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Claims  |
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I claim:
1. A method of treating cardiac arrhythmias, which comprises the steps of:
(a) positioning the distal tip of each of one or more catheters at a site
adjacent to or within a patient's heart;
(b) sensing location information at the site;
(c) sensing local information concerning the heart's electrical activity at
the site;
(d) processing sensed information from steps (b) and (c) to create one or
more data points;
(e) repeating steps (a) , (b) , (c) and (d) one or more times to create
sufficient data points for a map of the heart's electrical pathways; and
(f) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
2. The method of 1 which comprises an additional step before step (f)
wherein said data points or said map is transmitted to receiving means.
3. The method of claim 2 which comprises a further step before step (f)
wherein said data points or said map received by receiving means is
projected onto an image receiving means.
4. The method of claim 3 which compromises a yet further step before step
(f) wherein the location of a mapping/ablation catheter distal tip is
superimposed on said projected data points or map on said image receiving
means.
5. A method for treating cardiac arrhythmias, which comprises the steps of:
(a) obtaining a perspective image of a patient's heart;
(b) positioning the distal tip of each of one or more catheters at a site
adjacent to or within the heart;
(c) sensing location information at the site;
(d) sensing local information concerning the heart's electrical activity at
the site;
(e) processing sensed information from steps (c) and (d) to create one or
more data points;
(f) repeating steps (b) , (c) , (d) and (e) one or more times to create
sufficient data points for a map of the heart's electrical pathways;
(g) superimposing said data points from step (e) or map from step (f) on
the perspective image of the heart; and
(h) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
6. The method of claim 5 which comprises an additional step before step (h)
wherein said data points or map and said perspective image are transmitted
to receiving means.
7. The method of claim 6 which compromises a further step before step (h)
wherein the location of a mapping/ablation catheter distal tip is
superimposed on the perspective image of the organ or bodily structure.
8. The method of claim 6 which comprises an additional step before step (h)
wherein said data points or said map and said perspective image received
by receiving means are projected onto an image receiving means.
9. The method of claim 8 which compromises a yet further step before step
(h) wherein the location of a mapping/ablation catheter distal tip is
superimposed on said projected data points or map and said perspective
image on the said image receiving means.
10. A method for treating cardiac arrhythmias, which comprises the steps
of:
(a) positioning the distal tip of each of one or more reference catheters
at a site adjacent to or within a patient's heart;
(b) positioning the distal tip of each of one or more mapping/ablating
catheters at a site adjacent to or within the heart;
(c) sensing location information at each site;
(d) sensing local information concerning the heart's electrical activity at
a site with each mapping/ablating catheter distal tip;
(e) processing sensed information from steps (c) and (d) to create one or
more data points;
(f) repeating steps (b) , (c) , (d) , and (e) one or more times to create
sufficient data points for a map of the heart's electrical pathways; and
(g) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
11. The method of claim 10 which comprises an additional step before step
(g) wherein said data points or said map is transmitted to receiving
means.
12. The method of claim 11 which comprises a further step before step (g)
wherein said data points or said map received by receiving means are
projected onto an image receiving means.
13. The method of claim 12 which compromises a yet further step before step
(g) wherein the location of a mapping/ablation catheter distal tip is
superimposed on said projected data points or map on said image receiving
means.
14. A method for treating cardiac arrhythmias, which comprises the steps
of:
(a) positioning the distal tip of each of one or more reference catheters
at a site adjacent to or within a patient's heart;
(b) positioning the distal tip of each of one or more mapping/ablating
catheters at a site adjacent to or within the heart;
(c) sensing location information at each site;
(d) determining relative location of the mapping/ablating catheter distal
tip relative to reference catheter distal tips;
(e) sensing local information concerning the heart's electrical activity at
a site with each mapping/ablating catheter distal tip;
(f) processing sensed information from steps (d) and (e) to create one or
more data points;
(g) repeating steps (b) , (c) , (d) and (e) one or more times to create
sufficient data points for a map of the heart's electrical pathways; and
(h) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
15. The method of claim 14 which comprises an additional step before step
(h) wherein said data points or said map is transmitted to receiving
means.
