Prognostic value of modified coronary flow capacity by 13N-ammonia myocardial perfusion positron emission tomography in patients without obstructive coronary arteries

Background: Vasodilator capacity of coronary circulation is an important diagnostic and prognostic tool in patients with coronary artery disease (CAD). We aimed to clarify the incidence of coronary microvascular dysfunction (CMD), defined as impaired modified coronary flow capacity (mCFC) proposed by Johnson and Gould and measured by N-13-ammonia myocardial perfusion positron emission tomography (PET), in patients without obstructive CAD and to evaluate the risk of future cardiovascular events. Methods: This retrospective study recruited 407 consecutive CAD-suspected patients who underwent both pharmacological stress/rest N-13-ammonia PET and coronary angiography. Of the 407 patients, 137 patients (median age, 70 years; 63 women) were eligible and followed up (median, 19.8 months). Endpoints were defined as cardiovascular death or major adverse cardiovascular events (MACEs), such as cardiovascular death, nonfatal myocardial infarction, unplanned hospitalization for any cardiac reasons, and unplanned coronary revascularization. The impaired mCFC group included patients with mildly to severely reduced regional CFC in, at least, one vascular territory (n = 34), while the remaining patients (n = 103) were categorized as having preserved mCFC. Results: Overall, cardiovascular death and MACEs occurred in five (4%) patients. The Kaplan-Meier curve showed a significant reduction in event-free survival for cardiovascular death (p = 0.004) and MACEs (p < 0.0001) in the impaired mCFC group, compared to the preserved mCFC group. Impaired mCFC was independently associated with the incidence of both cardiovascular death and MACEs after propensity-score adjustments [hazard ratio (HR), 10.7; 95% confidence interval (CI), 1.0-106.0; p = 0.04 and HR, 9.5; 95% CI, 2.5-36.2; p < 0.001, respectively]. Conclusions: In CAD-suspected patients without obstructive coronary arteries, impaired mCFC was observed in approximately 25% and was associated with a higher risk of cardiovascular death and MACEs. The mCFC concept can help identify patients who would benefit from specific therapies or lifestyle modifications to prevent future MACEs and can clarify potential mechanisms of CMD. (C) 2021 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.