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

Abstract

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 (-1.33 ±1.09% vs. -0.03 ± 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 (-0.33 ± 0.76% vs. -1.63 ± 1.15%, P = 0.02). Furthermore, during convalescence from NSTEMI, L-FMC reduced (-1.37 ± 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.

Figures

Figure 1

Raw data from a representative scan illustrating the measurement of low-flow-mediated constriction and flow-mediated dilatation; the brachial artery was continuously imaged for 11 min (1 min rest, 5 min cuff inflation, and 5 min cuff deflation). Low-flow-mediated constriction was calculated from data acquired during the last 30 s of cuff inflation. Flow-mediated dilatation was calculated as maximum percentage change in the vessel diameter from baseline following cuff release.

Figure 2

Mean percentage change in the vessel diameter compared with baseline for each individual measurement during the last 30 s before cuff deflation (at time = 0) during repeated healthy volunteer studies, P = 0.97 (n= 10).

Figure 3

Separate (A) and composite (B) brachial flow-mediated dilatation and low-flow-mediated constriction before and after diagnostic angiography (n= 8).

Figure 4

Correlation of brachial flow-mediated dilatation to low-flow-mediated constriction among (A) healthy volunteers (n= 10) and (B) patients with coronary atherosclerosis (n= 42).

Figure 5

Association of extent and severity of coronary atherosclerosis (coronary score index, CSI) with (A) flow-mediated dilatation, (B) low-flow-mediated constriction, and (C) composite score of flow-mediated dilatation plus low-flow-mediated constriction (n= 36).

Figure 6

Flow-mediated dilatation and low-flow-mediated constriction before and 2 h after percutaneous coronary intervention (n= 10). Upper graphs: separate (A) and composite (B) brachial flow-mediated dilatation and low-flow-mediated constriction (*P = 0.02 and **P < 0.01). Lower graph: mean percentage change in the vessel diameter compared with baseline for each individual measurement during the last 30 s before cuff deflation (at time = 0), analysis of variance, P < 0.001.

Figure 7

Flow-mediated dilatation and low-flow-mediated constriction at the time of non-ST-segment elevation myocardial infarction (baseline) and after a period of convalescence (follow-up), n= 11. Upper graphs: separate (A) and composite (B) brachial flow-mediated dilatation and low-flow-mediated constriction (*P = 0.02 and **P < 0.01). Lower graph: mean percentage change in the vessel diameter compared with baseline for each individual measurement during the last 30 s before cuff deflation (at time = 0), analysis of variance, P < 0.001.