Ventricular collagen matrix and alterations.

There is a complex extracellular structural matrix in the heart. This matrix appears to be composed of a variety of fibrils and fibers extending from the cell surface to the basal lamina and from the basal lamina to the matrix. The extensions into the extracellular region interconnect with a system of collagen bundles. The latter are so located that they would tether the myocytes to each other as well as tether the capillaries to the myocetes. There is an extensive weave of collagen analogous to the perimysium of skeletal muscle that separates groups of myocytes. The weave surrounding a group of myocytes is connected to adjacent weave patterns by long, tendonlike structures. The collagen matrix around cells disappears 2-3 hr after coronary-artery occlusion. In the periinfarct region of viable cells, the matrix is similarly lost and is replaced by scarlike collagen. Encephalomyocarditis virus causes a similar loss of the matrix in necrotic as well as some adjacent nonnecrotic regions. Replacement of the lost matrix is by scar tissue. The long-term appearance of the replacement fibrosis closely resembles the appearance of diffuse fibrosis as seen in a variety of conditions. These observations suggest that diffuse fibrosis can occur secondary to loss of the matrix both with and without myocyte necrosis. This may help explain the diffuse left ventricular fibrosis as seen in a variety of human disease.