Brachial Artery "Low-Flow Mediated Constriction" Is Associated with Myocardial Perfusion Defect Severity and Mediated by an Altered Flow Pattern during Occlusion.

INTRODUCTION: The relationship between low flow-mediated constriction (LFMC), a new proposed measure of endothelial function, with cardiovascular disease severity and its hypothesized stimulus, that is, low flow, has not been comprehensively evaluated. The study evaluated association between change in brachial artery diameter during constriction with severity of myocardial perfusion defect (PD) and alterations in different components of flow profile. METHODS: Brachial artery responses to occlusion were assessed in 91 patients and 30 healthy subjects. Change in anterograde and retrograde blood flow velocities (delta anterograde blood flow velocity and retrograde blood flow velocity), anterograde shear rate and retrograde shear rate (delta ASR and RSR, respectively), and oscillatory shear index (delta) during forearm occlusion at 50 mm Hg above systolic pressure, from baseline was calculated. Myocardial perfusion was evaluated in patients using exercise single positron emission computed tomography and % myocardial PD was calculated from summed stress score. RESULTS: LFMC emerged as independent predictor of defect severity after correcting for age and gender (p = 0.014). Sixty-seven patients (73.6%) and 15 healthy subjects (50%) showed constriction during occlusion. In stepwise backward regression analysis, RSR contributed 35.5% and ASR contributed 20.1% of the total 63.9% variability in artery diameter during occlusion. CONCLUSION: The results suggest that LFMC is independently associated with myocardial perfusion severity and is "mediated" by an altered flow profile during occlusion.