Regional Myocardial Blood Flow in Lambs with Concentric Right Ventricular Hypertrophy

Abstract

Chronically hypertrophied right ventricles function normally under high systolic pressures, whereas normal right ventricles fail when they are acutely subjected to similar pressures. This phenomenon may be partly due to adaptation of the coronary circulation as well as to hypertrophy. Knowledge of the magnitude and distribution of coronary blood flow and the degree of coronary vascular reserve are important in understanding the function of hypertrophied myocardium. We studied these variables in 16 awake, 5-12-week-old, tranquilized lambs; 9 of the lambs had had their main pulmonary artery banded at 2 days of age. Pressures, cardiac output, and coronary blood flow (radioactive microsphere method) were measured at rest and during two stress states-isoproterenol and dextran infusion. Ventricular function was similar in control and banded lambs. We found significant right ventricular hypertension and both right ventricular and septal hypertrophy in the banded lambs. Total coronary blood flow per gram was slightly higher in banded lambs in all states, and right ventricular flow per gram was significantly elevated at rest and during isoproterenol infusion. Right ventricular coronary resistance per gram was significantly lower in banded lambs in all states. These changes demonstrate that hypertrophied right ventricular tissue is not ischemic at rest, since there is vascular reserve. The changes also raise the question of increased vascularity in hypertrophied myocardium. Right ventricular oxygen supply per unit oxygen demand was increased in banded lambs at rest and during isoproterenol infusion. This finding suggests that hypertrophied myocardium has inefficient oxygen utilization, low oxygen extraction, or both. KEY WORDSradioactive microspheres coronary vascular resistance pulmonary stenosis subendocardial flow coronary blood flow Dextran 70 isoproterenol

Effects of exerimental right ventricular hypertrophy on myocardial blood flow in conscious dogs.

“…Whereas the observed effects of right ventricular hypertrophy on myocardial blood flow are not totally dissimilar from those reported by Archie et al (12), several important differences do exist. First, in our study, right ventricular hypertrophy is associated with significant and selective increases in right ventricular flow per gram, i.e., no change in left ventricular flow per gram occurred, as contrasted with statistically insignificant increases in both right and left ventricular flow as reported by Archie et al (12).…”

“…First, in our study, right ventricular hypertrophy is associated with significant and selective increases in right ventricular flow per gram, i.e., no change in left ventricular flow per gram occurred, as contrasted with statistically insignificant increases in both right and left ventricular flow as reported by Archie et al (12). Second, to avoid the marked direct and indirect effects of anesthesia on myocardial function and blood flow (25), our experiments were performed on fully conscious dogs, whereas Archie et al (12) employed sedated animal preparations.…”

“…First, in our study, right ventricular hypertrophy is associated with significant and selective increases in right ventricular flow per gram, i.e., no change in left ventricular flow per gram occurred, as contrasted with statistically insignificant increases in both right and left ventricular flow as reported by Archie et al (12). Second, to avoid the marked direct and indirect effects of anesthesia on myocardial function and blood flow (25), our experiments were performed on fully conscious dogs, whereas Archie et al (12) employed sedated animal preparations. And third, in our study, the pressure overloadinduced hypertrophy was produced in adult, fully developed dogs, subjected to both short-and long-term pressure overload, whereas Archie et al (12), banded the pulmonary artery of 2-d-old lambs and subsequently studied the effects of the pressure overload 5-12 wk later.…”

“…Second, to avoid the marked direct and indirect effects of anesthesia on myocardial function and blood flow (25), our experiments were performed on fully conscious dogs, whereas Archie et al (12) employed sedated animal preparations. And third, in our study, the pressure overloadinduced hypertrophy was produced in adult, fully developed dogs, subjected to both short-and long-term pressure overload, whereas Archie et al (12), banded the pulmonary artery of 2-d-old lambs and subsequently studied the effects of the pressure overload 5-12 wk later. Whereas in the adult animal, the increase in right ventricular mass is thought to be primarily a result of an increase in cell size but not cell number (26,27), in the newborn, both hypertrophy and hyperplasia may account for the increase in ventricular mass.…”

“…The changes in myocardial blood flow associated with right ventricular hypertrophy have been examined less extensively (11,12). Because of the frequent clinical occurrence of right ventricular hypertrophy in response to pulmonary hypertension, as well as congenital pulmonary artery stenosis, it seems important to evaluate both the level and the regional distribution of coronary blood flow associated with chronic, severe, right ventricular hypertrophy in a conscious animal model.…”