Abstract
Background: Coronary microvascular dysfunction (CMD) is characterized by impaired myocardial flow reserve (MFR) in patients with non-obstructive coronary artery disease (CAD). The real-world incidence of CMD, risk factors for decreased MFR, and characteristics of the two CMD endotypes (classical and endogenous) in this population remain unclear.
Methods and Results: After screening 1,313 patients with suspected or known CAD who underwent 13N-ammonia positron emission tomography (PET), 345 with non-obstructive CAD were retrospectively enrolled in the study. Stress/resting myocardial blood flow (MBF) was quantified using 13N-ammonia PET. PET-assessed CMD (impaired MFR <2.0) was diagnosed in 60 (17%) patients. Independent predictors of decreased MFR included older age, female sex, anemia, and hypertension; however, these factors accounted for only 32% of the observed variability in MFR. Symptomatic status was not an independent predictor of decreased MFR. Patients with classical CMD (resting MBF <1.3 mL/min/g) had higher summed stress scores and stress/resting coronary vascular resistance, whereas patients with endogenous CMD (resting MBF ≥1.3 mL/min/g) showed female dominance, higher stress MBF, and a higher resting rate-pressure product.
Conclusions: Among patients with non-obstructive CAD, approximately 1 in 5 had PET-assessed CMD. Age, female sex, anemia, and hypertension were independent clinical factors associated with impaired MFR, which explained a limited portion of its variability. Further examination of unidentified or unmeasured factors is warranted.
