MODULATING EFFECT OF REGIONAL MYOCARDIAL PERFORMANCE ON LOCAL MYOCARDIAL PERFUSION IN THE DOG

We studied the effect of regional contractile performance on regional coronary blood flow and flow distribution in 10 dogs. The left anterior descending (LAD) coronary artery was cannulated and perfused. Maximal vasodilation was obtained with adenosine. Consequently, variations of LAD flow reflected changes of extravascular resistance. Lidocaine injected in the LAD caused a localized reduction of contractile performance as shown by the absence of systolic wall thickening. Global left ventricular performance and pressure were unchanged. Coronary extravascular resistance diminished and LAD flow increased from 4.8±0.5 to 6.2±0.6 ml/min per g (P<0.02). The endocardial:epicardial ratio increased from 1.02±0.07 to 1.28±0.07 (P<0.001). Isoproterenol in the LAD augmented systolic wall thickening. Regional coronary flow diminished from 5.1±0.5 to 3.3±0.4 ml/min per g (P<0.001), and the endocardial:epicardial ratio diminished from 1.08±0.07 to 0.75±0.07 (P<0.01). These data indicate that myocardial contractility is a major component of extravascular coronary resistance and is a mechanical determinant of coronary blood flow and its transmural distribution.