U.S. patent application number 10/807941 was filed with the patent office on 2004-09-16 for electrophysiological cardiac mapping system based on a non-contact non-expandable miniature multi-electrode catheter and method therefor.
This patent application is currently assigned to Case Western Reserve University. Invention is credited to Rudy, Yoram.
Application Number | 20040181160 10/807941 |
Document ID | / |
Family ID | 32965125 |
Filed Date | 2004-09-16 |
United States Patent
Application |
20040181160 |
Kind Code |
A1 |
Rudy, Yoram |
September 16, 2004 |
Electrophysiological cardiac mapping system based on a non-contact
non-expandable miniature multi-electrode catheter and method
therefor
Abstract
A system and method for determining electrical potentials on an
endocardial surface of a heart is provided. The system includes a
spiral-shaped non-contact, multi-electrode catheter probe, a
plurality of electrodes disposed on an end portion thereof, means
for determining endocardial potentials based on electrical
potentials measured by the catheter probe, a matrix of coefficients
that is generated based on a geometric relationship between the
probe surface, and the endocardial surface.
Inventors: |
Rudy, Yoram; (Shaker
Heights, OH) |
Correspondence
Address: |
FOLEY HOAG, LLP
PATENT GROUP, WORLD TRADE CENTER WEST
155 SEAPORT BLVD
BOSTON
MA
02110
US
|
Assignee: |
Case Western Reserve
University
Cleveland
OH
|
Family ID: |
32965125 |
Appl. No.: |
10/807941 |
Filed: |
March 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10807941 |
Mar 24, 2004 |
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09463427 |
Mar 29, 2000 |
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09463427 |
Mar 29, 2000 |
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PCT/US98/15712 |
Jul 29, 1998 |
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60054342 |
Jul 31, 1997 |
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Current U.S.
Class: |
600/509 |
Current CPC
Class: |
A61B 6/12 20130101; A61B
8/0883 20130101; A61B 5/6857 20130101; A61B 2034/2053 20160201;
A61B 5/6855 20130101; A61B 5/6852 20130101; A61B 17/22012 20130101;
A61B 5/341 20210101; A61B 5/6856 20130101; A61B 6/503 20130101;
A61B 8/0833 20130101; A61B 5/287 20210101 |
Class at
Publication: |
600/509 |
International
Class: |
A61B 005/04 |
Goverment Interests
[0001] This research is supported by the National Institutes of
Health, Grant No. 2 RO1 HL-33343 (Sponsor: NIH-NHLRI).
Claims
What is claimed is:
1. A probe for measuring electrical potentials in a heart cavity,
the probe comprising: a terminal end portion including a plurality
of electrodes, the terminal end portion conformed into a spiral
shape and positioned for non-contact with the endocardial surface,
where the probe is inserted percutaneously.
2. A probe according to claim 1 further comprising means for
conforming the terminal end portion into a spiral shape.
3. A probe according to claim 1, where the terminal end portion
comprises a generally cylindrical shape.
4. A probe according to claim 1, where the spiral shape includes at
least one of: a pigtail shape and a helix.
5. A probe according to claim 1, where the probe provides
electrical potentials for reconstructing endocardial potentials on
the endocardial surface.
6. A probe according to claim 5, where the reconstruction is based
on a beat-by-beat basis.
7. A method for measuring electrical potentials in a heart cavity,
the method comprising: inserting a percutaneous probe into the
heart cavity, the probe including a terminal end portion having a
plurality of electrodes, the terminal end having a spiral shape,
and, positioning the probe for non-contact with the endocardial
surface of the heart, measuring the electrical potentials in the
heart cavity with the probe.
8. A method according to claim 8, further comprising conforming the
terminal end portion into the spiral shape after inserting.
9. A method according to claim 8, further comprising conforming the
terminal end portion into the spiral shape before inserting
10. A method according to claim 8, where the terminal end portion
includes a cross-section that is generally cylindrical.
11. A method according to claim 8, where the spiral shape includes
at least one of: a pigtail shape and a helix.
12. A method according to claim 8, further comprising, based on the
measured electrical potentials and geometry data associated with
the probe and the heart, reconstructing endocardial potentials on
the endocardial surface of the heart.
13. A system for determining electrical potentials on an
endocardial surface of a heart, the system comprising: a
spiral-shaped catheter probe adapted to be positioned for
non-contact with the endocardial surface during measurement in a
cavity of the heart, the terminal end portion having a plurality of
electrodes to measure electrical potentials in the cavity, an
imaging means for capturing geometric data on the probe and the
endocardial surface; processor instructions for determining a
geometric relationship between the probe surface and the
endocardial surface based on the geometric data, and, processor
instructions for determining endocardial potentials based on the
measured electrical potentials and the geometric relationship.
14. A system according to claim 13, where the imaging means
includes at least one of: a CT scan, an MRI, an ultrasound, and an
X-ray.
15. A system according to claim 13, further including processor
instructions for generating at least one of: electrograms and
isochrones.
16. A method to determine electrical potentials throughout an
endocardial surface of a heart, the method comprising: inserting a
spiral-shaped catheter probe into a cavity of the heart, the probe
positioned in a cavity of the heart for non-contact with the
endocardial surface during measurement, the probe having a terminal
end portion having a plurality of electrodes to measure electrical
potentials, measuring electrical potentials at the plurality of
electrodes during a single heart-beat, determining a geometric
relationship between the probe surface and the endocardial surface,
and, determining the endocardial potentials based on the measured
electrical potentials during the single heart-beat and the
geometric relationship.
17. A method according to claim 16, where determining a geometric
relationship includes providing an image of the endocardial surface
and the probe based on at least one of: a CT scan, an MRI, an
X-ray, and an ultrasound.
18. A method according to claim 16, where inserting includes
inserting at least one of: a pigtail-shaped probe and a
helix-shaped probe.
