The effect of regional myocardial ischemia on series elastic and contractile elements of glycerinated heart muscle in dogs.

The response of the contractile and the series elastic elements to ischemia was studied with isometric contraction and quick release methods after measuring the passive length-tension relationship in glycerinated heart muscle fibers of dogs at resting state. Myocardial infarction was induced by ligating left coronary artery. Muscle fibers taken from the ischemic area three hours after ligation demonstrated reduction in maximal developed tension (P0), the maximal rate of tension development (dp/dtmax) and Vmax. The time to peak tension (t0) was increased. As in fresh papillary muscle the modulus of elasticity of active glycerinated muscle increased in proportion to load. The stiffness of the series elastic element elevated significantly in ischemic muscle fibers. The passive stiffness in resting state showed a decrease in the slope accompanied by an increase in the intercept in ischemic heart muscle. Therefore, increased stiffness of the series elastic element and diminished contractility are present following acute myocardial infarction.