Effects of Calcium on the Electrocardiogram

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Abstract
Effects of calcium on myocardial cells were investigated in the in situ canine heart. Ninety-three experiments were performed on 28 anesthetized dogs. Solutions of high or low calcium concentrations were perfused into the coronary artery through an artificial coronary circuit. Surface and intracellular electrograms were simultaneously recorded. The most prominent effect of low calcium was the prolongation of the membrane action potential duration. The most prominent effects of high calcium were a shortening or disappearance of phase 2 and a decrease in the amplitude of phase 2. The mechanism of S-T segment elevation is discussed in association with these findings. These observations show that true S-T segment elevation can be caused by the faster repolarization of cardiac muscle cells in the injured area.

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