U.S. patent application number 12/418601 was filed with the patent office on 2009-08-13 for high density atrial fibrillatrion cycle length (afcl) detection and mapping system.
This patent application is currently assigned to C.R. Bard Inc.. Invention is credited to Tim Collins, Remi Dubois, Sylvain Fanier, Ding S. He, David P. MacAdam, Minoru Mashimo.
Application Number | 20090204113 12/418601 |
Document ID | / |
Family ID | 35450614 |
Filed Date | 2009-08-13 |
United States Patent
Application |
20090204113 |
Kind Code |
A1 |
MacAdam; David P. ; et
al. |
August 13, 2009 |
High Density Atrial Fibrillatrion Cycle Length (AFCL) Detection and
Mapping System
Abstract
Systems and methods to assist in locating the focus of an atrial
fibrillation include the association of atrial fibrillation cycle
length values and statistics relating thereto with temporal
locations on an electrogram of a given electrode, and/or the
coordination of electrode locations with respective the spectral
analyses of electrogram signals and further parameters and
statistics relating thereto. Ablation therapy can proceed under
guidance of such information.
Inventors: |
MacAdam; David P.;
(Millbury, MA) ; Mashimo; Minoru; (Windham,
NH) ; Fanier; Sylvain; (La Celle, FR) ;
Collins; Tim; (West Newbury, MA) ; He; Ding S.;
(Tyngsboro, MA) ; Dubois; Remi; (Paris,
FR) |
Correspondence
Address: |
Leason Ellis LLP
81 Main Street, Suite 503
White Plains
NY
10601
US
|
Assignee: |
C.R. Bard Inc.
Murray Hill
NJ
|
Family ID: |
35450614 |
Appl. No.: |
12/418601 |
Filed: |
April 5, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11120633 |
May 2, 2005 |
|
|
|
12418601 |
|
|
|
|
60572281 |
May 17, 2004 |
|
|
|
Current U.S.
Class: |
606/41 ;
600/509 |
Current CPC
Class: |
A61B 5/361 20210101;
A61B 2018/00642 20130101; A61B 2018/00351 20130101; A61B 18/1492
20130101; A61B 5/7257 20130101; A61B 5/287 20210101; A61B
2018/00577 20130101; A61B 5/316 20210101; A61B 18/14 20130101; A61B
2018/00839 20130101 |
Class at
Publication: |
606/41 ;
600/509 |
International
Class: |
A61B 18/14 20060101
A61B018/14; A61B 5/0408 20060101 A61B005/0408 |
Claims
1-26. (canceled)
27. An ablation and mapping procedure, comprising the steps of:
percutaneously advancing a catheter into at least one heart
chamber, the catheter having multiple electrodes supported along a
distal portion thereof; associating in a memory of a machine one or
more locations of the electrodes within the at least one heart
chamber; capturing electrocardiogram signals associated with at
least one electrode of the catheter at one or more of the locations
for at least a prescribed time period; for at least a portion of
the captured electrocardiogram signals over at least the prescribed
time period, transforming the electrogram signals into a frequency
domain representation; coordinating the frequency domain
representation with respective locations of the multiple electrodes
to define a set of data points; outputting a depiction of a heart
on a display; and outputting the data points in the depiction of
the heart.
28. A system for performing diagnostics on electrocardiogram data
along a distal portion thereof captured by a catheter that supports
plural electrodes, comprising: a monitor operative to display
electrophysiology data; an input configured to accept a time-domain
representation of one or more electrocardiogram (EGM) signals
obtained by the electrodes at respective different locations within
the heart; a processor connected to receive the signals from the
input over a time interval; software executable by the processor
and configured to (i) transform the time-domain EGM signals into a
frequency domain representation over at least a portion of the time
interval, (ii) identify said respective different locations of each
electrode within the heart, (iii) cause a depiction of a heart to
be displayed on the monitor, and (iv) include information related
to the frequency domain representation in the depiction of the
heart in association with said respective different locations of
the electrodes at which each EGM signal was obtained.
29. The system of claim 28, wherein the information related to the
frequency domain representation is a FFT of at least one of the one
or more EGMs.
30. The system of claim 29, wherein the software is further
configured to arrange the FFT for display on the monitor as a plot
of frequency versus magnitude.
31. The system of claim 28, wherein the software applies a Welch
algorithm to the EGMs to obtain the information related to the
frequency domain representation.
32. The system of claim 28, further comprising an interface
suitable for providing parameters used by the software in
transforming the time-domain EGM signals.
33. The system of claim 32, wherein the interface includes controls
selectable by a user to invoke pre-transformation processing of the
time-domain EGM signals.
34. The system of claim 33, wherein one of the controls of the
interface comprises a digital filter adapted to filter the EGM data
prior to FFT computation.
35. The system of claim 33, wherein one of the controls of the
interface comprises a non-linear function that operates upon the
time-domain EGM signals.
36. The system of claim 28, wherein the information related to the
frequency domain representation is a numeric frequency value
representative of a dominant frequency in the frequency domain
representation.
37. The system of claim 28, wherein the information related to the
frequency domain representation comprises both a FFT of at least
one of the one or more EGMs and a numeric frequency value
representative of a dominant frequency in the frequency domain
representation.
38. The system of claim 28, wherein the at least a portion of the
time interval is no less than about 4 seconds.
39. The system of claim 28, wherein the at least a portion of the
time interval is between about 4 seconds and 10 seconds.
40. The system of claim 28, wherein the software is further
configured to identify said respective different locations and to
simultaneously display on the monitor the information related to
the frequency domain representation in association with plural ones
of said identified locations.
41. The system of claim 40, wherein the information related to the
frequency domain representation is a FFT of at least one of the one
or more EGMs.
42. The system of claim 40, wherein the information related to the
frequency domain representation is a numeric frequency value
representative of a dominant frequency in the frequency domain
representation.
43. The system of claim 40, wherein the information related to the
frequency domain representation comprises both a FFT of at least
one of the one or more EGMs and a numeric frequency value
representative of a dominant frequency in the frequency domain
representation.
44. The system of claim 40, wherein the software is further
configured to arrange the FFT for display on the monitor as a plot
of frequency versus magnitude.
45. The system of claim 40, wherein the software applies a Welch
algorithm to the EGMs to obtain the information related to the
frequency domain representation.
46. The system of claim 40, further comprising an interface
suitable for providing parameters used by the software in
transforming the time-domain EGM signals.
47. The system of claim 46, wherein the interface includes controls
selectable by a user to invoke pre-transformation processing of the
time-domain EGM signals.
48. The system of claim 47, wherein one of the controls of the
interface comprises a digital filter adapted to filter the EGM data
prior to FFT computation.
49. The system of claim 47, wherein one of the controls of the
interface comprises a non-linear function that operates upon the
time-domain EGM signals.
50. The system of claim 40, wherein the at least a portion of the
time interval is no less than about 4 seconds.
51. The system of claim 40, wherein the at least a portion of the
time interval is between about 4 seconds and about 10 seconds.
52. The system of claim 28, wherein the software is further
configured to include visual representations of each electrode in
the depiction of the heart in association with the respective
different identified locations.
53. The system of claim 28, wherein the software is further
configured to include a visual representation of the catheter in
the depiction of the heart in association with a location of the
catheter when the time-domain representation of one or more ECM
signals is obtained.
