RESUMO
Certain antiarrhythmic drugs that inhibit myocardial repolarizing currents decrease defibrillation energy, but the effect of blocking particular currents on defibrillation is not well understood. We therefore investigated the effect of barium, a relatively selective blocker of inwardly rectifying potassium current (Ik1) on voltage and energy requirements for defibrillation in an open-chest dog model. Defibrillation energy and voltage requirements were assessed by delivering monophasic shocks through epicardial electrode patches at varying voltages to construct a dose-dependent curve of energy and voltage versus success in defibrillation. The energy and voltage for 50% success in defibrillation (E50 and V50, respectively) were determined by logistic regression. Monophasic action potential duration at 90% repolarization (MAPD90) was measured with a contact electrode, and ventricular refractory period (VERP) was measured. After baseline measurements were obtained of E50, V50, MAPD90, and VERP, saline (control) (n = 6) or barium (1.1 mg/kg/min for 5 min followed by 0.25 mg/kg/min) (n = 11) was administered. Defibrillation voltage and energy requirements and electrophysiologic measures were repeated after 30 and 120 min of barium or saline infusion. In control animals, there was no significant change with time in V50 (2.0 +/- 12.4 and -0.2 +/- 16.0% at 30 and 120 min, respectively), VERP (+3 +/- 5 and -2 +/- 3% at 30 and 120 min, respectively) or MAPD90 (+1 +/- 4 and -2 +/- 6, at 30 and 120 min, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
