Segmental post-PCI physiological gradients using ultrasonic or optical flow ratio

Background Segmental pressure gradients post percutaneous coronary intervention (PCI) may detect residual disease and potential targets for optimization. Ultrasonic flow ratio (UFR) or optical flow ratio (OFR) provide simultaneous physiological and morphological data using a single imaging catheter. Notably, both have been validated against wire based FFR Objectives To evaluate the utility of UFR and OFR to identify residual disease post-PCI. Methods The present study is a sub analysis of the ASET (Acetyl Salicylic Elimination Trial) JAPAN pilot study Phase I which showed the feasibility and safety of low dose prasugrel monotherapy following PCI in Japanese patients presenting with chronic coronary syndrome and an anatomical SYNTAX score <23. Patients with complete intra-vascular imaging pullback data were included with UFR/OFR acquired in all patients post-PCI. Quantitative and qualitative assessment of IVUS or OCT pullbacks was performed by automatically delineating vessel, lumen, and stent contours every 0.5 mm using QCU-CMS (version 4.69, Division of Image Processing, Leiden University Medical Centre). UFR or OFR was calculated using the respective IvusPlus or OctPlus software, Pulse Medical, Shanghai, China.(13)(15) All UFR and OFR tracings, and IVUS and OCT pullbacks were analyzed at the CORRIB Core lab, Galway, Ireland by two analysts blinded to clinical and procedural data. Anatomically focal lesions distal and proximal to the stent were evaluated in segments ≥5mm long. UFR/OFR virtual pullback curves were used to calculate intra-stent pressure gradients and physiologically define lesions as focal or diffuse by segmental pressure drops ≥0.05 over lengths <10mm or ≥10mm, respectively. Results The median post-PCI UFR/OFR was 0.93 (0.88-0.96) with 69/195 vessels (35.4%) having a UFR/OFR≤0.90. There were significantly more focal anatomical and physiological lesions proximal and distal to the stent in vessels with a UFR/OFR≤0.90 versus >0.90. In vessels with a UFR/OFR≤0.90 there was moderate agreement (weighted kappa=0.553, p<0.001) between anatomical and physiological focal lesions proximal to the stent, whilst it was fair (weighted kappa=0.219, p=0.002) distally. In-stent gradient had poor discriminative ability to detect significant stent under-expansion. The performance of a proximal or distal virtual FFR gradient to detect proximal or distal anatomically focal disease was good (AUC–0.835 and 0.877, respectively) Conclusions UFR/OFR enables suboptimal vessel physiology post-PCI to be detected and helps identify the precise anatomical location with corroboration from intra-vascular imaging. Adequately powered physiology optimization trials using UFR/OFR will determine the role of combined morphology and physiological evaluation post PCI in improving clinical outcomes.