Whole cycle non-hyperaemic pressure ratios have better stability than diastolic ratios after percutaneous coronary intervention due to changes in diastolic coronary haemodynamics

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 <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