon the comparison of the derived tissue
impedances.
22. A system according to claim 16 wherein the processing means
derives the resistivities of the tissue lying in each of the
multiple paths.
23. A system according to claim 22 wherein the processing means
compares the derived tissue resistivities of the multiple
paths.
24. A system according to claim 23 wherein the processing means
generates an output based upon the comparison of the derived tissue
resistivities.
25. A system according to claim 16 and further including a catheter
tube having a distal end that carries the three dimensional
array.
26. A system according to claim 25 wherein the means for
transmitting electric current and the processing means includes a
multiplexer/demultiplexer element at least a portion of which is
carried by the catheter tube.
27. A system for examining tissue within the heart comprising at
least three spaced apart electrodes, means for locating at least
two of the electrodes within the heart for contact with endocardial
tissue, generator means operable in one mode for transmitting
electrical current in a first path through a region of heart tissue
between a first pair of the electrodes, at least one of which is
within the heart, the generator means being operable in another
mode for transmitting electrical current in a second path through
heart tissue in the region between a second pair of the electrodes,
at least one of which is within the heart, without substantially
altering position of first pair of electrodes, processing means for
deriving a tissue electrical characteristic based, at least in
part, upon sensing the impedances of the tissue lying in the first
and second paths, and means for generating an output of the derived
electrical characteristic in spatial relation to the location of
the first and second paths.
28. A system according to claim 27 wherein the processing means
derives the electrical characteristic by measuring the voltages in
the first and second paths and dividing the measured voltages by
the measured currents transmitted through the paths to derive the
tissue impedances, and wherein the generated output includes the
derived tissue impedances in spatial relation to the location of
the first and second paths.
29. A system according to claim 27 wherein the processing means
derives the resistivities of the tissue lying in the first and
second paths, and wherein the generated output includes the derived
tissue resistivities in spatial relation to the location of the
first and second paths.
30. A system according to claim 27 wherein the generated output
comprises a tabular listing.
31. A system according to claim 27 wherein the generated output
comprises a graphic display.
32. A system according to claim 27 wherein the locating means
establishes substantially simultaneous, constant contact between at
least two of the electrodes and endocardial tissue.
33. A system according to claim 27 and wherein the locating means
establishes substantially simultaneous, constant contact between at
least two of the electrodes and endocardial tissue, and wherein at
least one of the remaining electrodes comprises an electrode
located outside the heart.
34. A system according to claim 27 wherein the locating means
establishes substantially simultaneous, constant contact between
all the electrodes and endocardial tissue.
35. A system according to claim 27 wherein the locating means
includes a catheter tube having a distal end that carries at least
two of the electrodes.
36. A system according to claim 35 wherein the generator means and
processing means includes a multiplexer/demultiplexer element at
least a portion of which is carried by the catheter tube.
37. A system according to claim 27 wherein the locating means
includes a three dimensional structure for supporting at least two
of the electrodes.
38. A system according to claim 37 wherein the locating means
includes a catheter tube having a distal end that carries the three
dimensional structure.
39. A system according to claim 38 wherein the generator means and
processing means includes a multiplexer/demultiplexer element at
least a portion of which is carried by the catheter tube.
40. A system according to claim 27 and further including means for
emitting energy to ablate myocardial tissue within the heart.
41. A method for examining tissue within the heart comprising the
steps of transmitting electrical current in a first path through a
region of tissue between a first pair of electrodes, at least one
of which is located within the heart in contact with endocardial
tissue, transmitting electrical current in a second path through
tissue in the region between a second pair of the electrodes, at
least one of which is located within the heart in contact with
endocardial tissue, without substantially altering the position of
the first pair of electrodes, and deriving the electrical
characteristics of tissue lying in the first and second paths
based, at least in part, upon sensing the impedances in the first
and second paths.
42. A method according to claim 41 and further including the step
of comparing the derived electrical characteristic of the first
path with the derived electrical characteristic of the second
path.
43. A method according to claim 42 and further including the step
of creating an output based upon the comparison of derived
electrical characteristics.
44. A method according to claim 41 and further including the step
of creating an output of the derived electrical characteristics in
spatial relation to the location of the first and second paths.
45. A method according to claim 41 wherein, in the step of deriving
the electrical characteristic, voltages are measured in the first
and second paths and the measured voltage in each path is divided
the measured current transmitted through the associated path to
derive tissue impedances.
46. A method according to claim 45 and further including the step
of comparing the derived tissue impedances.
47. A method according to claim 46 and further including the step
of creating an output based upon the comparison of the derived
tissue impedances.
48. A method according to claim 46 and further including the step
of creating an output of the derived tissue characteristics in
spatial relation to the location of the first and second paths.
49. A method according to claim 41 wherein, in the step of deriving
the electrical characteristic, the resistivities of the tissue
lying in the first and second paths are derived.
50. A method according to claim 49 and further including the step
of comparing the derived tissue resistivities.
51. A method according to claim 50 and further including the step
of creating an output based upon the comparison of the derived
tissue resistivities.
52. A method according to claim 50 and further including the step
of creating an output of the derived tissue resistivities in
spatial relation to the location of the first and second paths.
53. A method for examining tissue within the heart comprising the
steps of positioning a array of spaced apart electrodes in contact
with a region of endocardial tissue in a desired position,
transmitting electrical current from the spaced apart electrodes in
multiple paths through a region of heart tissue without altering
the position of the array, and deriving the electrical
characteristics of tissue lying in the multiple paths based, at
least in part, to sensing tissue impedances in the multiple
paths.
54. A method according to claim 53 and further including the step
of comparing the derived electrical characteristics of the multiple
paths to each other.
55. A method according to claim 54 and further including the step
of creating an output based upon the derived electrical
characteristics.
56. A method according to claim 54 and further including the step
of creating an output of the derived electrical characteristics in
spatial relation to the multiple paths.
Description
FIELD OF THE INVENTION
[0001] The invention relates to systems and methods for mapping the
interior regions of the heart for treatment of cardiac
conditions.
BACKGROUND OF THE INVENTION
[0002] Physicians examine the propagation of electrical impulses in
heart tissue to locate aberrant conductive pathways. The aberrant
conductive pathways constitute peculiar and life threatening
patterns, called dysrhythmias. The techniques used to analyze these
pathways, commonly called "mapping," identify regions in the heart
tissue, called foci, which are ablated to treat the
dysrhythmia.
[0003] Conventional cardiac tissue mapping techniques use multiple
electrodes positioned in contact with epicardial heart tissue to
obtain multiple electrograms. Digital signal processing algorithms
convert the electrogram morphologies into isochronal displays,
which depict the propagation of electrical impulses in heart tissue
over time. These conventional mapping techniques require invasive
open heart surgical techniques to position the electrodes on the
epicardial surface of the heart.
[0004] Furthermore, conventional epicardial electrogram processing
techniques used for detecting local electrical events in heart
tissue are often unable to interpret electrograms with multiple
morphologies. Such electrograms are encountered, for example, when
mapping a heart undergoing ventricular tachycardia (VT). For this
and other reasons, consistently high correct foci identification
rates (CIR) cannot be achieved with current multi-electrode mapping
technologies.
[0005] Researchers have taken epicardial measurements of the
electrical resistivity of heart tissue. Their research indicates
that the electrical resistivity of infarcted heart tissue is about
one-half that of healthy heart tissue. Their research also
indicates that ischemic tissue occupying the border zone between
infarcted tissue and healthy tissue has an electrical resistivity
that is about two-thirds that of healthy heart tissue. See, e.g.,
Fallert et al., "Myocardial Electrical Impedance Mapping of
Ischemic Sheep Hearts and Healing Aneurysms," Circulation, Vol. 87,
No. 1, January 1993, 199-207.