16. The method of claim 15 which comprises a further step before step (h)
wherein said data points or said map received by receiving means is
projected onto an image receiving means.
17. The method of claim 16 which compromises a yet further step before step
(h) wherein the location of a mapping/ablation catheter distal tip is
superimposed on said projected data points or map on the said image
receiving means.
18. A method for treating cardiac arrhythmias, which comprises the steps
of:
(a) obtaining a perspective image of a patient's heart;
(b) positioning the distal tip of each of one or more reference catheters
at a site adjacent to or within the heart;
(c) positioning the distal tip of each of one or more mapping/ablating
catheters at a site adjacent to or within the heart;
(d) sensing location information at each site;
(e) sensing local information concerning the heart's electrical activity at
a site with each mapping/ablating catheter distal tip;
(f) processing sensed information from steps (d) and (e) to create one or
more data points;
(g) repeating steps (b) , (c) , (d) , (e) and (f) one or more times to
create sufficient data points for a map of the heart's electrical
pathways;
(h) superimposing said data points from steps (f) and (g) on the
perspective image of the heart; and
(i) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
19. The method of claim 18 which comprises an additional step before step
(i) wherein said data points or map and said perspective image are
transmitted to receiving means.
20. The method of claim 19 which compromises a further step before step (i)
wherein the location of a mapping/ablation catheter distal tip is
superimposed on the perspective image of the organ or bodily structure.
21. The method of claim 19 which comprises a further step before step (i)
wherein said data points or map and said perspective image received by
receiving means are projected onto an image receiving means.
22. The method of claim 21 which compromises a yet further additional step
before step (i) wherein the location of a mapping/ablation catheter distal
tip is superimposed on said projected data points or map on said image
receiving means.
23. A method for treating cardiac arrhythmias, which comprises the steps
of:
(a) obtaining a perspective image of the heart;
(b) positioning the distal tip of each of one or more reference catheters
at a site adjacent to or within the heart;
(c) positioning the distal tip of each of one or more mapping/ablating
catheters at a site adjacent to or within the heart;
(d) sensing location information at each site;
(e) determining relative location of each mapping/ablating catheter distal
tip relative to reference catheter distal tips;
(f) sensing local information concerning the heart's electrical activity at
a site with each mapping/ablating catheter distal tip;
(g) processing sensed information from steps (e) and (f) to create one or
more data points;
(h) repeating steps (b), (c), (d), (e), (f), and (g) one or more times to
create sufficient data points for a map of the heart's electrical
pathways;
(i) superimposing said data points from steps (g) and (h) on the
perspective image of the heart; and
(j) ablating a portion of the heart whose electrical pathways cause said
arrhythmias.
24. The method of claim 23 which comprises an additional step before step
(i) wherein said data points or map and said perspective image are
transmitted to receiving means.
25. The method of claim 24 which compromises a further step before step (i)
wherein the location of a mapping/ablation catheter distal tip is
superimposed on the perspective image of the organ or bodily structure.
26. The method of claim 24 which comprises a further step before step (i)
wherein said data points or map and said perspective image received by
receiving means are projected onto an image receiving means.
27. The method of claim 26 which compromises a yet further step before step
(i) wherein the location of a mapping/ablation catheter distal tip is
superimposed on said projected data points or map on said image receiving
means.
28. The method of claim 1, 5, 10, 14, 18, or 23, wherein sensing location
information is achieved using a nonionizing field. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention is directed to an apparatus and method for treating a
cardiac arrhythmia such as ventricular tachycardia. More particularly,
this invention is directed to an improved apparatus and method whereby
there is faster identification of an active site to be ablated.
BACKGROUND OF THE INVENTION
Cardiac arrhythmias are the leading cause of death in the United States.
