Heterogeneity of myocardial oxygen metabolism of the right ventricle

To determine whether the right ventricular (RV) myocardial oxygen metabolism was heterogeneous, oxygen extraction ratios (EO2) and regional myocardial blood flow (RMBF) of the basal, middle and apical regions of the RV free wall were studied in open-chest dogs.After control studies, the following interventions were applied; 1) atrial pacing (200 beats/ sec), 2) intravenous infusion of isoproterenol (1.0μg/kg/min) and 3) pulmonary artery constriction to raise RV systolic pressure to 40-50mmHg. The venous blood from three anterior cardiac veins was sampled directly, and RMBF was measured using colored microspheres. EO2 was significantly lower in all areas of the RV compared to that in the left ventricle (LV). In control, the basal region of the RV extracted more oxygen than the apical region (p<0.01), and RMBF tended to be lower in the basal than the apical. Thus, myocardial oxygen consumption in the control did not differ in each area of the RV. During all interventions, greater increases in EO2 were observed in the apical and middle regions than in the basal region, and RMBF increased by a similar amount in all three regions. Therefore, we suspected that oxygen metabolism in the RV was dependent on not only RMBF but also EO2, and varied from region to region. This heterogeneity of oxygen metabolism tended to disappear under RV overload.