Coronary Collaterals: A Comprehensive Review

Coronary collateral circulation consists of pre-existing arterial connections that can be recruited and enlarged when a coronary stenosis develops. This review traces their developmental and anatomic basis and summarizes how metabolic and inflammatory milieu modulate growth. We appraise assessment methods, showing the limits of visual angiographic grading and emphasizing a function-first approach that includes the collateral flow index, intracoronary electrocardiography during brief occlusion, and quantitative perfusion by cardiac magnetic resonance and positron emission tomography. Across acute infarction and chronic total occlusion, stronger collaterals are linked to smaller infarcts, less microvascular injury and hemorrhage, greater myocardial salvage, and better ventricular recovery, although anatomy does not always reflect true perfusion. Therapeutic opportunities are led by exercise training and external counterpulsation, with metabolic and biologic strategies emerging. Artificial intelligence can standardize angiographic interpretation and estimate collateral function without additional hardware, supporting objective, bedside decision-making. We outline practical gaps and propose a concise, function-first framework for integrating collaterals into routine care.