RESUMO
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.
