Experimental cardiac tamponade: A hemodynamic and doppler echocardiographic reexamination of the relation of right and left heart ejection dynamics to the phase of respiration

A hallmark of cardiac tamponade is pulsus paradoxus. However, the exact mechanism of pulsus paradoxus and the relation of left and right ventricular ejection dynamics remain controversial, with some studies suggesting an inverse relation in ventricular filling and ejection and others citing a more important role for the effects of right heart ejection dynamics delayed by transit through the pulmonary artery bed. To specifically reexamine this issue, six sedated but spontaneously breathing dogs were studied during experimental cardiac tamponade with use of extensive hemodynamic instrumentation and Doppler methods. During cardiac tamponade, left ventricular systolic pressure decreased from 125.8 ± 12.1 to 81.7 ± 26.7 mm Hg (p < 0.01) and cardiac output from 5.86 ± 1.48 to 2.34 ± 0.98 liters/min (p < 0.001); mean pericardial pressure increased from −1.2 ± 0.8 to 10.5 ± 3 mm Hg (p < 0.001) and pulsus paradoxus from 4.3 ± 1.6 to 10.7 ± 1.2 mm Hg (p < 0.001) compared with baseline values. An inverse relation in left and right ventricular ejection dynamics that was very close to 180° out of phase was seen throughout the respiratory cycle in multiple hemodynamic and Doppler variables including peak systolic pressures, aortic and pulmonary flow velocities and ventricular ejection times. Simultaneous recording of the transmitral pressure gradient provided indirect evidence that the ventricular ejection dynamics were directly related to changes in ventricular filling. However, the magnitude of ventricular pressure or output flow velocity for each respiratory cycle was variable, depending on the exact timing of filling and ejection in relation to the phase of respiration. Variation in left ventricular output due to changes in right ventricular output delayed by transit through the pulmonary vasculature was not recognized in any animal. It is concluded that in spontaneously breathing dogs with acute cardiac tamponade, peak ventricular pressures, ventricular ejection times and pulmonary and aortic flow velocities have an inverse relation that is very close to 180° out of phase.