Morphological characteristics and endothelial dysfunction in patients with myocardial bridging assessed by intracoronary ultrasound

초록

Background: Myocardial bridging (MB) was described when a segment of coronary artery travels through the myocardium. Although intravascular ultrasound (IVUS) is highly useful for visualizing arterial wall and surrounding structures, detailed morphological IVUS characteristics and its relations to endothelial dysfunction are not clarified. Methods: A total 74 patients (pts; 43 men, mean age; 54.3±10.1 yrs) who underwent diagnostic coronary angiography with acetylcholine (Ach) provocation test and in whom typical angiographic ‘milking effects’ in left anterior descending artery were selected for IVUS examination and off-line analysis. Results: A specific, echolucent narrow muscular band-like structure (‘half-moon’) surrounding MB segment and characteristic systolic compression with delayed relaxation in diastole of MB was observed in all pts. The half moon located within, outside of the MB segment were 40.5% (30/74), 6.8% (5/74) respectively and both within and outside was 52.7% (39/74). Focal (discrete) type half-moon was 37.8% (28/74), Multifocal type 31.1% (23/74) and Diffuse (>30mm) type 31.1% (23/74). Narrow (≤1mm) type half moon was 81.1% (60/74), Broad type (>1mm) was 14.9% (11/74) and Mixed type was 4.1% (3/74). Curved type half moon was 87.8% (65/74), Straight type 4.1% (3/74) and Mixed type was 8.1% (6/74). Actual mean MB length was 48.3 ± 31.1 mm (range; 2 to 148 mm). Interestingly, 90.5% (67/74) of the pts showed no atherosclerotic lesions within the MB segment and only 5.4% (4/74) had mild plaque within the MB segment. Significant atherosclerotic plaques were commonly found in the proximal or distal of the MB segment. Significant focal or diffuse spasm was induced in inside (8.1%), outside (2.7%) or both side (89.2%) of MB segment by Ach provocation test in 68.9% (51/74) of pts. Conclusion: All MB pts had the characteristic half-moon sign which causing systolic compression in MB segment by IVUS. The most common morphological characteristics of half-moon were focal, narrow and curved type. The MB segment commonly spared from the atherosclerotic lesions and frequently associated with Ach induced endothelial dysfunction.