Description
BACKGROUND OF THE INVENTION
[0002] This invention relates to an apparatus and method for
electrophysiological cardiac mapping. More particularly, the
invention is directed to a system based on a nonexpandable,
noncontact, miniature, multielectrode catheter which is used to
measure electrical potentials within a heart cavity. These measured
potentials are then used, along with data on the geometric
relationship between the catheter and the endocardial surface, to
reconstruct maps representing endocardial electrical activity. In
this regard, electrograms and isochrones are reconstructed.
[0003] While the invention is particularly directed to the art of
electrophysiological cardiac mapping, and will be thus described
with specific reference thereto, it will be appreciated that the
invention may have usefulness in other fields and applications.
[0004] By way of background, endocardial potential mapping is a
tool for studying cardiac excitation and repolarization processes.
Mapping endocardial potential distribution and its evolution in
time is useful for analyzing activation and repolarization patterns
and for locating arrhythmogenic sites and regions of abnormal
electrical activity in the heart. Accurate localization of
arrhythmogenic sites is important to the success of
non-pharmacological interventions, such as catheter ablation.
[0005] Unfortunately, current techniques of mapping potentials
directly from the endocardium present certain difficulties. For
example, the well-known "roving" probe approach is 1) limited in
the number of recording sites, 2) too time consuming and 3) only
operative to collect data over a plurality of heart beats, instead
of a single beat. Therefore, this approach is not useful on a
beat-by-beat basis to study dynamic changes in the activation
process.
[0006] In addition, multiple electrode balloons or sponges have
also been used to map electrical activity of the heart by way of
measuring potentials within a heart cavity. Although capable of
mapping the entire endocardium, these devices occlude the heart
cavity and require open heart surgery, heart-lung bypass and other
complicated and high risk procedures.
[0007] Another device having a multiple-spoke, basket-shaped
recording catheter allows simultaneous acquisition of potential
data from multiple electrodes without occluding the cavity.
However, the basket is nonetheless limited in the number of
electrodes so that spatial resolution is relatively low. Moreover,
it is difficult to insure that all electrodes make contact with the
endocardium. Also, the basket can be entangled in intracavitary
structures such as the chordae tendineae. The fact that the basket
must be collapsed prior to catheter withdrawal from the ventricle
adds complexity and risk to this procedure.
[0008] Still another known device for detecting endocardial
potentials uses an electrode array catheter that can be expanded
within the heart chamber but does not occlude the heart chamber.
However, this system still involves undesirable expansion of a
device in the heart chamber. The expanded element may interfere
with intracavity structures and adds complexity to the system
because it must be collapsed before removal. Moreover, it is
difficult to determine the location of the electrodes within the
chamber. Also, the array may not expand as desired, leading to
inaccuracies in mapping.
[0009] Taccardi et al. developed an alternative indirect mapping
approach that makes use of a large (too large for clinical
applications) intracavitary multielectrode catheter-probe (olive
shaped or cylindrical), that can be introduced into the blood
filled cavity without occluding it. The probe permits simultaneous
recording of intracavitary potentials from multiple directions but,
unlike the balloon, is not in direct contact with the endocardium
and does not record actual endocardial potentials. The
intracavitary probe potentials exhibit smoothed-out distributions
and do not reflect details of the excitation (or repolarization)
process that can be detected and located by direct endocardial
recordings. It is highly desirable, therefore, to develop an
approach for reconstructing endocardial potentials, electrograms
and isochrones from data recorded with a small, non-expanding
intracavitary catheter-probe that can be introduced percutaneously,
does not occlude the ventricle, and/or does not require opening
large structures (e.g. basket or balloon) inside the cavity.
[0010] Accordingly, it would be desirable to have available a
multielectrode catheter probe that can be introduced
percutaneously, without expanding inside the ventricular cavity,
and provide accurate reconstructed endocardial potentials,
electrograms and isochrones.
[0011] The present invention contemplates a new and improved system
and method for electrophysiological cardiac mapping using a
non-contact, non-expandable catheter which resolves the above
referenced difficulties and others and attains the above referenced
desired advantages and others.
SUMMARY OF THE INVENTION
[0012] A system for determining electrical potentials on an
endocardial surface of the heart is provided. In one aspect of the
invention, the system contains a noncontact, non-expandable,
miniature catheter probe that is percutaneously positioned inside a
heart cavity. A plurality of electrodes are disposed on an end
portion of the probe whereby electrical potentials within the heart
cavity are measured. Also included is a means for generating a
matrix of coefficients which is then used along with the electrical
catheter potentials to determine endocardial potentials.
[0013] In a further aspect of the invention, the probe assumes a
curved shape inside the cavity.
[0014] In a further aspect of the invention, the system includes
means for generating electrograms and isochrones based on the
determined endocardial potentials.
[0015] In a further aspect of the invention, the curved shape of
the terminal end of the electrode catheter resembles a "J", "U",
"O", helix, pigtail, or any general curved shape.
[0016] In a further aspect of the invention, the system includes a
means for conforming the terminal end portion of the probe to the
first elongated shape and a means for conforming the terminal end
of the end portion of the probe into the second curved shape.
[0017] In a further aspect of the invention, a method for
implementing the system is provided.
[0018] Further scope of the applicability of the present invention
will become apparent from the detailed description provided below.
It should be understood, however, that the detailed description and
specific examples, while indicating preferred embodiments of the
invention, are given by way of illustration only, since various
changes and modifications within the spirit and scope of the
invention will become apparent to those skilled in the art.
