Cardiac metabolism and electromechanics of human heart

The effects of substrates on the metabolic inhibitor-induced changes in the action potential and contraction of papillary muscles obtained from patients undergoing corrective open-heart surgery were studied. Anoxia produced a marked shortening of the action potential duration and a decrease in the resting potential, rate of rise of action potential, effective refractory period, and contractility. In anoxic muscle, although glucose completely restored the action potential duration, effective refractory period, and resting potential to control levels, it was unable to completely restore the contractility to the control level. Substrate depletion and metabolic inhibitors (iodoacetate, dinitrophenol) produced effects similar to that of anoxia, but at a faster rate. Glucose restored the action potential and, to a lesser extent, contractility to the control level in dinitrophenol-treated muscle but was ineffective in so doing the iodoacetate-treated muscle. Pyruvate, however, was effective in restoring the action potential and contracility in iodoacetate-treated muscle. Pretreatment of the muscle with glucose and, particularly, with glucose plus insulin prevented the combined effects of anoxia and lack of glucose on the action potential and contractility for a prolonged period. These results suggest that intravenous infusion of glucose and insulin before and during surgery might prevent or reduced the effect of anoxia on the electrical and mechanical activity of the heart during open-heart surgery.