Coronary vasodilator reserve in young dogs with moderate right ventricular hypertrophy

The effects of experimental right ventricular (RV) pressure overload and RV hypertrophy on coronary vasodilator reserve in young animals is not well established. Therefore, we measured coronary vasodilator reserve in the right ventricle of dogs from 7 to 12 months old with moderate RV hypertrophy due to pulmonary artery banding performed 3 to 7 days after birth. In the 5 dogs with pulmonary artery banding, substantial RV hypertension developed (RV pressure at rest, 73 +/- 11 mm Hg) as did RV hypertrophy (ratio of RV free wall/left ventricular free wall weight, 1.86 +/- 0.41 gm/kg). The reactive hyperemic response following brief coronary occlusions was used as an index of coronary vasodilator reserve. The ratios of peak reactive hyperemic response to resting flow, however, were not significantly different in the 5 banded dogs compared with 7 control animals (3.6 +/- 1.0 versus 2.6 +/- 0.6); this implies that the extent of vasodilator reserve was similar with or without moderate RV hypertrophy. In addition, myocardial blood flow, as determined using radioactive microspheres, was not significantly different at rest: 0.57 +/- 0.09 ml/min per gram in the banded dogs versus 0.48 +/- 0.12 ml/min per gram in the controls. Uniform transmural distribution of blood flow was maintained during infusion of isoproterenol, which was used to increase myocardial oxygen requirements in both groups. Minimum coronary vascular resistance was significantly lower in the banded than the control dogs (1.5 +/- 0.6 versus 6.2 +/- 2.3; p less than 0.01). This difference suggests that the cross-sectional area of the right coronary vascular bed increased with the development of RV hypertrophy.