DESCRIPTION OF THE DRAWINGS
[0019] The present invention exists in the construction,
arrangement, and combination of various parts of the device and
steps of the methods, whereby the objects contemplated are attained
as hereinafter more fully set forth, specifically pointed out in
the claims, and illustrated in the accompanying drawings in
which:
[0020] FIG. 1(a) is a representative illustration of the system
according to the present invention;
[0021] FIG. 1(b) is an illustration of the catheter according to
the present invention positioned within a heart cavity;
[0022] FIG. 2 is a side view of an end portion of a catheter probe
according to the present invention having a first shape;
[0023] FIG. 3 is a side view of the end portion of the catheter
probe according to the present invention having a second shape;
[0024] FIGS. 4(a)-(e) are side views of the end portion of various
catheter probes according to the present invention having another
second shape;
[0025] FIG. 5(a) is a functional block diagram of the processor
according to the present invention;
[0026] FIG. 5(b) is a flow diagram illustrating a software tool
implemented according to the present invention;
[0027] FIG. 6 is a flow chart showing the method according to the
present invention;
[0028] FIG. 7 is a schematic representing the geometry of a human
ventricular cavity containing a probe;
[0029] FIG. 8 shows selected sites on the endocardial surface for
electrogram display in utilizing the present invention;
[0030] FIG. 9 includes electrograms showing results obtained using
the present invention;
[0031] FIG. 10 includes electrograms showing results obtained using
the present invention;
[0032] FIG. 11 includes electrograms showing results obtained using
the present invention;
[0033] FIG. 12 includes isochrone maps showing results obtained
using the present invention;
[0034] FIG. 13 includes isochrone maps showing results obtained
using the present invention;
[0035] FIG. 14 is an illustration explaining geometric and
rotational errors;
[0036] FIG. 15 includes electrograms showing results obtained using
the present invention;
[0037] FIG. 16 includes isochrone maps showing the effects of probe
rotation of 5/on the present invention;
[0038] FIG. 17 includes isochrone maps showing the effects of probe
rotation of 10/on the present invention;
[0039] FIG. 18 includes isochrone maps showing the effects of probe
rotation of 5/and 10/on the present invention;
[0040] FIG. 19 includes electrograms showing the effects of probe
shift on the present invention;
[0041] FIG. 20 includes isochrone maps showing the effects of probe
shift on the present invention;
[0042] FIG. 21 includes isochrone maps showing the effects of probe
shift on the present invention;
[0043] FIG. 22 includes electrograms showing the +effects of
twisting on the present invention;
[0044] FIG. 23 includes isochrone maps showing the effects of
twisting on the present invention;
[0045] FIG. 24 includes electrograms showing the effects of
catheter probe shape on the present invention;
[0046] FIG. 25 includes isochrone maps showing the effects of
catheter shape on the present invention;
[0047] FIG. 26 includes isochrone maps showing the effects of
catheter shape on the present invention;
[0048] FIG. 27 includes isochrone maps showing the effects of
catheter shape on the present invention;
[0049] FIG. 28 includes isochrone maps showing the effects of
catheter shape on the present invention;
[0050] FIG. 29 includes measured and computed potential maps;
and,
[0051] FIG. 30 includes measured and computed potential maps.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] A mathematical inverse methodology for reconstruction of
endocardial potentials, electrograms and isochrones from
non-contact, intracavitary probe measurements has been developed
and validated. A study in an isolated canine left ventricle (LV)
demonstrated that the inversely computed endocardial potential maps
reconstruct with good accuracy and resolve the major features of
the measured endocardial potential maps, including maxima, minima
and regions of negative and positive potentials. A more recent
systematic evaluation demonstrated that computed temporal
electrograms and isochrones also closely approximate their directly
measured counterparts. The isochronal maps correctly captured the
regions of early and late activation for a single pacing site and
for two simultaneous pacing sites separated by 17 mm. Moreover, the
entire activation sequence was closely approximated, including
regions of nonuniform conduction (e.g. isochrone crowding
indicating slow conduction). The size of the probe, though, was too
large for clinical application.
[0053] The reconstruction methodology can be adapted to the
clinical environment with two additional developments: (1)
reduction in size of the intracavity multielectrode probe; and (2)
noninvasive determination of the geometric relationship between the
probe and the endocardium. A 9-French (3-mm) multielectrode
catheter that can be introduced percutaneously has been developed.
The present invention demonstrates that endocardial potentials can
be reconstructed from a 3-mm cylindrical probe with accuracy.
[0054] In the experiments (the results of which are outlined herein
with reference to FIGS. 8-30), the geometry of the endocardium was
determined invasively after completion of the potential
measurements. The ability to measure the geometry directly improved
accuracy. However, the fact that the geometry was not obtained at
the time of potential measurements introduced an error, since
myocardial changes upon termination of perfusion changed somewhat
the positions of the intramural needles. Moreover, all computations
assumed a single cavity geometry (end-diastolic volume) throughout
the experiment, whereas the degree of blood filling varied between
pacing protocols and between time frames during a given protocol.
The probe positions/orientation within the cavity was estimated
using an automated optimization procedure and was subject to error
as well.
[0055] Nonetheless, the experiments confirm that, in spite of
geometry errors, electrograms and isochrones can be reconstructed
over the entire endocardium with good accuracy. This property is
useful in terms of clinical application of the approach.
[0056] As will be described below, existing noninvasive imaging
techniques, such as ultrasound, can provide the endocardial
geometry and probe position simultaneously and at the time of
potential measurements. This constitutes an improvement over the
method used in the experiments. The geometric robustness of the
reconstruction procedure implies that it could be combined with a
noninvasive imaging modality (high accuracy can be achieved with
transesophageal echocardiography for example) to reconstruct
endocardial potentials, electrograms, and isochrones on a
beat-by-beat basis in the clinical catheterization laboratory.
[0057] Referring now to the drawings wherein the showings are for
purposes of illustrating the preferred embodiments of the invention
only and not for purposes of limiting same, FIG. 1(a) provides a
view of the overall preferred embodiment. As shown, the system 10
includes a catheter probe 12--which is positioned in a cavity of
the heart H by well known methods--a processor (or computer) 14, an
imaging (or geometry determining) device 16, an output device 18
(which may take the form of a display (as shown), or a printer or
other suitable output device), and a mechanism 20 for steering and
manipulating an end portion of catheter probe 12. FIG. 1(b) shows
the catheter 12 (shown in an exemplary curved shape) positioned in
the heart H.
