Cardiovascular Engineering and Technology, Vol. 2, No. 1, March 2011 (Ó 2010) pp. 35–47 DOI: 10.1007/s13239-010-0029-z Computer-Aided Patient-Specific Coronary Artery Graft Design Improvements Using CFD Coupled Shape Optimizer 1 2 3 4 ONUR DUR, SINAN TOLGA COSKUN, KASIM OGUZ COSKUN, DAVID FRAKES, 5 1,5 LEVENT BURAK KARA, and KEREM PEKKAN 1Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA; 2Department of Vascular Surgery, Horst Schmidt Kliniken, Wiesbaden, Germany; 3Department of Thoracic Cardiovascular Surgery, University of Go¨ttingen, Go¨ttingen, Germany; 4School of Biological and Health Systems Engineering, Arizona State University, Tempe, AZ, USA; and 5Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA (Received 29 June 2010; accepted 1 November 2010; published online 18 November 2010) Associate Editor Peter McHugh oversaw the review of this article. Abstract—This study aims to (i) demonstrate the efficacy of a coronary bypass surgery procedures based on acute hemo- new surgical planning framework for complex cardiovascular dynamic readjustments of aorta-CA flow. This methodology reconstructions, (ii) develop a computational fluid dynamics may provide a rational to aid surgical decision making in (CFD) coupled multi-dimensional shape optimization meth- time-critical, patient-specific CA bypass operations before in od to aid patient-specific coronary artery by-pass graft vivo execution. (CABG) design and, (iii) compare the hemodynamic effi- ciency of the sequential CABG, i.e., raising a daughter Keywords—Surgical planning, Coronary artery, Bypass parallel branch from the parent CABG in patient-specific 3D graft, CFD, Hemodynamics, Shape optimization, Sequential settings. Hemodynamic efficiency of patient-specific complete revascularization scenarios for right coronary artery (RCA), graft, WSS, WSSG, Surgical design. left anterior descending artery (LAD), and left circumflex artery (LCX) bypasses were investigated in comparison to the stenosis condition. Multivariate 2D constraint optimiza- INTRODUCTION tion was applied on the left internal mammary artery (LIMA) graft, which was parameterized based on actual Statistics from the American Heart Association surgical settings extracted from 2D CT slices. The objective identify coronary heart diseases (CHD) as the principal function was set to minimize the local variation of wall shear cause of morbidity and mortality in the western stress (WSS) and other hemodynamic indices (energy dissi- 14,42 pation, flow deviation angle, average WSS, and vorticity) world. Major causes of CHD include atheroscle- that correlate with performance of the graft and risk of rosis and complications related to congenital cardiac re-stenosis at the anastomosis zone. Once the optimized 2D defects. Atherosclerosis involves the agglomeration of graft shape was obtained, it was translated to 3D using an fatty substances, cholesterol, and other deposits on the in-house ‘‘sketch-based’’ interactive anatomical editing tool. inner lining of an artery together with transverse The final graft design was evaluated using an experimentally validated second-order non-Newtonian CFD solver incorpo- growth of smooth muscle cells (i.e., artheroma). This rating resistance based outlet boundary conditions. 3D results in reduced blood flow and other pathological patient-specific simulations for the healthy coronary anat- complications.42 omy produced realistic coronary flows. All revascularization Bypass conduits provide an alternative route techniques restored coronary perfusions to the healthy around critically blocked arteries. Current surgical baseline. Multi-scale evaluation of the optimized LIMA graft enabled significant wall shear stress gradient (WSSG) anastomosis techniques and the design of synthetic relief (~34%). In comparison to original LIMA graft, coronary artery bypass grafts (CABG) frequently lead sequential graft also lowered the WSSG by 15% proximal to post-surgical complications such as intimal thick- to LAD and diagonal bifurcation. The proposed sketch- ening, restenosis, and eventual long term graft failure. based surgical planning paradigm evaluated the selected Failure presents in 5–20% of patients within 1–5 years, and approximately 50% of patients within 10 years after CABG surgery.5 Pathological hemodynamic Address correspondence to Kerem Pekkan, Department of states are usually precursors of intimal hyperplasia or Biomedical Engineering, Carnegie Mellon University, 700 Technol- ogy Dr., Pittsburgh, PA 15219, USA. Electronic mail: kpekkan@ platelet deposition and may result in graft occlu- 6,13,57 andrew.cmu.edu sion. From a fluid mechanics perspective, 35 1869-408X/11/0300-0035/0 Ó 2010 Biomedical Engineering Society 36 DUR et al. abnormalities in coronary flow