Absence of atherosclerosis evolution in the coronary arterial segment covered by myocardial tissue in cholesterol-fed rabbits

Abstract

The evolution of atherosclerotic lesions is suppressed in the intima of the human coronary artery, beneath myocardial bridges. To elucidate the mechanism of the protective effect, we investigated morphological changes using the rabbit coronary artery as a model. Rabbit fed a 1%-cholesterol diet were killed at intervals up to 20 weeks. Two short segments of the left coronary arteries running in the epicardial adipose tissue (EpiLAD) and subsequently running in the myocardium (MyoLAD) were compared morphologically. The intima of the EpiLAD had flat endothelial cells with a polygonal shape, and demonstrated raised atherosclerotic lesions with increase in serum cholesterol level. In contrast, the intima of the MyoLAD was free of atherosclerotic lesions throughout the study, and the endothelial cells were spindle-shaped and engorged. While ferritin particles reached only the surroundings of the internal elastic lamina in the MyoLAD, they permeated into the media of the EpiLAD. We suggest that myocardial bridges suppress coronary atherosclerosis by an alteration of endothelial permeability, which may be due to changes in haemodynamic force tending towards a higher shear stress. The data provide an insight into the relationship between haemodynamics and the development of coronary atherosclerosis.

Myocardial Bridge as a Structure of “Double-Edged Sword” for the Coronary Artery

“…6). 38) Furthermore, in the rabbits, the endothelial cell shapes by scanning electron microscopy exhibited similar changes to those of human LAD across MB. These fi ndings indicate that the LAD intima proximal to the entrance of the human MB or rabbit myocardial covering is susceptible to atherosclerosis due to increased permeability through high shear stress across the endothelium, when either MB or myocardial covering is present in the LAD.…”

Myocardial bridges are free from atherosclerosis: Overview of the underlying mechanisms

“…It was reported that the intima of a mural coronary segment is significantly thinner (66.3 µm) than the proximal portion (406.6 µm) of the artery (10). Endothelial cell permeability was found to be increased in atherosclerotic epicardial segments of hypercholesterolemic rabbits, but not within myocardial bridges (11). Other studies indicated that the intimal layer of a bridge is spared from foam cells and synthetic-type vascular smooth muscle cells, which precipitate plaque formation (12).…”

Ponte miocárdica: evolução clínica e terapêutica

“…Study data have shown a significant variation regarding the frequency, incidence and prevalence rates and the angiographic results. The angiographic prevalence of myocardial bridges is < 5% 6-8 , a fact attributed to thin myocardial bridges that cause little compression to the tunneled segment and are present in most cases that the area below the MB is spared in atherosclerotic disease, whereas the proximal area is prone to the development of atheroclerosis 9,10 . In the present study, 27.6% of the patients presented involvement of the proximal segment of the bridge due to varying degrees of CAD.…”