[0006] This observed physiological phenomenon, when coupled with
effective, non-intrusive measurement techniques, can lead to
cardiac mapping systems and procedures with a CIR better than
conventional mapping technologies.
SUMMARY OF THE INVENTION
[0007] A principal objective of the invention is to provide
improved probes and methodologies to examine heart tissue
morphology quickly, accurately, and in a relatively non-invasive
manner.
[0008] One aspect of the invention provides systems and methods for
examining heart tissue morphology using three or more spaced apart
electrodes, at least two of which are located within the heart in
contact with endocardial tissue. The systems and methods transmit
electrical current through a region of heart tissue lying between
selected pairs of the electrodes, at least one of the electrodes in
each pair being located within the heart. Based upon these current
transmissions, the systems and methods derive the electrical
characteristic of tissue lying between the electrode pairs.
[0009] This electrical characteristic (called the
"E-Characteristic") can be directly correlated to tissue
morphology. A low relative E-Characteristic indicates infarcted
heart tissue, while a high relative E-Characteristic indicates
healthy heart tissue. Intermediate E-Characteristic values indicate
the border of ischemic tissue between infarcted and healthy
tissue.
[0010] According to this aspect of the invention, the systems and
methods derive the tissue E-Characteristic of at least two
different tissue sites within the heart without altering the
respective positions of the endocardial electrodes. The systems and
methods make possible the differentiation of regions of low
relative E-Characteristic from regions of high relative
E-Characteristic, without invasive surgical techniques.
[0011] Another aspect of the invention provides systems and methods
that generate a display showing the derived E-Characteristic in
spatial relation to the location of the examined tissue regions.
This aspect of the invention makes possible the mapping of the
E-Characteristic of heart tissue to aid in the identification of
possible tissue ablation sites.
[0012] How the E-Characteristic is expressed depends upon how the
electrical current is transmitted by the electrode pair through the
heart tissue.
[0013] When one of the electrodes in the pair comprises an
indifferent electrode located outside the heart (i.e., a unipolar
arrangement), the E-Characteristic is expressed in terms of tissue
impedance (in ohms). When both electrodes in the pair are located
inside the heart (i.e., a bipolar arrangement), the
E-Characteristic is expressed in terms of tissue resistivity (in
ohm.multidot.cm).
[0014] In a preferred embodiment, the systems and methods employ
electrodes carried by catheters for introduction into contact with
endocardial tissue through a selected vein or artery. The systems
and methods transmit electric current and process information
through signal wires carried by the electrodes. The electrodes can
be connected to a multiplexer/demultiplexer element, at least a
portion of which is carried by the catheter, to reduce the number
of signal wires the catheter carries, and to improve the
signal-to-noise ratio of the data acquisition system.
[0015] Other features and advantages of the inventions are set
forth in the following Description and Drawings, as well as in the
appended Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a plan view, with portions in section, of a system
for examining and mapping heart tissue morphology according to the
features of the invention, shown deployed for use within the
heart;
[0017] FIG. 2 is a plan view, with portions in section, of the
system shown in FIG. 1 in the process of being deployed for use
within the heart;
[0018] FIG. 3 is a view of the mapping probe and process controller
associated with the system shown in FIG. 1;
[0019] FIG. 4 is an enlarged perspective view of an electrode
carrying spline associated with the probe shown in FIG. 1;
[0020] FIG. 5 is a cross sectional view of an alternative
embodiment of an electrode that can be associated with the probe
shown in FIG. 1, taken generally along line 5-5 in FIG. 6;
[0021] FIG. 6 is an enlarged perspective view of an alternative
embodiment of an electrode carrying spline that can be associated
with the probe shown in FIG. 1;
[0022] FIGS. 6A to 6C and associated catheter tube are views of a
flexible electrode support body that can carry the electrodes and
deployed in the heart according to the invention;
[0023] FIG. 7 is a schematic view of the current generator module
and switching element of the process controller for the system
shown in FIG. 1;
[0024] FIG. 8 is a diagrammatic view of the current generator
module and switching element when operated in a Unipolar Mode;
[0025] FIG. 9 is a diagrammatic view of the current generator
module and switching element when operated in a Bipolar Two
Electrode Mode;
[0026] FIG. 10 is a diagrammatic view of the current generator
module and switching element when operated in a Bipolar Four
Electrode Mode;
[0027] FIGS. 11 and 12 are schematic views of the details of the
switching element shown in FIGS. 7 to 10;
[0028] FIG. 13 is a schematic view of the signal processor module
of the process controller for the system shown in FIG. 1;
[0029] FIG. 14 is a schematic view of the E-Characteristic
computing system of the signal processor module shown in FIG.
13;
[0030] FIG. 15 is an illustrative, idealized display of the
absolute tissue E-Characteristic values derived by the system shown
in FIG. 14 arranged in spatial relation to a region of the
heart;
[0031] FIG. 16 is a flow chart showing the operation of the system
that arranges the derived absolute tissue E-Characteristic values
into groups of equal values;
[0032] FIG. 17 is a representative display of the groups of equal
E-Characteristic values derived by the system shown in FIG. 16
arranged in spatial relation to a region of the heart; and
[0033] FIG. 18 is a diagrammatic view of an alternative embodiment
of a controller that can be used in association with the system
shown in FIG. 1;
[0034] FIG. 19 is a diagrammatic view of the pacing module that the
controller shown in FIG. 18 includes;
[0035] FIG. 20 is a diagrammatic view of the host processing unit
and electrogram signal processing module with which the controller
shown in FIG. 18 is associated;
[0036] FIG. 21A is a view of four representative electrograms that
can be used to compute electrogram events;
[0037] FIG. 21B is a flow chart showing the methodology for
computing an electrogram event for processing by the controller
shown in FIG. 18;
[0038] FIG. 22 is a flow chart showing the operation of the means
for constructing an iso-display of the computed electrogram
event;
[0039] FIG. 23 is a representative iso-chronal display;
[0040] FIG. 24 is a flow chart showing the operation of the means
for constructing an iso-conduction display of the computed
electrogram event;
[0041] FIG. 25 is a representative iso-conduction display;
[0042] FIG. 26 is a flow chart showing the operation of the means
for matching iso-E-Characteristics with iso-conduction
information;
[0043] FIG. 27 is a representative display of the matched
iso-E-Characteristics and iso-conduction information;
[0044] FIG. 28 is a flow chart showing the operation of the means
for detecting a possible ablation site based upon the information
obtain in FIG. 26;
[0045] FIG. 29 is a representative display of the matched
Iso-E-Characteristics and iso-conduction information, after
selection of a threshold value, identifying a potential ablation
site; and
[0046] FIG. 30 is a plan view of an ablation probe being used in
association with the system shown in FIG. 1.
[0047] The invention may be embodied in several forms without
departing from its spirit or essential characteristics. The scope
of the invention is defined in the appended claims, rather than in
the specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] FIGS. 1 to 3 show the components of a system 10 for
examining heart tissue morphology. FIG. 1 shows the system 10
deployed and ready for use within a selected region 12 inside a
human heart.
[0049] As FIGS. 1 and 2 show, deployment of the system 10 does not
require invasive open heart surgical techniques. Instead, the
system 10 includes an introducer 14 and an outer guide sheath 16
that together direct a multiple electrode probe 18 into the
selected region 12 within the heart through a selected vein or
artery. FIG. 3 shows the probe 18 in its entirety.
[0050] The physician uses the probe 18 in association with a
process controller 20 (see FIG. 3) to take multiple, sequential
measurements of the transmission of electrical current by heart
tissue. From these, the E-Characteristic of the tissue is derived.
In the illustrated and preferred embodiment, these measurements are
used to assist the physician in identifying appropriate ablation
sites within the heart.
[0051] FIG. 1 and the other figures generally show the system 10
deployed in the left ventricle of the heart. Of course, the system
10 can be deployed in other regions of the heart, too. It should
also be noted that the heart shown in the Figures is not
anatomically accurate. The Figures show the heart in diagrammatic
form to demonstrate the features of the invention.
I. Non-invasive System Deployment
[0052] As FIG. 1 shows, the introducer 14 has a skin-piercing
cannula 22. The cannula 22 establishes percutaneous access into the
selected vein or artery (which is typically the femoral vein or
artery). The other end of the introducer 14 includes a conventional
hemostatic valve 24.
[0053] The physician advances the outer guide sheath 16 through the
introducer 14 through the vein or artery into the selected heart
chamber 12. The hemostatic valve 24 yields to permit the
introduction of the outer guide sheath 16 through it, but otherwise
conforms about the outer surface of the sheath 16, thereby
maintaining a fluid tight seal.
[0054] Preferably, the guide sheath 16 includes a precurved distal
tip region 26, like a conventional "pig tail" catheter. The
precurved distal tip region 26 assists in steering the guide sheath
16 into position within the heart chamber 12.
[0055] The physician advances the probe 18 through the handle 28 of
the outer sheath 16. The handle 28 includes a second conventional
hemostatic valve 30 that yields to permit the introduction of the
flexible body 32 of the mapping probe 18 through it. At the same
time, the valve 30 conforms about the outer surface of the body 22
to maintain a fluid tight seal.
[0056] Further details of the deployment and use of the introducer
14 and guide sheath 16 to establish a pathway for the probe 18 are
set forth in pending U.S. patent application Ser. No. 08/033,641,
filed Mar. 16, 1993, entitled "Systems and Methods Using Guide
Sheaths for Introducing, Deploying, and Stabilizing Cardiac Mapping
and Ablation Probes."
II. The Tissue Examination Probe
[0057] As FIGS. 1 and 3 best show, the probe 18 has a handle 34
attached to the proximal end of the flexible catheter body 32. The
distal end of the catheter body 32 carries a three dimensional
structure 36. In FIGS. 1 and 3, the structure 36 takes the form of
a basket. It should be appreciated that other three dimensional
structures could be used.
[0058] The three dimensional basket structure 36 carries an array
of electrodes 38.
[0059] As FIG. 1 shows, when deployed inside the heart chamber 12,
the basket structure 36 holds the electrodes 38 in intimate contact
against the endocardial surface of the heart chamber 12.
[0060] The catheter body 32 passes through the outer guide sheath
16. The sheath 16 has an inner diameter that is greater than the
outer diameter of the catheter body 32. As a result, the sheath 16
can slide along the catheter body 32. The sheath handle 28 helps
the user slide the sheath 16 along the catheter body 32.
[0061] As FIG. 2 shows, forward movement of the sheath handle 28
(i.e., toward the introducer 14) advances the distal end of the
slidable sheath 16 upon the basket structure 36. In this position,
the slidable sheath 16 captures and collapses the basket structure
36, entirely enclosing the basket structure 36.
[0062] As FIG. 1 shows, rearward movement of the sheath handle 28
(i.e., away from the introducer 14) retracts the slidable sheath 16
away from the basket structure 36. This removes the compression
force, and the basket structure 36 opens to assume its prescribed
three dimensional shape.
[0063] The probe 18 also preferably includes a sliding hemostat
sheath 40. The physician slides the sheath 40 about the basket
structure 36 to protect it during its advancement through the
introducer 14. Once the basket structure 36 enters the guide sheath
16, the physician slides the hemostatic sheath 40 away rearward
toward the probe handle 34. Further details of the use of the
sheath 40 are disclosed in the above-identified pending Patent
Application.
[0064] The basket structure 36 can itself be variously constructed.
In the illustrated and preferred embodiment (see FIG. 3), the
basket structure 36 comprises a base member 42 and an end cap 44.
Generally flexible splines 46 extend in a circumferentially spaced
relationship between the base member 42 and the end cap 44.
[0065] In the illustrated embodiment, eight, rectilinear splines 46
form the basket structure 36. However, additional or fewer splines
46 could be used, as could splines of different configurations.
[0066] In this arrangement, the splines 46 are preferably made of a
resilient inert material, like Nitinol metal or silicone rubber.
The splines 46 are connected between the base member 42 and the end
cap 44 in a resilient, pretensed condition, shown in FIG. 3.
[0067] As FIG. 1 shows, the resilient splines 46 bend and conform
to the endocardial tissue surface they contact. As FIG. 2 shows,
the splines 46 also collapse into a closed, compact bundle in
response to the external compression force of the sliding sheath
18.
[0068] In the illustrated embodiment (see FIG. 4), each spline 46
carries eight electrodes 38. Of course, additional or fewer
electrodes 38 can be used.
[0069] As will be described later, the system 10 can be operated in
either a unipolar mode or a bipolar mode. The basket electrodes 38
can therefore be arranged in thirty-two bi-polar pairs, or as
sixty-four uni-polar elements.
[0070] In the illustrated and preferred embodiment (as FIG. 4 best
shows), the electrodes 38 are mounted to each spline 46 to maximize
surface contact to endocardial tissue, while at the same time
minimizing exposure to the surrounding blood pool. Incidental
exposure of the electrodes 38 to blood while in contact with heart
tissue introduces an unwanted artifact to E-Characteristic
measurement, because the resistivity of blood is about three times
lower than the resistivity of heart tissue. This artifact can skew
the E-Characteristic measurement to a lower value, thereby reducing
the desired contrast between healthy and infarcted tissue.
[0071] In the preferred embodiment (see FIG. 4), the electrodes 38
are made of platinum or gold plated stainless steel bands affixed
to only one side of the splines 46. This is the side of the spline
46 that, in use, contacts endocardial tissue. The opposite surface
of the splines 46 (which, in use, contacts the blood pool) is free
of electrodes.
[0072] In an alternative arrangement (see FIGS. 5 and 6), the
electrodes 38 can take the form of rings that encircle the entire
spline 46. In this arrangement, the rear side of the electrodes 38,
which during use face the blood pool, are coated with an
electrically insulating material 49 to prevent current transmission
into blood.
[0073] It is believed that no more than 20% of the electrode
surface should be exposed to the blood pool during use. Preferable,
less than 5% of the electrode should be so exposed during use.
[0074] In an alternative arrangement (see FIGS. 6A to 6C), one or
more of electrodes 38 can be introduced into the heart chamber
through a vein or artery on a single flexible electrode support
body 300, and not on a basket structure like that earlier
described. The body 300 is illustrative of a family of flexible,
elongated electrode supports of various alternative constructions.
In the preferred and illustrated embodiment, the body 300 is about
1 to 2.5 mm in diameter and about 1 to 5 cm long.