include recirculation haptic user interface with an easy-to-access digital zones, low/oscillating shear stresses, vortices, and areas sketch-based modeling environment, i.e., tablet, that of stagnation within the CABG. These parameters takes user strokes as input, and seamlessly converts relate to the variation in strain rate within the conduit, them into precise three-dimensional (3D) geometric which in turn are influenced strongly by the shape of data. This allows surgeons to construct and edit ana- the flow domain.28 Therefore, in order to improve the tomical structures directly in 3D precisely the way they success of the surgery, the optimal anastomosis envisage on a two dimensional (2D) image. geometry and angle have been actively researched. To date, CFD has been utilized primarily for iden- Walsh et al.53 demonstrated that the use of cuffs (i.e., tifying an optimal design, based on trial-and-error, Miller cuff) and patches (i.e., Taylor patch) can sig- among a small number of geometrical variations and nificantly reduce abnormal wall shear stress (WSS) and intuitive design alternatives. More recently, several wall shear stress gradient (WSSG) by up to 60% in investigators have demonstrated the benefits of cou- patient-specific models, when compared to a conven- pling computer simulations with numerical shape tional distal end-to-side anastomosis. Studies based on optimization to provide cost-effective methods for the idealized femoral bypass geometries provided a better design of the medical devices,1,15 surgical connec- insight on the influence of various design parameters tions,25 and particularly CABGs.2,39,43 The challenges such as the advantage of an acute anastomosis angle, associated with CFD coupled shape optimization for i.e., 10–20°,3,11 creating enlarged lumen sections clinical problems have been identified previously by around the toe region to reduce WSS parameters and Marsden et al.25 enable smooth transition of the flow from graft to host Current CABG design paradigms target improved artery,3,22,23 and influence of the proximal artery hemodynamics to achieve reduced hyperplasia at the flow.3,20 Apart from these local design considerations, distal anastomosis region by modulating the anasto- the bulk shape of the bypass conduits has received little mosis angle1 and vessel curvature39,43 in simplified 2D attention. Based on the rapid variation of high and low tubular conduits. Studies incorporating out-of-plane wall shear stress along the sinusoidal shaped vessel features reported notable variations in end-to-side geometries, ill-shaped grafts may also be prone to anastomosis hemodynamics.31,47 Hence, although atherosclerosis development. in-plane (2D) optimization is appropriate to identify Computational fluid dynamics (CFD) provide a the primary design features, an accurate assessment on viable tool for pre-surgical planning and device design, the CABG hemodynamics requires patient-specific 3D and for improving the design of surgeries and inter- anatomical information for reliable feedback. ventions used in cardiovascular medicine.33,35,40,49–51 One objective of this study was to demonstrate the Coupled with accurate reconstructions of anatomical efficacy of a novel sketch-based surgical planning data (via magnetic resonance imaging, angiograms, or framework for complex cardiovascular problems, and computational tomography),12 CFD simulations pro- to develop a CFD coupled multi-dimensional shape vide the ability to quantify local hemodynamics and optimization method to aid patient-specific CABG allow evaluating the performance of surgical design design. Hemodynamic efficiency of patient-specific templates26,27,37 and candidate endovascular devices.58 complete revascularization scenarios for right coronary Anatomical three-dimensional shape editing is one artery (RCA), left anterior descending artery (LAD) of the major challenges of the pre-surgical planning and left circumflex artery (LCX) bypasses were inves- paradigm as cardiovascular geometries involve non- tigated in comparison to the stenosis condition. Single uniform vessel caliber and curvature, and conduits objective multivariate constraint optimization was require complex multiple inlet–outlet geometries, applied to improve the patient-specific design of the which cannot be easily modified by combinations of end-to-side anastomosis of left internal mammary mathematically simple binary operations or shape artery (LIMA) to the distal site of the stenosed LAD. primitives offered by state-of-art CAD software.19 We The 2D optimization procedure was comprised of introduced the first generation ‘interactive’ surgical geometry creation, parameterization, mesh generation, planning tool, SURGEM,36 which incorporates a two- finite element