[0058] The end portion 30 of catheter probe 12, as shown in FIG. 2,
is generally cylindrical in cross section and has disposed thereon
a plurality of electrodes, exemplary shown at 32. It should be
noted that herein, like numerals in the drawings indicate like
elements. Preferably, the catheter probe is a 9-French (9 F), 3.0
mm catheter; however, any usable style and size will suffice. For
clinical applications, of course, the catheter is preferably of a
size to facilitate percutaneous introduction into the cavity. The
number of electrodes may vary depending on the needs of the
particular application. Of course, varying the number of electrodes
consequently impacts the results obtained using the invention, as
will be more particularly described hereinafter.
[0059] As illustrated in FIG. 3, the end portion of the catheter
probe 12 may be conformed to a curved shape of FIG. 3 once
positioned in the heart cavity. As shown, the exemplary shape is
that of a "J". It should be emphasized that the label "J" (and
other similar labels) refers to the end portion of the catheter
that has electrodes disposed thereon, not the entire catheter. The
end portion is conformed to this shape by known methods and the
mechanism 20 represented generally in FIG. 1, as those skilled in
the art will appreciate.
[0060] Of course, the precise shape of the end portion 30 of the
catheter probe 12 may be varied to suit a particular application of
the catheter probe. For example, the end may be conformed to a "U,"
"O", pigtail, helix or any known curve. As is shown in FIG. 4(a),
the exemplary "U" shaped catheter end portion shape is shown
whereby the end portion is further manipulated from the J-shape to
resemble a "U". The angle of curvature is preferably the same as
that of the J-shaped configuration but it is recognized that the
angle of curvature may be varied without affecting the scope of the
invention. FIGS. 4(b)-(e) show curved catheters having end portions
conformed to an "O", a pigtail, a helix, and a general
representative curve, respectively. It should be appreciated that
varying the shape of the end portion of the catheter probe impacts
the results obtained using the invention, as will be more
particularly described hereinafter but, importantly, the invention
and resultant test data indicate that a noncontact, nonexpandable,
miniature multielectrode catheter probe of any shape or
configuration (including straight) is useful for cardiac
mapping.
[0061] Referring now to FIG. 5(a), functional blocks of the
processor 14 are described. Those skilled in the art will
appreciate that the processor 14 actually includes suitable
software and hardware (including, for example, memories) that
accomplish the functions described. In one embodiment, the software
tool implemented takes the general form of that described in
connection with FIG. 5(b), although neither the processor nor the
tool is so limited. For example, it should be recognized that the
software tool of FIG. 5(b) has features involving testing and
validation which are not specifically described in connection with
FIG. 5(a) but would be apparent to those of skill in the art.
[0062] Specifically, as shown in FIG. 5(a), data on geometry of the
endocardium and probe are input to the processor 14 from the
imaging device 16. Such data may be generated using existing
imaging modalities such as x-ray, ultrasound, computed tomography
(CT), magnetic resonance imaging (MRI), . . . etc. Preferably, the
invention is implemented using bi-plane x-ray techniques enhanced
with fluoroscopy. These techniques result in determination of a
geometric envelope that approximates the heart chamber.
[0063] As is shown in FIG. 5(a), at least one of these known
imaging routines is available to provide data to determine a
geometric relationship of the endocardial surface (or envelope) and
probe surface (block 141) based on the input of the imaging device
16. A matrix of coefficients A, described in more detail below, is
also generated (block 142) in the processor. In addition, data,
i.e. electrical potentials measured in the heart cavity, is input
to the processor from the probe 12. These data are stored in the
processor (block 143). Endocardial potentials may then be
determined by the processor based on the stored electrical
potentials and the matrix of coefficients (block 144). Electrograms
and isochrone maps are also generated for display and evaluation
(block 145). The results, of course, may be output.
[0064] As noted above, the software tool may take the general form
of the flow diagram illustrated in FIG. 5(b), but those skilled in
the art will appreciate that such a program, which (as will be
described) also accommodates testing and validation processes, may
well be modified and/or evolve into a modified tool (to resemble,
for example, only the features described in connection with FIG.
5(a)) as the present invention is modified as a result of
additional development or needs of users. Those skilled in the art
will also appreciate that the description of this software tool
necessarily overlaps with the description in connection with FIG.
5(a) because the processor of FIG. 5(a) implements such software
tools in the described embodiment.
[0065] As shown, information is input to the system (step 500).
Specifically, parameters are input to the system by the user (step
502). Geometry data and potential data are also input (steps 504,
506). It should be recognized that in a clinical setting, the
geometry data is generated by imaging device 16 and potential data
is generated by catheter probe 12; however, if the software tool is
T implemented for testing and validation purposes, the geometry
data may be known parameters, such as those associated with
geometric spheres and torso tanks (used in testing), that are
simply input to the system. The overall control program is
implemented (step 508) and it is determined whether to use the
software tool for testing and validation (using sphere or torso
tank data (steps 510, 512)) or clinical application (using clinical
data (step 514)). Appropriate processing is then conducted on the
data (steps 516, 518 or 520), as will be apparent to those skilled
in the art, to prepare the data for necessary mathematical
manipulation.
[0066] Next, a boundary element method (further described below) is
applied (step 522). At that time, forward (step 524) or inverse
(step 526) computations, as necessary, are performed. Of course,
for clinical applications, only inverse computations (as described
below) are used. Once the data is computed, processing of the data
for output is accomplished (step 528).
[0067] Referring now to FIG. 6, the overall method 600 by which
endocardial potentials (and electrograms and isochrones) may be
determined according to the present invention is described.
