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The electrophysiological effects of intravenous magnesium on human sinus node, atrioventricular node, atrium, and ventricle

The effects of intravenously (IV) administered magnesium chloride (MgCl) on electrophysiologic and electrocardiographic variables were studied in 13 patients undergoing a routine electrophysiologic assessment for clinical indications. An infusion of 12 mmol of MgCl was given during a 10‐min period and relevant electrophysiologic variables were determined before and after the infusion. Serum Mg levels increased from 0.78±0.03 (mean±SEM) before to 1.52±0.08 ms after the infusion (p<0.0001). Magnesium treatment caused a significant prolongation in PR interval (from 151±8 to 174±8 ms, p<0.001) as well as in QRS duration (from 90±4 to 101±6 ms, p <0.05). Likewise, intra‐atrial (PA) as well as atrioventricular (AV) nodal (AH) conduction times were significantly prolonged (from 33±3 to 46±3 ms, p<0.01, and from 85±6 to 94±6 ms, p<0.05, respectively). Mean effective and functional atrial refractory periods increased (from 228±8 to 256±10 ms, p<0.01 and from 292±9 to 320±11 ms, p<0.001, respectively), as did mean AV node functional refractory period (from 399±29 to 422±27 ms, p<0.02). No significant change occurred with regard to sinus node function (as estimated from heart rate, sinus node recovery time, and calculated sinoatrial conduction time) or ventricular refractoriness. It is concluded that IV Mg has several electrophysiologic effects that may be beneficial in the treatment/prevention of supraventricular tachyarrhythmias.