Heart failure: An electron microscopic study of the left ventricular papillary muscle in aortic insufficiency in the rabbit

Abstract

The left ventricular papillary muscle was studied by electron microscopy in 31 rabbits subjected to experimental aortic insufficiency and sacrificed at different stages (from 2 days to 10 months) after valvulotomy. The fixation was performed quickly after stopping the heart in diastole, by means of an intra-coronary venous injection of iso- or slightly hyper-osmotic fixative. The electron microscopic appearances were quite different depending on the date of death. From the second to the twenty-first days, there were many modifications of the cellular picture, related to increased protein synthesis, or to disturbances in cellular metabolism. Myofibrillar “lesions” (stretching of the I-band and Z-line, which predominate beneath the intercalated disc) may represent either growth of the myofilaments or true lesions of contractile proteins. During the later stages (from 1 to 10 months after valvulotomy), there were two types of modifications: the “usual” appearances of hypertrophy, and “clarification” of certain cells with a decrease in the density of structural proteins and an increase of the surface occupied by sarcoplasm. There was no longer any myofibrillar or cellular damage, apart from some appearances thought to be covered by a state of under-contractility. Heart failure, which was not always easy to establish, was correlated with the extent of cellular alterations in the early stages, but poorly in the later ones. Throughout the whole experiment the average sarcomere length, apart from very localized stretching of the I band in the early stages, never differed from controls.