54. The system of claim 28, wherein the information related to the
frequency domain representation includes one or more indicators
that are representative of the frequency domain transformation.
55. The system of claim 52, wherein the indicators comprise colors
such that each color represents a different value in the frequency
domain representation.
56. The system of claim 52, wherein the indicators comprise
isochronal bands each representing a different value in the
frequency domain representation.
57. A system for performing diagnostics on electrocardiogram data
along a distal portion thereof captured by a catheter that supports
plural electrodes, comprising: a monitor operative to display
electrophysiology data; an input configured to accept a time-domain
representation of one or more electrocardiogram (EGM) signals
obtained by the electrodes at respective different locations within
the heart; a processor connected to receive the signals from the
input over a time interval; software executable by the processor
and configured to (i) transform at least one time-domain EGM signal
into a frequency domain representation over at least a portion of
the time interval, (ii) identify said respective different
locations of each electrode within the heart, (iii) cause a
depiction of a heart to be displayed on the monitor, and (iv) cause
information related to the frequency domain representation to be
displayed on the monitor in association with the location of each
electrode at which the EGM signal was obtained.
58. The system of claim 57, wherein the software is further
configured to include visual representations of each electrode in
the depiction of the heart in association with the respective
different identified locations.
59. The system of claim 57, wherein the software is further
configured to include a visual representation of the catheter in
the depiction of the heart in association with a location of the
catheter when the time-domain representation of one or more ECM
signals is obtained.
60. The system of claim 57, wherein the information related to the
frequency domain representation includes one or more indicators
that are representative of the frequency domain transformation.
61. The system of claim 58, wherein the indicators comprise colors
such that each color represents a different value in the frequency
domain representation.
62. The system of claim 58, wherein the indicators comprise
isochronal bands each representing a different value in the
frequency domain representation.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to intervention and treatment
of heart conditions such as atrial arrhythmias and more
particularly atrial fibrillation with regard to characteristics of
the heart tissue itself, and more particularly the present
invention concerns the use of atrial fibrillation cycle length
determinations in the mapping, diagnosis, treatment and prevention
and intervention of atrial fibrillation as well as
computer-implemented systems and interfaces relating thereto.
BACKGROUND OF THE INVENTION
[0002] Atrial fibrillation together with atrial flutter is the most
commonly sustained arrhythmia found in clinical practice. Although
there has been an increased awareness in the last several years of
the potentially serious clinical consequences of both arrhythmias,
their basic electrophysiological mechanisms and optimal management
strategies only recently have been understood. Atrial fibrillation
(AF) involves rapid and chaotic beating of the individual fibers of
the heart muscle such that synchronous contraction is not
maintained. This inevitably results in that part of the heart
ceasing to pump blood, which in turn can lead to embolic stroke.
Atrial fibrillation is characterized by the presence of multiple
reentrant circuits that may be active simultaneously, precluding
the synchronous activation of enough atrial myocardium to generate
an identifiable p wave or coordinated atrial contraction. Either a
sinus impulse or a stable atrial flutter reentrant circuit (flutter
wave) may degenerate into the multiple reentrant circuits (multiple
wavelets) characteristic of atrial fibrillation. (Cox et al., J.
Thoracic. Cardiovas. Surg. 101: 402-405 1991).
[0003] Atrial fibrillation currently afflicts over three million
persons in the United States. (Cox et al., J. Thoracic. Cardiovas.
Surg. 101: 402-405 1991). It is the most commonly sustained
arrhythmia, increasing progressively in prevalence with advancing
age, and occurring in 2%-4% of the population over the age of 60.
Atrial fibrillation is associated with atherosclerosis, chronic
rheumatic heart disease, hypertensive heart disease and stroke.
[0004] Our current understanding is that atrial fibrillation (AF)
is initiated most often by a focal trigger from the orifice of or
from within one of the pulmonary veins. Though mapping and ablation
of these triggers appears to be curative in most patients with
paroxysmal AF, there are a number of limitations to ablating focal
triggers via mapping and ablating the earliest site of activation
with a "point" radiofrequency lesion. One way to circumvent these
limitations is to determine precisely the point of earliest
activation. Once the point of earliest activation is identified, a
lesion can be generated to electrically isolate the trigger. By
electrically isolating one or more of the triggers in the pulmonary
veins from the left atrium with a lesion, firing from within those
veins would be unable to reach the body of the atrium, and thus
could not trigger atrial fibrillation.
[0005] There are several catheter-based therapeutic modalities
currently being used for the treatment of atrial fibrillation.
However, there is still recurrence of atrial fibrillation after
catheter ablation. It is difficult to predict the long-term success
or recurrence. In the attempt to increase the long-term success
rate, several modified therapies are proposed and practiced, for
example, adding one or more linear lesions in the left atrium, the
right atrium, or both, and creating a larger area of lesions that
surround the left atrial tissue and junction of the pulmonary
veins. However, the mechanism of this kind of approach is not clear
and may in fact be destructive to mechanical function of the heart
in the long term. Therefore, what is needed in the art is a more
predictive approach and tools therefor that are able to evaluate
the substrate of atrial arrhythmias, which include atrial
fibrillation, and to provide direction for future intervention in
addition to the elimination of the arrhythmic foci. Furthermore,
what is needed in the art is a predictive parameter that can
indicate long-term success likelihood to the
electrophysiologist.
[0006] U.S. Pat. No. 6,081,746 discusses AFCL in the context of
pacing the heart. This patent recognizes that the AFCL varies with
regions of the heart, but suggests that the AFCL value sensed at
the Bachmann's Bundle is adequate for use in pacing despite
variations that may exist through the heart tissue.
[0007] Atrial cycle length is an important intrinsic property of
atrial tissue. It provides a characterization of the substrate of
the atrial tissue of AF patients. However, due to the chaotic
nature of waveforms during AF, it is difficult to interpret cycle
length of atrial tissue on a beat-by-beat basis. Rather, an average
atrial fibrillation cycle length ("AFCL") has been manually
calculated by electrophysiologists to determine the vulnerability
of atrial tissue to AF trigger. It also is used to aid operators in
deciding whether or not to create any or any additional lesions
using an ablation catheter or other instrument. To determine the
Atrial Fibrillation Cycle Length (AFCL), EP physicians have used a
conventional catheter by moving the catheter within and around the
atrium to survey the targeted atrial tissue; the AFCL is manually
calculated by taking the total cycle length at a certain period,
e.g. 2 seconds, divided by the total peaks of atrial activation.
Electrocardiograms are analyzed carefully to reject low-amplitude
potentials and to detect double potentials associated with block,
correlation with the surface ECG was used to eliminate the
ventricular electrocardiogram. The procedure is subjective, tedious
and is time-consuming and has not provided a convenient, rapid, and
repeatable approach to evaluating and utilizing AFCL
determinations. The present invention addresses one or more of
these and other deficiencies in the prior art.
SUMMARY OF INVENTION
[0008] The invention concerns the automated determination of atrial
fibrillation cycle length values and the manipulation and
derivation of further parameters and statistics therefrom.
Electrocardiogram signals can be annotated using this information
and one or more maps can be created which coordinate location
information of indwelling catheter electrodes with AFCL data and
its derivatives. Ablation therapy can proceed under guidance of
such maps.
