Endothelial-dependent microvascular dysfunction related to scintigraphic myocardial perfusion defects

We tested the hypothesis that scintigraphic myocardial perfusion defects during exercise in patients with. normal coronary angiogram may be related to endothelial-dependent microvascular dysfunction in response to sympathetic stimulation such as cold pressor test (CPT). Methods: Thirty-eight patients were classified into two groups according to the presence or absence of exercise-induced scintigraphic myocardial perfusion defects on (201) thallium SPECT images. CPT and nitroglycerin (NTG) application was performed during dynamic positron-emission-tomography (PET) to establish blood-flow mediated vasoreactivity and endothelium-independent vascular responses of coronary microcirculation, respectively. Results: Twenty-eight patients (10 smokers, 10 hypercholesterolemic and 8 hypertensive pts.) revealed regional myocardial perfusion defects with a mean reversibility of the original stress defect of 20+/-3 %, whereas 10 patients had normal scintigraphic imaging. In patients with exercise-induced myocardial perfusion defects, the corresponding responses of regional myocardial blood flow (RMBF) to CPT were significantly reduced as compared to patients with normal perfusion imaging (RMBF: 0.75+/-0.16 to 0.78+/-0.20 versus 0.75+/-0.15 to 1.38+/-0.26 mL . g(-1) min(-1); ppound0.03, respectively). The vascular responses of each study group are given in the Table 1 (mean +/- SD) (Fig. 1). In addition, there was a significant correlation between the endothelium-dependent responses of RMBF to CPT and the severity of exercise-induced scintigraphic regional myocardial perfusion defects (r=0.95, p=0.001) (Fig. 2). Conclusions: Exercise-induced scintigraphic myocardial perfusion defects in patients with angina pectoris but normal coronary angiogram may be related to at least in part endothelial-dependent microvascular dysfunction.