The Coronary Venous System in Acute Coronary Syndrome: A Narrative Review.

Acute coronary syndrome (ACS) remains a leading cause of death and morbidity worldwide. The pathophysiology of ACS has been largely interpreted through abnormalities of the coronary arteries and the microvascular bed. However, the coronary circulation is fundamentally a closed-loop system, in which the venous component represents the final link in myocardial blood return. In contrast to the extensive literature on arterial and microvascular disease, there are relatively few studies on the coronary venous system (CVS) in the context of ACS. The CVS is important in relation to ACS from two complementary perspectives. First, structural or functional abnormalities of the CVS can contribute to myocardial ischemia; second, coronary venous flow can reflect the hemodynamic outcomes of acute ischemia and reperfusion. The 'vascular waterfall' phenomenon is considered one of the primary mechanisms governing coronary venous return, linking myocardial compression and venous pressure to the flow from the coronary sinus (CS) into the right atrium. Experimental and clinical evidence has shown that CS thrombosis is associated with myocardial infarction and may also complicate ACS. Furthermore, studies evaluating CS blood flow generally show a decrease in the acute phase of ischemia and an increase after reperfusion. However, the existing evidence is limited and largely based on small observational studies. Therefore, this review aimed to examine the pathophysiological mechanisms and hemodynamic behavior of the CVS in ACS, starting from embryological development.