Background: Coronary hemodynamics and physiology specific for bifurcation lesions\nwas not well understood. To investigate the influence of the bifurcation angle on the\nintracoronary hemodynamics of side branch (SB) lesions computational fluid dynamics\nsimulations were performed.\nMethods: A parametric model representing a left anterior descendingââ?¬â?first diagonal\ncoronary bifurcation lesion was created according to the literature. Diameters obeyed\nfractal branching laws. Proximal and distal main branch (DMB) stenoses were both set\nat 60 %. We varied the distal bifurcation angles (40Ã?°, 55Ã?°, and 70Ã?°), the flow splits to the\nDMB and SB (55 %:45 %, 65 %:35 %, and 75 %:25 %), and the SB stenoses (40, 60, and\n80 %), resulting in 27 simulations. Fractional flow reserve, defined as the ratio between\nthe mean distal stenosis and mean aortic pressure during maximal hyperemia, was\ncalculated for the DMB and SB (FFRSB) for all simulations.\nResults: The largest differences in FFRSB comparing the largest and smallest bifurcation\nangles were 0.02 (in cases with 40 % SB stenosis, irrespective of the assumed\nflow split) and 0.05 (in cases with 60 % SB stenosis, flow split 55 %:45 %). When the SB\nstenosis was 80 %, the difference in FFRSB between the largest and smallest bifurcation\nangle was 0.33 (flow split 55 %:45 %). By describing the Ã?â?PSB\nâË?â??QSB relationship using a\nquadratic curve for cases with 80 % SB stenosis, we found that the curve was steeper\n(i.e. higher flow resistance) when bifurcation angle increases (Ã?â?P = 0.451*Q + 0.010*Q2\nand Ã?â?P = 0.687*Q + 0.017*Q2 for 40Ã?° and 70Ã?° bifurcation angle, respectively). Our analyses\nrevealed complex hemodynamics in all cases with evident counter-rotating helical\nflow structures. Larger bifurcation angles resulted in more pronounced helical flow\nstructures (i.e. higher helicity intensity), when 60 or 80 % SB stenoses were present. A\ngood correlation (R2 = 0.80) between the SB pressure drop and helicity intensity was\nalso found.\nConclusions: Our analyses showed that, in bifurcation lesions with 60 % MB stenosis\nand 80 % SB stenosis, SB pressure drop is higher for larger bifurcation angles\nsuggesting higher flow resistance (i.e. curves describing the Ã?â?PSB\nâË?â??QSB relationship\nbeing steeper). When the SB stenosis is mild (40 %) or moderate (60 %), SB resistance is minimally influenced by the bifurcation angle, with differences not being clinically\nmeaningful. Our findings also highlighted the complex interplay between anatomy,\npressure drops, and blood flow helicity in bifurcations.
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