The effect of myocardial bridging of the coronary artery on vasoactive agents and atherosclerosis localization

Abstract

The relationship between alterations in the immunohistochemical expression of three vasoactive agents [endothelial nitric oxide synthase (eNOS), endothelin-1 (ET-1), and angiotensin-converting enzyme (ACE)] and the occurrence human atherosclerosis was investigated in relation to the myocardial bridge (MB) of the left anterior descending coronary artery (LAD), an anatomical site that experiences increased shear stress. Five millimetre cross-sections of LADs with MB from 22 autopsied cases were taken from the left coronary ostium to the cardiac apex and were immunohistochemically stained with antibodies against eNOS, ET-1, and ACE. The extent of atherosclerosis in each section was calculated using the atherosclerosis ratio (intimal crosssectional area/medial cross-sectional area) determined by histomorphometry. The results were analysed according to their anatomical location relative to the MB, either proximal, beneath, or distal. The extent of atherosclerosis was signi®cantly lower beneath the MB, compared with proximal and distal segments. The expression of eNOS, ET-1, and ACE was also signi®cantly lower beneath the MB. The expression of these agents correlated signi®cantly with the extent of atherosclerosis. Because nitric oxide, after its production by eNOS, is believed to be degraded by superoxide radicals, the effect of eNOS expression on atherosclerosis remains controversial. However, the present ®ndings clearly indicate that the expression of ET-1 and ACE is directly related to the development of human coronary atherosclerosis in vivo through shear stress.

Myocardial bridging increases the risk of coronary spasm

“…46 Furthermore, an immunohistochemical study has shown that the expression of endothelial nitric oxide synthase is suppressed beneath MB. 47 These findings support our hypothesis that vascular dysfunction occurs in MB segments.…”

Prevalence and predictors of bridging of coronary arteries in a large Indonesian population, as detected by 64-slice computed tomography scan

“…Several pathology studies have been performed assessing the extent of atherosclerosis, particularly within the bridge, in patients with MB [34]. Altogether, the data suggest that MB is associated with the decreased development of atherosclerosis under and proximal to the tunnelled artery, although it is unclear whether this is an independent factor [35]. It seems that MB located within 5 cm from the left coronary ostium may prevent atherosclerosis in the proximal part of LAD [36].…”

Ausência de arteriosclerose na porção intramiocárdica das artérias coronárias

“…In 2001, Masuda et al [13] investigated the relationship between the expression of main vasoactive agents such as endothelin-1 (ET-1), the angiotensin converting enzyme (ACE) and endothelial nitric oxide synthase (eNOS), with its location in relation to myocardial bridge and the degree of involvement by arteriosclerosis. They found that in the intramyocardial portion of the left anterior descending artery there was no histopathological sign indicating the beginning of arteriosclerosis in the intima and that the arteriosclerosis rate is significantly smaller in the myocardial bridge portion in relation to the proximal and distal segments of the bridge.…”

“…They established a significant association between both the differential expression of vasoactive agents along the anterior descending coronary artery with less expression in the myocardial bridge as an association between decreased expression of vasoactive agents with lower arteriosclerosis rates. It was demonstrated that the expression of vasoactive agents is related to an altered hemodynamic stress on the vascular wall, suggesting that the decrease of shear stress, beyond interfering with the lipid transfer phase to the vascular wall in arteriogenesis, also works to reduce the expression of vasoactive agents (Figure 3) [13].…”