194 Dynamic Changes in Electrogram Morphology at Functional Lines of Block in Reentrant Circuits During Ventricular Tachycardia in the Infarcted Canine Heart: A New Method to Localize Reentrant Circuits from Electrogram Features Using Adaptive Template Matching EDWARD J. CIACCIO, PH.D.,'^ MELVIN M. SCHEINMAN, M.D.,' VITALTY FRIDMAN. B.E.E.,' HEIKO SCHMITT, M.D.,' JAMES COROMILAS, M.D.,'* and ANDREW L. WIT. PH.D.' From the Departments of 'Pharmacology and "^Medicine, and the ^Cenler for Biomedical Engineering, College of Physicians and Surgeons. Columbia University, New York, New York; and the -^Department of Medicine, University of California at San Francisco, San Francisco. California Localization of Reentrant Circuits Using ATM. introduction: Fractionated, low- amplitude or long-duration electrograms have limited specificity for locating reentrant circuits causing ventricular tachycardia (VT). In this study a new method is described, adaptive template matching (ATM), based on the quantification of beat-to-beat changes in electrograms, for locating functional reentrant circuits that are relatively stable and cause monomorphic VT. Methods and Results: Monomorpbic VTs were induced in 4-day-old infarcted canine hearts by programmed stimulation and reentrant circuits mapped in the epicardial border zone witb a 196 or 312 bipolar electrode array. For ATM analysis, a template electrogram from each electrode, during an early cycle, was matched with all subsequent (input) electrograms at the same site by weigbdng tbe inputs of amplitude, duration, average baseline, and pbase lag. The mean square error (MSE) between template and input was the criterion used to adapt the weights, and was also a measure of cbanges in electrogram sbape that occur from cycle to cycle. The variance of each of the weighting parameters at all electrode sites were plotted on a representation of tbe electrode array, and the location of the functional lines of block bounding tbe central common patbway of reentrant circuits withfigure-of-eightcharacteristics, overlaid on tbe ATM map. Peaks of high variance were found to be coincident witb functional lines of block during all taebycardia episodes. Conclusion: Specific beat-to-beat cbanges in electrograms occur at functional lines of block in reentrant circuits tbat can be quantified by ATM analysis, suggesting that tbese regions might be located without activation mapping. Tbe metbod migbt be useful to guide ablation catheter position. iJ Cardiovasc Electrophysiol Vol. W. pp. 194-213. February 1999) reentry, mapping, electrograms, ventricular tachycardia, ablation Introduction A great deal of information is present in ex- tracellular electrogram morphology about the Supported by Gram R37 HL-31393 and Program Project Grant HL-30557 from the Heart. Lung and Blotiil Institutes. National Institutes of Health. Address for correspondence: Edward J, Ciaccio, Ph.D.. Department of Pharmacology and Center for Biomedical Engineering, College of Physicians and Surgeons of Columbia University. 630 West I68ih Street. New York, NY 10032. E-mail: ciaccio@columhia.edu Manuscript received 11 June 1998: Accepted for publication 6 November 1998. physiology of conduction of the cardiac im- pulse.'"* For this reason, the characteristics of electrograms in reentrant circuits are of interest and have been investigated because they might provide information on mechanisms of slow con- duction and block that cause reentry. Particular attention has been paid to the occurrence, loca- tion, and causes of low-amplitude or long-dura- tion potentials, double potentials, and fraction- ated electrograms.'^"'-' In addition, it has been reasoned that if electrogram characteristics in reentrant circuits are specific, they might provide an easy and rapid means for locating those cir-