Circulation, Vol 74, 1355-1364, Copyright © 1986 by American Heart Association
F Morady, LA DiCarlo Jr, M de Buitleir, RB Krol, JM Baerman and WH Kou
The short-term effects of incremental doses of procainamide (7.5, 15, 22.5,
and 30 mg/kg) on right ventricular effective refractory period,
intraventricular conduction, and induction of ventricular tachycardia were
determined in 31 patients who had a history of sustained, unimorphic
ventricular tachycardia. QRS duration during incremental ventricular pacing
was used as an index of rate-dependent changes in intraventricular
conduction. The mean plasma procainamide concentrations corresponding to
the incremental doses were 5.5 +/- 1.2 (+/- SD), 9.0 +/- 1.6, 12.6 +/- 2.2,
and 16.3 +/- 3.2 mg/liter. Each incremental dose of procainamide up to a
dose of 30 mg/kg resulted in a significant increment in right ventricular
effective refractory period and each dose up to 22.5 mg/kg potentiated a
rate-dependent prolongation of QRS duration. After the 7.5 mg/kg dose of
procainamide, induction of ventricular tachycardia was suppressed in eight
of 31 patients. After higher doses of procainamide, induction of
ventricular tachycardia was suppressed in two additional patients. In three
of 10 patients in whom the induction of ventricular tachycardia was
suppressed by 7.5, 15, or 22.5 mg/kg of procainamide, sustained unimorphic
ventricular tachycardia was again inducible after a higher dose of
procainamide. In three of 31 patients, only nonsustained ventricular
tachycardia was inducible after a 7.5 to 22.5 mg/kg dose of procainamide;
however, in two of these three patients, sustained ventricular tachycardia
was again inducible after administration of a higher dose of procainamide.
In conclusion, during electropharmacologic testing with procainamide, it is
worthwhile to test a dose of 7.5 mg/kg, because this dose is often
effective in patients who respond to this drug. However, the results of
this study indicate that procainamide may be effective in suppressing the
induction of sustained ventricular tachycardia at a relatively low plasma
concentration, but not at a higher plasma concentration. Therefore, during
long-term therapy with procainamide it may be important to avoid plasma
procainamide concentrations not only lower, but also higher than the
concentration that results in the suppression of induction of tachycardia.
ARTICLES
Effects of incremental doses of procainamide on ventricular refractoriness, intraventricular conduction, and induction of ventricular tachycardia
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