The effect of diphenylhydantoin (Dilantin) and quinidine on left ventricular function in dogs

The effect of Dilantin upon left ventricular performance was investigated in an open-chest dog preparation and compared to that of quinidine under identical conditions. An initial intravenous injection of Dilantin produced a transient negative inotropic effect upon the left ventricle. The magnitude of the negative inotropic effect was similar following comparable dose levels of quinidine base, but the duration of the effect was more transient after Dilantin. The maximal negative inotropic effect following a second Dilantin injection was greater than that following an initial injection. After the second injection of quinidine, however, the degree of myocardial depression was similar to that following the initial injection. Again, the duration of the effect after Dilantin was more transient than after quinidine. The results with Dilantin are in keeping with the fact that most potent antiarrhythmic agents depress ventricular function. Insofar as such data may be applied to clinical situations, one must weigh the harmful transient negative inotropic effect of Dilantin against its beneficial antiarrhythmic property.