Coronary blood flow and distribution in right ventricular hypertrophy

Myocardial blood flow and distribution in animals with righ ventricular (RV) hypertrophy have not been studied extensively in the experimental laboratory. This study was carried out to investigate whether or not ischemia can be induced in the hypertrophied right ventricle. Ten adult foxhounds underwent banding of the pulmonary artery. One year later coronary flow and distribution were studied by use of radioactive microspheres. Myocardial oxygen supply and demand were estimated by planimetry of aortic and RV pressure tracings. Data were obtained in the control state, during atrial pacing to a heart rate of 200 +/- 4 beats/min (mean +/- SD), during aorta-right atrial shunting to reduce mean aortic pressure to 60 +/- 6mm Hg, and during aortic constriction to produce a mean aortic pressure of 145 +/- 8mm Hg. RV weight/body weight ratio was 2.2 +/- 0.2 gm/kg(normal, 1.3 +/- 0.1 gm/kg) (p less than 0.001). RV free wall thickness was 11.3 +2- 0.7 mm (normal, 6.7 +/- 0.4 mm) (p less than 0.001). At rest, RV oxygen supply/demand ration was 4.7, and the RV subendocardial/subepicardial (Endo/Epi) flow ratio was 0.93. During atrial pacing, RV supply/demand was 54% of control (p less than 0.01), RV Endo/Epi ratio was 1.00 (p less than 0.05), and right coronary artery (RCA) resistance was 59% of control (p less than 0.01). Aorto-right atrial shunting resulted in an RV supply/demand ratio of 31% of control (p less than 0.01), RV Endo/Epi ratio of 0.95, and RCA resistance of 45% of control (p less than 0.01). During aortic constriction, RV supply/demand ratio was 132% of control (p less than 0.05), RV Endo/Epi ratio was 0.92, and RCA resistance was 146% of control (p less than 0.01). Phasic RCA flowmeter tracings demonstrated an increased proportion of diastolic flow in the study animals as compared to normal animals. In conclusion, myocardial blood flow and distribution in the hypertrophied right ventricle remained normal at rest and during hemodynamic stress. Compensatory mechanisms which maintain normal flow and distribution may include changes in RCA resistance and phasic flow patterns. Under the imposed conditions, RV ischemia and failure did not occur.