Initially, a probe 12 is percutaneously positioned in the cavity of
a heart by known methods (step 602). If desired, the end portion of
the probe is then conformed, utilizing mechanism 20, to a curved
shape such as those shown in FIGS. 3 and 4(a)-(e) (step 604). It is
recognized that conforming the end portion may not be necessary if
the results obtained by using the straight catheter (of FIG. 2, for
example) are acceptable. Potentials are then measured in the cavity
(step 606) and stored (step 608).
[0068] A geometric relationship between the probe surface and the
endocardial surface (or envelope) is also determined (step 610).
The geometry is, of course, determined using the imaging device 16.
Based on this data on the geometric relationship, a matrix of
coefficients A is generated. (step 612).
[0069] Next, endocardial potentials are determined based on the
stored potentials and the matrix of coefficients (step 614).
Electrograms and isochrones are then generated by the processor
(steps 616 and 618) and displayed (step 620). The procedure is then
ended (step 622).
[0070] The mathematical computations accomplished by the processor
14 involved in implementing the present invention described above
relate to and should be analyzed by considering "forward"
computations, i.e. calculating catheter probe potentials from known
endocardial surface potentials, and "inverse" computations, i.e.
calculating endocardial surface potentials based on measured probe
potentials. Of course, the inverse computation is the computation
that is used for implementation of the present invention (e.g. step
614 in FIG. 6), but understanding the forward computation is also
useful.
[0071] While various forward and inverse computations are known,
the computations involved in connection with the present invention
are as follows. More particularly, computation of probe potentials
based on measured endocardial potentials (the "Forward Problem")
requires solving Laplace's equation in the cavity volume (.OMEGA.)
bounded by the probe surface (S.sub.P) and the endocardial surface
(S.sub.e), as illustrated in FIG. 7.
[0072] Below is a description of the mathematical formulation.
Further details can be found in previous publications such as
Khoury D S, B. Taccardi, Lux R L, Ershler P R, Rudy Y,
"Reconstruction of endocardial potentials and activation sequences
from intracavitary probe measurements" Circulation, 91:845-863
(1995); Rudy Y, Messinger-Rapport B J, "The inverse problem in
electrocardiography solutions in terms of epicardial potentials,"
CRC Crit Rev Biomed Eng., 16:215-268 (1988); Rudy Y, Oster H S,
"The electrocardiographic inverse problem," CRC Crit Rev Biomed
Eng., 20:25-46 (1992), Messinger Rapport B J, Rudy Y,
"Computational issues of importance to the inverse recovery of
epicardial potentials in a realistic heart-torso geometry," Math
Biosci, 97:85-120 (1989) (published erratum in Math Biosci,
99(1):141 (1990 April)).; Oster H S, Rudy Y, "The use of temporal
information in the regularization of the inverse problem of a
electrocardiography," IEEE Trans Biomed Ena., 39:65-75 (1992); and
Messinger Rapport B J, Rudy Y, "Regularization of the inverse
problem in electrocardiography. A model study," Math Biosci,
89:79-118 (1988), all of which are hereby incorporated herein by
this reference.
[0073] The behavior of potential, V, within .OMEGA. is governed by
Laplace's equation:
.gradient..sup.2V=0 in .OMEGA. (1)
[0074] subject to the boundary conditions: 1 V = V e on a subset of
S p ( 2 ) .differential.V/.differential.n=0on S.sub.p (3)
[0075] where V.sub.p is the potential on the probe surface;
.differential.V/.differential.n=0 implies that current cannot enter
the nonconducting probe. A well-known Boundary Element Method (BEM)
(See, for example, Brebbia C A, Dominguez J, Boundary elements: An
Introductory Course, McGraw-Hill Book Co., New York (1989) or
Brebbia et al., Boundary Element Techniques. Theory and
Applications in Engineering, Springer Verlag, Berlin (1984)) is
used to numerically solve for the potentials in a realistic
geometry cavity-probe system. This results in the following
equation that relates the probe potentials to the endocardial
potentials:
V.sub.P=A .multidot.V.sub.e (4)
[0076] where VP is a vector of probe potentials of order N.sub.p
(probe surface nodes), V.sub.e is a vector of endocardial
potentials of order N.sub.e (endocardial surface nodes), and A is
an N.sub.p.times.N.sub.e matrix of influence coefficients
determined by the geometric relationship between the probe surface
and the endocardial surface. The intracavitary probe potentials can
be calculated from the endocardial potentials using equation (4).
Since the forward computation is a stable and accurate process, the
computed probe potentials provide an accurate estimate of cavity
potentials measured by an actual probe of the same design and in
the same intracavitary position. This calculation is useful to
verify data that are obtained using the inverse computation.
[0077] The matrix A in equation (4) is determined by the
geometrical relationship between the endocardial surface and the
probe surface. Specifically, it requires specification of node
positions (corresponding to electrode positions) on the probe and
node positions on the endocardium. Geometry data, as noted above,
is obtained from the imaging device 16 which, again, may involve
any of the known imaging modalities. Errors in determining the node
positions on these two surfaces, especially probe electrodes, may
be amplified due to the nature of the inverse procedure and might
consequently introduce errors in the reconstructed endocardial
potentials. Accordingly, accurate T determination of geometry is
important for implementation.
[0078] In order to compute endocardial electrograms and isochrones,
endocardial potential maps are first computed in a quasi-static
fashion for every millisecond throughout the endocardial activation
process. Computing endocardial potentials is the first step in
computing temporal electrograms and isochrones. To compute
endocardial potentials from probe potentials, the relationship
between V.sub.e and V.sub.P established in equation (4) must be
inverted. However, because of the ill-posed nature of the problem
(as described in Rudy Y, Messinger-Rapport B J, "The inverse
problem in electrocardiography: solutions in terms of epicardial
potentials," CRC Crit Rev Biomed Eng., 16:215-268 (1988)), one
cannot simply invert matrix A to obtain the endocardial potentials
(V.sub.e) from probe potentials (V.sub.P). A Tikhonov
regularization technique is used to stabilize the procedure (See,
for example, Tikhonov A N, Arsenin V Y, "Solution of Ill-Posed
Problems," 27-94, V H Winston & Sons, Washington, D.C. (1977),
or Tikhonov et al., "Solutions of ill-posed problems," (trans. from
Russian) Wiley, NY (1977), which are incorporated herein by
reference), and the solution for endocardial potentials is obtained
by minimizing the objective function: 2 min v e [ ; V p - A V e r;
2 + t ; V e r; 2 ( 5 )
[0079] or, more generally, minimizing
.vertline..vertline.V.sub.p-A.multidot.V.sub.e.vertline..vertline..sup.2+t-
F[V.sub.e]
[0080] where t is a regularization parameter, whose optimal value
was determined using the CRESO (composite residual and smoothing
operator) method (See, Colli-Franzone P, Guerri L, Taccardi B.
