STRUCTURAL REMODELING AND MECHANICAL DYSFUNCTION OF CARDIAC MYOCYTES IN HEART-FAILURE

End stage heart failure due to ischemic (ICM) or dilated (DCM) cardiomyopathy is characterized by a dilated, relatively thin-walled ventricle. The hypothesis has been proposed that the structural basis of ventricular expansion is due to side-to-side slippage of myocytes within the wall. Although this represents one potential mechanism for the observed phenomena of chamber dilatation and subsequent wall thinning, the degree of slippage claimed is not necessarily in harmony with the magnitude of chamber enlargement and mural thinning. Moreover, sarcomere extension was not examined in the base to the apical regions of the heart, leaving open the question as to the role of changes in resting sarcomere length in acute chamber dilatation. In this regard, an alternative etiology for the detrimental cardiac architectural rearrangement seen in dilated failure can be supplied by postulating the occurrence of maladaptive remodeling of cardiac myocyte morphology. In this model, myocytes increase in length by an increase in the number of sarcomeres in series, thus increasing chamber diameter in an attempt to maintain cardiac output. However, these cells do not enlarge to any significant degree in the transverse diameter preventing the heart from developing adequate force. This hypothesis is supported by recent evidence from patients with ICM and DCM indicating that myocyte lengthening alone could account for all the dilatation observed. Furthermore, it appears that the thinning of the ventricular wall in failure is due to inadequate transverse growth of cardiac myocytes coupled with scattered myocyte cell loss throughout the ventricular wall. The ultimate consequence is that the ratio of myocyte length to myocyte width is increased in heart failure. Evidence also indicates that these long, slender myocytes have a reduced ability to shorten and/or develop adequate force to compensate for the extent of chamber dilation. Thus, differential myocyte cell growth is postulated to be the primary event involved in the pathological morphometric changes observed during dilated cardiac failure. A molecular mechanism may be involved in the activation and expression of fetal or atrial genes controlling myocyte shape.