BACKGROUND: The electrophysiological mechanisms of spontaneous termination of sustained monomorphic ventricular tachycardia (SMVT), in the postinfarction heart, generally considered secondary to a reentrant mechanism, have not been fully investigated.METHODS AND RESULTS: Epicardial activation maps of spontaneous termination of 20 different episodes of SMVT (lasting 30 seconds to 10 minutes) from 8 dogs, 4 to 5 days after one-stage ligation of the left anterior descending coronary artery, were analyzed with the use of 254 bipolar electrode recordings with high density (2.5 to 2.8 mm between bipolar electrodes) in the ischemic zone. All ventricular tachycardias (VTs) were due to circus movement reentry with a characteristic figure-8 configuration. Termination always occurred when the two circulating wave fronts blocked in the central common pathway (CCP). Two basic mechanisms of spontaneous termination were observed: (1) In 15 episodes, acceleration of conduction occurred in parts of the reentrant circuit and was associated with slowing of conduction and finally conduction block in the CCP. Acceleration of conduction occurred in the last few cycles of VT both at the outer border of the arcs of functional conduction block in the "normal" myocardial zone and at the pivot points to the entrance to the CCP. When acceleration of conduction was compensated on a beat-to-beat basis by an equal degree of slowing in the CCP, there was no discernible change in the cycle length of the VT in the ECG. In some episodes, the termination of the original reentrant circuit was followed by the development of a different, slower reentrant pathway that lasted for one or a few cycles prior to termination. (2) In 5 VT episodes, the activation wave front in the CCP abruptly broke across a stable arc of functional conduction block, resulting in premature activation of the CCP and conduction block.CONCLUSIONS: Distinct electrophysiological changes always preceded spontaneous termination of stable SMVT. The electrophysiological basis for acceleration of conduction in parts of the reentrant circuit during the last few beats prior to termination and of the abrupt reactivation across a stable arc of block remains to be determined.
Animals Dogs