ELECTROPHYSIOLOGIC EFFECTS OF MAGNESIUM-SULFATE INFUSION IN PATIENTS WITH CARDIAC CONDUCTION DEFECTS

We report the electrocardiographic and electrophysiologic effects of magnesium (Mg) sulfate infusion in 25 normomagnesemic patients (16 men and 9 women, aged 22-74 years; mean +/- SD, 60.4 +/- 11.9) with different cardiac conduction impairments. Ten patients had chronic ischemic hear-t disease, two had idiopathic dilated cardiomyopathy, two had hypertensive heart disease. three had valvular heart disease, five had sclerodegenerative heart disease and three had no clinical evidence of cardiac disease. Five patients had trifascicular block [first degree atrioventricular (A-V) block + right bundle branch block (RBBB) + left anterior hemiblock (LAH)], eight had bifascicular block (6 RBBB + LAH, 2 first degree A-V block + RBBB), four had isolated first degree A-V block and eight had bundle branch block [5 RBBB, 3 left bundle branch block (LBBB)]. Before and during Mg infusion (50 mg/min/60 min) we evaluated the A-V (P-R), intraatrial (P-A), suprahisian (A-H), infrahisian (H-V) conduction times, electrical ventricular systole (Q-T), Q-T index (Q-Tc) intraventricular conduction time (QRS) and heart rate. At the end of infusion the P-R, P-A, A-H, H-V increased from 215.4 +/- 36.6, 33.6 +/- 9.1, 112.8 +/- 37.3, 69.0 +/- 12.8 ms to 217.6 +/- 37.1 (p < 0.002), 33.8 +/- 9.4 (NS), 114.2 +/- 38.1 (p < 0.005), 69.6 +/- 13.3 (NS) ms. QRS complex did not change (125 +/- 16.9 ms). Mg did not cause significant changes in heart rate (from 74.2 +/- 6.7 to 73.5 +/- 6.2 bpm), QTc (from 421 +/- 28.3 to 421 +/- 30.6) and arterial blood pressure (from 132 +/- 11/78 +/- 6 to 131 +/- 7/77 +/- 5 mmHg). Mg serum levels increased after infusion from 2.14 +/- 0.16 to 2.37 +/- 0.14 mg/dl (p < 0.01).