Electrocardiographic evidence for a cardioprotective effect of nifedipine during experimental hypercalcemia.

To investigate the effect of nifedipine on hypercalcemic electrocardiographical alterations, steadily increasing hypercalcemia was induced in guinea-pigs by continuous calcium gluconate infusion until cardiac arrest occurred. During the experimental time the electrocardiograms were continuously recorded and compared in animals with and without pretreatment by nifedipine (Adalat). The hypercalcemia-induced electrocardiographical alterations intensified during increasing serum calcium levels. Ascending serum potassium and magnesium levels indicated increasing cell damage with a leak of these mainly intracellular ions. Pretreatment by nifedipine did not significantly influence the hypercalcemia-induced bradycardia and augmentation of the P-Q interval except a small and transient effect during relatively low calcium levels. The drug, however, exerted a distinct normalizing effect on hypercalcemic reduction of the S-T segment and the Q-T interval despite of an unaltered development of hypercalcemia. Accordingly, the cellular potassium and magnesium leaks were markedly reduced and the survival time during calcium infusion was significantly prolonged after nifedipine pretreatment. These electrophysiological data are in agreement with our previous cytochemical studies, which showed a protective effect of nifedipine against hypercalcemia-induced overloading of the cellular calcium depots in myocardial cells. Whether this cardio-protective effect of nifedipine during hypercalcemia can be used therapeutically in hypercalcemic crisis, has to be examined in clinical studies.