Correlation between divalent cation concentration and electrocardiogram in canine myocardial infarction.

Myocardial infarction is accompanied by changes in serum divalent cation concentrations. The effects of these changes on the electrical activity of the heart have not been fully determined. In six mongrel dogs, major coronary arteries were catheterized and occluded with metal beads; in five dogs the arteries were catheterized, but left patent. Serum magnesium concentrations ([Mg++]), zinc concentrations ([ZN++1]), copper concentrations ([Cu++]), calcium concentrations ([Ca++]), and ECGs were monitored in each dog at one, 24, 48, and 72 hours after surgery. Only dogs with coronary artery occlusion had ST segment changes (1.9 +/- 0.4 mm) in chest lead V4. Serum [Mg++] and [Zn++] decreased (approximately 20%) only after coronary artery occlusion and only at 24 hours after the procedure. Runs of ventricular tachycardia and premature beats were prevalent at this time. Serum [Cu++] was different in that it increased (approximately 30%) at 48 and 72 hours in the dogs with and without coronary artery occlusion. No changes were observed in serum [Ca++]. Decreases in serum [Mg++] and Zn++] coincided with the periods of dysrhythmia in the ischemic hearts. Elevation of serum [Cu++] was not specifically associated with myocardial ischemia and, within these physiologic limits, it appeared to be without effect on cardiac electrical activity.