Assessment of surgical revascularization completeness with quantitative myocardial blood flow distribution derived from CCTA in severe coronary artery disease

Background Complete revascularization remained the "holy grail" in the treatment of patients with severe coronary artery disease (CAD). However, there is no universally accepted definition of complete revascularization after coronary bypass graft surgery (CABG). The current assessment methods are visual, categorical, and biased by the operator's intention. Moreover, no method to date provides an individualized quantification of residual ischemia burden. Purpose We aim to provide an individualized method to assess the completeness of surgical revascularization through quantitative myocardial blood flow distribution derived from coronary computed tomography angiography (CCTA) that could reflect the actual functional ischemia burden after CABG. Methods Patients with 3VD and/or left main CAD were enrolled in the first-in-human FAST TRACK CABG trial for surgical revascularization guided solely by CCTA and fractional flow reserve derived from CCTA (FFRCT). Following CABG, the study protocol mandated a 30-day follow-up CCTA, which provides graft patency and topographical adequacy of the bypass graft anastomoses. The pre- and post-CABG CCTA were analyzed. The FFRCT value and percent myocardial blood flow distribution (%MBF) were computed for all 16 SYNTAX score segments using the validated method of Keulards et al(1). On pre-CABG CCTA, the myocardium located distal to the site where the FFRCT value dropped below 0.80 on the vessel centerline was considered ischemic, and the %MBF of the subtended myocardium was summed into the total percent ischemic myocardium (Figure 1). Following CABG, the segment was considered adequately revascularized when a non-narrowed graft was anastomosed distally to the site of FFRCT≤0.8 on the pre-operative CCTA. The change in percent ischemic myocardium and the residual ischemic burden were calculated for each patient (Figure 2). Results CCTA, FFRCT, and %MBF were obtained pre- and post-CABG in 96 patients, and the percent ischemic myocardium was computed per patient. At baseline, the average percent ischemic myocardium was 72.0(19.1)%. Post-CABG, the residual percent ischemic myocardium was 13.6(15.1)%. Residual percent ischemic myocardium <10% was achieved in 44 patients (44.8%). The first diagonal branch(n=13), distal LCX(n=12), and the first obtuse marginal branch(n=10) were the most frequent segments not revascularized, which subtended an average MBF of 12.2(3.5)%, 16.7(8.4)%, and 11.3(7.3)%, respectively. The main reason for inadequate revascularization was surgical deferral, with graft occlusion accounting for only 13.6% of the residual ischemic segments. Conclusion Percent ischemic myocardium and the completeness of surgical revascularization can be assessed with CCTA-derived %MBF. This novel method allows clinicians to assess the individualized ischemia burden and the completeness of revascularization that could be incorporated into personalized CABG planning.Figure 1Figure 2