Instantaneous Wave-Free Ratio (iFR) Correlates With Fractional Flow Reserve (FFR) Assessment of Coronary Artery Stenoses and Myocardial Bridges in Children.

OBJECTIVES: Instantaneous wave-free ratio (iFR) has been proven to correlate with coronary flow reserve better than fractional flow reserve (FFR) and is non-inferior to FFR in guiding coronary revascularization in ischemic heart disease. There has been no study validating the utility of iFR in children. METHODS: We performed a retrospective review of clinically indicated cases in which both FFR and iFR were obtained at Texas Children's Hospital from July, 2016 to March, 2019. FFR and iFR were obtained at baseline. Adenosine FFR (FFRa) was used for assessment of coronary artery (CA) stenoses and diastolic dobutamine FFR (dFFRd) for myocardial bridges (MBs). FFRa or dFFRd ≤0.8 and iFR ≤0.89 indicated significant flow impairment. RESULTS: A total of 22 coronary arteries (9 CA stenoses and 13 MBs) were assessed in 20 patients with median age of 13 years (range, 4-21 years) and median weight of 60 kg (range, 19-110 kg). iFR correlated with FFRa (Spearman's rho, 0.87; P<.01) in CA stenoses and with dFFRd (Spearman's rho, 0.74; P<.01) in MBs and agreed with FFR in 20/22 cases (90.9%). In 1 patient with CA stenosis and 1 MB with normal FFR, iFR was positive and both patients underwent coronary revascularization. CONCLUSIONS: iFR correlated with FFR in the assessment of CA stenoses in children. iFR does not require administration of pharmacological agents; thus, it may reduce procedural time, cost, and complications, and result in more widespread adoption of invasive assessment of CA lesions in young patients.