Personalized surgical planning for coronary bypass graft configurations using patient-specific computational modeling to avoid flow competition in arterial grafts

Objectives

Flow competition between coronary artery bypass grafts (CABG) and native coronary arteries is a significant problem affecting arterial graft patency. The objectives of this study were to compare the predictive hemodynamic flow resulting from various total arterial grafting configurations and to evaluate whether the use of computational fluid dynamics (CFD) models capable of predicting flow can assist surgeons to make better decisions for individual patients by avoiding poorly functioning grafts.

Methods

Sixteen cardiac surgeons declared their preferred CABG configuration using bilateral internal mammary and radial arteries for each of 5 patients who had differing degrees of severe triple vessel coronary disease. Surgeons selected both a preferred 'aortic' strategy, with at least one graft arising from the ascending aorta, and a preferred "anaortic" strategy which could be performed as a "no-aortic touch" operation. CT coronary angiograms of the 5 patients were coupled to CFD models using a novel flow solver "COMCAB." Twelve different CABG configurations were compared for each patient of which 4 were "aortic" and 8 were "anaortic." Surgeons then selected their preferred grafting configurations after being shown predictive hemodynamic metrics including functional assessment of stenoses (instantaneous wave-free ratio; fractional flow reserve), transit time flowmetry graft parameters (mean graft flow; pulsatility index) and myocardial perfusion.

Results

A total of 87.5% (7/8) of "anaortic" configurations compared to 25% (1/4) of "aortic" configurations led to unsatisfactory grafts in at least 1 of the 5 patients (P = 0.038). The use of the computational models led to a significant decrease in the selection of unsatisfactory grafting configurations when surgeons employed "anaortic" (21.25% (17/80) vs. 1.25% (1/80), P < 0.001) but not "aortic" techniques (5% (4/80) vs. 0% (0/80), P = 0.64). Similarly, there was an increase in the selection of ideal configurations for "anaortic" (6.25% (5/80) vs. 28.75% (23/80), P < 0.001) but not "aortic" techniques (65% (52/80) vs. 61.25% (49/80), P = 0.74). Furthermore, surgeons who planned to use more than one unique "anaortic" configuration across all 5 patients increased (12.5% (2/16) vs. 87.5% (14/16), P<0.001).

Conclusions

"COMCAB" is a promising tool to improve personalized surgical planning particularly for CABG configurations involving composite or sequential grafts which are used more frequently in anaortic operations.

Comparison of diagnostic performance between quantitative flow ratio, non-hyperemic pressure indices and fractional flow reserve

Background

Quantitative flow ratio (QFR) is an estimate of fractional flow reserve (FFR) and is derived from 3-dimensional quantitative coronary angiography. The DILEMMA score is an angiographic technique developed to predict FFR. Unlike other diastolic indices such as instantaneous wave-free ratio (iFR), diastolic pressure ratio (dPR) and dPR_25-75, neither QFR nor DILEMMA score require pressure wires. This study sought to compare the diagnostic performance of QFR, diastolic indices and DILEMMA score to predict FFR.

Methods

Between January 2010 and December 2013, patients who underwent invasive coronary angiography and FFR assessments were retrospectively studied. iFR and dPR were derived from FFR pressure tracings. QFR was computed using commercial software.

Results

Eighty-five lesions (25% FFR significant) were included in this study. Median FFR was 0.88 (0.81-0.92). QFR (r_s=0.801), iFR (r_s=0.710), dPR (r_s=0.716), dPR_25-75 (r_s=0.715) and DILEMMA score (r_s=-0.623) significantly correlated with FFR (P<0.001). QFR ≤0.8 had a specificity, sensitivity, positive predictive value (PPV) and negative predictive value (NPV) of 95%, 86%, 86% and 95% respectively of predicting significant FFR (P<0.001). Receiver-operating characteristic (ROC) analysis revealed the AUC to predict significant FFR for QFR (0.947), iFR (0.880), dPR (0.883), dPR_25-75 (0.880) and DILEMMA score (0.916) were not significantly different. However, QFR was a better predictor of FFR than iFR (0.947 vs. 0.770, P<0.01).