[0009] The invention also concerns spectral analysis of electrogram
signals to assist in the identification of atrial fibrillation, and
encompasses the simultaneous display across locations in one or
more cardiac chambers of information concerning the dominant
frequency and/or AFCL, and/or other parameters and statistics.
Consistent with this aspect of the invention, an ablation and
mapping procedure comprises percutaneously advancing a catheter
into at least one of the atria, the catheter having multiple
electrodes supported along its distal portion. One or more
locations of the electrodes within the atria are associated in a
memory of a machine. Electrocardiogram signals associated with at
least one electrode of the catheter at one or more of the locations
are captured for at least a prescribed time period. The electrogram
signals are transformed into a frequency domain representation for
at least a portion of the captured electrocardiogram signals over
at least the prescribed time period. The frequency domain
representation is coordinated with respective locations of the
multiple electrodes to define a set of data points which are output
on a display.
[0010] Also consistent with this aspect of the invention, a system
for performing diagnostics on electrocardiogram data comprises a
monitor operative to display electrophysiology data, an input
configured to accept a time-domain representation of one or more
electrocardiogram (EGM) signals obtained by electrodes at
respective different locations within the heart, a processor
connected to receive the signals from the input over a time
interval, and software executable by the processor. The software is
configured to transform the time-domain EGM signals into a
frequency domain representation over at least a portion of the time
interval and to cause information related to the frequency domain
representation to be displayed on the monitor in association with
said respective different locations.
[0011] In accordance with another aspect of the invention, a method
for annotating an electrocardiogram with an atrial fibrillation
cycle length (AFCL) value that is displayable on a display of an
electrophysiology system is provided. That method comprises
providing an electrocardiogram signal within the electrophysiology
system, accepting input to the electrophysiology system to define a
time segment of interest within the electrocardiogram signal,
locating successive activation signals within the time segment of
interest on each electrocardiogram signal, determining one or more
AFCL values using the located successive activation signals, and
associating on the display of the electrophysiology system at least
one of the determined AFCL values together with the
electrocardiogram signal.
[0012] In accordance with yet another aspect of the invention, an
electrophysiology system comprises inputs configured to receive
plural electrocardiogram signals from multiple intracardiac
electrodes that have been disposed at respective locations within a
heart, software operative to apply a finite impulse response (FIR)
filter to the plural electrocardiogram signals so as to output a
location along a time-axis of one or more activation signals
detected in the plural electrocardiogram signals and to determine
one or more atrial fibrillation cycle length (AFCL) values, and an
output configured to display the plural electrocardiogram signals
associated with each respective intracardiac electrode on a
display. The output comprises a first window configured to display
along the time-axis the plural electrocardiogram signals in
association with at least one of the one or more AFCL values, and a
second window configured to display a map that coordinates at least
one determined AFCL value with the locations within the heart of
the respective intracardiac electrodes.
[0013] In accordance with still another aspect of the invention, an
ablation and mapping procedure is provided which comprises
percutaneously advancing a catheter into at least one of the atria,
the catheter having multiple electrodes supported along a distal
portion thereof, associating in a memory of a machine one or more
locations of the electrodes within the at least one of the atria,
and capturing electrocardiogram signals associated with at least
one electrode of the catheter at one or more of the locations. For
at least a portion of the captured electrocardiogram signals, this
method calculates one or more discrete atrial fibrillation cycle
length (AFCL) values. The calculated discrete AFCL values are
coordinated with respective locations of the multiple electrodes to
define a set of data points, a continuous isochronal representation
of AFCL is extrapolated from the set of data points, and the
extrapolated representation is output on a display.
[0014] In accordance with a further aspect of the invention, an
electrophysiology system comprises a monitor operative to display
electrophysiology data, an input configured to accept signals from
plural cardiac leads, a processor configured to receive the signals
from the input and to influence the electrophysiology data
displayable on the monitor, and software executable by the
processor. The software in accordance with this aspect of the
invention is configured to operate upon signals from the plural
cardiac leads so as to determine at least one value representative
of an atrial fibrillation cycle length (AFCL) and to cause
information related to the at least one value to be displayed on
the monitor.
[0015] These and other aspects, features and advantages will be
apparent from the accompanying detailed description and Drawing
Figures of certain embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0016] These and various other features and aspects of the present
invention will be readily understood with reference to the
following detailed description taken in conjunction with the
accompanying drawings, in which like or similar numbers are used
throughout, and in which:
[0017] FIG. 1 is a schematic diagram of a system configured to
implement the methods of the present invention.
[0018] FIG. 2 is a flow diagram of a method in accordance with an
aspect of the invention that determines and presents AFCL data.
[0019] FIG. 3 is an illustration of an electrophysiology system
display showing AFCL data in association with defined portions of
individual electrocardiograms.
[0020] FIG. 3A is a schematic illustration of a data structure that
can be used in implementing the preferred embodiment.
[0021] FIG. 4 is a flow diagram of a diagnostic and optionally
therapy/intervention process that utilizes AFCL data.
[0022] FIG. 5 is a schematic illustration of a display showing an
AFCL data map.
[0023] FIG. 6 illustrates an exemplary screen of the interface
which is suitable for selecting or establishing the protocol for
generating a frequency domain representation of electrogram
signals.
[0024] FIGS. 7A, 7B and 7C illustrate exemplary screens showing
frequency domain information in association with the relative
locations of plural electrodes, and, in the case of FIG. 7B, in
association with the absolute locations of plural electrodes.
[0025] FIG. 8 illustrates an exemplary screen of the interface
which is suitable for displaying simultaneously both time- and
frequency-domain representations of electrogram signals, as well as
further information as shown in the figure and described below.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0026] By way of overview and introduction, when heart cells are
activated, the electrical polarization caused by the normal voltage
difference of about 90 mV between the inside and outside of the
cells collapses and the heart tissue is said to "depolarize."
Depolarized heart tissue which has not been given adequate time to
re-establish its normal voltage difference and will not produce a
new activation in response to a further intrinsic or extrinsic
electrical stimulus is referred to as refractory tissue. After
depolarization, heart cells begin to re-establish the normal
voltage difference ("repolarization"). Tissue which has been
afforded an adequate length of time to re-establish a sufficiently
large voltage difference to once again become susceptible to
depolarization is no longer refractory. The time interval which is
required after a cell has been depolarized until it is again
non-refractory is called the refractory period. In a fibrillating
heart, depolarization wavefronts move through the myocardium along
re-entrant pathways in a chaotic manner. The time period required
for a given depolarization wavefront to traverse and complete a
circuit along some re-entrant pathway of tissue in the atrium is
the atrial fibrillation cycle length (AFCL). Due to variations in
the substrate of cardiac tissue, certain locations can have AFCLs
that differ enough so as to disturb the main course of the
activation wave. The period following an activation when tissue
becomes non-refractory again is referred to as the "excitable gap."
The excitable gap follows the refractory period of the AFCL.
[0027] Referring now to the drawings, and particularly to FIG. 1,
there is shown an EP system 100 for receiving and processing
electrical signals according to one illustrative embodiment of the
present invention. In the illustrated embodiment, the EP system 100
includes a signal sensing unit 120, which may take different forms,
such as a standard 12-lead ECG, intracardiac lead, or combination
thereof. Sensors useful for collecting electrophysiological data on
a fibrillating atrium or ventricle that are useful for determining
local fibrillation cycle lengths according to the principles of
this invention include those that are conventional in the art. Such
sensors generally comprise a conventional sensing electrode or
electrodes, positioned in or on the heart in locations suitable for
monitoring the electrical activity associated with a fibrillating
heart and producing analog electrocardiogram ("EGM" or
"electrogram") signals in response thereto. The electrodes can be
mounted on a multiple-electrode expandable mesh-like catheter,
fixed size and adjustable circular loop catheter, basket catheter,
balloon-like catheter, longitudinal shaft catheter, etc.
Multiple-channel electrograms can be collected at different
anatomic locations including multi-chamber locations in the heart
via the multiple-electrode catheter. An amplifier operatively
connected so as to amplify the EGM signals and a waveform digitizer
that digitizes the EGM signals to produce digital EGM data provide
a digital data stream upon which signal processing can be
performed.
[0028] The signal sensing unit 120 is electrically connected to a
signal processing device 140, which receives the sensed signals
from the unit 120 and is configured or programmed to process the
digital EGM data in accordance with the selected mode of operation,
be it diagnostic, therapeutic, mapping, or intervention. The signal
processing device ("signal processor" or "processor") 140 is
preferably connected to a suitable display 300, which will present
the processed signals to a clinician or other interested person,
under control of an interface manager 160 which may be combined
with the signal processing device 140 as a single hardware unit.
Information can be stored and recalled from a storage device 180.
Preferably the signal processing device 140, interface manager 160,
and display 300 comprise the EP LabSystem (trademark) Pro of C.R.
Bard, Inc., Murray Hill, N.J., or the like. The EP LabSystem
(trademark) Pro supports a variety of data gathering and processing
functions that are standard in electrophysiology procedures, and
can be configured to implement the processes described herein
through software (e.g., modules, procedures, functions, or objects)
or firmware. The processor 140 communicates with the memory or
storage 180 which configures the processor to implement the
processes of the present invention under control of the interface
manger 160.
[0029] In one illustrative embodiment, the special features of the
system of the present invention are implemented, in part, by a
processor using program information stored in a memory of the
signal processing device 140 that is configured to process
electrophysiologic information related to the arrhythmic cardiac
substrate. The processor 140 can access one or more files or
software, as necessary, to implement the required functions, as
described in the accompanying flow diagrams. The interface manager
160 enables the operator to interact with graphical objects
rendered on the display 300 using a conventional pointer device or
touch screen so as to change the values of their properties, invoke
their methods, instantiate new objects, or terminate active
processes.
[0030] Referring now to FIG. 2, the operation of the signal
processing device 140 in determining AFCL values is described in
conjunction with the above structural description of the EP system
100.
[0031] At step 205, a patient can be prepared for an
electrophisiological study or treatment, in accordance with
convention, including having one or more catheters introduced into
his or her heart, at least one of the catheters including sensing
electrodes such as noted above. The sensing electrodes can be
introduced and positioned at predefined locations within a heart or
can be tracked and positioned using flouroscopy, MRI, CT,
ultrasound imaging or echoing, impedance, or electromagnetic
localization techniques (e.g., voltage, current, or magnetic field
gradients), as known in the art, and can be in tissue-contacting or
floating relation to the heart wall, if internally positioned. EGMs
that are captured by the sensing electrodes can be recorded or
buffered at step 210 into the memory of the EP system 100. These
steps can precede the AFCL determinations or can be part of a live,
that is, "real-time," procedure.
[0032] At step 215 the EP system operator provides configuration
parameters to the EP system 100 for the AFCL determination. The
configuration step can be initiated automatically upon selection by
the operator of the AFCL-determination function. The configuration
parameters can include, among other settings, an identification of
(1) which of the electrograms are to be analyzed, (2) the time
epoch to be tracked (e.g., a one, five or thirty second interval),
(3) a filter used to digitally process the electrogram signals and
identify each new cycle in the interval, and (4) any filter
settings that may be specific to (that is, trained for) the
patient. Configuration also can be set in accordance with default
values to permit the operator to make customizations while the AFCL
routines are actively processing the sensed EGM data.
[0033] Insofar as there may be multiple sensing electrodes each
displayable on a different channel of the EP system 100, during the
configuration step, the operator can identify certain channels on
which the AFCL analysis is to be made. The channels include data
from sensing electrodes at particular locations within the
heart--which locations do not change over the sampling interval,
and so the selection of channels may be assisted with location
information that correlates the location of a given sensor with its
present location within the heart.
[0034] If the time epoch is defined in the configuration step, then
an operator need only identify the beginning or end of an
electrogram segment that is of interest, as described below, in
order to define a segment of interest ("SOI") over which the AFCL
determinations are made.
[0035] The filter of the preferred embodiment is a finite impulse
response ("FIR") filter. The FIR filter can be configured to detect
activation signals (e.g., depolarization wavefronts passing through
a particular cardiac site) within the electrogram through the use
of digital signal processing. Detection of an activation signal
with a FIR filter comprises a non-zero output signal (known as
"ringing") that constitutes the impulse response of the filter to
an impulse received at its inputs. The "impulse response" of the
FIR filter is defined by its set of FIR coefficients, and in the
preferred embodiment, the FIR has 5 taps, that is, five
coefficient/delay pairs which are accumulated into an output
signal. Thus, during the configuration step, the impulse response
of the filter is defined by setting the filter's coefficient
values. The impulse response of a FIR is considered "finite"
because there is no feedback in the filter. Consequently, an
impulse input to the filter (that is, a sample of value "1"
followed by many samples of value "0"), will eventually result in
an output that is all zeros. However, the initial impulse will
cause a non-zero "ringing" output which fades to zero after the
sample has made its way in the delay line past all the
coefficients. An appropriate setting of the coefficient values of
the FIR is necessary in order to detect activation signals. A
linear filter and appropriately selected coefficients are preferred
and can even preserve phase information which may be mapped in
accordance with a further aspect of the invention.
[0036] A default set of values can be set for the coefficients that
defines an impulse response that is consistent with empirically
monitored activation signals. In other words, the filter can be
trained against a set of known data, with the coefficients adjusted
so that the filter rings in response to a prescribed electrical
signal pattern corresponding to a known activation signal. Thus,
for example, electrogram data from a number of persons of the same
age and health can be used to train the response of a FIR filter
which results in a set of coefficient values that can be stored in
the EP system 100 and recalled during the configuration step as a
default setting. In this way, patient-independent data can be used
to configure the FIR filter to detect activation signals. The
operator can make adjustments from the default values such as the
number or magnitude of the rings before detecting the event as an
activation, or the number of points of deflection from a nominal
baseline value in the EGM signal. Alternatively or in addition,
patient-specific data can be used to train the FIR filter or
fine-tune its response to a given patient. Yet another alternative
is to use artificial intelligence to compare electrograms against a
knowledge database of previously-classified signals, and create a
filter (that is, a set of coefficient values) that is dynamically
tuned with regard to the electrogram signals being observed.
[0037] As discussed below, the filter's coefficient values can be
readily changed by the operator if the operator has a particular
perspective concerning which events constitute an activation or
when an activation commences.
