Chronic hypokalemia and the left ventricular responses to epinephrine and preload.

The effects of moderate, chronic (5 days) potassium depletion on cardiac function were assessed in 14 normokalemic and 13 hypokalemic open chest, anesthetized dogs. Cardiac responses to intravenous bolus injection of 2.5 micrograms/kg body weight epinephrine (10 normokalemic and 11 hypokalemic dogs) and to rapidly increased preload (8 dogs in each group) were evaluated. Hypokalemic dogs received a low potassium diet plus chlorthalidone. Plasma potassium levels were lower (p less than 0.001) in the hypokalemic dogs (3.2 +/- 0.1 mEq/liter [mean +/- SEM]) than in the normokalemic dogs (4.1 +/- 0.1). The inotropic response to epinephrine was lower in hypokalemic than in normokalemic dogs, the response of the maximal rate of rise of left ventricular pressure was 20% greater (p less than 0.03) and the response of the peak rate of change of ejection power was 60% greater in the normokalemic dogs. The relaxation response to epinephrine (the maximal rate of fall of left ventricular pressure) was 33% lower (p less than 0.02) in hypokalemic dogs. Responses to rapid volume expansion were impaired by hypokalemia; maximal stroke volume index was 31% lower (p less than 0.01), maximal cardiac index was 26% lower (p less than 0.01) and the peak response to the maximal rate of filling was 51% lower (p less than 0.01). There were no differences in basal cardiac function. Therefore, modest potassium depletion within the clinical range impaired the contractile and relaxation responses to epinephrine and preload and impaired rapid filling.