Reduction of maximal coronary vasodilator capacity in conscious dogs with severe right ventricular hypertrophy.

Abstract

Right coronary reactive hyperemia and the maximal coronary vasodilator response to adenosine were examined in conscious, normal dogs and dogs with right ventricular (RV) hypertrophy. RV hypertrophy was induced by chronic (5-7 months) pulmonary artery stenosis. With RV hypertrophy, RV weight to body weight ratio rose by 70% (P < 0.001), right coronary artery blood flow (Doppler ultrasonic technique) rose from 17 +/- 1 to 51 +/- 5 ml/min, and RV transmural blood flow (radioactive microsphere technique) increased from 0.78 +/- 0.06 to 1.62 +/- 0.10 ml/min per g, while the RV endocardial:epicardial perfusion ratio decreased from 1.36 +/- 0.04 to 1.0 +/- 0.02. Excess blood flow debt repayment following release of a 15-second right main coronary artery occlusion was attenuated markedly (P < 0.001) to 107 +/- 22% from the normal value of 325 +/- 41%. Maximal coronary vasodilator capacity (to iv adenosine) was reduced in the hypertrophied right ventricle, as reflected by a lower (P < 0.05) level of maximal transmural blood flow and a higher (P < 0.02) level of minimum coronary vascular resistance per gram of hypertrophied right ventricle compared to normal. During maximal coronary vasodilation, the endocardial:epicardial perfusion ratio decreased (P < 0.001) below unity in the hypertrophied right ventricle to a level (0.83 +/- 0.06) significantly lower (P < 0.001) than normal (1.16 +/- 0.03). Thus, the development of severe RV hypertrophy is characterized by an attenuated coronary response to acute ischemia and by a reduction in maximal coronary vasodilator capacity. We conclude that the increase in cardiac mass which results from chronic pulmonary artery stenosis is not accompanied by a proportionate increase in cross-sectional area of coronary vessels supplying the hypertrophied ventricle.