Risk factors for unsuccessful restoration of coronary flow reserve after coronary bypass surgery

Objectives: Coronary flow reserve (CFR) is a strong predictor of cardiovascular events and prognosis in patients with coronary artery disease. This study aimed to evaluate preoperative factors associated with the unsuccessful restoration of CFR after coronary artery bypass grafting (CABG). Methods: : Included in this study were the 65 patients who presented with functionally significant left anterior descending artery (LAD) lesions confirmed by both fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR), and who underwent successful CABG at our hospital within the study period. After CABG, graft patency was confirmed by coronary computed tomography angiography, and CFR in the LAD artery was measured by echocardiography. We defined postoperative CFR <2.5 as impaired CFR, and CFR >= 2.5 as preserved CFR. Results: Of the 65 patients, 14 patients (22%) showed impaired CFR, while 51 patients had preserved CFR. Patients with impaired CFR had significantly higher HbA1c (6.7% vs. 6.0%, P < 0.01), greater use of insulin (43% vs. 4%, P < 0.01), longer lesion length (33 mm vs. 25 mm, P = 0.044), and lower iFR (0.69 vs 0.81, P = 0.01) than those with preserved CFR, although both groups had comparable FFR (0.65 vs 0.64, P = 0.46). In receiver operating characteristic curve analysis, iFR had a significantly larger area under the curve than FFR in terms of the prediction of impaired CFR (0.74 vs 0.42, P = 0.01). Conclusions: Poorly-controlled preoperative diabetes, greater reliance on insulin, longer lesion length and lower iFR were associated with postoperative impaired CFR, suggesting the involvement of microvascular dysfunction.