Role of afterload in determining regional right ventricular performance during coronary underperfusion in dogs.

The relationship between coronary perfusion pressure and regional myocardial performance of the right ventricular free wall was studied, in the presence or absence of right ventricular hypertension in 13 open-chest dogs. The right coronary artery was perfused through a shunt from a carotid artery. Regional systolic shortening of the right ventricular free wall was measured by means of a sonomicrometric technique at various levels of coronary perfusion pressure. Regional shortening was insensitive to coronary perfusion pressure or flow when it was above 31 mm Hg or 0.27 ml/min per g. Once coronary perfusion was below this critical level, regional shortening in both base to apex and circumferential orientations decreased linearly, depending on the degree of perfusion pressure. Despite the presence of a monoexponential relationship between coronary perfusion pressure or flow and regional shortening, a direct linear relation between perfusion pressure and flow was consistently noted, with or without pulmonary artery banding, suggesting that there is limited autoregulation of right coronary flow. The critical perfusion pressure for maintaining regional myocardial function of the right ventricle was highly dependent on the level of right ventricular systolic pressure (r = 0.64 - 0.72, P less than 0.05). Thus, right ventricular systolic pressure was one of the important determinants of regional wall motion during coronary underperfusion.