Magnesium reduces free radical concentration and preserves left ventricular function after direct current shocks.

OBJECTIVE Our objective was to determine if magnesium reduces free radicals generated by direct current countershock and preserves left ventricular contractile function. BACKGROUND We have previously shown that magnesium reduces free radicals in a coronary occlusion-reperfusion model, and therefore also might reduce free radical generation by direct current shocks. METHODS In eight swine weighing 18-27 kg (mean: 22 kg), using electron paramagnetic resonance, we monitored continuously the coronary sinus concentration of ascorbate free radical, a measure of free radical generation (total oxidative flux). Epicardial shocks (30 J) using a truncated exponential biphasic waveform (5/5 ms) were administered. Each animal received two shocks, one without and one with magnesium, 80 mg/min IV, beginning 10 min before the shock and continuing to 15 min after the shock. Percent fractional area shortening of the left ventricular cavity was determined by 2-dimensional echocardiography. RESULTS Magnesium shocks resulted in a significantly lower increase in the ascorbate free radical concentration (0.6+/-4.6%) than no-magnesium shocks (16+/-3.3%, P<0.05) at 12 min after the shock. Total radical flux was reduced 72% (P<0.05), and left ventricular fractional area shortening was preserved: baseline: 69+/-2.6%, no-magnesium shocks: 41+/-2.8% (P<0.05, versus baseline) and magnesium shocks 61+/-3.7%. CONCLUSIONS Magnesium pre-treatment reduced oxygen free radicals generated by direct current shocks; post-shock left ventricular contractile function was not impaired. Magnesium may be cardioprotective during epicardial ('surgical') defibrillation.