Key result
DL-sotalol significantly prolonged the ventricular effective refractory period from 241 to 302 msec at 600 msec cycle length, without reverse use-dependency even after isoproterenol administration.
Why the study?
Does dl-sotalol and its modulation by isoproterenol affect the ventricular effective refractory period and conduction in patients undergoing electrophysiologic study?
Does dl-sotalol and its modulation by isoproterenol affect the ventricular effective refractory period and conduction in patients undergoing electrophysiologic study?
DL-sotalol prolongs the ventricular effective refractory period without reverse use-dependency, even after isoproterenol administration, which may contribute to its antiarrhythmic efficacy.
Answers are grounded in this paper and cite their sources.
Small study indicates dl-sotalol prevents VT induction; leaves open clinical relevance and isoproterenol effects.
The interaction between dl-sotalol and isoproterenol on the ventricular effective refractory period (VERP) and conduction were examined in an electrophysiologic study of 9 patients at drug-free baseline, after 14 days of dl-sotalol administration (320 mg/day), and after the administration of isoproterenol. In all 9 patients, ventricular tachyarrhythmia could not be induced after dl-sotalol treatment. Isoproterenol was administered as a loading dosage of 0.025 microgram/kg for 5 min with a maintenance dosage of 0.0025 microgram/kg/min. The VERP and the QRS duration were determined at paced cycle lengths of 600, 400 and 300 msec. DL-sotalol and dl-sotalol + isoproterenol had no effect on ventricular conduction at the three cycle lengths. The VERP was significantly prolonged after dl-sotalol treatment at paced cycle lengths of 600 (241 +/- 16 to 302 +/- 28 msec, p < 0.001), 400 (223 +/- 21 to 280 +/- 23 msec, p < 0.001) and 300 msec (202 +/- 16 to 256 +/- 24 msec, p < 0.005), but there was a parallel shift of the VERP, suggesting the absence of use-dependent effects on the VERP. The dl-sotalol-induced VERP prolongation was partially reversed by isoproterenol, but it remained significantly prolonged above baseline values at paced cycle lengths of 600 (241 +/- 16 to 281 +/- 18 msec, p < 0.01), 400 (223 +/- 21 to 258 +/- 20 msec, p < 0.01) and 300 msec (202 +/- 16 to 247 +/- 22 msec, p < 0.01). The shortening of the VERP was greater at longer basic cycle lengths (600 and 400 msec) than at the shorter paced cycle length (300 msec, p < .05), but the percentage increase of the VERP was similar at the three basic cycle lengths of 600 (16%), 400 (15%) and 300 (20%) msec, indicating the lack of reverse use-dependency. The absence of reverse use-dependency of dl-sotalol on the VERP, even after isoproterenol administration, may be beneficial in the therapy of ventricular tachyarrhythmias and may account in part for the high efficacy of this drug.
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Naitoh et al. (1998) studied Ventricular tachyarrhythmia (n=9). DL-sotalol and Isoproterenol vs. Drug-free baseline was evaluated on Ventricular effective refractory period (VERP) at paced cycle length of 600 msec (p=<0.001). DL-sotalol significantly prolonged the ventricular effective refractory period from 241 to 302 msec at 600 msec cycle length, without reverse use-dependency even after isoproterenol administration.
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