Drug-induced narrowing of the width of the zone of entrainment as a predictor of the subsequent non-inducibility of reentrant ventricular tachycardia after an additional dose of an antiarrhythmic drug

Antitachycardia burst pacing for pleomorphic reentrant ventricular tachycardias associated with non-coronary artery diseases: a morphology specific programming for ventricular tachycardias

To study the role of antitachycardia burst pacing in patients with reentrant pleomorphic ventricular tachycardia (VT) associated with non-coronary artery diseases, the efficacy of antitachycardia pacing and appropriate antitachycardia pacing cycle length were evaluated in each pleomorphic VT morphology of seven patients. Seven patients were included in this study. Clinically documented pleomorphic VTs were reproduced in an electrophysiologic study. For each VT, rapid ventricular pacing was attempted from the apex of the right ventricle at a cycle length which was 20 ms shorter than that of VT and repeated after a decrement of the cycle length in steps of 10 ms until the VT was terminated or accelerated. All 16 VTs could be entrained by the rapid pacing, and 13 of the 16 VTs (81%) were terminated, whereas pacing-induced acceleration was observed in the other 3 VTs of the 3 patients. VT cycle length (VTCL), block cycle length (BCL) which was defined as the longest VT interrupting paced cycle length, %BCL/VTCL and entrainment zone which was defined as VTCL minus BCL, varied in each VT morphology of each patient. In two patients, antitachycardia pacing was effective in all VT morphologies and the maximum difference of the %BCL/VTCL among the pleomorphic VTs was less than 10%. Thus, antitachycardia pacing seemed to be beneficial for these patients. In the other 5 patients, a difference of more than 10% in %BCL/VTCL was observed among the pleomorphic VT morphologies and/or at least one VT morphology showed pacing-induced acceleration. Compared to the 13 terminated VTs, three accelerated VTs had a wide entrainment zone [160 +/- 44 vs 90 +/- 48 ms, p < 0.04] and small %BCL/VTCL [61 +/- 6 vs 77 +/- 11%,p<0.03]. In pleomorphic VTs associated with non-coronary artery diseases, responses to rapid pacing was not uniform; VT might be terminable or accelerated even in the same patient. We need to pay close attention when programming antitachycardia pacing in patients with pleomorphic VT.

Beneficial effect of amiodarone on pacing induced terminability of reentrant ventricular tachycardia

A 33 year-old woman was referred to our hospital for further treatment of ventricular tachycardia (VT). During treatment with amiodarone (200 mg/day), clinical VT at the cycle length of 510 ms was induced. During the VT, rapid ventricular pacing was repeated at progressively shorter cycle lengths after a decrement of 10 ms steps. The VT was entrained by the rapid pacing and reproducibly terminated at a paced cycle length of 380 ms. Four weeks after reducing the amiodarone to 100 mg/day, programmed stimulation was repeated. The VT with the same morphology but with a slightly shorter cycle length of 480 ms was again induced. However, at this time, rapid pacing from the same site could not terminate VT and transient acceleration developed at a shorter paced cycle length of 260 ms. The QT (QTc) interval, effective refractory period at the pacing site and width of the paced QRS complex were similar before and after changing the amiodarone treatment. The most characteristic change of VT in the second study was a widening of the entrainment zone, which was calculated as the difference between VT cycle length and the longest pacing cycle length which interrupts VT during the entrainment (from 130 to > 220 ms), and it may be explained by the preferential shortening of the action potential duration and/or facilitation of the depressed cell to cell conduction within the reentry circuit. Amiodarone must exert a preferential action in the reentry circuit and modulate the conduction property as well as the effective refractory period. We should pay close attention to the efficacy of antitachycardia pacing during the modification of amiodarone treatment.

Effects of class I and III antiarrhythmic drugs on ventricular tachycardia-interrupting critical paced cycle length with rapid pacing

The most common mechanism of sustained ventricular tachycardia (VT) is re-entry with an excitable gap, but the electrophysiologic properties and response to antiarrhythmic drugs in the area of slow conduction are not yet fully known. The purpose of this study was to assess the effects of a class I antiarrhythmic drug (procainamide) and class III agents (amiodarone, E-4031, and MS-551) on re-entrant VT using the width of the zone of entrainment. The cycle length (CL) of VT (VTCL), the block CL that was the longest paced CL that interrupted the VT, and the width of the zone of entrainment, defined as the difference between VTCL and block CL, were compared before and after treatment with antiarrhythmic drugs. The VTCL was prolonged significantly from 308+/-63 to 410+/-77 msec after procainamide (p<0.005) but was not changed after the administration of the class III agents: from 294+/-50 to 292+/-13 msec after amiodarone, and from 305+/-47 to 313+/-31 msec after E-4031 or MS-551 (p=NS). The block CL was prolonged from 255+/-61 to 331+/-70 msec after procainamide (p <0.01), from 256+/-20 to 260+/-25 msec after amiodarone, and unchanged after E-4031 or MS-551 (253+/-31 msec before and 270+/-43 msec after) (p=NS). The width of the zone of entrainment as a representative of the width of the excitable gap was changed from 52+/-26 to 79+/-35 msec (p<0.05) after procainamide, whereas it was unchanged after amiodarone (48+/-7 msec before and 43+/-7 msec after) and after E-4031 or MS-551 (50+/-10 msec before and 40+/-9 msec after). Therefore, amiodarone, E-4031, and MS-551 did not affect VTCL and block CL whereas procainamide increased these parameters. The excitable gap substituting as the zone of entrainment was increased by procainamide but slightly reduced by amiodarone, E-4031, and MS-551. The effects of these antiarrhythmic drugs on the excitable gap of re-entrant VT were variable and should be examined further.