Brachial artery low-flow-mediated constriction is increased early after coronary intervention and reduces during recovery after acute coronary syndrome: characterization of a recently described index of vascular function

Aims The endothelium plays a role in regulating vascular tone. Acute and dynamic changes in low- flow- mediated constriction (L- FMC) and how it changes with regard to traditional flow-mediated dilatation (FMD) have not been described. We aimed to investigate the changes in brachial artery L-FMC following percutaneous coronary intervention (PCI) and during recovery from non-ST-segment elevation myocardial infarction (NSTEMI). Methods and results FMD was performed in accordance with a previously described technique in patients before and after PCI and in the recovery phase of NSTEMI, but in addition, L-FMC data were acquired from the last 30 s of cuff inflation. About 135 scans were performed in 96 participants (10 healthy volunteers and 86 patients). Measurement of brachial L-FMC was reproducible over hours. L-FMC was greater among patients with unstable vs. stable coronary atherosclerosis (21.33 +/- 1.09% vs. 20.03 +/- 1.26%, P < 0.01). Following PCI, FMD reduced (4.43 +/- 2.93% vs. 1.66 +/- 2.16%, P < 0.01) and L-FMC increased (20.33 +/- 0.76% vs. 21.63 +/- 1.15%, P 0.02). Furthermore, during convalescence from NSTEMI, L-FMC reduced (21.37 +/- 1.19% vs. 0.01+ 0.82%, P < 0.02) in parallel with improvements in FMD (2.54 +/- 2.19% vs. 5.15+ 3.07%, P < 0.01). Conclusion Brachial L-FMC can be measured reliably. Differences were observed between patients with stable and unstable coronary disease. L-FMC was acutely increased following PCI associated with reduced FMD and, in the recovery from NSTEMI, L-FMC reduced associated with increased FMD. These novel findings characterize acute and subacute variations in brachial L-FMC. The pathophysiological and clinical implications of these observations require further study.