The most common cardiac arrhythmia is ventricular tachycardia (VT), i.e.,
very rapid and ineffectual contractions of the heart muscle. VT is the
cause death of approximately 300,000 people annually.
In the United States, from 34,000 to 94,000 new patients are diagnosed
annually with VT. Patients are diagnosed with VT after either (1)
surviving a successful resuscitation after an aborted sudden death
(currently 25-33% of sudden death cases) or (2) syncope, i.e., temporary
loss of consciousness caused by insufficient cerebral circulation. The
number of VT patients is expected to increase in the future, estimated to
range between 61,000 and 121,000 patients annually in five years, as a
result of early detection of patients at risk for sudden death by newly
developed cardiac tests, advances in cardiopulmonary resuscitation, better
medical management of acute myocardial infarction patients, and the
demographic shift to a more aged population.
Without proper treatment most patients diagnosed with VT do not survive
more than two years. The most frequent current medical treatment consists
of certain antiarrhythmic drugs or implantation of an automatic
implantable cardiac defibrillator (AICD). Drug treatment is associated
with an average life span of 3.2 years, a 30% chance of debilitating side
effects, and an average cost of approximately $88,000 per patient. In
contrast, AICD implantation is associated with a life expectancy of 5.1
years, a 4% chance of fatal complications, and a cost of approximately
$121,000 per patient.
In a majority of patients VT originates from a 1 to 2 mm lesion that is
located close to the inner surface of the heart chamber. A treatment of VT
in use since 1981 comprises a method whereby electrical pathways of the
heart are mapped to locate the lesion, i.e , the active site, and then the
active site is physically ablated. In most instances the mapping and
ablation are performed while the patient's chest and heart are open. Also,
the mapping procedure has been carried out by sequentially moving a
hand-held electrical recording probe or catheter over the heart and
recording the times of arrival of electrical pulses to specific locations.
These processes are long and tedious.
Attempts to destroy, i.e., ablate, the critical lesion are now quite
successful, but are currently limited to a small number of patients who
can survive a prolonged procedure during which they have to remain in VT
for almost intolerable periods of time. The time-consuming part of the
treatment is the localization, i.e., identifying the site, of the target
lesion to be ablated. Another limitation preventing the widespread use of
catheter ablation for VT is poor resolution of target localization, which
in turn compels the physician to ablate a large area of the patient's
heart. The reduction in heart function following such ablation becomes
detrimental to most patients with pre-existing cardiac damage. However,
once the target is correctly identified, ablation is successful in almost
all patients.
An improved procedure for treatment of VT must include a faster, more
efficient and accurate technique for identifying, or "mapping", the
electrical activation sequence of the heart to locate the active site.
In electrophysiologic examinations, and in particular in those using
invasive techniques, so-called electrical activation mapping is frequently
used in combination with an x-ray transillumination. The local electrical
activity is sensed at a site within a patient's heart chamber using a
steerable catheter, the position of which is assessed by transillumination
images in which the heart chamber is not visible. Local electrical
activation time, measured as time elapsed from a common reference time
event of the cardiac cycle to a fiducial point during the electrical
systole, represents the local information needed to construct the
activation map data point at a single location. To generate a detailed
activation map of the heart, several data points are sampled. The catheter
is moved to a different location within the heart chamber and the
electrical activation is acquired again, the catheter is repeatedly
portrayed in the transillumination images, and its location is determined.
Currently catheter location is determined qualitatively or
semi-qualitatively by categorizing catheter location to one of several
predetermined locations. Furthermore, the transillumination method for
locating the catheter does not convey information regarding the heart
chamber architecture.
The present technique requires the use of a transillumination means during
each of the subsequent catheter employments. This means that if the
subsequent catheter locating is achieved by ionizing radiation, the
patient and the physician must be subjected to a radiation exposure beyond
that which would be required only for producing the basic image of the
heart chamber architecture.
A catheter which can be located in a patient using an ultrasound
transmitter allocated to the catheter is disclosed in U.S. Pat. No.
4,697,595 and in the technical note "Ultrasonically marked catheter, a
method for positive echographic catheter position identification." Breyer
et al., Medical and Biological Engineering and Computing. May, 1985, pp.
268-271. Also, U.S. Pat. No. 5,042,486 discloses a catheter which can be
located in a patient using non-ionizing fields and superimposing catheter
location on a previously obtained radiological image of a blood vessel.
There is no discussion in either of these references as to the acquisition
of a local information, particularly with electrical activation of the
heart, with the locatable catheter tip and of possible superimposition of
this local information acquired in this manner with other images,
particularly with a heart chamber image.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide an alternative method
for the permanent portrayal of the catheter during mapping procedures by a
method making use of non-ionizing rays, waves or fields, and thus having
the advantage of limiting the radiation exposure for the patient and the
physician.
It is also an object of the invention to provide a catheter locating means
and method that will offer quantitative, high-resolution locating
information that once assimilated with the sensed local information would
result a high-resolution, detailed map of the information superimposed on
the organ architecture.
It is a further object of the present invention to provide a mapping
catheter with a locatable sensor at its tip.
These and other objects of the invention will become more apparent from the
discussion below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram for acquiring a basic image;
FIG. 2 is a schematic block diagram representing a computerized endocardial
mapping algorithm;
FIG. 3 is a schematic block diagram representing a computerized pace
mapping algorithm;
FIG. 4 is a schematic block diagram representing output device
configuration of an embodiment of the invention;
FIG. 5 is a schematic block diagram for illustrating the mapping catheter
with the sensor at its tip and a locating method in accordance with the
principles of the present invention making use of a transmitting antenna
at the catheter tip;
FIG. 6 is a schematic block diagram representing use of the invention for
pace mapping;
FIG. 7 is a schematic block diagram representing the algorithm used to
calculate the cross-correlation index while pace-mapping;
FIG. 8 is a diagram representing the catheter used for mapping arrhythmias;
and
FIGS. 9 and 10 are each a schematic block diagram representing an aspect of
the invention.
SUMMARY OF THE INVENTION
A trackable mapping/ablation catheter, for use with reference catheters in
a field such as an electromagnetic or acoustic field, has (i) a
transmitting or receiving antenna for the relevant field within its tip,
(ii) a sensor at its tip for acquiring local information such as
electrical potentials, chemical concentration, temperature, and/or
pressure, and (iii) an appropriate port for delivering energy to tissue.
Receiving or transmitting antennas for the respective field are attached
to the patient in which the catheter is disposed. A receiver or
transmitter is connected to these antennas and converts the field waves
received into electrical locating or image signals. The sensed local
information of each site can be portrayed on a display at the respective
locations and combined with an image of the structure acquired in a
different manner such as by x-ray, NMR, or ultrasound. The resulting
information can be used to map the electrical pathways of the heart to
determine the situs of a lesion to be ablated.
DETAILED DESCRIPTION OF THE INVENTION
The above objects of the invention are achieved in a method for real-time
portrayal of a catheter in the heart chamber, which makes use of a
transmitter for electromagnetic or acoustic waves located at the tip of a
catheter, these waves being acquired by a receiving antenna attached to
the patient and being converted into electrical image signals. The image
of the catheter can then be superimposed on a heart chamber image
disclosing wall architecture acquired by same or other means of imaging.
In an alternative embodiment, the catheter tip may be a receiving antenna,
and the externally applied antennas may be transmitting antennas. The
sensor in the catheter tip is designed to acquire the information of
interest, and the acquisition of local activity at sites located by the
tracking methods is used to map the organ under study.
