Optimal right ventricular filling pressures and the role of pericardial constraint in right ventricular infarction in dogs.

Abstract

Previous studies have reported an important role for right ventricular function in the pathophysiology of the low cardiac output state that can accompany right ventricular infarction. Some studies have suggested that right ventricular distensibility impairs right ventricular filling and stroke output; others have demonstrated that the pericardium can mediate depressed left ventricular filling and stroke output. To determine the role of pericardial constraint and optimal volume loading in an experimental model of right ventricular wall infarction, six mongrel dogs were studied before and after right ventricular wall infarction and after volume loading. The pericardium was then opened in two phases. In the first phase, the pericardium was opened partially to allow the atria to distend freely, and in the second phase, the pericardium was opened completely. The animals were preinstrumented with two sets of piezoelectric crystals attached to the right ventricular free wall, one in the infarct and the other in the noninfarct territory. Left ventricular size was estimated by left ventricular crystals on the anterior wall of the left ventricle. Right ventricular and left ventricular Millar catheters were used to assess intracavitary pressure, and a flat balloon was used to assess intrapericardial pressure. Right ventricular infarction reduced cardiac output by 23% and stroke volume by 30%. End-diastolic segment length and transmural pressure of the left ventricle decreased. Volume loading restored cardiac output to baseline values and was mediated by a significant increase in end-diastolic length in the noninfarct territory. This was achieved by increasing right ventricular end-diastolic pressure from 9 +/- 2 to 16 +/- 3 mm Hg (p less than 0.01). Partial opening of the pericardium mediated significant increases in both end-diastolic segment lengths of the left ventricle and the noninfarct territory. Left ventricular end-diastolic pressure decreased slightly by 3 mm Hg (p = NS). Complete opening of the pericardium increased cardiac output and stroke volume and mediated a significant decrease in right and left ventricular end-diastolic pressures. Left ventricular transmural pressure and end-diastolic segment lengths of the left ventricle and the noninfarct territory increased. Left ventricular diastolic pressure-segment length relations were shifted upward by right ventricular infarction. A partial opening of the pericardium shifted this relation downward in all animals, and complete opening of the pericardium shifted the relation rightward and further downward. Cardiac output is restored to baseline values by volume loading sufficient to increase the right ventricular diastolic pressure to 16 +/- 3 mm Hg. Evidence of pericardial constraint was observed and appears to be mediated by an atrioventricular interaction in addition to the direct ventricular interaction.