[0038] Referring now to FIGS. 2 and 3, a portion of several EGMs
310 are displayed under control of the interface of the EP system.
In FIG. 3, the displayed portion of the EGMs are centered relative
to a time reference 315, namely, "8:17:48:257." The EGMs 310 can
include composite surface electrograms (denoted I and VI), and
individual intracardiac electrograms associated with particular
electrode placements (denoted RF dist, RF prox, and Ref 1-2). (The
portion displayed can be presented differently when the EGMs are
being captured in real-time.) Each of the EGMs is plotted along a
time axis and constitutes a time-domain representation of the
electrical activity of the heart detected at particular locations
that are being monitored on channels, as understood by persons of
ordinary skill in the art.
[0039] The user interface permits conventional pointer-driven
control over multiple objects on the display so as to enable the
operator to interact with displayed elements, tabs, pull-down menus
and the like. As indicated at step 220, the operator can scroll the
displayed portion of previously-recorded EGMs using a conventional
pointer such as a mouse, trackball, or touch-pad until an interval
of particular interest is displayed on the display 300. The
operator can use the pointer to select (e.g., by clicking at a
given location on the screen) begin and end points of a segment of
interest ("SOI"), and the system will accept such input, as at step
225. If an epoch has been defined, the SOI can be defined by
selecting only one point on the screen, such as a beginning point.
In FIG. 3, a SOI has been defined and is indicated by interval
markers 320,325 at the top of the display, and also by perforated
lines 330, 335 that pass vertically through the display of EGMs.
Within the SOI, AFCL or other analyses can be made with data made
available to EP system software for further processing, such as map
creation, diagnosis and ablation therapy. (When working with live
data, the epoch is a defined time period, such as the previous five
seconds, and the SOI is the epoch leading to the current time
during which triggering events are sensed.)
[0040] At step 230, the active software process can receive inputs
from the operator such as selection of one of the tabs 340 that
permit inspection of the captured or processed data in another
format (e.g., as a table) or of additional data on the display 300.
The selection made at step 230 can also be of a system function
such as to analyze selected EGMs (either selected during
configuration or thereafter (e.g., by clicking on the label such as
"RF dist" or "RF prox" to select or deselect a particular
channel)). At step 235, a test is made whether the EP system is to
analyze the selected EGMs and determine the AFCL. If not, then any
selection made at step 230 can result in other processes being
launched, as indicated at step 240.
[0041] On the other hand, if the AFCL determination has been
invoked (either at step 230 or previously), then the FIR filter
operates upon the EGM within the SOI to locate any activation
signals within the defined interval that is between lines 330 and
335. More particularly, the FIR filter constitutes a FIR digital
signal processor that applies programmed coefficient values against
the signals on each selected channel which are fed into the filter
as an input. The impulse response of the filter in response to each
sampled portion of the EGM signal results in ringing whenever an
activation signal event is detected because only those events
should match the filter's setting. Preferably, when the filter
rings sufficiently strong or "loud" for a given channel, a tick
mark 345 is automatically added to the EGM on that channel to
indicate each point in time, over the SOI, that corresponds to an
activation signal, as indicated at step 250, by including that time
location in the data structure for that channel and also by
displaying the mark in association with that channel at that time
location. Also, threshold values can be used to ignore other
signals and prevent false ringing for non activation-signal
events.
[0042] Other filters and detection schemes can be used to detect
activation signals within the EGM; however, the use of a FIR filter
is presently a preferred approach.
[0043] Next, a further software process is invoked to compute the
atrial fibrillation cycle length for the interval between each
successive marker, at step 255. There can be no cycle length value
for the first activation signal within the SOI because there is no
prior activation signal within the interval upon which the cycle
length can be computed. Optionally, an indicator such as "AF" can
be placed at this first tick mark 345. For each tick mark 345 after
the first one in the SOI, an AFCL value is calculated. The AFCL
value is as the relative time difference between successive tick
marks. In other words, an absolute value of AFCL can be determined
for successive activation events using only relative timing
differences between the detected activation signals. Thus, for
example, for the EGM on channel "RF dist," the atrial fibrillation
cycle length for successive activation events is calculated along
the SOI, starting at the AF tick mark and continuing until the last
tick mark within that interval. Preferably, each computed AFCL
value is displayed adjacent its respective tick mark 345 and a set
of values are thus determined.
[0044] Further, the computed AFCL values are preferably arranged
into a data structure that can be used and shared with one or
further software processes. With reference briefly to FIG. 3A, data
underlying the various graphical objects on the display 300 are
stored in a data structure 360 that is accessible by plural
software processes. Among the various processes that can access the
data are an averaging module, various statistics modules, mapping
modules that coordinate the electrophysiological values such as the
AFCL values or AAFCL values (discussed below) with other data such
as location coordinates, and prediction modules that can augment or
modify a map with indicators of potential atrial-fibrillation
recurrence points. The data structure associates the data relative
to a fixed time-position 315, and stores absolute values relative
to that point. This arrangement is advantageous because the
absolute AFCL values permit statistical calculations to be made by
additional software processes and be stored within a common data
structure, if desired. Thus, for example, for a given channel
"channel-1," the determined AFCL values, an average value, average
variation, the standard deviation, other statistics, and any label
for the channel such as "RD dist" or "Ref 1-2" can be stored in the
data structure as each data is established. In addition, the FIR
filter coefficient values or neural network settings can be stored
to permit recreation of the data or alterations to the data by
indexing to that particular time-position point. The contents of
the data structure 360 can supply information to construct and
destruct data points as described in U.S. patent application Ser.
No. 09/943,408, filed Aug. 30, 2001, entitled Software Controlled
Electrophysiology Data Management, which is hereby incorporated by
reference as if set forth in its entirety herein.
[0045] In FIG. 3, the computed AFCL values present significant
variation over the interval, ranging from 199 ms to 239 ms.
However, it should be recalled that the EGM is being sensed by one
electrode (or electrode pair) representing signals at one portion
of cardiac tissue. Accordingly, it is preferred that a further
software process be invoked to compute and display an average AFCL
("AAFCL") of each channel over the SOI, and more preferably display
the AAFCL in association with each respective channel. For example,
the AAFCL 350 for channel "RF dist" has the value "215" and is
set-off from the remainder of the display by highlighting
(illustrated as a box, but other or additional highlighting such as
the color, size, or formatting of the font can be used).
Alternatively, the AAFCL can be displayed in individual or
composite bar graph indicators which are especially useful when
real-time analysis is being performed. An individual bar graph can
provide a graphical display to the operator of the average on a
given channel being monitored, whereas a composite bar graph can
graphically inform the operator of the overall average AFCL among
the channels. Color coding can show which channels are above or
below the overall average, and high- and low-water-marks can be
provided to show the maximum deflection of the bar graph during the
observed interval or procedure. The average can be updated as a
moving average over a pre-selected number of beats.
[0046] At step 260, the AAFCL is calculated by the software by
summing the AFCLs at each tick mark in the interval SOI and
dividing the sum by the number tick marks minus 1. Expressed
mathematically,
AAFCL=(.SIGMA.|.sub.SOIAFCL)/(N-1),
where N is the total number of tick marks within the interval SOI.