[0075] As FIG. 27 shows, the body 300 is carried at the distal end
of a catheter tube 302 used to guide the body 300 into the heart. A
handle 304 is attached to the proximal end of the catheter tube
302. The handle 304 and catheter tube 302 carry a steering
mechanism 306 for selectively bending or flexing the support body
300 along its length, as the arrows in FIG. 6A show.
[0076] The steering mechanism 306 can vary. In the illustrated
embodiment (see FIG. 6C), the steering mechanism 306 includes a
rotating cam wheel 308 with an external steering lever 310 (as FIG.
6A shows). As FIG. 6C shows, the cam wheel 308 holds the proximal
ends of right and left steering wires 312. The wires 312 pass
through the catheter tube 302 and connect to the left and right
sides of a resilient bendable wire or spring (not shown) within the
ablating element support body 300.
[0077] As FIG. 6A shows, movement of the steering lever 310 flexes
or curves the support body 300 from a generally straight
configuration (shown in phantom lines in FIGS. 6A and 6B) into a
generally arcuate curve (shown in solid lines in FIGS. 6A and 6B).
Through flexing, the electrodes 38 can also be brought into
conforming, intimate contact against the endocardial tissue,
despite the particular contours and geometry that the wall
presents.
[0078] As shown in FIG. 6B, the electrodes 38 comprise rings
encircling the support body 300. In this arrangement, the rear
sides of the electrodes 38, which, in use, face the blood pool, are
preferably coated with the electrical insulating material 49 for
the reasons stated above. Alternatively, the electrodes 38 can be
affixed only to the tissue-contacting side of the support body 300,
thereby making the rear side of the support body 300 free of
electrodes 38, like the rectilinear spline 46 shown in FIG. 4.
[0079] The electrodes 38 carried by the support body 300, as FIG.
6B shows, can by used in association with the process controller 20
to take one or more E-Characteristic measurements, just as the
electrodes carried by the basket structure. The support body 300
can be moved sequentially to different endocardial sites to obtain
a plurality of E-Characteristic measurements, which can be
processed in the same manner as those taken by the stationary
basket structure.
[0080] Further details of flexible electrode carrying elements can
be found in copending U.S. patent application Ser. No. 08/138,142,
filed Oct. 15, 1993, entitled "Systems and Methods for Creating
Long, Thin Lesions in Body Tissue."
[0081] In the illustrated embodiments (see FIGS. 4 and 6), a signal
wire 47 made from a highly conductive metal, like copper, leads
from each electrode 46 (these signal wires are also shown
diagrammatically in FIG. 11). The signal wires 47 extend down the
associated spline 46, by the base member 42, and into the catheter
body 32. An inert plastic wrapping 43 preferably covers each spline
46 and electrode support body 300, except where the electrodes 38
project, to shield the signal wires.
[0082] The eight signal wires 47 for each spline 46 are twisted
together to form a common bundle. The eight common bundles (not
shown) are, in turn, passed through the catheter body 32 of the
mapping probe 18. The common bundles enter the probe handle 34.
[0083] The sixty-four signal wires 47 are connected within the
probe handle 34 to one or more external connectors 48, as FIG. 3
shows. In the illustrated embodiment, each connector contains
thirty-two pins to service thirty-two signal wires.
[0084] In an alternative arrangement (not shown), the electrodes 38
can be connected to a multiplexer/demultiplexer (M/DMUX) block (not
shown) to reduce the number of signal wires carried by the catheter
body 32. The M/DMUX block can comprise a multi-die integrated
circuit mounted on a flexible support and wrapped about the
catheter body 32. The signal-to-noise-ratio is thereby
improved.
III. Measuring and Mapping the Tissue E-Characteristic
[0085] The system 10 transmits electrical current in a selected
manner through the basket electrodes 38 in contact with endocardial
tissue. From this, the system 10 acquires impedance information
about the heart tissue region that the basket electrodes 38
contact. The system 10 processes the impedance information to
derive the E-Characteristic, which assists the physician in
identifying regions of infarcted tissue where ablation therapy may
be appropriate.
[0086] For these purposes (see FIG. 3), the system 10 includes the
process controller 20. The process controller 20 includes a current
generator module 50 and a signal processor module 52. The
connectors 48 electrically couple the basket electrodes 38 to both
the generator module 50 and the processor module 52.
A. The Current Generator Module
[0087] The generator module 50 conveys a prescribed current signal
to individual basket electrodes 38.
[0088] In the illustrated and preferred embodiment (see FIG. 7),
the generator module 50 includes an oscillator 54 that generates a
sinusoidal voltage signal. An associated interface 56 has a bus 58
that controls the frequency of the output voltage signal and a bus
60 that controls the amplitude of the output voltage signal. The
interface 56, in turn, is programmed by a host processor 206, which
will be described in greater detail later.
[0089] The oscillator 54 has as an output stage that includes a
voltage-to-current converter 62. In conventional fashion, the
converter 62 converts the sinusoidal voltage signal to current.
[0090] In the illustrated and preferred embodiment, the transmitted
current has an amplitude of about 0.1 milliamps to 5.0 milliamps.
The lower range of the current amplitude is selected to be high
enough to overcome the influence of the double layer at the
tissue-electrode interface on the E-Characteristic measurement. The
high range of the current amplitude is selected to avoid the
induction of fibrillation.
[0091] The current has a frequency in a range of about 5 to 50 kHz.
The range is selected to avoid the induction of fibrillation, as
well as provide contrast between infarcted tissue and healthy
tissue. The output of the converter 62 can comprise a constant
current with a constant frequency within the above range.
Alternatively, the interface 56 can control the modulation of the
frequency of the current signal within the prescribed range.
Deriving tissue E-Characteristic by transmitting currents with
different frequencies better differentiates among different tissue
morphologies. It has been determined that lower frequencies within
the range provide E-Characteristics yielding greater quantitative
contrast between infarcted and healthy tissues than higher
frequencies in this range.
[0092] The current output of the module 50 is supplied to the
basket electrodes 38 via supply path 68 through a switching element
64. The interface 56 electronically configures the switching
element 64 to direct current in succession to selected basket
electrodes 38 through their associated signal wires in either a
unipolar mode or a bipolar mode. Line 66 constitutes the control
bus for the switching element 64.
[0093] As FIG. 8 shows, when operated in a unipolar mode, the
current return path 70 to the generator module 50 is provided by an
exterior indifferent electrode 72 attached to the patient.
[0094] When operated in a bipolar mode, the current return path 70
is provided by an electrode carried on the basket structure 36
itself. In the illustrated and preferred embodiment, the bipolar
return electrode is either located immediately next to or three
electrodes away from the selected transmitting basket electrode
along the same spline. The first circumstance (shown in FIG. 9)
will be called the Bipolar Two Electrode Mode. The second
circumstance (shown in FIG. 10) will be called the Bipolar Four
Electrode Mode.
[0095] The configuration of the switching element 64 can vary. FIG.
11 diagrammatically shows one preferred arrangement.
[0096] FIG. 11 shows for illustration purposes a spline 46 with
seven adjacent electrodes 38, designated E1 to E7. Each electrode
E1 to E7 is electrically coupled to its own signal wire, designated
W1 to W7. The indifferent electrode, designated EI in FIG. 11, is
also electrically coupled to its own signal wire WI.
[0097] In this arrangement, the switching element 64 includes an
electronic switch S.sub.M and electronic switches S.sub.E1 to
S.sub.E7 that electrically couple the current generator to the
signal wires W1 to W7. The switch S.sub.M governs the overall
operating mode of the electrodes E1 to E7 (i.e., unipolar or
bipolar). The switches S.sub.E1 to S.sub.E7 govern the electrical
conduction pattern of the electrodes E1 to E7.
[0098] The switches S.sub.M and S.sub.E1 to E7 are electrically
coupled to the current source. The supply path 68 of the generator
module 50 is electrically coupled to the leads L1 of the switches
S.sub.E1 to E7 The return path 70 of the generator module 50 is
electrically coupled to the center lead L2 of the mode selection
switch S.sub.M. A connector 67 electrically couples the leads L3 of
the switches S.sub.M and S.sub.E1 to E7.
[0099] The center leads L2 of the selecting switches S.sub.E1 to E7
are directly electrically coupled to the signal wires W1 to W7
serving the electrodes E1 to E7, so that one switch S.sub.E(N)
serves only one electrode E.sub.(N).
[0100] The lead L1 of the switch S.sub.M is directly electrically
coupled to the signal wire WI serving the indifferent electrode
EI.
[0101] The interface 56 electronically sets the switches S.sub.M
and S.sub.E1 to E7 among three positions, designated A, B, and C in
FIG. 12.
[0102] As FIG. 12 shows, Position A electrically couples leads L1
and L2 of the associated switch. Position C electrically couples
leads L2 and L3 of the associated switch. Position B electrically
isolates both leads L1 and L3 from lead L2 of the associated
switch.
[0103] Position B is an electrically OFF position. Positions A and
B are electrically ON positions.
[0104] By setting switch S.sub.M in Position B, the interface 56
electronically inactivates the switching network 54.
[0105] By setting switch S.sub.M in Position A, the interface 56
electronically configures the switching element for operation in
the unipolar mode. The center lead L2 of switch S.sub.M is coupled
to lead L1, electronically coupling the indifferent electrode EI to
the return of the current generator. This configures the
indifferent electrode EI as a return path for current.
[0106] With switch S.sub.M set in Position A, the interface 56
electronically selectively configures each individual electrode E1
to E7 to emit current by sequentially setting the associated switch
S.sub.E1 to E7 in Position A. When the selected electrode E1 to E7
is so configured, it is electronically coupled to the supply of the
current generator and emits current. The indifferent electrode EI
receives the current sequentially emitted by the selected electrode
E1 to E7.
[0107] By setting switch S.sub.M in Position C, the interface 56
electronically isolates the indifferent electrode EI from the
electrodes E1 to E7. This configures the switching element for
operation in the bipolar mode.
[0108] With switch S.sub.M set in Position C, the interface 56 can
electronically alter the polarity of adjacent electrodes E1 to E7,
choosing among current source, current sink, or neither.
[0109] By setting the selected switch S.sub.E1 to E7 in Position A,
the interface 56 electronically configures the associated electrode
E1 to E7 to be a current source. By setting the selected switch
S.sub.E1 to E7 in Position C, the interface 56 electronically
configures the associated electrode E1 to E7 to be a current sink.
By setting the selected switch S.sub.E1 to E7 in Position B, the
interface 56 electronically turns off the associated electrode E1
to E7.
[0110] In the Bipolar Two Electrode Mode, the interface 56 first
configures the electrode E1 to be a current source, while
configuring the immediate adjacent electrode E2 to be a current
sink, while turning off the remaining electrodes E3 to E7. After a
preselected time period, the interface 56 then turns off electrode
E1, configures electrode E2 to be a current source, configures the
next immediate adjacent electrode E3 to be a current sink, while
keeping the remaining electrodes E4 to E7 turned off. After a
preselected time period, the interface 56 then turns off electrode
E2, configures electrode E3 to be a current source, configures the
next immediate adjacent electrode E4 to be a current sink, while
keeping the remaining electrodes E1 and E5 to E7 turned off. The
interface 56 cycles in this timed sequence until electrodes E6 and
E7 become the current source/sink bipolar pairs (the remaining
electrodes E1 to E5 being turned off). The cycle can then be
repeated, if desired, or ended after one iteration.
[0111] In the Bipolar Four Electrode Mode, the interface 56 first
configures the electrode E1 to be a current source, while
configuring the third adjacent electrode E4 to be a current sink,
while turning off the remaining electrodes E2, E3, and E5 to E7.
After a predetermined time period, the interface 56 turns off
electrode E1, configures electrode E2 to be a current source,
configures the next third adjacent electrode E5 to be a current
sink, while keeping the remaining electrodes E3, E4, E6, and E7
turned off. After a predetermined time period, the interface 56
turns off electrode E2, configures electrode E3 to be a current
source, configures the next third adjacent electrode E6 to be a
current sink, while keeping the remaining electrodes E1, E2, E4,
E5, and E7 turned off. The interface 56 cycles in this timed
sequence until electrodes E4 and E7 become the current source/sink
bipolar pairs (the remaining electrodes E1 to E3, E5, and E6 being
turned off. The cycle can then be repeated, if desired, or ended
after one iteration.
[0112] In the preferred embodiment, there is a switching element 64
for the electrodes on each basket spline, with the interface 56
independently controlling each switching element.
B. Computing Tissue E-Characteristic
[0113] As FIG. 13 shows, the signal processor module 52 includes a
data acquisition system 74. While current is emitting by a selected
basket electrode, the system 74 senses the voltage in the tissue
path using selected electrodes on the basket 36.
[0114] Based upon the data acquired by the system 74, the host
processor 206 computes the E-Characteristic of the tissue path as
follows:
[0115] (1) When operated in the Unipolar Mode, the E-Characteristic
is the impedance of the tissue path, computed based upon the
following equation: 1 Impedance ( ohms ) = PathVoltage ( volts )
PathCurrent ( amps )
[0116] The PathVoltage and PathCurrent are both root mean squared
(RMS) values.
[0117] In the unipolar mode (see FIG. 8), the voltage is measured
between each transmitting electrode and the indifferent electrode
(or between EI and E(n), where n represents the location of the
current emitting electrode). The impedance computed by the host
processor 206 in this mode reflects not only the impedance of the
underlying myocardial tissue, but also includes the impedance of
the other tissue mass in the path. The computed impedance in this
mode therefore is not the actual impedance of the myocardial tissue
itself. Rather, it provides a relative scale of impedance (or
E-Characteristic) differences of the myocardial tissue lying in
contact with the spline electrodes.
[0118] (2) When operated in the Bipolar Mode, the E-Characteristic
of the tissue is the resistivity of the tissue path, computed as
follows:
Resistivity(ohm.multidot.cm)=Impedance(ohm).times.k(cm)
[0119] 2 Impedance ( ohms ) = PathVoltage ( volts ) PathCurrent (
amps )
[0120] where k is a dimensional constant (in cm) whose value takes
into account the methodology employed (i.e. either Bipolar Two
Electrode Mode or Bipolar Four Electrode Mode) and the geometry of
the electrode array (i.e., the size and spacing of the
electrodes).
[0121] In general, k is approximately equal to the average cross
sectional area of the current path divided by the distance between
the voltage sensing electrodes. The accuracy of the k value can be
further improved, if desired, empirically or by modeling.
[0122] The PathVoltage and PathCurrent are both root mean squared
(RMS) values.
[0123] When operated in the Bipolar Two Electrode Mode (see FIG.
9), the voltage is measured between the two adjacent current
emitting/receiving electrodes (or between E(n) and E(n+1)). When
operated in the Bipolar Four Electrode Mode (see FIG. 10), the
voltage is measured between the two adjacent electrodes lying in
between the current transmitting electrode and the third adjacent
return path electrode (or between E(n+1) and E(n+2)).
