Whole cycle non-hyperaemic pressure ratios have better stability than diastolic ratios after percutaneous coronary intervention due to changes in diastolic coronary haemodynamics
Authors: Aetesam-Ur-Rahman M , Zhao T , Paques K , Oliveira J , Khialani B , Kyranis S , Braganza D , Clarke S , Bennett M , West N , Hoole S 
Published: October 2021

Abstract

Background
Post percutaneous intervention (PCI) fractional flow reserve (FFR) value of ≥0.90 is an accepted marker of procedural success, and similarly, a cut-off of ≥0.95 has recently been proposed for post-PCI instantaneous wave free ratio (iFR). However, the stability of non-hyperaemic pressure ratios (NHPRs) and microcirculatory resistance post-PCI, is not well characterised. as submaximal hyperaemia post-PCI may affect them.

Purpose
We performed this study to assess stability and reproducibility of NHPRs measured immediately post-PCI and repeated at 30 minutes post-PCI.

Methods
Seventy-seven patients undergoing pressure wire guided PCI (age 63.77±10.67 years, male 71%,) had haemodynamic assessment done immediately post-PCI and after a recovery period 30 minutes (Figure A, B). Manual offline analysis was performed to derive resting pressure ratios during whole cycle: average ratio of distal coronary pressure to proximal aortic pressure at rest (Pd/Pa) and resting full cycle ratio (RFR); and during diastolic phase: average diastolic pressure ratio (dPR) and mathematically calculated iFRmat, measured by average Pd/Pa during wave free period (WFP) (from 25% into diastole until 5 msec before the end of diastole). We also measured coronary flow velocity by thermo-dilution time (Tmn) and basal microvascular resistance (BMR = Pa × Tmn × [(Pd − Pw) / (Pa − Pw)] baseline) corrected for coronary wedge pressure (Pw). Test-retest statistics was performed between NHPRs values immediately post-PCI and at 30 minutes. Moreover, crossover of NHPRs across the cut-off value of 0.95 was analysed to assess clinical utility of these indices for procedural success. p value of &lt;0.05 was deemed statistically significant.

Results
There were no differences in the baseline characteristics of the study patients. Sub-maximal hyperaemia was demonstrated by Tmn of 0.54 sec (0.32, 0.75) immediately post-PCI which settled by 30 minutes, Tmn of 0.67 sec (0.43, 0.91), p=0.01 (Figure C). The median BMR increased from 49.25 mmHg sec (32.74, 61.61) to 59.60 mmHg sec (39.24, 76.91) at 30 minutes, p=0.04 (Figure D). Despite this, there were no significant differences in the values of resting whole cycle ratios (Pd/Pa and RFR) as well as diastolic ratios (dPR and iFRmat), with whole cardiac cycle NHPRs having best stability post-PCI (Table). Furthermore, crossover above or below the cut-off value of 0.95 occurred in approximately 1 in 5 diastolic NHPRs measurements but was three-fold lower for whole cycle NHPRs.

Conclusion
NHPRs remain stable post-PCI, despite submaximal hyperaemia being detected and may legitimately be used immediately post-PCI to determine procedural success. However, the test-retest reproducibility and clinical utility of diastolic NHPRs (dPR and iFR) was inferior to whole cycle NHPRs (Pd/Pa and RFR).

Funding Acknowledgement
Type of funding sources: Public Institution(s). Main funding source(s): NIHR