Copyright © 1999 by the European Society of Cardiology.
Decreases by magnesium of QT dispersion and ventricular arrhythmias in patients with acute myocardial infarction
a Division of Cardiology, Helsinki University Central Hospital, Helsinki
b Department of Medicine, Jorvi District Hospital, Espoo, Finland
accepted July 12, 1998
Abstract
Aims
Magnesium treatment suppresses ventricular arrhythmias in acute myocardial infarction and possibly mortality after infarction, but the underlying mechanisms are inadequately understood. We tested whether the effect of magnesium could be attributed to an influence on the autonomic control of the heart, changes in disturbed repolarization, relief of ischaemia or limitation of myocardial injury.
Methods and Results
Fifty-nine consecutive patients with acute myocardial infarction were randomized to receive 70mmol of magnesium (n=31) infused over 24h or placebo (n=26). Occurrence of ventricular arrhythmias and heart rate variability (SD of 5-min mean sinus beat intervals over a 24h period, SDANN; low frequency/high frequency amplitude ratio, LF/HF ratio), and the number of ischaemic episodes on vectorcardiography were measured from the first day of treatment. QT dispersion corrected for heart rate was measured from the 12-lead ECG. Magnesium decreased the number of hourly ventricular premature beats (P<0·001) and the number of ventricular tachycardias (P<0·05). QT dispersion corrected for heart rate was decreased in both measurements at 24h and 1 week (P<0·001). SDANN and LF/HF ratio were unchanged. The number of ischaemic episodes on vectorcardiography were equal, and peak creatine kinase MB release did not differ between the groups. In testing the pathophysiological mechanisms, serum magnesium levels after infusion correlated with hourly ventricular premature beats (rs=–0·47;P<0·01), ventricular tachycardias (rs=–0·26;P<0·05), and QT dispersion corrected for heart rate (rs=–0·75;P<0·001), but not with SDANN, LF/HF ratio or peak creatine kinase MB. QT dispersion corrected for heart rate correlated with hourly ventricular premature beats (rs=0·48;P<0·001) and ventricular tachycardias (rs=0·27;P<0·05).
Conclusions
Magnesium suppresses early ventricular arrhythmias in acute myocardial infarction. The decreased arrhythmicity is related to enhancement of homogeneity in repolarization, but not to attenuation of prevailing is-chaemia, improvement of autonomic nervous derangements or myocardial salvage.
Key Words: Magnesium • acute myocardial infarction • QT dispersion
1 Correspondence: Hannu Parikka, MD, Division of Cardiology, Helsinki University Central Hospital, PO Box 340, FIN-00029, Helsinki, Finland.
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