Using the diastolic pressure ratio (dPR) to identify ischaemia-producing lesions in patients with coronary artery disease provides a similar diagnostic performance to the instantaneous wave-free ratio (iFR). A pooled analysis of pre-recorded pressure tracings from the diagnostic accuracy studies VERIFY 2 and CONTRAST compared dPR (using a commercially available algorithm of the diastolic hyperaemia-free ratio [DFR]) and a linear transform of Pd/Pa (the ratio of the distal coronary pressure to proximal aortic pressure) against iFR for numerical similarity and test/retest repeatability in 893 lesions from 833 patients.
Writing in the European Heart Journal, Nils P Johnson (University of Texas, Houston, USA) et al say: “Our dPR offers numerical equivalency to iFR. Despite different technical approaches for identifying the relevant period of diastole, the agreement between dPR and iFR, and the insensitivity of dPR to minor variations in its definition, further confirm numerical equivalency among resting metrics.”
VERIFY 2 was a prospective, single-centre study of 197 nearly consecutive subjects and 257 coronary lesions, in which resting pressure signals in the coronary artery were obtained, with simultaneous recordings of the aortic pressure and surface electrocardiogram (ECG). Two assessments of iFR were acquired in rapid, back-to-back sequence before the administration of any hyperaemic stimulus. Tracings and their associated real-time iFR values were anonymised for the pooled analysis. CONTRAST was a prospective, international study with 763 subjects from 12 centres with one lesion per subject. A simultaneous ECG was recorded, in addition to aortic and coronary pressure signals. Two resting assessments of iFR were performed but separated by hyperaemic stimuli of intracoronary contrast and intracoronary and/or intravenous adenosine. Anonymous tracings from CONTRAST were used for the analysis and iFR was recalculated. The final pooled analysis consisted of 255 lesions from 195 subjects (252 with valid, duplicate measurements) from VERIFY 2 and 638 lesions from 638 subjects (629 with valid, duplicate measurements) from CONTRAST.
The analysis found numerical equivalency between the metrics. The mean difference between dPR and iFR (Δ -0.006±0.011, r2 0.993, area under receiver operating characteristic [ROC] curve [AUC] 0.997) mirrored the difference of two iFR measurements repeated immediately (Δ <0.001±0.004, r2 0.998, AUC 1.00). Minor variations in the definition of dPR changed its value by <1–2% over a broad range of the cardiac cycle. Thus the authors point out: “dPR agrees with iFR to the same degree that iFR agrees with itself a few seconds later under stable conditions.”
A linear transform of Pd/Pa showed good diagnostic performance (Δ -0.012±0.031, r2 0.927, AUC 0.979). Post-hoc iFR values were validated against real-time iFR values and matched almost exactly (average Δ <0.001±0.004, 99.6% within ±0.01).
Johnson et al add: “When two tests agree as closely as dPR and iFR, performing clinical outcomes studies becomes both impossible and unnecessary. While a small minority of lesions demonstrated some binary discordance between dPR and iFR, <1% were consistent between both test and retest. The fact that dPR provides the same numerical value as iFR despite a different definition of the diastolic measurement period provides additional indirect evidence against unique properties of the so-called ‘wave-free period’, although our study did not perform wave intensity analysis directly.”
And, they concede: “We did not compare our dPR results to fractional flow reserve, but given the numerical equivalency between dPR and iFR, these results would be expected to mirror prior literature.”