Viganotti C, "Finite element approximation of regularized solutions
of the inverse potential problem of electrocardiography and t
applications to experimental data" Calcolo 1985, 22:91-186, and
Colli-Franzone et al., "Mathematical procedure for solving the
inverse problem of electrocardiography," Math Biosci, 77:353-96
(1985), which are incorporated herein by reference).
[0081] The approach to verifying the accuracy of the data obtained
is based on a combination of experimentally measured endocardial
potentials and simulated catheter probes in an isolated LV
preparation. The simulated catheter data is used to reconstruct
endocardial electrograms and isochrones, which are then evaluated
by direct comparison with their measured counterparts.
[0082] In contrast to potentials, electrograms and isochrones
provide complete spatio-temporal information for the entire
activation cycle. Endocardial electrograms provide temporal
information on activation in localized areas and are widely used in
clinical practice. Isochrones provide extensive spatio-temporal
information about the entire activation sequence that can be seen
in one glance. Isochronal maps also can identify spatial
nonuniformities of propagation such as regions of slow conduction
or areas of conduction block that are important mechanistic
properties of arrhythmogenic activity. Therefore, it is useful to
evaluate the accuracy with which electrograms and isochrones can be
reconstructed from the noncontact catheter. Single-site pacing
protocols as well as simultaneous dual-site pacing were employed.
Because electrograms and isochronal maps contain temporal
information from the entire cardiac cycle, their accurate
reconstruction places more demanding design criteria on the
catheter probe. The results below demonstrate that, as in the case
of potential reconstruction, endocardial electrograms and
isochrones can be accurately reconstructed from a noncontact,
nonexpandable, miniature multielectrode 9 F catheter that may, if
desired, assume a curved geometry inside the cavity, without the
need for expansion. The catheter need not be curved to work
effectively. Curvature simply enhances the results, as will be
demonstrated. The reconstruction is robust in the presence of
errors, indicating feasibility of the approach in the clinical
environment of the electrophysiology (EP) catheterization
laboratory.
[0083] To obtain an accurate estimate of probe potentials, the
forward computation of probe potentials from the measured
endocardial potentials was performed with a very large number of
electrodes (nodes) on the probe surface. In the simulation, probes
with 722 electrodes (30 circumferential rows.times.24
electrodes/row+two end electrodes) were used. This is several times
greater than the actual number of electrodes on the probe used in
the experiments. As confirmed by spherical model simulations, such
a large number of electrodes (nodes) results in very accurate probe
potentials. To study the effect of limited electrode density on the
reconstruction, different subsets of electrodes (nodes) were
selected on the surface of the simulated probe. The uniform spatial
distribution of electrodes over the probe surface was preserved.
The selected subset of probe potentials was then used in the
inverse reconstruction of endocardial potentials. This process was
performed for probes of different sizes and shapes.
[0084] The reconstruction of endocardial potential maps is
performed in a quasi-static approach throughout the cardiac cycle,
i.e., at a given time instant, the endocardial map is computed from
the probe potentials recorded at the same time. Once all
endocardial potential maps are reconstructed, the data are
reorganized according to electrode (node) and temporal electrograms
depicting potential vs. time can be reconstructed for any position
on the endocardial surface. In this study, endocardial potentials
and electrograms were computed for 50 positions, where the tip
electrodes of endocardial recording needles were located, allowing
a direct comparison of the computed electrograms with the actual
measured electrograms.
[0085] Endocardial isochrones, depicting the activation sequence of
the endocardial surface, were constructed from the computed
endocardial electrograms. The time derivatives, dV/dt, of the
inversely reconstructed endocardial electrograms were computed, and
the time instant associated with the maximum negative dV/dt
("intrinsic deflection") at a particular site was taken as the
activation time of that site.
[0086] Over the entire endocardial surface, 50 electrograms were
computed. Electrograms at 5 selected sites are shown in the
results. FIG. 8 shows the positions of these selected (numbered)
sites. For both single and dual pacing cases, site 1 was chosen to
be the earliest (one of the earliest, in the dual pacing case)
measured endocardial activation site, while sites 2 to 4 are
activated progressively later in time. Site 5 corresponds to a site
that is remote from the center of the cavity and therefore far away
from the catheter probe. The asterisks correspond to pacing
sites.
[0087] In the following description of experimental results, three
representative simulated catheter probes are compared in terms of
accuracy of T reconstructed endocardial electrograms and
isochrones. The probes are: a cylindrical 7.6 mm diameter probe
(generally too large for percutaneous application), a cylindrical
3.0 mm diameter probe (equivalent to a 9 F catheter that can be
introduced percutaneously), and a 3.0 mm diameter probe bent in the
cavity into a J-shape (close to the natural shape assumed by a
catheter in the cavity). Results with simulated probes larger than
the 7.6 mm cylindrical probe are very similar to those of the 7.6
mm probe. Initial results for a simulated U-shaped catheter probe
are also shown to demonstrate the effects of different curved
catheter shapes on the reconstructions.
