Comparative analysis of post-PCI fractional flow reserve and quantitative flow ratio in predicting long-term Target Vessel Failure and hard endpoints

Abstract Background The role of functional assessment after angiographically acceptable post-PCI result is debatable. Purpose We sought to investigate the correlation between Fractional Flow Reserve measured directly after drug eluting stent (DES) implantation (post-PCI FFR) and post-PCI Quantitative Flow Ratio (post-PCI QFR), clarify their relationship with clinical parameters, and long-term target vessel failure (TVF: cardiac death (CD), non-fatal target vessel myocardial infarction (MI) and target vessel revascularisation (TVR)), and a composite of CD and MI (CD/MI). Method Coronary arteries that underwent post-PCI FFR measurement at our centre between 2012 and January 2021 were consecutively included in this registry. Post-PCI QFR was calculated blinded to the post-PCI FFR value. We analysed the influence of LAD vs. (non-LAD) location, gender, age, hypertension, diabetes mellitus, hyperlipidemia, indication (acute (ACS) vs. chronic coronary syndrome), stent diameter, in-stent restenosis (ISR) vs. de novo lesion category, estimated glomerular filtration rate, proximal vs. distal lesions, severe aortic stenosis, atrial fibrillation during the procedure (AF), and prior myocardial infarction in the supply area (prior MI) on post-PCI FFR and QFR. Optimal cut-off was determined by ROC curves. Results A total of 400 coronary arteries were analysed. LAD location (p<0.001), male gender (p=0.0029) and smaller stent diameter (p=0.0073) proved to be predictors of a lower post-PCI FFR. LAD location (p=0.001), ISR (p=0.02), distal location (p=0.0019), AF (p=0.042) and prior MI (p=0.029) were predictors of a lower post-PCI QFR. There was a systematic bias in post-PCI QFR compared to post-PCI FFR (bias 0.0614, 95% CI, 0.053 - 0.069). During a median follow-up of 45 months, 31 CD, 20 MI and 35 TVR occurred. Follow-up was complete in 100%. There was a significant inverse correlation between post-PCI FFR and TVF (p<0.001) as well as between post-PCI QFR and TVF (p=0.045). In-stent restenosis (p=0.014) and prior MI (p=0.002) were also predictors of higher TVF rate. The predictors of CD/MI were lower post-PCI FFR (p<0.001), smaller stent diameter (p=0.03), higher age (p=0.031) and ACS indication (p=0.048), whereas post-PCI QFR was not. The best post-PCI FFR cut-off to predict TVF was 0.87 (p<0.0001). There was no single optimal post-PCI QFR cut-off to predict TVF. Conclusion Post-PCI QFR shows a systematic bias compared to post-PCI FFR. Post-PCI FFR is a significant predictor of TVF as well as CD/MI, whereas post-PCI QFR predicts TVF. No significant correlation between post-PCI QFR and CD/MI could be demonstrated. Our findings underscore the importance of considering multiple clinical parameters in predicting long-term outcomes. The best post-PCI FFR cut-off to predict TVF was 0.87. However, there was no single, universally applicable post-PCI QFR threshold to predict TVF.