[0124] In either Bipolar Mode, the resistivity computed by the
processor 206 reflects the actual resistivity of the myocardial
tissue lying in contact with the spline electrodes. However, the
Bipolar Two Electrode Mode is more prone to electric artifacts than
the Bipolar Four Electrode Mode, such as those due to poor
electrical contact between electrode and tissue.
[0125] As FIG. 14 shows, the voltage signals sensed by the basket
electrodes 38 are passed back through the switching element 64 to
the data acquisition system 74. As FIG. 11 shows, a signal
conditioning element 224 preferably corrects alterations to the
signal-to-noise ratio occurring in the voltage signals during
propagation through the probe body 32.
[0126] The data acquisition system 74 includes a multiplexer 76
that selects and samples in succession the voltage associated with
each transmitting electrode E(n) carried by the basket structure
36. For each selected current transmitting electrode E(n), the
multiplexer 76 samples for a prescribed time period the analog
sinusoidal voltage measured between the sensing electrodes.
[0127] A sample and hold element 80 stores the sampled analog
voltage signals. The stored signals are sent to an
analog-to-digital (A-to-D) converter 82, which converts the sampled
voltage signals to digital signals. The multiplexer 76 makes
possible the use of a single analog-to-digital conversion path.
[0128] The digital signals are sent to a host processor 206 through
an interface 226. The host processor 206, based upon a conventional
sorting scheme, obtains the peak voltage and, from that, computes
the RMS voltage. The host processor 206 then computes the
E-Characteristic, using the RMS voltage and RMS current (and, for
the Bipolar Mode, the constant k) as described above. The RMS
current is known by the processor 206, since it has been programmed
by it through the interface 56 (see FIG. 7).
C. Processing the E-Characteristic
[0129] The computed E-Characteristic values can be processed by the
system 10 in various ways.
[0130] In one embodiment (see FIG. 13), the signal processor module
includes means 90 for sorting the multiple computed
E-Characteristic values in absolute terms, arranging them according
to a preassigned electrode numbering sequence, representing
relative electrode position.
[0131] The means 90 can create as an output a table (either as a
graphic display or in printed form), as follows:
1TABLE 1 SPLINE ELECTRODE E-CHAR S1 El 75 S1 E2 114 S1 E3 68 S1 E4
81 S2 E1 69 S2 E2 71 S2 E3 67 S2 E4 66 S3 E1 123 S3 E2 147 S3 E3
148 S3 E4 140 ... etc ... ... etc ... ... etc ...
[0132] In Table 1, the spline elements of the basket are identified
as S1, S2, S3, etc. The electrodes carried by each spline element
are numbered from the distal end as E1, E2, E3, and so on. The
E-Characteristic values are expressed in terms of resistivity
(ohm.multidot.cm). The values expressed are idealized and given for
illustration purposes. In addition, or alternatively, the means 90
can also create as an output a two or three dimensional display
that spatially maps the relative position of the computed absolute
resistivity values, based upon basket electrode positions.
[0133] FIG. 15 shows a representative display of E-Characteristics
(expressed as resistivity values), based upon the data listed in
Table 1. In FIG. 15, circled Area A identifies a region of low
relative tissue resistivity, indicative of infarcted heart tissue.
Area B in FIG. 15 is a region of normal tissue resistivity,
indicative of healthy heart tissue.
[0134] Preferably, the signal processor module 52 also includes
means 92 (see FIG. 13) for arranging the derived absolute
E-Characteristics into groups of equal E-Characteristic values for
display in spatial relation to the location of the electrodes 38.
This output better aids the physician in interpreting the
E-Characteristics, to identify the regions of low relative tissue
E-Characteristics, where ablation may be appropriate.
[0135] As FIG. 16 shows, the means 92 includes a processing step
that computes the location of the electrodes 38 in a three
dimensional coordinate system. In the illustrated and preferred
embodiment, a three dimensional spherical coordinate system is
used.
[0136] The means 92 next includes a processing step that generates
by computer a three dimensional mesh upon the basket surface. The
points where the mesh intersect are called nodes. Some of the nodes
will overlie the electrodes on the basket. These represent knots,
for which the values of the E-Characteristic are known.
[0137] The values of the E-Characteristic for the remaining nodes
of the three dimensional mesh have not been directly measured.
Still, these values can be interpolated at each remaining node
based upon the known values at each knot.
[0138] One method of doing this interpolation is using three
dimensional cubic spline interpolation, although other methods can
be used. The cubic spline interpolation process is incorporated in
the MATLAB.TM. program, sold by The MathWorks Incorporated.
[0139] The means 92 creates an output display by assigning one
distinguishing idicium to the maximum E-Characteristic value
(whether actually measured or interpolated) and another
distinguishing idicium to the minimum E-Characteristic value
(again, whether actually measured or interpolated). In the
illustrated and preferred embodiment, the distinguishing indicia
are contrasting colors or shades.
[0140] The means 92 assigns computer generated intermediate indicia
to intermediate measured and interpolated values, based upon a
linear scale. In the illustrated and preferred embodiment, the
intermediate indicia are color hues between the two contrasting
colors or shades.
[0141] The means 92 projects the generated color (or selected
indicia) map upon the basket surface, based upon location of the
nodes in the three dimensional mesh. The means 92 thus creates as
an output a display showing iso-E-Characteristic regions.
[0142] FIG. 17 shows a representative display of iso-resistivity
regions, based upon the idealized, illustrative data listed in
Table 1.
D. Matching E-Characteristic and Tissue Conductivity
[0143] FIG. 18 shows another embodiment of a process controller 200
that can be used in association with the probe 18, as already
described.
[0144] The process controller 200 in FIG. 18, like the process
controller 20 shown in FIG. 3, includes the current generator
module 50 and the signal processing module 52 for deriving and
processing tissue E-Characteristics in the manners previously
discussed.
[0145] In addition, the process controller 200 in FIG. 18 includes
a module 202 for pacing the heart to acquire electrograms in a
conventional fashion. The pacing module 202 is electrically coupled
to the probe connectors 48 to provide a pacing signal to tone
electrode 38, generating depolarization foci at selected sites
within the heart. The basket electrodes 38 also serve to sense the
resulting electrical events for the creation of electrograms.
[0146] Operation of the pacing module 202 is not required when
ventricular tachycardia (VT) is either purposely induced (e.g., by
programmed pacing) or occurs spontaneously. In this situation, the
deployed basket electrodes 38 sense the electrical events
associated with VT itself.
[0147] The process controller 200 in FIG. 18 further includes a
second signal processing module 204 for processing the electrogram
morphologies obtained from the basket electrodes 38.
[0148] The process controller 200 in FIG. 18 also includes a host
processor 206 that receives input from the data acquisition system
74 and the electrogram processing module 204. The processor 206
analyzes the tissue E-Characteristic and electrogram information to
compute a matched filtered output, which further enhances the CIR
of ablation site identification.
[0149] The modules 202, 204, and 206 may be configured in various
ways.
[0150] In the illustrated and preferred embodiment (see FIG. 19),
the pacing module 202 includes a controller interface 208 coupled
to the host processor 206, which will be described in greater
detail later. The controller interface 208 is also coupled to pulse
generator 210 and an output stage 212.
[0151] The output stage 212 is electrically coupled by supply path
220 and return path 218 to the same switching element 64 as the
current generator module 50. The switching element 64 has been
previously described and is shown schematically in FIG. 11. As FIG.
