Echocardiographic and hemodynamic data were measured in closed-chest dogs during graded cardiac tamponade (pericardial pressure 5, 10, and 15 mm Hg) before and after production of diffuse ischemic left ventricular dysfunction. Left ventricular dysfunction was produced by intracoronary injection of nonradioactive microspheres (54+±3.9 mm diameter). Changes in left atrial pressure with cardiac tamponade were influenced by coexisting left ventricular dysfunction. Left atrial pressure increased

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... tamponade and was equal to pericardial pressure before left ventricular dysfunction was produced. However, after left ventricular dysfunction was produced, left atrial pressure was significantly higher than pericardial pressure before tamponade, but it fell toward pericardial pressure when tamponade was produced. Pulsus paradoxus (>10 mm Hg) was present in all animals with cardiac tamponade before left ventricular dysfunction but in only one animal afterward. During each level of tamponade, the inspiratory fall of aortic systolic pressure was greater before than with left ventricular dysfunction. The slope of the linear regression between pericardial pressure and millimeters of mercury of inspiratory fall in aortic systolic pressure was significantly greater before than with left ventricular dysfunction (0.74±+0.12 versus 0.32+0.12,p<0.05). Left ventricular dysfunction caused a leftward and upward shift of the pericardial pressure-volume relation. As a result, right atrial and ventricular collapse occurred with significantly smaller volumes of pericardial fluid after than before left ventricular dysfunction. We conclude that pulsus paradoxus may be absent in cardiac tamponade with coexisting left ventricular dysfunction and unequal filling pressures. Echocardiographic signs of cardiac tamponade may occur with small effusions in the presence of left ventricular dysfunction. (Circulation 1990;82:1370-1376 C ardiac tamponade is a clinical syndrome characterized by elevated venous pressure, an exaggerated inspiratory fall in arterial systolic pressure (pulsus paradoxus), and, as a late event, by arterial hypotension. Pulsus paradoxus and echocardiographic evidence of right atrial and right ventricular collapse are useful signs because they may differentiate hemodynamically insignificant pericardial effusion from cardiac tamponade.1-5 However, clinical observations suggest that pulsus paradoxus may be absent in patients with left ventricular dysfunction and elevated left ventricular filling pressure.1,6 In addition, although it has been reported that right ventricular diastolic collapse is sensitive to alterations in ventricular load,7,8 little is known about the effects of left ventricular dysfunction on chamber collapse during cardiac tamponade. These gaps in our knowl-edge are particularly relevant in view of the increasing numbers of patients with cardiac tamponade and coexisting cardiovascular disease.9 Accordingly, we studied cardiac tamponade in an animal model of ischemia-induced left ventricular failure to test the hypothesis that pulsus paradoxus is not present when cardiac tamponade occurs with concomitant left ventricular dysfunction manifested by elevated left ventricular filling pressure. We also examined the influence of left ventricular dysfunction on atrial and right ventricular collapse during tamponade. Methods Initial Study Studies were performed in eight nonconditioned, heartworm-free mongrel dogs (mean weight, 19.6+1.2 kg) anesthetized with pentobarbital sodium (25 mg/kg i.v.), intubated, and ventilated with a positive pressure respirator (Harvard Apparatus, Millis, Mass). The chest was opened through a left lateral thoracotomy at the fourth intercostal space and Tygon catheters were secured in the left atrial appendage and pericardial space. The pericardium was closed and the catheters were tunneled subcuta-by guest on