Background Myocardial bridge (MB) is characterized by focal compression of a coronary artery in systole by an overlying band of myocardium. Chronic compression and relaxation of the myocardial bridge may produce endothelial dysfunction by direct stress.
Objective The goal of this study was to assess the hypothesis that the myocardial bridge alters endothelial function, thus influencing the plaque formation.
Methods We studied 128 patients (54.7±10.9 yr, 42 men) with typical angiographic systolic milking effects having greater than a 30 % reduction in diameter of the coronary artery during systole after intracoronary nitrate (NTG, 200 μg) infusion. There were 231 control patients without overt coronary artery disease including MB (54.1±3.2 yr, 111 men). Endothelial function was estimated by incremental acetylcholine infusion (Ach: 20, 50 and 100 μg/min) into the left coronary ostium. Assessments using intracoronary ultrasound (ICUS) were obtained in 74/128 patients with MB and 81/231 controls.
Results The mean vasoconstrictive response to maximal Ach was more pronounced at the bridging segments than at matched segments in the controls (-71.9±4.4 vs. -30.3±2.6, p = 0.009). Coronary vasoconstriction (> 50 %) to Ach was seen more frequently in the MB group than in controls (114/128 (89.8 %) vs. 81/231 (35.1 %), p = 0.007). There was no significant correlation between the severity of MB and vasoconstriction in response to Ach. As determined by ICUS, there was a typical half-moon phenomenon in 71/74 (95.9 %) cases of the MB group, but not in controls (p<0.001). The plaques at the bridging segments were absent in 67/74 (90.5 %) and mild in 7/74 (9.5 %) cases, as compared with those of matched segments of the LAD in controls (plaque burden 5.91±1.37 % vs. 24.71±24.21 %, p = 0.002).
Conclusion Despite the prominent relationship between the MB and endothelial dysfunction, the bridging segments are spared from atherosclerotic plaque formation.
- endothelial function
- intracoronary ultrasound
- myocardial bridge
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