Dissociation between epicardial and transmural function during acute myocardial ischemia.

Abstract

We have previously developed a method employing cardiac positron-emission tomography (PET) with 15O (half-life 2.1 min)-labeled water (H2(15)O) and blood pool subtraction with C15O for assessment of myocardial perfusion. This study was performed to determine whether the method developed permits detection of the differences in blood flow, induced by vasodilator stress, indicative of functionally significant subcritical coronary stenosis despite normal perfusion at rest. Coronary stenoses were induced with a small Teflon cylinder placed in the left anterior descending coronary artery of the closed-chest dog. Regional myocardial blood flow was assessed tomographically with H(2)15O given intravenously and C15O given inhalation. Blood flow distal to the stenoses was normal under conditions of rest. However, significant reductions in the hyperemic response to dipyridamole were detected consistently in regions distal to 50% to 70% diameter stenoses. Flow distal to stenoses more than doubled in absolute terms in response to dipyridamole but was only 43 +/- 9% of the increased flow in normal regions in the same dogs or in corresponding anterior regions in normal dogs. Relative myocardial blood flow measured noninvasively with PET correlated closely with the distribution of radiolabeled microspheres measured in vitro (r = .88). Thus, assessment of myocardial blood flow with H(2)15O and PET in dogs at rest and during vasodilator-induced stress permits detection of physiologically significant coronary stenoses. The procedure should therefore prove useful diagnostically for the detection of coronary insufficiency in patients as well as for the assessment of clinical interventions designed to augment regional perfusion.