Coronary Physiology Beyond Coronary Flow Reserve in Microvascular Angina

Angina with no angiographic stenosis, commonly called "microvascular angina," encompasses a wide continuum of coronary pathophysiology in conflicting published reports. Comprehensive quantitative myocardial perfusion offers new insights beyond overly simplistic coronary flow reserve. Integrating regional absolute stress flow, relative stress flow, coronary flow reserve, and qualitative subendocardial perfusion gradient on tomograms of relative images, provides correct diagnosis, quantitative physiological classification, and potential treatment. Angina without angiographic stenosis is associated with abnormal quantitative perfusion with rare, but instructive, exceptions. However, microvascular dysfunction without angina is common, particularly associated with risk factors. Reduced subendocardial/epicardial relative activity is common with diffuse coronary artery disease without focal stenosis with or without angina depending on the severity of reduced subendocardial perfusion. Precision quantitative myocardial perfusion in 5,900 cases objectively classifies angina with no angiographic stenosis into 4 categories: subendocardial ischemia due to diffuse coronary artery disease (most common), overlooked stenosis, diffuse microvascular dysfunction due to risk factors or specific microvasculopathies, and nonischemic cardiac pain mechanisms (rare), or some mix of these prototypes, of which 95% associate with risk factors, or subclinical or clinically manifest coronary atherosclerosis needing vigorous risk factor treatment.