Pathology of the Heart Following Chronic Cardiac Lymphatic Obstruction

The histopathologic effects of impaired cardiac lymph drainage was studied in 22 dogs by excising the cardiac lymph node with its adjoining lymphatics. Dye injections and pathologic‐anatomic examinations were performed from 1 hour up to 9 months after the original procedure. Regeneration of major lymph channels was not detected, and only 3 animals showed lymph drainage along alternate pathways. Gross distention of subepicardial lymph vessels was present in 5 animals only and was never observed later than after 2 months. Hence the observations indirectly suggest the presence of functioning lymphovenous communications. The histopathologic changes were confined to the endocardium and atrioventricular valves, whereas no abnormalities of the myocardium were detected by light microscopy. In the initial stages the subenocardial and valvular lymphatics appeared distended, and from 2–3 weeks onwards a moderate increase in connective tissue was observed in the subendocardial areas. Changes were more pronounced in the mitral and tricuspid valves, which developed deposits of myxoid substance. After 2 months a substantial increase of mesenchymal tissue and fibers was also observed, leading to a marked thickening of the valvular leaflets. These changes persisted throughout the observation period and were believed to be of permanent character. The observations suggest that impaired cardiac lymph drainage may be of significance to rheumatic heart disease and to myxoid valve degeneration in humans.