Contribution of Asynergic Contraction to Halothane-Induced Myocardial Depression

Abstract

We investigated the possibility that myocardial asynergy (dyscoordinate contraction) is a contributing mechanism to the impairment of cardiac function produced by halothane. Coronary cineangiograms were performed in seven dogs, awake and at 1, 2, and 3 MAC halothane. The relative motions between four arterial bifurcations (six segments) were plotted as an indication of changing ventricular dimensions. To quantitate ventricular asynergy, we calculated anisotropy (AI) and asynchrony (AS), the coefficient of variation of mean shortening (S-) and of mean time to half shortening (T-50), respectively, of the six segments. From these a myocardial performance index (MPI) was derived: MPI = S-/AI + T-50 + AS. In general, S- and MPI decreased with increasing halothane concentration. Anisotropy showed a trend, although usually insignificant, toward increasing, while AS did not change. These observations have two implications. First, asynergy of contraction contributes little, if anything, to halothane-induced impairment of myocardial performance. Second, changes in measurements of intact cardiac performance, such as dP/dtmax, may be reasonably valid during halothane, provided loading conditions are taken into account.