207 Intracoronary adenosine derived coronary flow reserve and index of microvascular resistance

Background and Aims Coronary function testing performed as an adjunct during invasive angiography, aids diagnosis of coronary microvascular dysfunction. Intravenous (IV) adenosine infusion for the induction of stable hyperaemia is the reference approach for this assessment. However, logistics and systemic side-effects limit clinical adoption. Intracoronary (IC) adenosine represents a quicker, alternative means of achieving myocardial hyperaemia. We investigated the feasibility and diagnostic value of intracoronary adenosine-derived indices of microvascular function. Methods and Results We performed invasive coronary function testing with a thermistor/pressure diagnostic guidewire (PressureWire X, Abbott) in 100 arteries from 76 consecutive patients undergoing investigation for suspected angina between Nov 2022 - Sep 2023 in 2 regional cardiac centres. All patients provided written informed consent. Repeated 3-ml thermodilution injections of room-temperature normal saline were performed at rest, after low-dose (90-microgram), and subsequently high-dose (210-microgram) IC bolus injection of adenosine via the guiding catheter. Finally, thermodilution was repeated during systemic hyperaemia from IV adenosine infusion (140 micrograms/kg/min). Responses were recorded on linked software (CoroFlow, Coroventis). Coronary flow reserve (CFR) and index of microvascular resistance (IMR) were calculated using mean (MeanTmn), first (1stTmn) and minimum (MinTmn) transit times for both low- and high-dose IC adenosine. ROC curves were used to determine the accuracy for each, and identify optimal cut-offs to predict IV CFR<2.0 and IMR≥25. The study population included 43.4% females, median age 62 (IQR 57–68) years. The presentation was stable angina in 69 (90.8%) patients. Smoking history was present in 40 (52.6%), hypertension 40 (52.6%), and diabetes mellitus 11 (14.5%). The evaluated coronary arteries (n=100) comprised the left anterior descending in 66, left circumflex in 28 and right coronary in 6. The median (IQR) IV adenosine fractional flow reserve (FFR)= 0.89 (0.83–0.94), CFR 3.1 (2.1–4.7) and IMR 17 (13–28). Low-dose IC adenosine demonstrated greater accuracy versus high-dose for predicting IV adenosine-derived CFR and IMR. Indices derived from MeanTmn outperformed those calculated from 1stTmn and MinTmn. Low-dose IC adenosine CFR<2.8 (AUC 0.97 [95% CI: 0.94–1.00]) had the best sensitivity (100.0%), specificity (81.6%), PPV (63.2%) and NPV (100.0%) for predicting IV adenosine CFR<2.0. Low-dose IC adenosine IMR≥20 (AUC 0.93 [95% CI: 0.88–0.98]) had the best sensitivity (96.8%), specificity (78.3%), PPV (66.7%), NPV (98.2%) for predicting IV adenosine IMR≥25. There were good correlations between MeanTmn-derived low-dose IC adenosine CFR and IV adenosine CFR (r=0.79, r2=0.62; p<0.001), and MeanTmn-derived low-dose IC adenosine IMR and IV adenosine IMR (r=0.78, r2=0.60; p<0.001). Transient (<5 sec) AV block occurred in 1 patient with low-dose IC adenosine and 17 with high-dose. Four patients had chest pain with IC, versus 72 with IV adenosine (Fisher's p<0.001). Conclusions Our study provides novel data on the feasibility and diagnostic value of IC adenosine for estimating CFR and IMR, compared with systemic hyperaemia using IV adenosine. A hybrid algorithm incorporating IC adenosine CFR≥2.8 and IMR<20 for the rapid exclusion of abnormal IV CFR/IMR may encourage uptake of microvascular function testing amongst clinicians. External validation in larger populations is warranted. Conflict of Interest Nil