An average AFCL determination is desirable when operating on live
data because the variation and scrolling of discrete AFCL data
points could be difficult to assess by an operator, yet the average
value can provide a more stable reference for the operator to
consider and for map creation. A bar graph representation of
parameters such as the AAFCL is desirable as well in order to
improve comprehension by an operator of the computed
information.
[0047] Other parameters can be calculated at step 265 by the same
or further software processes to develop further information on the
heart being analyzed for presentation on the display 300 in
association with a respective EGM, as indicated at step 270. Such
further parameters can include statistics that can be used to gauge
the data being collected and may comprise variance calculations
among the AFCL values or the standard deviation within the data
set. These statistics can assist in developing a map of AFCL, with
interpolated and extrapolated contours being derivable between the
individual values and across EGM channels, assuming that the
general location of the sensing electrodes is known such that the
collected data can be rendered in a meaningful way.
[0048] The other parameters can include a Fourier analysis
performed using a fast Fourier transform, for example, to identify
dominant or recurrent frequencies in the data and their locations.
Such information can be used to predict and identify on the display
300 a location for ablation. For example, variance of the cycle
length in the time domain may influence the frequency domain
representation of the data, and so the frequency domain
representation of AFCL values for a given electrocardiogram can
provide utility in identifying an epicenter of a focus. As a simple
case, a frequency domain representation can comprise frequency
plotted along one axis, position along another axis (or two axes),
and amplitude along a third axis or in a color if three axes have
been used. The fast Fourier transformation (FFT) technique is
described in Theory and Application of Digital Signal Processing,
L. R. Rabiner and B. Gold, Prentice-Hall, Englewood Cliffs, N.J.
1975 p. 357-381. As a result of the transformation into the
frequency domain, a number of parameters can be calculated and
displayed such as the frequency of maximum amplitude and its
location relative to the sensing electrodes, or a frequency
analysis over the SOI.
[0049] Any of the values or statistics concerning AFCL can be
displayed or not in response to user control received as an input
through the interface manager 160. These values and statistics can
be displayed in bar graphs that provide a graphical representation
of that calculation for any given channel or as a composite derived
from the data on various channels.
[0050] At step 275, the operator can input adjustments that he or
she may wish to make to the markers based on his or her
professional interpretation of the EGMs. More particularly, the
operator can delete a given tick mark (e.g., because one of the
markings appears to be a double potential resulting from a
conduction block), or insert a tick mark even if its potential did
not satisfy the filter's trigger, which is tested at step 280. If
such adjustments are made, they have the effect of changing the
absolute AFCL value of the next tick mark in the SOI after that
point of adjustment, assuming that the adjusted AFCL value was not
the last tick mark in the interval. When a tick mark is inserted,
an AFCL value is computed for that new tick mark, and the AFCL
value for the next tick mark is re-computed, as described above.
The software recalculates these particular values by looping back
to step 255, and preferably updates the data structure 360
accordingly.
[0051] Alternatively, the operator may wish to shift a tick mark
345 to a new location if the operator disagrees with the position
that the EP system 100 placed that tick mark. As noted above, the
system places marks in accordance with the impulse response of the
FIR, which in turn is a function of the coefficient values used by
the FIR filter. As a default, for example, the FIR may ring loudest
at the onset of the fastest deflection in the EGM (as shown). The
operator, however, may prefer a different triggering characteristic
for a given patient, and can drag a given tick mark to a new
location. This has the effect of adjusting the coefficient values
of the FIR filter itself, which is tested at step 285 and if true,
causes all of the data for each of the selected channels to be
updated based on the filter response using the newly-set
characteristic. The software effects the re-calculation of all of
this data by looping back to step 250, preferably also updating the
data structure 360.
[0052] Other inputs are possible, such as selecting to display a
map of the AFCL data or an image of the distal portion of one or
more catheters within the heart at the locations where the data is
being sensed. Other functions and operations of the EP system 100
are accessed by an input that causes the process of FIG. 2 to end
at step 290.
[0053] When using a electrode array, such as an expandable wire
mesh in which a multiplicity of electric sensors are positionable
within a chamber, multi-channel data can be gathered with AFCL
points for the multiplicity of sensors thereby providing data
useful in defining a high-resolution AFCL map.
[0054] Referring now to FIG. 4, a diagnostic process for mapping
data relating to atrial fibrillation cycle length is described in
connection with a live procedure in which ablation therapy is
possible.
[0055] When an electrophysiology system 100 configured with
software as described above is provided, AFCL values and
information derived therefrom are available for mapping on a
monitor connected to the EP system. As noted above, AFCL data is
calculated from EGMs associated with particular electrodes on a
catheter, and more preferably on a multi-electrode catheter. As
noted below, AFCL data can be a frequency domain transformation of
the EGM signals. Each electrode has a location which is tracked in
a conventional manner, and the AFCL data is correlated at step 410
with the location of a particular electrode at which it was
positioned when the EGM data was provided to the EP system. The
AFCL data to be mapped can be, for example, an individual value
that is captured during the SOI, but more typically comprises an
average AFCL of all AFCLs computed over the SOI. Alternatively, the
AFCL data can be a statistic concerning the AFCL data such as the
AFCL variance or AFCL standard deviation. Within the meaning of
"AFCL data," the inventors include data resulting from a Fourier
transformation of the AFCL values such as the peak frequency, peak
frequency variation, and standard deviation in the frequency.
Preferably, the operator controls the nature of AFCL data to be
displayed by interacting with the interface manager 160 and inputs
his or her selection using a pointer.
[0056] At step 420, a portion up to the entirety of a heart chamber
is depicted on a monitor. It Can be the same monitor 300 that
displays the EGM data, or a different monitor. Preferably, the
depiction is shown in its own window or frame. The depiction can be
a simple wire frame rendering or cartoon (model) of the chamber,
and can be depicted in two or three dimensions. For example, a wall
of the atrium might be depicted in step 420 within a window 500, as
shown in FIG. 5.
[0057] At step 430, the software includes the AFCL data in the
depiction, as illustrated in FIG. 5. Preferably, the AFCL data is
presented in color, though in FIG. 5 four isochronal bands of AAFCL
values 530-560 are illustrated and differentiated from one another
using differing hatch lines. The map can be a color isochronal map
showing the different AF cardiac cycle lengths across the heart
wall which can be identified by operating EP physician to assess
the nature of the substrate that may be vulnerable to arrhythmic
trigger. In the event that there are isochronal markings on the
map, the differences in cycle length across the atrial substrate
can provide a visual indication to EP physicians (a) if the atrial
substrate is (still) susceptible to AF, or (b) which region or
regions of atrial tissue are more vulnerable to recurrence of
AF.
[0058] The isochronal map provides a visual tool to EP physicians
to identify the vulnerable arrhythmic substrate and find the
targeted area for intervention. The isochronal map provides an
evaluation tool to assess the results of the treatment such as the
effectiveness of PV isolation and the need for a left isthmus line,
etc. The isochronal map provides a predictive value of the
arrhythmias treatment, e.g. the outcome of the catheter ablation
for the treatment of atrial fibrillation, as well as the likelihood
of recurrence. The treatment decision could be made based on the
detected AFCL at a specific location, e.g. to create focal or
linear lesion in the local heart tissue with the shortest AFCL to
create a conduction block or modify the substrate accordingly.
