208 Contrast derived indices of coronary microvascular function

Background and Aims Coronary function testing to measure index of microcirculatory resistance (IMR) and coronary flow reserve (CFR) may be performed at the time of invasive coronary angiography to aid the diagnosis of microvascular angina. Intravenous (IV) adenosine infusion is used to induce stable hyperaemia. Logistics and systemic side-effects limit clinical adoption. Iodinated contrast medium (iohexol) is used during standard diagnostic angiography and induces transient, submaximal hyperaemia. We investigated the feasibility and diagnostic value of contrast-derived indices of coronary microvascular function. Methods and Results Consecutive patients with suspected angina who underwent clinically-indicated invasive coronary angiography at 2 regional cardiac centres between Jul 2021 and Nov 2022 were included. Coronary function testing was performed using a temperature/pressure diagnostic guidewire (PressureWire X; Abbott). Exclusion criteria include advanced kidney disease. Repeated 3 ml thermodilution injections were performed at rest, immediately after an 8 ml bolus of iohexol, and during IV adenosine (140 micrograms/kg/min) infusion. Responses were recorded on linked software (CoroFlow; CoroVentis). Contrast-derived IMR (cIMR) and CFR (cCFR) were calculated using the mean, minimum and first measured transit times respectively. ROC analysis was performed for each. In total, 106 vessels from n=93 patients were included. The median age was 63 years; 62.4% female. Co-morbidities include 46.2% smoking history, 12.9% diabetes mellitus and 66.7% hypertension. The vessels tested were 88.2% left anterior descending, 4.3% circumflex and 7.5% right coronary artery. 90.6% of vessels were non-obstructive, with median FFR=0.88 (IQR 0.85–0.92). cIMR derived from mean transit times of the second contrast bolus (ROC AUC 0.88 [95% CI: 0.81–0.96]) cutoff of >46 had the best sensitivity (89.3%; 25/28), specificity (76.7%; 56/73), PPV (59.5%; 25/42), and NPV (94.9%; 56/59) by the Youden index for predicting IV adenosine IMR≥25. There was good correlation between cIMR and IV adenosine IMR (r=0.74, r2=0.55; p<0.001). cCFR derived from the first transit time of the second contrast bolus (ROC AUC 0.75 [95% CI: 0.63–0.87]) cutoff of ≤2.2 had the best sensitivity (93.8%; 15/16), specificity (61.2%; 52/85), PPV (31.3%; 15/48), and NPV (98.1%; 52/53) by the Youden index for predicting IV adenosine CFR<2.0. There was good correlation between cCFR and IV adenosine CFR (r=0.42, r2=0.18; p<0.001). No adverse events were noted. Conclusions Our study provides novel data on the feasibility and diagnostic value of contrast-derived IMR and CFR. The enhanced diagnostic yield from repeat contrast injection is potentially an effect of incremental hyperaemia. A hybrid algorithm incorporating contrast-derived IMR≤46 and CFR>2.2 for the rapid exclusion of microvascular angina may be considered. External validation in larger populations is warranted. Conflict of Interest Nil