Association between peripheral and coronary microvascular function and the impact of myocardial bridging

The reactive hyperemia index (RHI) is a marker of peripheral microvascular function influenced by both endothelium-dependent and independent mechanisms. Myocardial bridging (MB) may impact coronary microvascular function, but its effect on the relationship between RHI and coronary microvascular function remains unclear. In this cross-sectional study, 38 patients underwent noninvasive RHI assessment alongside invasive coronary microvascular function testing. MB was identified via coronary angiography, while endothelium-dependent and independent coronary microvascular function were evaluated using coronary flow reserve in response to intracoronary administration of acetylcholine and microvascular resistance reserve in response to intravenous administration of adenosine, respectively. Among 38 patients (mean age: 59 years, 34% male), 14 had MB. RHI correlated with an index of endothelium-independent coronary microvascular function (r = 0.34, p = 0.04), whereas it did not correlate with that of endothelium-dependent function. This correlation persisted in patients without MB (r = 0.54, p = 0.01) but was lost in those with MB (p = 0.83). RHI is associated with endothelium-independent coronary microvascular function, but MB disrupts this relationship, suggesting a local impact on coronary microvascular physiology.