[0059] The map need not present AFCL data in isochronal form. As
noted above, frequency domain transformations of AFCL data can
provide data and derived statistics for additional maps based on
AFCL data to inform the physician of the nature of the cardiac
substrate.
[0060] Optionally, an image or identifier of the current location
of the catheter(s) within the mapped chamber can be shown in the
map as well, as indicated at step 440. In FIG. 5, catheters 510 and
520 are illustrated.
[0061] A decision can then be made to determine if treatment need
be applied, e.g., to apply energy to block the re-entry circuits so
as to modify the substrate, as tested at step 450. For example, in
conventional atrial fibrillation ablation therapy, an ablation
procedure might seek to isolate one or more pulmonary veins,
whereas the software of the present invention can be utilized to
determine if extra lesions are indicated to treat the atrial
substrate outside of the pulmonary veins. Alternatively, AFCL
diagnostics can be used to make an initial determination of where
in a heart a lesion is to be made based on AFCL data.
[0062] In connection with further aspects of the invention,
diagnostic determinations can be performed as a spectral analysis
using frequency-domain representations of the electrogram signals,
and in particular with regard to either the regularity in the
dominant frequency observed at multiple cardiac locations
(including among multiple chambers) or a gradient observed in the
dominant frequencies observed among such locations. Empirically,
the mean dominant frequency (DF) from 30 second EGM recordings have
been found to correlate well with manually measured mean AFCL
(measuring a bipolar signal in the coronary sinus using a FFT
window length of 4096 msec (resolution 0.244 Hz) and a sliding
window of every 1 sec) which provides a basis for a new paradigm in
diagnostic analysis of atrial fibrillation in which spectral rather
than temporal analysis is correlated with cardiac locations in
order to identify foci. It has been also been empirically
demonstrated that the mean DF correlates well with mean uRI
(defined below) and mean AFCL correlates well with the standard
deviation (SD) in the cycle length.
[0063] Software configured in accordance with this aspect of the
invention executes in the processor 140 and transforms time-domain
representations of conventional EGMs into a frequency domain
representation, for example, using a FFT over a time interval.
Preferably, the time interval is at least about 4 seconds in order
to ensure sufficient resolution, and preferably is a time interval
on the order of about 4 seconds to about 10 seconds so that the
clinician can strike a balance between sufficient resolution and
speed of data analysis. The frequency-domain representation can be
obtained for each electrode of the catheter in a unipolar manner or
for each bipole-electrode pair, and each such frequency domain
representation can be illustrated as a plot of frequency verses
magnitude, or can be represented by other parameters or statistics
such as the dominant frequency (DF) within the plotted sample. A
variety of conventional algorithms can be employed in order to
perform the FFT, including by way of example a classic FFT
algorithm or a PD Welch algorithm.
[0064] Referring now to FIG. 6, the protocol to be used in
establishing the frequency-domain representation ("FDR") of one or
more EGM signals can be entered through a protocol selection screen
600 which is preferably part of the interface manager 160. All of
the parameters necessary to compute FFT are stored in a protocol,
and previously-stored protocols can be loaded or removed using
suitable controls provided on at least the main screen 800 (See
area 820 of FIG. 8) The protocol selection screen 600 provides
controls with which a user can interact in order to establish the
conditions upon which the FDR is generated. The protocol to be used
can be retrieved by entering a protocol name into text box 610.
Entry of data in this box and pressing an enter key preferably
causes the interface manager to search for and retrieve
previously-saved protocol settings which can be presented to the
user as selections in the remaining selections on the protocol
selection screen. The user can identify a directory for exporting
data by entering suitable path information into text box 620. The
user can browse for existing paths using button 622. A selection of
channels is provided in region 630, from which the user can select
particular channels for FDR display or all channels. The user has
the option of selecting pre-processing of the EGM signals in region
640, as described below. The time interval for applying the FFT to
the EGMs as well as the resolution for the mathematical processing
is set in region 650, and can commence with regard to existing data
files (e.g., from the beginning to last point in the file or from
arbitrary points therein) or by repeatedly sliding the time
interval in a user-settable interval. The resolution is the number
of points on which the FFT is computed (the frequency resolution
(Hz) is 1/FFT resolution). The algorithm that can be chosen in the
present implementation is either "classic" or "Welch," although
other algorithms can be employed without loss of generality. The
Welch algorithm compute an average FFT over a window that is 2
times larger than the FFT resolution. Details about FFT and Welch
processing can be found in the following references: M. Hayes,
Statistical Digital Processing and Modeling: John Wiley & Sons,
1996; P. Stoica and R. L. Moses, Introduction to Spectral Analysis.
Englewood Cliffs, N.J., 1997; and P. D. Welch, "The Use of Fast
Fourier Transform for Estimation of Power Spectra: A Method Based
on Time Averaging Over Short Modified Periodograms", IEEE
Transaction on Audio and Electroacoustics, vol. AU-15, pp. 70-73,
1967. If sliding windows are desired, the user checks the box
"sliding windows" and specifies the distance in sample between two
consecutive windows; in that case, a FFT is computed every
specified number of samples.
[0065] The display of results can include any of several parameters
selectable, as at region 660, and can include by way of example a
Dominant Frequency (DF), an unbiased Regularity Index (uRI), and an
Organization Index (OI). The content of data exported to a file can
be user set as well, as indicated at region 670, and can be flagged
to receive the FFT, tables including parameters relating to the FDR
such as the DF and the uRI for each FFT, and the OI for each FET. A
new protocol with these settings can be saved or canceled using
buttons 680, 690, respectively. The data can be exported in a
number of manners, however, it is presently preferred that there be
one export file for each computed channel with FFT values of the
spectrum, each such file being compatible with spreadsheet software
such as Excel made available by the Microsoft Corporation.
[0066] Preferably, the "DF" is the frequency for which the spectrum
is maximal in the 1 Hz to 20 Hz band. "uRI" is an index that
measure the relative power of DF and harmonics peaks over all
spectrum in the 1 Hz to 20 Hz band. "OI" is an index that measures
the narrowness of the DF and harmonics peaks. One FFT can be
computed every second in order to monitor DF, uRI and OI over time,
and a sliding window can be used to encompass more than one
second's worth of data.
[0067] The pre-processing selections in region 640 provide the user
with several options that affect the data that is submitted to the
FFT algorithm. The digital-filter option 642 can be 4th order
bandpass Butterworth filter between 1 and 20 Hz. The filter permits
band-pass filtering of the EGM data prior to FFT computation to
eliminate frequencies outside of the passband or above the cut-off
of a low pass filter. The pre-processing can take on other forms
such as a linear function (e.g., to digitally amplify or attenuate
the signal) or a non-linear function (e.g., absolute value or
squaring (that is, raising to the second power)). Selection of the
power processing option causes computation of the power of the EGM
signal, that is, the square of the signal, and so the FFT will be
of the power-signal rather than the raw EGM data, and the resulting
plot is called the Power Spectral Density, within which the same
parameters discussed above can be observed and analyzed. The
"Hammings windows" option allows the user to use a smoothing window
before FFT computation; this option is only valid if "classic FFT"
is computed, when the Welch algorithm is selected, Hamming window
is automatically applied. The "Evrett" check box is a special
pre-processing and methodology to compute FFT, and details of this
protocol are described in T. Everett, J. Moorman, L. Kok, J. Akar,
and D. Haines, "Assessment of Global Atrial Fibrillation
Organization to Optimize Timing of Atrial Defibrillation",
Circulation, vol. 103, pp. 2857-2861, 2001.