11 shows in phantom lines, the pacing module 202 and current
generator module 50 are connected to the switching element 64.
[0152] The controller interface 208 includes control buses 214,
216, and 218. Bus 214 conveys pulse period control signals to the
pulse generator 210. Bus 216 conveys pulse amplitude control
signals to the pulse generator 210. Bus 219 constitutes the control
bus path for the switching element 64.
[0153] When used to pace the heart, the switching element 64
distributes the signals generated by the pacing module 202 to
selected basket electrodes 38. The pacing sequence is governed by
the interface 208, which the host processor 206 controls.
[0154] The resulting electrogram signals sensed by the basket
electrodes 38 are also passed back through the switching element 64
to the host processor 206 and the processing module 204 through the
same analog processing path as the E-Characteristic signals, as
FIG. 11 shows, and as already described.
[0155] FIG. 20 schematically shows the components of the host
processor 206 and the electrogram processing module 204.
[0156] The host central processing unit (CPU) 206 communicates with
a mass storage device 230 and an extended static RAM block 232. A
user interactive interface 234 also communicates with the CPU
206.
[0157] As FIG. 20 shows, the interactive user interface 234
includes an input device 244 (for example, a key board or mouse)
and an output display device 246 (for example, a graphics display
monitor or CRT).
[0158] The CPU 206 also communicates with the current generator
module 50; pacing module 202 and the interface 226 for the system
74, as previously described. In this way, the CPU 206 coordinates
overall control functions for the system 10.
[0159] As FIG. 20 shows, the electrogram processing module 204
includes a bus 235 and a bus arbiter 236 that receive the digital
output of the A-to-D converter 82 through the interface 226. The
bus arbiter 236 arbitrates the distribution of the digital
electrogram morphology signals to one or more digital signal
processors 238, which also form a part of the processing module 204
and which also communicate with the CPU 206.
[0160] The illustrated and preferred embodiment employs four signal
processors 238 operating concurrently, but different numbers of
processors 238 can be used. If N is the total number of basket
electrodes and M is the number of processors 238, then each
processor 238 is responsible for processing the signals coming from
N/M electrodes in the Unipolar Mode and N/(2M) electrodes in the
Bipolar Two or Four Mode.
[0161] To speed up data processing, each processor 238 includes a
static RAM block 240. The data is processed real-time and stored in
the blocks 240.
[0162] The signal processors 238 include various means for
processing the electrogram signals as follows:
[0163] (i) to detect the earliest depolarization event;
[0164] (ii) to construct from the electrogram signals iso-chronal
or iso-delay maps of the depolarization wavefronts, depending upon
how the electrograms are obtained, which can be presented on the
display device 246 for viewing by the physician; and
[0165] (iii) to construct from the electrogram signals
iso-conduction maps, which can also be presented on the display
device 246 for viewing by the physician.
[0166] The CPU 206 employs additional means for processing the
electrogram signals and the E-Characteristic signals as
follows:
[0167] (iv) to match the iso-conduction maps with the
iso-E-Characteristic maps, which can be presented on the display
device 246 for viewing by the physician; and
[0168] (v) based upon the matched output of (iv), to identify a
potential ablation site.
(i) Identifying the Earliest Depolarization Event
[0169] FIG. 21B shows the means 250 for detecting the early
depolarization event.
[0170] The CPU 206 displays the electrograms on the display 246 of
the interactive user interface 234 (see FIG. 21A). After analyzing
the display 246, the physician can manually choose a reference time
for conventional electrogram beat clustering purposes. The
physician can use the mouse or a keyboard device 244 for this
purpose.
[0171] In the situation where ventricular tachycardia is purposely
induced or is occurring spontaneously, the electrogram beats are
clustered relative to the reference time to compute the propagation
time when an electrogram for ventricular tachycardia is sensed by
each electrode 38. For all the beats in the selected cluster, the
physician manually selects the earliest depolarization event for
each electrode 38. The interactive interface 234 transmits the
physician's choice to the host CPU 206, which creates a matrix of
the computed propagation times.
[0172] In the situation where the heart is being paced by the
module 202, the beats are clustered relative to the reference time
for computing the activation delay for each electrogram. The
activation delay is measured between the pacing pulse and the
earliest depolarization event. For all the beats in the selected
cluster, the physician manually selects the earliest depolarization
event for each electrode 38. In this situation as before, the
interactive interface 234 transmits the physician's choice to the
host CPU 206, which creates a matrix of the computed activation
delays.
[0173] FIG. 21A shows four representative electrograms of a heart
undergoing VT. FIG. 21A shows the reference time selected for beat
clustering purposes and the early depolarization events selected
for the purpose of illustration. From this, the propagation times
t.sub.1; t.sub.2; t.sub.3; t.sub.4 can be computed as the
differences between the time of the depolarization event and the
reference time in each electrogram.
(ii) Constructing an Iso-Chronal or Iso-Delay Displays
[0174] FIG. 22 shows the means 252 for creating either an
iso-chronal display of the propagation times (when VT is induced or
spontaneously occurs) or an iso-delay display of activation times
(when the module 202 is used to pace the heart). For purposes of
description, each will be called the "computed electrogram
event."
[0175] The means 252 generally follows the same processing steps as
the means 92 (see FIG. 16) for creating the iso-E-Characteristic
display.
[0176] The means 252 includes a processing step that computes the
location of the electrodes in a spherical coordinate system.
[0177] The means 252 next generates by computer a three dimensional
mesh upon the basket surface. The points where the mesh intersect
are called nodes. Some of the nodes overlie the electrodes on the
basket. These represent knots, for which the values of the computed
electrogram event are known.
[0178] The values of the computed electrogram event for the
remaining nodes of the three dimensional mesh have not been
directly measured. Still, these values can be interpolated at each
remaining node based upon the known values at each knot.
[0179] As before, three dimensional cubic spline interpolation can
be used, although other methods can be used.
[0180] The means 252 creates an output display on the device 246 by
assigning one color the maximum value of the computed electrogram
event (whether actually measured or interpolated) and another color
to the minimum value of computed electrogram event (again, whether
actually measured or interpolated). Computer generated intermediate
hues between the two colors are assigned by the host CPU 206 to
intermediate measured and interpolated values, based upon a linear
scale.
[0181] The means 252 projects the generated color map upon the
basket surface, based upon location of the nodes in the three
dimensional mesh.
[0182] FIG. 23 shows a representative display generated according
to this processing means. The CPU 206 generates this display on the
display device 246 for viewing by the physician.
[0183] A potential ablation site can be identified at regions where
a rapid transition of hues occurs. Area A on FIG. 23 shows such a
region.
[0184] When the electrograms used for beat clustering show an
induced or spontaneous VT, the resulting display is an iso-chronal
map of the examined tissue region. When the electrograms used for
beat clustering are based upon a paced heart, the display is an
iso-delay map of the examined tissue region.
(iii) Creating Iso-Conduction Display
[0185] FIG. 24 shows the means 254 for creating an iso-conduction
displays of the computed electrogram event.
[0186] An iso-conduction display more rapidly identifies the
regions of slow conduction which are candidate ablation sites, than
an iso-chronal or iso-delay display. The iso-conduction display
requires less subjective interpretation by the physician, as the
regions of slow conduction stand out in much greater contrast than
on an iso-chronal or iso-delay display.
[0187] The means 254 draws upon the same input and follows much of
the same processing steps as the means 252 just described. The
means 254 computes the location of the electrodes in a spherical
coordinate system and then generates a three dimensional mesh upon
the basket surface. The means 254 interpolates the computed
electrogram event for the nodes based upon the known values at the
knots.