[0088] It should also be recognized that potential maps may also be
generated using the system and method of the present invention. For
example, FIG. 29 shows measured and computed potentials for a
single pacing site using 122 and 62 electrodes, respectively, for
the noted catheters. FIG. 30 shows similar data for dual pacing
sites.
[0089] FIG. 9 shows the reconstruction of endocardial electrograms
from different probes containing 122 electrodes. The activation
sequence is initiated by pacing from a single site. Measured
endocardial electrograms at 5 selected sites are shown at the top,
reconstructed electrograms at corresponding sites are shown at the
bottom. The correlation coefficients (CC) between the measured and
computed electrograms are printed next to each computed
electrogram. Over the entire endocardium, computed electrograms at
50 endocardial sites resemble the measured electrograms very well.
CC values at all sites are near 1.0.
[0090] FIG. 10 shows reconstruction of endocardial electrograms
from the probes using a subset of 62 electrodes. The cylindrical
7.6 mm probe performs almost as accurately as with 122 electrodes,
except for the distant site (site 5). The cylindrical 3.0 mm and
curved probes reconstruct 96% of the electrograms with CC greater
than 0.90. There are discontinuities ("jagged" appearance or
spikes) in some of the computed electrograms, which do not exist in
the measured ones. Although the discontinuities cause deterioration
of the appearance of the electrograms, the general shapes of the
electrograms are preserved. Electrogram at the distant site (site
5) reconstructed from the curved probe resembles the measured
electrogram in terms of shape and amplitude. The computed
electrograms at a few nodes contain large spikes in certain time
frames, the computed electrograms resemble the measured ones very
well except during the spikes. The spike can be removed by data
interpolation.
[0091] FIG. 11 shows endocardial electrograms reconstructed from
the probes with 62 electrodes for a dual-site pacing protocol. The
overall performance of the J-probe is most acceptable, with high
CC. The distant node electrogram (site 5) is also reconstructed
with very high accuracy.
[0092] Endocardial isochrones were constructed from both measured
and inversely reconstructed endocardial electrograms. FIG. 12 shows
the isochrones computed from the reconstructed electrograms of FIG.
9 and FIG. 10. The measured isochrone map is shown in the top panel
and the computed isochrone maps in the bottom panels. The position
of the earliest activation time in the measured isochrone map is
located at the pacing site, indicated by an asterisk (*). The map
shows that activation starts at the postero-lateral region and
progresses to the anteroseptal region towards the base of the LV.
The regions of both earliest activation and latest activation in
the measured isochrone map are accurately reconstructed in the
computed isochrone map by the 7.6 mm cylindrical and curved
catheter with either 122 or 62 electrodes. In contrast, the
reconstructed isochrones using the 3.0 mm cylindrical probe with 62
electrodes (second row) exhibit distortion of the earliest
activation region, and the latest region (red) divides into two
regions. The intermediate isochrones between the earliest and
latest activation times in the computed isochrone map closely
resemble the measured isochrones for all three probes. The
reconstructed earliest activation time (17 ms) is accurate. The
latest time of activation reconstructed by the curved catheter with
62 electrodes is 60 ms as compared to the measured value of 63
ms.
[0093] FIG. 13 shows the activation sequences (isochrones)
initiated by the dual-pacing protocol of FIG. 11. The measured
isochrone maps (FIG. 13 top panel) depict two distinct earliest
activation regions at the vicinity of the two pacing sites. The
earliest activation times determined from the measured electrograms
are 18 ms for the two posterior pacing sites. The latest activation
region is at the anteroseptal region close to the base of the LV,
with activation time of 55 ms. In the isochrone maps computed from
the curved catheter with 122 or 62 electrodes (bottom row), the two
distinct earliest activation regions are correctly reconstructed.
The earliest activation times in the computed isochrone maps are
exactly 18 ms. The region of latest activation in the computed
isochrone map is located at the anteroseptal region near the base
of the LV, in good agreement with its actual location in the
measured isochrone map. In contrast, only one of the T two early
activation sites is present in the reconstructed isochrones
obtained from the 7.6 mm and 3.0 mm cylindrical probes.
[0094] Geometrical errors can occur in determining the probe
position inside the ventricular cavity. The two most probable
errors are shifts and rotations of the probe as a rigid object. For
the curved probe, twisting, i.e. rotation about the probe's own
axis is also possible. These geometrical errors are illustrated in
FIG. 14.
[0095] The effects of a 5-degree rotation error on electrogram
reconstruction are shown in FIG. 15. All probes used are with 62
electrodes. For the 7.6 mm cylindrical probe, 88% of all the
electrograms are reconstructed with CC greater than 0.95. The 3.0
mm cylindrical probe reconstructs 92% of the electrograms with CC
greater than 0.95. Of the J-probe reconstructed electrograms, 90%
have CC greater than 0.95. It should be noticed that a uniform
degree of angular rotation actually results in different position
errors for electrodes on the different probes. The 3.0 mm
cylindrical probe experiences the smallest distance change, while
electrodes on the J-probe "arm" experience the largest position
error. This explains why the accuracy of J-probe reconstructions is
sensitive to this type of error. In contrast, the 3.0 mm
cylindrical probe tolerates the rotational error better than other
disturbances.
[0096] FIG. 16 shows the isochrones computed from the electrograms
of FIG. 15, which demonstrates the effects of a 5-degree angular
rotation. FIG. 17 shows the results for 10-degree rotation. Despite
the fact that the rotated J-probe has experienced a distance
change, it still recovers acceptable activation regions. In the
left column of FIG. 17, the J-probe and the 3.0 mm cylindrical
probe recover the earliest activation region while the 7.6 mm
cylindrical probe does not. In the right column, the J-probe
recovers the earliest and latest activation regions with the least
pattern deformation compared to the other probes. FIG. 18 shows the
effects of probe rotation on a dual-pacing protocol. The 7.6 mm
cylindrical probe recovers only one of the two pacing sites; the
3.0 mm cylindrical probe also reconstructs only one (the same)
pacing site with greater smoothing. The J-probe identifies the two
simultaneous pacing sites with high correlation coefficients of
0.88 for 5 degree rotation and 0.92 for 10 degree rotation.
