Resting ratios
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).
Outcome
An outcome study showed equal outcome between different resting indices, including Pd/Pa (4).
Guideline
ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/STS 2017 Appropriate Use Criteria for Coronary Revascularization in Patients With Stable Ischemic Heart Disease (5):
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”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 […]”
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”Substitution of one of the newer physiological measurements for FFR may be considered provided the appropriate reference values are used”
More
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: