Clinical meaning
Coronary microvascular dysfunction (CMD) involves impaired function of coronary arterioles (< 500 μm) that cannot be visualized on standard coronary angiography. The pathophysiology includes endothelial dysfunction with reduced nitric oxide bioavailability, smooth muscle dysfunction with impaired vasodilation, microvascular remodeling with increased wall-to-lumen ratio, and extravascular compressive forces. CMD is the underlying mechanism in many patients with angina and non-obstructive coronary arteries (ANOCA/INOCA), affecting up to 50% of patients referred for angiography who have no significant epicardial stenosis. The coronary flow reserve (CFR < 2.0) and index of microcirculatory resistance (IMR > 25) are invasive measures of microvascular function. CMD is associated with adverse cardiovascular outcomes including MI, HF, and CV death despite normal angiography.
Diagnosis & workup
Diagnostics & workup: - Invasive coronary function testing: coronary flow reserve (CFR < 2.0 abnormal), index of microvascular resistance (IMR > 25), acetylcholine provocation for epicardial/microvascular spasm - Cardiac PET: gold standard non-invasive test for myocardial blood flow reserve (MBFR < 2.0 suggests CMD) - Cardiac MRI: stress perfusion defects without corresponding LGE (ischemia without infarction) - Coronary angiography: exclude obstructive CAD (< 50% stenosis in all epicardial vessels = ANOCA) - Echocardiography with coronary flow reserve assessment in LAD using Doppler - Exercise or pharmacological stress testing: may show ST depression/symptoms despite normal epicardial arteries - Endothelin-1 and inflammatory markers (hsCRP) — may be elevated - Screen for CV risk factors: lipid panel, HbA1c, BP assessment