ON THE MECHANISMS OF VENTRICULAR-TACHYCARDIA ACCELERATION DURING PROGRAMMED ELECTRICAL-STIMULATION

Background. The pathophysiological mechanisms leading to acceleration of ventricular tachycardia (VT) are still unclear. Methods and Results. High-resolution epicardial mapping was used to study the mechanisms of VT acceleration by programmed electrical stimulation (PES) in a model of sustained reentrant VT in Langendorff-perfused rabbit hearts (n = 40). Three different mechanisms responsible for acceleration of VT were identified: 1) induction of double-wave reentry (n = 6), defined as the occurrence of two successive activation waves circulating in the same direction in the same circuit; 2) change to a functionally determined circuit (n = 4), defined as reentry of the impulse around a functional line of block without involvement of a fixed obstacle; and 3) change of the reentrant circuit to reentry within a different, faster anatomic pathway (n = 3). Analysis of 81 episodes of sustained monomorphic VT induced by PES in 74 patients with clinically documented sustained VT in the setting of chronic coronary artery disease showed that in 22 episodes VT was suddenly accelerated by PES (mean cycle length, from 345 +/- 73 to 277 +/- 71 msec, p