Based on the CONTRAST study data with 627 analysable patients, (1, 3) and the RESOLVE study with 1593 analysable measurements (2), it was shown that Pd/Pa has an excellent correlation with iFR of r = 0.96 and r=0.97, respectively.
When iFR was measured in the same vessel twice, the same correlation of r = 0.96 between repeated measurements was shown (1), see figure below.
Based on the CONTRAST study data, using iFR ≤0.89 as a reference standard, the agreement with Pd/Pa and its best cut-off value were Pd/Pa ≤0.91 (3).
In the RESOLVE study the best cut-off to predict FFR ≤0.80 was iFR ≤0.90 and Pd/Pa ≤0.92 (2).
ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/STS 2017 Appropriate Use Criteria for Coronary Revascularization in Patients With Stable Ischemic Heart Disease (5):
”Newer physiological measurements that do not require hyperemia measure […] during the whole cardiac cycle or the wave-free portion of the cycle […] have similar diagnostic concordance with FFR […]”
”Substitution of one of the newer physiological measurements for FFR may be considered provided the appropriate reference values are used”
Coronary auto-regulation explains why resting pressure indices, including Pd/Pa, can be used to detect the haemodynamic significance of coronary artery stenoses (6).
FFR, iFR, and Pd/Pa showed a similar performance when compared with PET imaging-derived blood flow (7).
Videos regarding the class effect among resting indices:
Johnson NP. et al. Continuum of Vasodilator Stress From Rest to Contrast Medium to Adenosine Hyperemia for Fractional Flow Reserve Assessment. JACC Cardiovasc Interv. 2016 Apr 25;9(8):757-767. (CONTRAST)
Jeremias A. et al. Multicenter core laboratory comparison of the instantaneous wave-free ratio and resting Pd/Pa with fractional flow reserve: the RESOLVE study. J Am Coll Cardiol. 2014 Apr 8;63(13):1253-1261.
Lee JM. et al. Clinical Outcome of Lesions With Discordant Results Among Different Invasive Physiologic Indices - Resting Distal Coronary to Aortic Pressure Ratio, Resting Full-Cycle Ratio, Diastolic Pressure Ratio, Instantaneous Wave-Free Ratio, and Fractional Flow Reserve. Circ J. 2019 Oct 25;83(11):2210-2221.
Patel MR. et al. ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/STS 2017 Appropriate Use Criteria for Coronary Revascularization in Patients With Stable Ischemic Heart Disease: A Report of the American College of Cardiology Appropriate Use Criteria Task Force, American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2017 May 2;69(17):2212-2241.
Nijjer SS. et al. Coronary pressure and flow relationships in humans: phasic analysis of normal and pathological vessels and the implications for stenosis assessment: a report from the Iberian-Dutch-English (IDEAL) collaborators. Eur Heart J. 2016 Jul 7;37(26):2069-80.
de Waard GA. et al. Fractional flow reserve, instantaneous wave-free ratio, and resting Pd/Pa compared with [15O]H2O positron emission tomography myocardial perfusion imaging: a PACIFIC trial sub-study. Eur Heart J. 2018 Dec 7;39(46):4072-4081.