The aforementioned known electromagnetic or acoustic technology permits a
simple portrayal of the catheter, because the catheter differs greatly
from its environment (biological tissue) with respect to the interaction
of x-rays. The catheter locating technique can be employed with an imaging
method and with a corresponding, real-time imaging system which makes use
of non-ionizing radiation. The non-x-ray image which portrays the catheter
can be combined with an image disclosing heart chamber architecture
acquired in an appropriate way. The problem of excess radiation exposure
is thus overcome; however, the demands made on the non-ionizing imaging
system with respect to its applicability and resolution are rather high.
A further possibility, therefore, is to use the nonionizing field as part
of a locating method, as opposed to an imaging method. Locating methods
differ from imaging methods in the following ways: Imaging methods are
primarily used to topically correctly portray and resolve a number of
subjects or subject points within an image within specific limits. This
property is known as the multi-target capability in radar technology and
is not present in locating methods. Locating methods operate precisely and
unambiguously only in the case wherein a single subject is to be
portrayed, i.e., to be located. As an example, the catheter tip is a
suitable subject point. The advantage of the locating method is that wave
fields can be used wherein the employed wave-length, which is defined by
the frequency and phase velocity of the surrounding medium (tissue), can
be relatively high, and need not be on the order of magnitude of the
locating precision. As is known, range decreases greatly with increasing
frequency given non-ionizing waves, such as electromagnetic waves and
acoustic waves.
It is thus possible, given the use of a locating method, to make use of
relatively long wavelengths, and thus lower frequencies. Moreover, the
outlay for signal bandwidth and aperture is much smaller in locating
methods than in imaging methods, particularly in view of the spectral
(signal) and spatial (aperture) occupation density. It is sufficient to
bring the subject point to be located into interaction with only a few
extracorporeal aperture support points, for example, three to five
transmitters or receivers, given a few discreet frequencies, for example,
three to five frequencies. On the basis of this interaction, ranges or
range differences with reference to the subject position and the various
aperture supporting points, the combination of which makes an unambiguous
and exact positional identification (locating) of the subject point
possible, are determined by measuring phase relationships or transit time
relationships. The subject point, i.e., the catheter tip, must be marked
for this purpose in a suitable manner.
As in conventional pathfinder technology, it is necessary that the catheter
image and the heart chamber image be combined with each other in a proper
three-dimensional correspondence, and it is also necessary that the heart
chamber architecture does not displace or deform during the treatment. To
correct for displacement of the heart chamber that occurs during the
cardiac cycle the catheter location is sampled at a single fiducial point
during the cardiac cycle. To correct for displacement of the heart chamber
that may occur because of breathing or patient movement, a set of more
than two locatable catheters is placed at specific points in the heart
chamber during the mapping procedures. The location of these reference
catheters supplies the necessary information for proper three-dimensional
correspondence of the heart chamber image and the mapping catheter
location.
The above principles can be applied for mapping other structures of the
body, for example, of the urinary bladder, brain, or gastrointestinal
tract. Dependent upon the examination technique, the catheter may be
replaced by a needle whose tip is the locatable sensor port.
In a broader perspective the invention encompasses four aspects: the first
is intended to process locating information; the second processes sensed
electrical information; the third integrates previously processed
information; and the fourth processes the integrated information to
generate a topographical map of the sensed variable. These aspects are
described in more detail below.
Catheters will be introduced percutaneously into the heart chambers. Each
catheter will be trackable (using the previously described methodology).
Preferably three reference catheters will be left in known landmarks, and
a fourth catheter will be used as the mapping/ablation catheter. The
locations of the three reference catheters will be used to align the
location of the heart chamber relative to its location on the "basic
image."
1. Image and Location Processor
Image acquisition: A method and device to acquire images of the heart
chambers from available imaging modalities (e.g., fluoroscopy, echo, MRI,
etc.). The image is to be acquired with sufficient projections (e.g.,
bi-plane fluoroscopy, several longitudinal or transverse cross-sections of
echocardiography) to be able to perform 3-dimensional reconstructions of
the cardiac chambers' morphology.
Images will be acquired at specific times during the ablation procedure:
the basic image will be recorded at the beginning of the procedure to
allow determination of the cardiac chamber anatomy and of the positions of
reference catheters in the heart. This image will be used thereafter as
the basic source of information to describe the heart chamber morphology.
