Computational Fluid Dynamics Analysis of the Effect of Plaques in the Left Coronary Artery
PURPOSE The most frequent cause of ischemic heart disease is atherosclerosis. The atherosclerotic process is responsible for lumen stenosis in coronary arteries leading to impaired blood flow and reduced perfusion. The most important human epicardial artery is the left main coronary stem (LMS) which divides into two "daughter" branches: left anterior descending artery (LAD) and left circumflex artery (LCX). LMS is responsible for the blood supply to 80% of the left ventricular wall, apex and interventricular septum. Therefore, the diagnosis with coronary angiography of significant LMS stenosis is associated with a much poorer prognosis than in the case of other epicardial arteries. Undoubtedly, this finding is associated with fast qualification to revascularization, but at the same time leaves evaluation of the phases of plaque development "neglected" in this part of the coronary system. The situation is compounded by the fact that no ultrasound criteria for LMS have been established so far to correctly determine the severity of atherosclerosis and qualification for percutaneous coronary intervention (PCI). The aim of study was to evaluate plaques in LMS and proximal LAD and LCX segments in patients with symptomatic multivessel coronary disease who underwent PCI. MATERIAL AND METHODS The present retrospective analysis was performed in 48 patients with significant stenoses in middle segments of LAD and LCX. The study population was divided into 2 equal groups. Group 1 (Gr1) consisted of patients with angiographically normal LMS, whereas group 2 (Gr2) was composed of patients with angiographically moderate stenosis in LMS (diameter stenosis - %DS 30-50%). Revascularization in each case was preceded by intracoronary ultrasound (ICUS) during which LMS, as well as proximal segments of LAD and LCX over a distance equal to LMS were studied. Quantitative angiography (QCA) included measurements of reference diameter (RD) and %DS. Planimetric and volumetric measurements during ICUS were done at 1 mm intervals and vessel diameter (VD), minimal lumen area (LAmin), lumen stenosis (%LS), plaque burden (PB), plaque volume (PV), and remodeling index were determined. Additionally, a new ICUS parameter representing the distribution of atherosclerotic plaque - plaque volume index (PVI) was proposed. CONCLUSIONS 1. Sequential development of the atherosclerotic plaque occurs in LMS and proximal segments of LAD and LCX. The proximal segment of LAD is especially predisposed to plaque formation, followed by LMS and LCX. 2. PVI is the parameter best suited for determination of atherosclerotic plaque distribution. PVI = 1.45 is the borderline value between insignificant and moderate plaque size in LMS. 3. The significant correlation between diameters and areas of LMS and proximal segments of its branches allows for calculation of expected size of LMS. The lumen area of LMS measured with ICUS should be the sum of lumen areas of its branches, whereas in moderate LMS stenosis the area should exceed 75% of the sum. 4. LMS LA < 6.0 mm2 and %LS > 50% satisfy the criteria qualifying for revascularization.