Conclusions

QFR had excellent correlation and accuracy as measured against FFR. When compared to other diastolic indices and DILEMMA score, QFR performed at least as well as the other indices. QFR predicts FFR better than it predicts iFR. QFR is a convenient tool to assess significance of coronary stenosis and a reliable alternative to pressure-wire based indices. Prospective studies are required to investigate the performance and cost-effectiveness of QFR when independently used to guide clinical decision making.

Reliability of Instantaneous Wave-Free Ratio (iFR) for the Evaluation of Left Main Coronary Artery Lesions

The assessment of the left main coronary artery (LMCA) by coronary angiography has several limitations. The fractional flow reserve (FFR) is useful for the functional evaluation of LMCA stenoses. The instantaneous wave-free ratio (iFR), a resting index, was developed to simplify functional coronary assessment. However, its performance for LMCA stenoses has yet to be explored. The iFR was measured at rest, and the FFR was measured under maximal hyperemia. We calculated that a sample size of 90 lesions would have provided 90% power at a 5% significance level to detect an Area Under the Curve (AUC) < 0.7 for the iFR to identify FFR-positive stenoses. A total of 91 measurements were performed on angiographically intermediate LMCA stenoses at three centers. The comparison between the iFR and the FFR showed a significant correlation (r = 0.67, p < 0.001). At receiver operating characteristic (ROC) analysis, the iFR revealed a good diagnostic performance when compared to the FFR (AUC = 0.84; p < 0.001). A classification agreement between the iFR and the FFR was recorded in 81% of cases. The left ventricular ejection fraction (LVEF) was an independent predictor of the discrepancy between the FFR and iFR values (p = 0.040). The present study is the first demonstrating that the assessment of LMCA stenoses with the instantaneous wave-free ratio is a reliable adenosine-free alternative to classic fractional flow reserve. If confirmed in larger populations, these findings could be of relevance for real world daily practice.

Physiologic assessment of moderate coronary lesions: a step towards complete revascularization in coronary artery bypass grafting

Background

An accurate diagnostic assessment of coronary artery disease is crucial for patients undergoing coronary artery bypass grafting (CABG). Fractional flow reserve (FFR) and instantaneous wave-free ratio (iFR) to guide complete revascularization have not been adequately studied in patients prior to CABG. We compared an anatomic to a physiologic assessment of moderate coronary lesions (40-70% stenosis) in patients referred for CABG.

Methods

We retrospectively reviewed 109 medical records of patients who underwent CABG at Tulane Medical Center from 2014 to 2016. Patients were divided into an FFR/iFR-guided and an angiography-guided group. Clinical characteristics, procedural outcomes, and clinical outcomes for the two groups were compared over an 18-month follow-up period.

Results

There were significantly higher rates of three-vessel anastomoses (85.7% vs. 74.7%, P<0.05) and venous grafting (85.7% vs. 76.8%, P<0.05) in the FFR/iFR group. The FFR/iFR group had a lower rate of grafts placed to the left anterior descending artery (LAD) distribution than the angiography group (7.1% vs. 29.5%, P<0.05). The FFR/iFR group had a higher rate of grafts placed to the left circumflex (LCx) artery distribution than the angiography group (28.6% vs. 9.5%, P<0.05). We observed a trend toward reduction in major adverse cardiac events (MACEs) (7.1% vs. 11.6%, P=0.369) and angina (0.0% vs. 6.3%, P=0.429) in the FFR/iFR group compared to the angiography group over 18 months.

Conclusions

Physiologic assessment of coronary lesions can effectively guide complete revascularization in patients undergoing CABG. Moreover, FFR/iFR-guided CABG was associated with significantly higher rates of three-vessel anastomoses, venous grafting, and graft distribution to the circumflex system.