Characterization of spontaneous changes in electrogram morphology

The spontaneous termination of sustained, monomorphic ventricular tachycardia caused by reentry is studied in the epicardial border zone (EBZ) of the canine heart with a healing myocardial infarction, by measuring changes in electrogram morphology. Bipolar electrograms were recorded simultaneously from 196 sites with a computerized mapping system, and were used to locate the reentrant circuit and the site at which the reentrant impulse blocked when tachycardia terminated spontaneously. An algorithm based on the time average of the mean square error (MSE) gradient between a template and an input signal is used for parametric modeling of the activation interval, for several simultaneously recorded time series electrograms. The algorithm is used to update the parameters: amplitude, DC bias, activation duration, and phase, according to the derivative of the performance surface, which is estimated using finite differences as a numerical approximation. Preliminary findings obtained from measurements of a sequence of 19 activation intervals immediately preceding a spontaneous termination, for 5 electrogram recording sites suggest: 1) based on summary statistics of ranks, parameter variability from cycle to cycle over the sequence decreases in the order site of spontaneous termination > other areas of the circuit > areas away from the circuit, 2) the duration of activation and the DC bias were the best predictors of the location of reentry and the site of termination, and 3) cyclic oscillations, behaving either as an alternans or possessing a longer period, were evident to varying degrees in all 5 electrogram. The approach described herein for signal analysis is potentially applicable as a clinical tool for defining the region of reentry and the likely site of termination. The information acquired by parametric modeling, as the model is revised using more data, is expected to be important to provide an improved understanding of the relationship between electrogram morphology and the substrate of the EBZ.<
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