[0097] It has been determined that reconstruction quality under the
disturbance of rotation is related to the probe position inside the
cavity, more specifically, the position of the J-probe relative to
the characteristic sites (pacing site, earliest or latest
activation region) influences the reconstruction quality. One
possible approach is to simply rotate the same catheter probe in
the cavity and record the potentials during two beats, with
different rotational positions. Another solution is to introduce a
second catheter probe into the cavity with an angle between the two
probes, to provide data from two orientations during a single beat.
Also as will be shown later, increasing the arm length of the
J-probe to form a U-probe helps improve the accuracy of the
reconstruction.
[0098] The effects of a shift in probe position on electrogram
reconstruction are shown in FIG. 19. Overall, 68% of the recovered
electrograms have correlation coefficients higher than 0.90. The
3.0 mm J-probe gives accurately reconstructed electrograms of the
early activation sites (column 1, 2, 3) and of the distant node
(column 5). However, it fails to accurately recover the latest
activation site (column 4), the electrogram is severely
distorted.
[0099] This is also reflected in the isochronal map of FIG. 20 left
column, which is computed from the electrograms of FIG. 19 (2 mm
shift). The early activation region is recovered with high accuracy
by the 7.6 mm probe and the J-probe. The 3.0 mm cylindrical probe
reconstructs the earliest activations site, which has shifted in
the lower right direction. The cylindrical probes perform better
than the J-probe in the latest activation region. 3 mm shift has
the same effects on isochrone reconstruction as shown in FIG. 20,
right column. FIG. 21 shows the same simulation for a dual pacing
protocol. For 2 mm shift error, the 7.6 mm cylindrical probe
reconstructs the earliest region with some distortion. The 3.0 mm
cylindrical probe-only recovers one of the two pacing sites. The
J-probe reconstructs the two earliest activation sites, also with
some deformation of patterns in this region. Even for 3 mm shift
error, the two earliest activation regions can be distinguished by
the J-probe.
[0100] It has been determined that the tolerance of the
reconstruction to probe shift errors is also related to the
position of the probe inside the cavity. If a certain region of the
endocardial surface is close to some probe electrodes, the region
tolerates better positional errors. The reconstruction quality
under the effects of shifting errors can also be improved by using
similar approaches as those suggested in the context of the
rotation errors.
[0101] FIG. 22 shows the electrograms reconstructed from a J-probe
with 5 degrees, 10 degrees and 15 degrees twist errors, and FIG. 23
shows the corresponding isochrones. Electrograms display
significant morphological distortions in most of the nodes. For 5
and 10 degrees twist, even with major morphological changes in the
electrograms, the isochrones still recover the earliest activation
region and the latest activation region (although the latter is
smoothed out). Under 15 degrees twist, the latest activation region
is completely smoothed out. For the dual-pacing protocol, the
J-probe with 5 degrees twist can still identify the two earliest
activation sites accurately. Under higher twist error, the two
pacing sites merge together and can not be separated.
[0102] The J-probe used in this simulation study is characterized
by a relatively short arm, as shown in FIG. 3. It serves to
represent a large variety of curved catheter probes with either
different curvature or other shapes, such as "U", or "O", or any
curved shape. In order to evaluate the effects of different
catheter shapes on the reconstruction quality, simulations for a
U-shaped catheter probe (FIG. 4) have also been conducted. FIG. 24
shows the electrograms reconstructed from the 3.0 mm probe, the
J-probe and a 3.0 mm U-probe also with 62 electrodes. The U-probe
has the same curvature as the J-probe. Note that the computed
electrograms from the 3.0 mm cylindrical and J-probe are the same
as shown in FIG. 10. From the cylindrical probe to the U-probe, the
accuracy of the reconstruction progressively improves with the
length of the "arm". The U-probe reconstructs the electrograms with
very high accuracy, without any discontinuities or spikes. FIG. 25
left column shows the isochrones computed from the electrograms of
FIG. 24. The improvement in the latest activation region of the
isochrones reconstructed by the U-probe is evident. The right
column of FIG. 25 shows the reconstructed isochrones from the three
catheter probes with only 42 electrodes. The 3.0 mm cylindrical and
J-shaped probes fail to recover the earliest activation region,
however, the U-probe still accurately reconstructs both the
earliest and latest activation regions. Reconstructed isochrones
for the dual pacing protocol from the catheter probes are shown in
FIG. 26. Only the U-probe, with either 62 or 42 electrodes,
recovers the two distinct earliest activation regions accurately.
FIG. 27 shows the reconstructed isochrones from the catheters under
5-degree rotation error. The performance of the U-probe is
comparable or relatively better than the J-probe. Similarly, FIG.
28 shows the reconstructed isochrones from the catheters under 2 mm
shift error. In the single pacing case (left column), the U-probe
is the only one that recovers both the earliest and latest
activation regions.
[0103] The results from the present study indicate that a
noncontact, nonexpandable, miniature multielectrode catheter is
useful for cardiac mapping. Although curving the catheter is not
necessary to obtain relatively accurate results, such curving
results in improved results in many respects. As is apparent from
the above data, although a large number of electrodes is desirable
when we consider the quality of the inverse reconstruction, it may
raise other issues in design and manufacturing of the probe and the
data acquisition system. Thus, for a J-probe, 60 probe electrodes
or more is desirable because it reconstructed the endocardial
electrograms and isochrones with good accuracy. However, the
U-probe was found to tolerate reduced electrode number down to 42
very well.
[0104] The above description merely provides a disclosure of
particular embodiments of the invention and is not intended for the
purpose for limiting the same thereto. As such, the invention is
not limited to only the above described embodiments. Rather, it is
recognized that one skilled in the art could conceive alternative
embodiments that fall within the scope of the invention.
* * * * *