The image and location processor identifies (i) the location of chamber
boundaries using the methods of edge enhancement and edge detection, (ii)
catheter locations relative to the chamber boundaries, and (iii) the
dynamics of chamber morphology as a function of the cardiac cycle.
By analyzing the displacement of the catheter tips during the cardiac cycle
the image processor will calculate the regional contractile performance of
the heart at a given moment during the mapping/ablation procedure. This
information will be used to monitor systolic contractile functions before
and after the ablation procedure.
The location processor identifies the locations of catheters. The locations
of the reference catheters are used to align the current position of the
heart chamber with that of the "basic image." Once current location data
is aligned with the "basic image," location of the mapping and ablation
catheter is identified and reported.
2. Electrophysiologic (EP) Processor
The electrophysiologic signal processor will acquire electrical information
from one or more of the following sources:
A. ECG tracings (by scanning the tracing);
B. Body surface ECG recordings, either from a 12-lead system (X,Y,Z
orthogonal lead system) or from a modified combination of other points on
the patient's torso; and
C. Intra-cardiac electrograms, from the ablation/recording catheter, and/or
from a series of fixed catheters within the heart chambers.
At each of the mapping/ablation stages, namely, sinus rhythm mapping, pace
mapping and VT mapping, the EP processor will determine the local
activation time relative to a common fiducial point in time. The local
activation time recorded at each stage will furnish part of the
information required to construct the activation map (isochronous map).
The electrophysiologic processor will also perform the following signal
processing functions:
2. A. Origin Site Determination
Determine the most likely origin site of the patient's arrhythmia based
upon the body surface ECG tracings during VT. The most likely VT origin
site will be detected by analyzing the axis and bundle morphology of the
ECG, and by using the current knowledge of correlation between VT
morphology and VT origin site.
2.B. Sinus Rhythm Mapping
2.B.1 Delayed Potential Mapping
Using intracardiac electrograms recorded from the mapping catheter tip
during sinus rhythm the EP processor will detect and then measure the time
of occurrence of delayed diastolic potentials. Detection of late diastolic
activity either by (1) ECG signal crossing a threshold value during
diastole; or by (2) modelling the electrical activity at a user-defined
normal site and then comparing the modelled signal with the actual signal,
and estimating the residual from the normal activity; or by (3) using a
band pass filter and searching for specific organized high-frequency
activities present during diastole; or by (4) using cross-correlation and
error function to identify the temporal position of a user-defined delayed
potential template. This analysis will be performed on a beat-by-beat
basis, and its results will be available to the next stage of data
processing and referred to as the time of delayed potential occurrence.
2.C. Pace Mapping
2.C.1 Correlation Map.
In a "pace mapping mode" the ECG processor will acquire ECG data while the
patient's heart is paced by an external source at a rate similar to the
patient's arrhythmia cycle length. The ECG data will be acquired from the
body surface electrograms, and the signal will be stored as a segment of
ECG with a length of several cycles. The signal acquired will then be
subjected to automatic comparison with the patient's own VT signal (see
FIG. 7). The comparison between arrhythmia morphology and paced morphology
will be performed in two stages: First, the phase shift between the
template VT signal and the paced ECG morphology would be estimated using
minimal error or maximal cross-correlation for two signals. Then, using
this phase shift estimated from an index ECG channel, the similarity of
the VT and the paced ECG morphology will be measured as the average of the
cross-correlation or the square error of the two signals of all channels
recorded.
This two-stage calculation will be repeated each time using a different ECG
channel as the index channel for determining the phase shift.
At the end of this procedure the minimal error or the maximal
cross-correlation found will be reported to the operator as a
cross-correlation value (ACI) of this pacing site.
2.C.2 Local Latency
The ECG processor will measure the pacing stimulus to ventricular
activation. The earliest ventricular activat | | |
