RESEARCH ARTICLES CURRENT SCIENCE, VOL. 111, NO. 2, 25 JULY 2016 368 *For correspondence. (e-mail: grajukm@gmail.com) Influence of variable bifurcation angulation and outflow boundary conditions in 3D finite element modelling of left coronary artery on coronary diagnostic parameter Kalimuthu Govindaraju 1, *, Irfan Anjum Badruddin 2 , Girish N. Viswanathan 3 , Sarfaraz Kamangar 2 , N. J. Salman Ahmed 4 and Abdullah A. A. A. Al-Rashed 5 1 Centre for Engineering Programs, HELP College of Arts and Technology, Kuala Lumpur, Malaysia 2 Department of Mechanical Engineering, University of Malaya, Malaysia 3 Consultant Interventional Cardiologist, Derriford Hospital, Plymouth, UK 4 Centre for Energy Sciences, Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, Malaysia 5 Department of Automotive and Marine Engineering Technology, College of Technological Studies, The Public Authority for Applied Education and Training, Kuwait Theoretical impact of left coronary bifurcation angu- lation (BA) variations and percentage of flow distribu- tion variations (FDV) in coronary artery branches (CAB) on anatomic assessment of bifurcated lesions, is investigated by considering fractional flow reserve (FFR) as a standard diagnostic parameter. According to Medina classification, computational models of coro- nary bifurcation lesions types of (1, 0, 0), (0, 1, 0) and (0, 0, 1) were developed. The models included BA of 30, 45, 60, 75, 90 and 120. Computational fluid dynam- ics analysis was performed under hyperaemic flow con- dition and FFR was evaluated with percentage of FDV in CAB. For any fixed percentage of flow in the CAB and change in BA, FFR was significantly affected in the lesion type (1, 0, 0) whereas no significance was found in the lesion types (0, 1, 0) and (0, 0, 1). Percent- age of FDV in CAB for any fixed BA significantly al- tered FFR in all the lesion types. Overall, 5%, 41% and 73% variations in FFR were found in (1, 0, 0), (0, 1, 0) and (0, 0, 1) respectively. The variation of BA could not be neglected in in vitro anatomical assessment for lesion type (1, 0, 0) but not in case of (0, 1, 0) and (0, 0, 1). Nev- ertheless, percentage of FDV in CAB is significantly al- tered FFR in the left coronary bifurcation lesions, which lead to underestimation of stenosis severity and post- ponement of coronary interventional procedure. Keywords: Bifurcation angulation, computational fluid dynamics, coronary branch flow, FFR, left coronary artery. FROM clinical practice, coronary artery bifurcations are regions where the flow is strongly disturbed, which is a potential risk for development of atherosclerotic lesions at the site of branching 1,2 . An artery bifurcation plays a key role in pressure distribution, where side-branches steal flow from the main vessel similar to collaterals. Left coronary artery (LCA) has short left main stem (LMS) and quickly divides into left anterior descending (LAD) and left circumflex (LCX) with an angle between them 1,3 . The angle between these two coronary branches differs in dimension and shape from person to person. There is a direct correlation between coronary angulations and sub- sequent haemodynamic changes 1 . Variations in LCA angles disturb flow pattern and prone to change the wall pressure and shear stress gradient 1,4 . A bifurcation lesion is the narrowing of coronary artery that may occur in LMS, in LAD and/or in LCX 5 . Medina et al. 6 proposed a simple bifurcation lesion classification con- sisting of a binary value (1, 0). Any narrowing with critical stenosis of 50% and above in any segment receives a binary value 1; otherwise, binary value 0 is assigned starting from left to right. The three suffixes are separated by commas 7 . Recent studies on effect of plaque distributed in the left coronary bifurcation have shown that plaque distribution has a direct effect on flow parameters at stenotic loca- tions 8,9 . Murray 10 predicted the percentage of distribution of total flow rate through side branches (SB), by correlat- ing flow ratio through SB, with ratio of the diameter of SB to the third power. Groen et al. 11 showed that Mur- ray’s law can be reasonably applied when the percentage of area stenosis is 65, whereas for stenosis 66% it is inadequate in predicting the flow ratio at the bifurcation. Coronary bifurcation lesions have been one of the most challenging lesion subsets in the field of percutaneous co- ronary intervention (PCI) 12 . Anatomic severity assess- ment of bifurcation lesions using angiography is limited due to vessel overlap, angulation and foreshortening 13 . Therefore, a standardized physiological assessment of bifurcation lesions is required, which can be done with frac- tional flow reserve (FFR) 12,14,15 (ratio of distal coronary pressure to aorta pressure under hyperaemic condition).