The Efficacy of DL-Sotalol in Reentrant Ventricular Tachycardia with Special Reference to the Width of the Zone of Entrainment

Aims: In selecting effective antiarrhythmic agents for reentrant ventricular tachycardia (VT), there is no hallmark which can predict drug-efficacy. In this study, the ability of dl-sotalol to suppress the inducible VT was assessed during an electrophysiologic study with special reference to the zone of entrainment, an index of the excitable gap. Methods and Results: In 21 patients, monomorphic sustained VT was induced and entrained with rapid ventricular pacing at progressively shorter cycle lengths until VT was terminated at a critical length (=block cycle length) and the width of the zone of entrainment was calculated as the difference between the cycle length of VT and the VT-interrupting critical cycle length: the longest cycle length at which 1:1 conduction fails within the zone of slow conduction. The effective refractory period was measured by extrastimulus technique. After the administration of dlsotalol (240-320mg/day for>14 days), the drug efficacy was evaluated by an electrophysiologic study and the relation to the basal electrophysiological parameters were analyzed. After the administration of dl-sotalol, the cycle length of the sinus rate, the QT interval, and the effective refractory period were prolonged significantly. In 11 patients, VT was not induced (responders) to the end of the entire protocol of induction. In another 10 patients, dl-sotalol proved a failure and a slower VT with a similar width of zone of entrainment remained inducible. The cycle length of VT and the width of the zone of entrainment did not differ between the responders and non-responders to dl-sotalol: 300±72 vs. 275±21 msec and 57±27 vs. 50±16 msec, respectively. Conclusions: The VT induction was prevented by dl-sotalol in 52%, but the cycle length, the zone of entrainment of VT, and other variables were not different between the responders and non-responders to dl-sotalol.