Invasive assessment of coronary microvascular dysfunction in patients with angina and unobstructed coronary arteries (ANOCA) - Comparison of Doppler- and Thermodilution derived measurements

Introduction Invasive coronary function testing has the ability to identify coronary microvascular dysfunction endotypes in patients with angina but unobstructed coronaries (ANOCA). Such an approach is recommended by the 2024 ESC Guidelines on Chronic Coronary Syndrome. However, challenges remain regarding the different measurement techniques and routes of adenosine injection. The current study compared coronary flow reserve and microvascular resistance measured by the Doppler and the Thermodilution technique as well as intracoronary versus intravenous adenosine administration. Methods Between 2018 and 2024 a total number of 238 consecutive patients with ANOCA undergoing coronary function testing for suspected microvascular angina was recruited in 2 German cardiovascular centres (mean age 63±11 years, 57% female). All patients underwent wire-based assessment of coronary flow reserve (CFR) and microvascular resistance in the left anterior descending artery. The bolus thermodilution technique was applied in 122 patients (CFR/IMR, CFRThermo) and the Doppler technique in another 116 patients (CFR/HMR, CFRDoppler). All measurements were performed according to a standardised protocol using either intracoronary or intravenous adenosine. The Guideline recommended cut-offs for CFR (<2.5), HMR (>2.5) and IMR (>25) were used. Results Overall, coronary microvascular dysfunction was diagnosed in 48% of all patients. Impaired CFR was found in 20% of cases, impaired microvascular resistance in 14% and both abnormalities in another 14% of cases. There was a significant difference between the frequency of an abnormal CFR among patients with CFRThermo (32/122, 26%) and patients with CFRDoppler (50/116, 43%, p=0.007). Moreover, median CFR was higher in the CFRThermo compared to the CFRDoppler group (3.4 [IQR2.0] vs. 2.6 [IQR 0.9], p<0.0005). Conversely, impaired microvascular resistance was more often observed with the thermodilution compared to Doppler the technique (44% vs. 12%, p<0.0005). Comparison of thermodilution-derived CFR in patients receiving iv adenosine (n=77) to those receiving ic adenosine (n=45) did not reveal any statistically significant differences (3.2 vs. 3.5, p=0.10, Figure 1). Multivariable analysis revealed arterial hypertension (odds ratio 2.76, confidence interval 1.48 – 5.14, p<0.001) as independent predictor for an abnormal CFR. Conclusion Coronary microvascular dysfunction is frequently found in ANOCA patients. Depending on the technique used there are marked differences in the frequency of impaired coronary flow reserve and microvascular resistance. Both, intravenous and intracoronary adenosine administration is feasible.