Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-02-04
2001-06-12
Getzow, Scott M. (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06246908
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for rapidly predicting the success or failure of an arrhythmia therapy pulse or shock to the heart of a subject, so that the need for an additional or alternate therapy pulse can be more rapidly determined and such pulse, if necessary, then delivered.
BACKGROUND OF THE INVENTION
Since defibrillation is probabilistic and shock strength dependent, shocks of the same strength sometimes succeed and other times fail (Davy J M et al,
Am. Heart J.
1987;113:77-84). It would be very useful if there were a way to predict defibrillation outcome soon after the shock so that the rescue shock could be delivered quickly with less time spent in ventricular fibrillation (VF) (Weaver W D et al,
Journal of the American College of Cardiology
1986;7:752-7; Echt D S et al, Pacing and
Clin. Electrophys.
1988;11:1315-1323).
Several studies have investigated activation before and after successful and failed shocks to try to predict defibrillation outcome. Those studies that used different shock strengths focused on the observation that the postshock interval (i.e. the interval between the shock and the first postshock activation) can be used to predict the shock outcome. In these studies the shock strengths for successful episodes were generally higher than for the failed episodes. Other studies that used the same shock strength for both successful and failed episodes did not find this relationship. Despite this controversy, all studies agree that, following shocks near the defibrillation threshold, a few organized ectopic cycles of activation occur prior to degeneration into VF for failed shocks or return to sinus rhythm for successful shocks. (Chen P -S, et al.:
J. Clin. Invest.
1986;77:810-823; Shibata N et al:
Am. J Physiol.
1988;255: H902-H909; Tovar O H and Jones J L:
Am. J Physiol.
1997;272: H1011-H1019; Zhou X, et al.:
Circ. Res.
1993;72:145-160; Usui M, et al:
J Cardiovasc. Electrophysiol.
1996;7:322-334). Hence, there remains a need for new ways to predict defibrillation outcome promptly after the delivery of a cardiac therapy pulse.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a method for predicting the outcome of arrhythmia therapy in a subject in need thereof. The method comprises the steps of: (a) detecting an arrhythmia in the heart of a subject; (b) delivering a first arrhythmia therapy pulse to the heart of the subject; and then (c) determining the presence or absence of overlapping cycles in the heart of the subject, the presence of overlapping cycles indicating that the first arrhythmia therapy pulse did not successfully treat the arrhythmia. The determining step is preferably carried out within the first 3, 5 or 10 cardiac cycles (inclusive) following the arrhythmia therapy pulse (and preferably within about one second of the first arrhythmia therapy pulse). The method then preferably further comprises the step of: (d) delivering a second arrhythmia therapy pulse if overlapping cycles are determined. The method can be used to treat any of a variety of different atrial and ventricular arrhythmias, particularly atrial and ventricular fibrillation.
While the determining step described above may be carried out by any suitable means, it is preferably carried out by calculating an overlapping cycle index. The overlapping cycle index may be calculated from the wavefront conduction time of a given cycle and the intercyle interval of the cycle subsequent to the given cycle. Preferably, the given cardiac cycle is within the first 2, 4, 9 or 10 cycles following the first arrhythmia therapy pulse. Thus, the determining step is carried out within the first 3, 5 10 or 11 cardiac cycles following the first arrhythmia therapy pulse.
A second aspect of the present invention is an apparatus for delivering an arrhythmia therapy pulse to a subject in need thereof and rapidly predicting the outcome of the arrhythmia therapy. The apparatus comprises: (a) a detector for detecting an arrhythmia in the heart of a subject; (b) a therapy pulse generator (e.g., a battery and capacitor circuit with suitable control circuitry) operatively associated with the detector for delivering a first arrhythmia therapy pulse to the heart of the subject; and (c) a microprocessor, control circuit or the like, which may be implemented in hardware, software, or both hardware and software, providing for determining means for determining the presence or absence of overlapping cycles in the heart of the subject following the first arrhythmia therapy pulse, the presence of overlapping cycles indicating that the first arrhythmia therapy pulse did not successfully treat the arrhythmia. Control circuitry or other suitable triggeringmeans may be operatively associated with the determining means and the therapy pulse generator for triggering the delivery of a second arrhythmia therapy pulse by the therapy pulse generator if overlapping cycles are detected.
The apparatus is preferably an implantable cardioverter defibrillator (ICD). Thus the apparatus typically includes a housing, with the detector, the therapy pulse generator, and the determining means contained within the housing. A defibrillation electrode may be formed on the outer surface of the housing to provide an “active can” electrode.
The foregoing and other objects and aspects of the invention are described in the drawings herein and the specification set forth below.
REFERENCES:
patent: 5978704 (1999-11-01), Ideker et al.
patent: 5978705 (1999-11-01), KenKnight
patent: 5987354 (1999-11-01), Copper et al.
patent: 6006131 (1999-12-01), Cooper et al.
Walker et al.;Abstract 738-2-Postshock Epicardial Activation Patterns Predict Outcome of Attempted Defibrillation,JACC Abstracts—Oral, 147A (1996).
Hamer et al.;Factors Related to the Induction of Ventricular Fibrillation in the Normal Canine Heart by Programmed Electrical Stimulation,JACC, 3(3):751-759 (1984).
Chattipakorn Nipon
Ideker Raymond E.
KenKnight Bruce H.
Getzow Scott M.
Myers Bigel & Sibley & Sajovec
UAB Research Foundation
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