Electropharmacologic effect of a standard dose of intravenous procainamidein patients with sustained ventricular tachycardia

Background: Patients with inducible sustained ventricular tachycardia (VT) sometimes receive intravenous procainamide during electrophysiologic testin g. Unfortunately, the responses to intravenous and subsequent oral drug the rapy are variable and may be discordant. Hypothesis: It was the aim of this study to determine whether this variabil ity might be explained by heterogeneity in the electropharmacologic respons e, even in a homogeneous population. Methods: We studied 42 patients who had spontaneous malignant ventricular a rrhythmia and were inducible to sustained monomorphous VT during electrophy siologic testing. Each received 15 mg/kg of intravenous procainamide follow ed by a 2 mg/min infusion. Serum levels were drawn immediately following pr ogrammed stimulation. The mean procainamide level was 6.7 +/- 1.4 mcg/ml wi th an N-acetyl procainamide level of 1.0 +/- 0.5 mcg/ml. The 14 procainamid e responders (5 of whom were noninducible and 9 whose VT cycle length incre ased > 100 ms) and the 28 nonresponders had similar procainamide and NAPA l evels (6.5 +/- 1.4 vs. 6.7 +/- 1.4 mcg/ml). Results: There was no significant difference in baseline clinical parameter s, His to ventricular electrogram (HV) interval, effective refractory perio d, or VT cycle length. Prolongation of the effective refractory period and infra His conduction time occurred to a similar extent in responders and no nresponders. Conclusion: We conclude that procainamide has a consistent dose-response re lationship with respect to refractoriness and conduction in patients with m alignant arrhythmias. However, acute antiarrhythmic efficacy of procainamid e cannot be predicted by clinical factors, drug levels, or drug-induced cha nges in common electrophysiologic parameters.