[0068] FIGS. 7A, 7B and 7C illustrate an exemplary display of the
spectral content of captured or real-time EGM signals from which
the regularity in the dominant frequency observed at multiple
cardiac locations can be seen, as well as any gradient in the
dominant frequencies among such locations. Optionally, the
orientation of the gradient can be highlighted to the user in the
window or frame 702, and maps of same value DF or other parameters
and statistics can be provided in the window or frame 702. In FIG.
7A, the relative orientation of ten electrode pairs for a lasso
catheter are illustrated in a window or frame 702 that can be
displayed on the monitor 300, such as by selecting tab 704. As can
be appreciated, the electrodes of this catheter construction assume
a loop-like shape within the cardiac chamber in which they are
deployed. In FIG. 7B, two electrode pairs are displayed for a four
pole ablation catheter and in FIG. 7C ten electrode pairs for a
multi-splined catheter are illustrated. In each case, the relative
orientation of the electrodes to one another is displayed in the
window or frame. Optionally, the display configuration can include
the DF (which is selected in these Figures) or a mean DF value. The
AFCL can also be displayed in a similar manner.
[0069] In addition, a numeric value of a dominant frequency (DF)
within the frequency domain representation is identified, as well
as which electrodes on the body of the catheter are associated with
each particular frequency domain plot, as shown in the window or
frame 702. Alternatively or in addition, the uRI and OI parameters
and other parameters and statistical information (including the
gradient in any change in dominant frequency from
electrode-to-electrode) can be displayed in association with any of
the electrodes. Thus, for example, the uRI and OI parameters can be
shown together with the FDR for a given electrode, instead of the
FDR yet at the relative or mapped location of that electrode, or
separately in a table or plot.
[0070] Advantageously, the FDR includes a DF calculation for each
electrode (electrode pair) position, and multiple DF calculations
are displayed on the monitor 300 for data that has been acquired
simultaneously across locations in one or more heart chambers. This
can be done using one or more catheters, each having multiple
poles. A large area, high density, mapping catheter is suitable for
this purpose. Optionally, a map of iso-DF calculations can be
presented using data acquired either at the same time or at
different times as an alternative presentation format to provide
the clinician with another representation of the response of the
cardiac substrate. Simultaneous acquisition of data is preferred
due to the chaotic nature of the cardiac signals during
fibrillation.
[0071] In a preferred implementation, a localization routine is
utilized to provide location information concerning the position of
each electrode (electrode pair) within the cardiac chamber and
thereby provide information to the user that can be used in
subsequent analysis or for repositioning the catheter and its
electrodes. As shown in FIG. 7B, an absolute location of the
electrode pair Ref 1-2 can be identified in the region 702 as a
location (X1, Y1, Z1) and the electrode pair Ref 3-4 can be
identified in the region 702 as a location (X2, Y2, Z2). Cartesian,
spherical or other coordinate systems can be employed, but
Cartesian is preferred. "Absolute location" as used herein refers
to an identifiable location of any particular electrode that can be
re-established even if a catheter or its electrodes have been moved
around the heart.
[0072] From FIG. 7 it can also be appreciated that the user
interface provides on the monitor FDR plots for each recording
channel that has been selected (i.e., through interaction with the
area 630 of the protocol selection screen 600). Thus, an FDR plot
is available for each anatomic location that is in contact with an
electrode or electrode bipole pair. The information being displayed
is captured as an event during a given time epoch that has been
defined by the user using the interface. Multiple events can be
captured to determine repeatability of the FDR over time. The
captured data can be reviewed at a later time, for example, to
compare the electrical response of pre- and post-operative cardiac
substrate.
[0073] Referring now to FIG. 8, a main screen 800 of the interface
manager for accessing the FDR of an EGM is shown. From the main
screen the user can select a recorded file to analyze (area 810),
load or edit a protocol and select the active protocol (area 820),
start the FFT computation (area 830) and export results achieved
using the selected protocol, observe information on the current
channel being drawn (area 840) including the channel name, the
leads, and a portion of the EGM, for instance, 5000 samples or so
at a sample rate of 1000 Hz (in which case the screen displays 5
seconds of the EGM signal at any given time, with a scroll bar
permitting navigation through the EGM, as desired), observe a
temporal plot of the EGM on the selected channel (area 850),
observe information on the FFT parameters used to draw in area 880
(area 860), specify options for the plot of the FFT in area 880
(area 870) including normalization, and observe the spectral
content of the current channel over the time interval (area
880).
[0074] As can be appreciated from FIG. 8, the user can be provided
with a display of both AFCL and FFT information, for one or more
channels. While AFCL information can be adequate to characterize a
focus of the AF by identifying the shortest cycle length, not all
electrograms permit measurement of AFCL (e.g., the data may be
fragmented). In any event, the FFT can reveal a dominant frequency
and thereby provide information concerning the location of a focus,
and this may be a clearer indicator of the location of the focus
than the time-domain-based AFCL in cases in which there is
fragmentation of the electrogram as that make an AFCL value
difficult to discern. In part, embodiments of the present invention
can provide a clinician with access to both analyses, displayable
either individually or simultaneously.
[0075] Area 870 controls the normalization of the FFT. If "no
normalization" is checked, the maximum signal of the displayed FFT
is the upper point of the area. However, if "channels
normalization" is used, the FFTs are normalized by the maximum
value of the spectrum for the displayed channel. If "record
normalization" is checked, the FFT is normalized by the maximum
value of the spectrum over the entire record. The user can also
choose to only display the pass-band of 1 Hz to 20 Hz using the
check box in area 870.
[0076] If the operator elects to ablate tissue, then the process
flow proceeds to step 460 at which ablation energy is permitted to
flow to the indwelling catheter(s), in accordance with conventional
procedures. Thereafter, at step 470, new EGMs are sensed by the
electrodes on the catheters 510, 520 and new AFCL data is computed,
as described above in connection with FIG. 2. On the other hand, if
ablation is not requested, then the flow advances to step 470,
described above. Since the diagnostic and optional
therapy/intervention procedure are performed live, the epoch for
the SOI is defined during configuration, as described above, and
includes a time period leading up to current time (such as 5
seconds).
[0077] Optionally, pre- and post-ablation maps can be superimposed
upon one another to provide a temporal superimposition of
information that can indicate whether the ablation has been
adequate to block a reentry circuit and/or to suitably modify the
substrate.
[0078] While the foregoing description has been directed primarily
to atrial fibrillation, the foregoing methods and systems can be
applied in the diagnosis and treatment of ventricular fibrillation,
and in the diagnosis and treatment of atrial fibrillation in which
one or more electrodes and/or catheters are disposed in one or both
of the ventricles as well as in one or both of the atria.
[0079] Having thus described preferred embodiments of the present
invention, it is to be understood that the foregoing description is
merely illustrative of the principles of the present invention and
that other arrangements, methods, and systems may be devised by
those skilled in the art without departing from the spirit and
scope of the invention as claimed below.
* * * * *