Presence of ramus intermedius increases the risk of atherosclerotic plaque formation at the left main bifurcation's region: A retrospective study from CT coronary angiography in UMMC

Abstract

<h2>Background</h2> Ramus intermedius (RI) is a variant vessel arising from the left main bifurcation angle (LMBA). Haemodynamically, its presence increases coronary turbulence flow and reduces the endothelial shear stress. In theory, this haemodynamic effect promotes atherosclerotic plaque formation, especially around the bifurcation region. <h3>Objectives</h3> This study aims to identify RI as a risk factor for atherosclerosis at the left main coronary artery (LMCA), proximal left anterior descending (LAD) and proximal left circumflex (LCx) using coronary computed tomography angiography (CCTA). <h3>Methodology</h3> A retrospective review was carried out on 374 CCTA cases in University Malaya Medical Centre (UMMC) between January 2017 and December 2018. The atherosclerotic plaque at the LMCA, proximal LAD and proximal LCx arteries were analysed in the presence or absence of RI. Statistical analysis was done using the chi-square test and binary logistic regression. <h3>Results</h3> RI was identified in 32.4% (<i>n</i> = 121) of patients. Age > 65 years old, male gender, diabetes, hypertension and RI were identified as significant risk factors for atherosclerosis. The presence of RI increases plaque formation by 8.5-fold for proximal and distal LMCA compared to those without RI (aOR: 8.5, 95% CI: 1.7, 43.0, <i>p</i> > 0.001). Meanwhile, at the proximal LAD, RI increases the risk for plaque formation by 3.7 folds (aOR: 3.7, 95% CI: 1.5, 9.4 <i>p</i> = 0.006) at the lateral wall and by 4.9 folds (aOR: 4.9, 95% CI: 1.7, 14.2, <i>p</i> = 0.003) for both lateral and medial wall. RI also independently increases the risk for atherosclerosis by 3 folds at the lateral and medial wall of proximal LCx (aOR: 3.7, 95% CI: 1.2, 11.4, <i>p</i> = 0.020). Lastly, RI increases the risk of obstructive stenosis in the LMCA, LAD and LCx by 3.9 folds (aOR: 3.9, 95% CI: 1.4, 10.5, <i>p</i> < 0.001). <h3>Conclusion</h3> Our findings suggest that the presence of RI independently increases the risk for atherosclerotic plaque formation in the left main stem and its proximity. RI in situ is believed to exert altered haemodynamic effect promoting atherosclerotic plaque formation.