Coronary and Systemic Hemodynamic Effects of Cardiac Pacing in Man with Complete Heart Block

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Abstract
Twelve subjects with an average age of 65.9 years who had complete heart block had cardiac output and coronary blood flow measured at three different rates of pacing. Cardiac output and calculated external work increased with rate from the slow to the intermediate rate, but declined at the fast rate. Even at the intermediate rate, cardiac output remained low as compared to standards for normal younger subjects. Coronary blood flow and left ventricular oxygen usage increased with cardiac rate. Cardiac efficiency, expressed as left ventricular work divided by left ventricular oxygen consumption, tended to decrease as cardiac rate rose; however, these changes were not statistically significant. Lactate consumption increased with rate, but changes in glucose and pyruvate consumption were not significant. Considering the circulatory system as a whole, the intermediate or normal resting rate was more efficient. At this rate the cardiac output and cardiac work were greatest, and the mixed venous oxygen content (which must reflect body tissue oxygenation) was highest, while the cardiac oxygen consumption and coronary blood flow were intermediate.