Potassium exchange in the human heart: effect of heart rate and myocardial ischemia.

The concentration of potassium ions, [K+], in the blood of the coronary sinus was recorded using catheter-tip potassium ion-selective electrodes during fixed rate atrial pacing for up to six minutes in five patients with normal hearts (control group) and in eight with coronary artery disease. Four patients with coronary artery disease developed pain in the chest and changes on the electrocardiogram during atrial pacing (ischemic group). In the control group, the coronary sinus [K+] began to rise after three seconds to a peak increase of 0.33 +/- 0.04 mmol.l-1 (p less than 0.001) and then returned to the resting value. On cessation of pacing, coronary sinus [K+] fell rapidly and transiently below the resting value. In the ischemic group, the coronary sinus [K+] began to rise after three seconds to a peak of 0.42 +/- 0.05 mmol.l-1 (p less than 0.01); it remained elevated throughout the period of atrial pacing (p less than 0.01) and fell rapidly and transiently below the resting value on cessation of pacing. Four patients with coronary artery disease did not develop ST segment depression during atrial pacing; in two the changes in coronary sinus [K+] were the same as those in the ischemic group, and in two they were similar to those in the control group. These data show that in man there is an immediate and transient loss of potassium from the myocardial cells when the heart rate is increased and that this loss is restored the heart rate returns to the resting rate. Myocardial ischemia causes a continuing efflux of potassium from myocardial cells.(ABSTRACT TRUNCATED AT 250 WORDS)