The role of the right heart in acute cardiac tamponade in dogs.

Because of anatomic differences between the right and left heart, we hypothesized that the reduction in left ventricular stroke volume during acute cardiac tamponade is the passive result of decreased pulmonary venous return due primarily to right heart compression. To test this hypothesis, two types of experiments were performed in dogs. Group 1: in fresh, potassium-arrested hearts, rightand left-sided cardiac chambers were filled to previously determined physiological end-diastolic pressures. When saline then was introduced into the pericardial space, right heart volumes were reduced more rapidly than left heart volumes in all cases. These data indicate that the right heart is compressed more easily than the left heart by pericardial fluid when initial filling pressures are in the physiological range. Group 2: in intact animals, abrupt cardiac tamponade was created by rapid injection of saline into the pericardial space. Measurement of ventricular pressures, and descending aortic and left pulmonary artery flow demonstrated a marked phase lag between changes in right and left ventricular stroke volumes and transmural end-diastolic pressures, with alterations in the right ventricle preceding those in the left. The decrease in left ventricular stroke volume required an average of 13 beats to equal the decrease in right ventricular stroke volume. These data indicate that left ventricular stroke volume is preserved after abrupt tamponade until pulmonary blood volume is diminished by unequal right and left ventricular outputs. We conclude that acute cardiac tamponade can occur without significant direct effects on the left heart. Changes in systemic cardiac output are primarily passive and reflect compression of the right heart, diminished right ventricular stroke volume, and decreased pulmonary blood volume. Circ Res 48: 701-710, 1981