Vive la difference: Factors and mechanisms predicting discrepancy between iFR and FFR.

FFR/iFR is discordant in 15-20% of cases, at times causing confusion about revascularization decisions. The CONTRAST substudy identifies lesion location, lesion severity, and bradycardia as major predictors for FFR/iFR discordance, with age a minor predictor. Each of these predictors can be explained physiologically through the mechanisms related to resting and hyperemic pressure loss across different patterns of atherosclerotic stenoses. A logical approach to using both resting and hyperemic pressure ratios is proposed.