Abstract
Myocardial potassium balance and hemodynamics were studied in 19 patients. In 12 patients the effect of diphenylhydantoin administration was studied and in 7 the effect of pretreatment with diphenylhydantoin on the ionic and hemodynamic responses to ouabain was observed. Diphenylhydantoin caused no change in myocardial potassium balance, but a significant fall in left ventricular dP dt and a brief increase in left ventricular end-diastolic pressure occurred. Heart rate, cardiac output, stroke work and brachial arterial pressure did not change. In patients pretreated with diphenylhydantoin, ouabain administration was followed by a significant loss of potassium from the myocardium. This was accompanied by a significant increase in left ventricular dP dt and a decrease in left ventricular end-diastolic pressure. No change occurred in heart rate, cardiac output, stroke work or brachial arterial pressure. These ionic and hemodynamic responses to ouabain after pretreatment with diphenylhydantoin are similar in magnitude and timing to those observed when only ouabain is administered. These results in man are compatible with theories of digitalis action which associate inotropic effect with the inhibition of membrane sodium- and potassium-activated adenosine triphosphatase and indicate that diphenylhydantoin acts on the heart by some mechanism other than stimulation of this enzyme.
Published Version
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