[0188] Unlike the previously described means 252, the means 254
computes the inverse of the magnitude of the spatial gradient of
the computed electrogram event. This inverse spatial gradient
represents the value of the conduction of the cardiac signal in the
examined tissue.
[0189] To carry out this processing step, the means 254 first
computes the spatial gradient computed electrogram event for each
node of the mesh. The methodology for making this computation is
well known.
[0190] Next, the means 254 computes the magnitude of the spatial
gradient, using, for example, known three dimensional vector
analysis. Then, the means 254 computes the inverse of the
magnitude, which represents the conduction value.
[0191] The means 254 clips all magnitudes larger than a
predetermined threshold value, making them equal to the threshold
value. This processing step reduces the effects of inaccuracies
that may arise during the mathematical approximation process.
[0192] The computation of conduction (i.e., the velocity of the
propagation) can be exemplified for the case when propagation times
are processed. By substituting the activation delays for
propagation times, one can compute the conductions for data
obtained from paced hearts.
[0193] The location of any point on the three-dimensional mesh
shown in FIG. 25 is given by the azimuth angle, .phi. and the
elevation angle, .delta.. The radius of the underlying surface is
normalized to one. The conduction is defined by EQUATION (1): 3
Conduction ( , ) = dspace d Prop_Time ( , ) EQUATION (1)
[0194] Given that the radius of the meshed surface is one, one
obtains the spatial gradient of propagation times: 4 d Prop_Time (
, ) dspace = Prop_Time ( , ) .times. + Prop_Time ( , ) .times.
EQUATION (2)
[0195] where .PHI. and .DELTA. are unity vectors of the spherical
coordinate system defining the directions of the azimuth and
elevation, respectively.
[0196] Thus, the conduction can be computed using EQUATION (3): 5
Conduction ( , ) = 1 ( Prop_Time ( , ) ) 2 + ( Prop_Time ( , ) ) 2
EQUATION (3)
[0197] which is actually the inverse of the spatial gradient
magnitude. When the conduction is numerically approximated, the
derivatives in EQUATION (3) can be computed by any numerical method
appropriate for the estimation of first derivatives.
[0198] The means 254 creates a display by assigning one color the
threshold conduction value (i.e., the maximum permitted value) and
another color to the minimum conduction value. Computer generated
hues are assigned to intermediate values, based upon a linear
scale, as above described.
[0199] The means 254 projects the generated color map upon the
basket surface, based upon location of the nodes in the three
dimensional mesh.
[0200] FIG. 25 shows a representative iso-conduction display
generated according to the just described methodology and using the
same data as the iso-chronal display shown in FIG. 23. The CPU 206
generates this display on the display device 246 for viewing by the
physician.
[0201] Area A in FIG. 25 shows a region of slow conduction, which
appears generally at the same location as the rapid hue transition
in FIG. 23 (also identified as Area A). FIG. 25 shows the more
pronounced contrast of the region that the iso-conduction display
provides, when compared to the iso-chronal display of FIG. 23.
Thus, the iso-conduction display leads to a more certain
identification of a potential ablation site.
(iv) Matching Iso-Conduction with Iso-E-Characteristic
[0202] FIG. 26 shows the means 256 for matching the iso-conduction
with the iso-E-Characteristic for the analyzed heart tissue.
[0203] The means 256 derives the values of the E-Characteristic at
the nodes of three dimensional mesh in the same manner already
described. Next, the means 256 normalizes these E-Characteristic
values into an array of numbers from 0.0 to 1.0. The number 1.0 is
assigned to the absolute lowest E-Characteristic value, and the
number 0.0 is assigned to the absolute highest E-Characteristic
value. E-Characteristic values between the absolute lowest and
highest values are assigned numbers on a linear scale between the
lowest and highest values.
[0204] The means 256 also derives the values of the computed
electrogram event at the nodes of three dimensional mesh in the
manner already described. The means 256 computes the inverse of the
magnitude of spatial gradient of the computed electrogram event, as
previously described, to derive the value of the conduction of the
cardiac signal in the examined tissue.
[0205] The means 256 then normalizes these conduction values into
an array of numbers from 0.0 to 1.0. The number 1.0 is assigned to
the absolute lowest conduction value, and the number 0.0 is
assigned to the threshold conduction value. As before, conduction
values between the absolute lowest and highest values are assigned
numbers on a linear scale between the lowest and highest
values.
[0206] The means 256 then applies, using known mathematical
computational techniques, a two dimensional matched filtering
process to the normalized conduction data using the normalized
E-Characteristic data as a template, or vice versa. Alternatively,
a two dimensional cross-correlation can be applied to the
normalized E-Characteristic and conduction. As used in this
Specification, "matching" encompasses both two dimensional matched
filtering, two dimensional cross-correlation, and a like digital
signal processing techniques.
[0207] The values obtained from the matched filtering process are
normalized, by dividing each value by the maximum absolute value.
After normalization, the value will range between 0.0 and 1.0.
[0208] The means 256 creates a display by assigning one color the
highest normalized matched filter value and another color to the
lowest normalized matched filter value. Computer generated hues are
assigned to intermediate values, based upon a linear scale, as
above described.
[0209] The means 256 projects the generated color map upon the
basket surface, based upon location of the nodes in the three
dimensional mesh.
[0210] FIG. 27 shows a representative display processed according
to the above methodology. The CPU 206 generates this display on the
display device 246 for viewing by the physician.
[0211] The display matches the normalized iso-conduction values
with the normalized iso-E-Characteristic values, in effect matching
electrograms with tissue E-Characteristics. This matching provides
more precise differentiation between regions of infarcted tissue
and regions of healthy tissue.
[0212] This information can be further processed to identify a
potential ablation site to maximize the CIR.
(v) Identifying a Potential Ablation Site
[0213] FIG. 28 shows a means 258 for identifying a potential
ablation site based upon the matched output of the normalized
conduction values and the normalized E-Characteristic values,
generated by the means 256.
[0214] The means 258 selects a threshold value. Tissue regions
having matched output values above the threshold constitute
potential ablation sites. Locating an optimal threshold value can
be done by empirical study or modeling. The threshold value for a
given set of data will also depend upon the professional judgment
of the physician.
[0215] FIG. 29 shows a representative display processed according
to the above methodology. In FIG. 29, a threshold of 0.8 has been
used for illustration purposes. Values greater than the threshold
of 0.8 have been set to 1.0, while values equal to or less than 0.8
have been set to 0.0. The CPU 206 generates this display on the
display device 246 for viewing by the physician.
[0216] FIG. 29 provides by sharp contrast between black and white
(with no intermediate hues) the potential ablation site (Area
A).
E. Ablating the Tissue
[0217] Regardless of the specific form of the output used, the
physician analyses one or more of the outputs derived from the
basket electrodes 38 to locate likely efficacious sites for
ablation.
[0218] The physician can now takes steps to ablate the myocardial
tissue areas located by the basket electrodes 38. The physician can
accomplish this result by using an electrode to thermally destroy
myocardial tissue, either by heating or cooling the tissue.
Alternatively, the physician can inject a chemical substance that
destroys myocardial tissue. The physician can use other means for
destroying myocardial tissue as well.
[0219] In the illustrated embodiment (see FIG. 30), an external
steerable ablating probe 100 is deployed in association with the
basket structure 36.
[0220] Various features of the invention are set forth in the
following claims.
* * * * *