Relation between coronary artery geometry and the distribution of early sudanophilic lesions

The relationship between the angle formed by the left circumflex (LCX) and left anterior descending (LAD) coronary arteries at the bifurcation of the left main coronary artery (LM) and the location of sudanophilia in the proximal portions of the LCX and LAD, was investigated, using a normalized index of disease severity (relative proximal involvement, RPI) to isolate the local effect of geometry on the predisposition to disease from that of other risk factors. Multiplane angiograms of the left coronary artery system of 15 hearts were digitized and processed to form a three-dimensional representation of the centerline of the lumen (termed the 'axis') of each coronary segment; the LM branch angle was objectively computed from the reconstruction. The coronary vessels were fixed in situ, removed from the hearts, opened longitudinally and stained with Sudan IV. The RPIs of the LAD and LCX were obtained by dividing the percentage sudanophilia seen en face in the first 1 cm of each vessel by the percentage sudanophilia in the first 5 cm. RPI was correlated negatively with LM branch angle, suggesting that a small LM branch angle may be a 'geometric risk factor' for proximal atherosclerotic disease in the daughter vessels. The correlation was stronger for the LCX than the LAD. These results would appear to be consistent with the notion that atherosclerosis is favored where a larger extent of the vessel experiences fluid dynamic wall shears near zero for an appreciable part of the pulsatile cycle.