The Effect of Ischemia and Alterations of Heart Rate on Myocardial Potassium Balance in Man

Myocardial electrolyte balance and lactate metabolism were studied in 30 patients before, during, and after a period of atrial pacing utilizing a continuous automated sampling technic with simultaneous electrocardiographic and hemodynamic observations. Eight patients with coronary artery disease who had no symptoms during pacing and four normal subjects demonstrated myocardial potassium loss but no abnormalities in lactate metabolism, the electrocardiogram, and hemodynamics during pacing. Myocardial potassium loss was correlated with increments in heart rate and was followed by potassium uptake during the post-pacing period. Eighteen subjects developed angina during pacing associated with hemodynamic and electrocardiographic abnormalities. This ischemic group showed significantly greater myocardial potassium loss during pacing than the non-ischemic group, and this was closely associated with myocardial lactate production at a ratio of 1 mEq of potassium being lost for each 2 millimoles of lactate produced. Increased acidity of coronary sinus blood also accompanied potassium loss during ischemia. No significant changes were seen in sodium balance in either group during the study.