Electrocardiographic and blood pressure changes in experimental pericardial effusion and occlusion of the venae cavae

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The electrocardiographic and blood pressure changes previously reported in the presence of artificial pericardial effusions have been confirmed with some additional detail, particularly concerning the recovery period. Change in position of the animal does not alter the extent or direction of the observed changes. Simultaneous rapid infusion of normal saline solution into the right or left auricle modifies the blood pressure changes, but not the electrocardiographic changes. Transient occlusion of the venae cavae or of the cavae and the pulmonary artery causes a comparable drop in systemic blood pressure, but does not reproduce the electrocardiographic changes of artificial pericardial effusion, and tends to produce changes less in degree and opposite in direction. This difference holds whether the experiments are performed on the same or on different animals. Some possible mechanisms by which pericardial effusion might produce electrocardiographic change are discussed and interference with venous return, chemical changes, and temperature changes eliminated from consideration as the primary mechanism. The effect of direct pressure on the myocardium, on the coronary vessels, and on the Thebesian vessels remains as an important possibility.