Ventricular fibrillation in acute experimental myocardial ischemia: protection by magnesium sulfate.

1. The efficacy of magnesium sulfate for prevention of ventricular fibrillation was compared with that of the calcium blocker verapamil and other antiarrhythmic drugs in 54 open-chested anesthetized dogs during a 3-h ligation of the circumflex coronary artery. Latency time to fibrillation, incidence of fibrillation and hemodynamic parameters were assessed. 2. Ventricular fibrillation occurred in 11 of 14 (79%) control dogs, in 2 of 8 (25%) dogs treated with magnesium sulfate (100 mg/kg) and in none of 8 animals treated with verapamil (0.2 mg/kg) (P = 0.014 and P = 0.0004, respectively, in comparison with controls); lidocaine (60 mg followed by 4 mg/min), amiodarone (5 mg/kg) and propafenone (4 mg/kg) had no effect on the incidence of fibrillation. 3. The latency time to fibrillation was 11.6 +/- 9.1 min in controls and it was shortened to 4.0 +/- 3.8 min (P = 0.039) in dogs treated with propafenone, but was unaffected by other drugs. 4. There was no correlation between pre-occlusion heart rate or blood pressure and fibrillation incidence. 5. In this experimental model, magnesium sulfate infusion had a protective effect against ventricular fibrillation that was similar to verapamil, suggesting that magnesium sulfate may be useful as an antifibrillatory agent during acute ischemia.