The delayed effects of pericardial removal

Abstract

The technic adopted for pericardial removal is described. It is pointed out that success of such intra-thoracic operations appears largely to depend on the avoidance of cooling of the lungs (by warming the ether-air mixture), and pleurae (by operating in a very warm room). The operations were made on 15 cats and observations covered periods ranging from 5 days to 17 mos. Pericardectomized cats are indistinguishable from normal ones on mere inspection. Neither the heart rate, nor the blood pressure, as recorded under chloralose narcosis, show abnormalities on comparison with controls. X-ray examinations showed that the cardiac shadow of the pericardectomized cat is permanently enlarged, indicating restraint of the normal heart by the pericardium. That restraint of the normal heart is only relative is shown by the often marked, though temporary, dilatation caused by chloroform or ethyl chloride narcosis. Far greater enlargement, however, is provoked by these drugs on the unrestrained pericardectomized heart. The characteristic globoid shape of the pericardectomized heart is not due to severance of the diaphragmatic attachments. If these are sectioned, and the pericardium left intact, the shape and size of the cardiac shadow remains normal. The permanently enlarged pericardectomized heart is found, both on direct inspection in the living, and on dissection in the dead animal, to be dilated rather than hypertrophied. Microscopic study of the epicardial layer shows that this becomes progressively hypertrophied after removal of the pericardium. This is due to increase in both elastic and collagen fibers, particularly the latter, and the thickness of the epi-cardium may be increased 10-fold as compared with normal. The serous layer generally remains unchanged; sometimes, however, it is reflected over small finger-like projections of the underlying connective tissue. Experiments were made with a view to ascertaining the reason for this increase in epicardial thickness. They point to its being due to friction against the pleurae, rather than to an effort at compensatory hypertrophy to make up for the absence of a fibrous pericardium. In conclusion, these experiments show (in the species studied) that the pericardium restrains the size and shape of the heart; that this restraint, however, is relative and not absolute; and that the fibrous pericardium is not an inextensible membrane in the living animal.