Lowered threshold for ventricular fibrillation in amiodarone-treated pigs undergoing cardiopulmonary bypass and cardioplegic arrest with St. Thomas' cardioplegic solution

The antiarrhythmic agent amiodarone has been suspected of causing reduced cardiac performance after extracorporeal circulation and cardioplegic arrest in patients. This has recently been confirmed in an experimental model where pigs were exposed to cardiopulmonary bypass and cold cardioplegic arrest with Bretschneider's solution. Due to the high concentration of the cardio-depressant agent procain in Bretschneider's solution, it could be speculated whether it is the combination of amiodarone and this solution that may be potentially deleterious, rather than amiodarone alone. To investigate this, adult pigs (75 +/- 2 kg at surgery) were treated with amiodarone for 30 +/- 2 days (1400 mg/day: n = 8, untreated controls: n = 4, blind experiment), followed by exposure to cardiopulmonary bypass with universal cooling to 28 degrees C and topical cold cardioplegic arrest with St. Thomas' solution for 60 min. Apart from 1 g of calcium (Ca2+) at the end of bypass, no inotropic drugs were administered. Cardiac reserve was tested by right ventricular pacing (200 beats/min until death or up to 30 min). The two groups did not differ concerning preload or afterload, heart rate, cardiac output, left ventricular pressure, arterial pressure or rate of change in left ventricular relaxation (-dP/dt) before or after bypass was terminated, while the rate of change in left ventricular contraction (+dP/dt) was lower in the amiodarone-treated pigs. The time on bypass, before stable hemodynamics had recovered, was prolonged in amiodarone-treated animals, 46 +/- 4 min versus 31 +/- 3 min in the controls (P < 0.05).