Thermodilution assessment of vasoreactivity and microvascular function in the absence of obstructive coronary artery disease

Introduction and objectives: Invasive diagnosis of vasoreactivity and microvascular function may be useful to optimize the management of patients with signs and/or symptoms of myocardial ischemia in the absence of significant coronary stenosis (INOCA). We analyzed the prevalence of the different endotypes, as well as the concordance between 2 diagnostic methods based on ther-modilution assessment. Methods: We prospectively included 60 patients with INOCA who underwent a vasoreactivity test with intracoronary acetylcholine, and measurement of absolute coronary blood flow (Q) and minimum microvascular resistance (R) using continuous thermodilution assessment. Finally, calculations of the coronary flow reserve (CFR) and index of microcirculatory resistance index (IMR) were made using the bolus thermodilution method considering CFR < 2 and MRI ≥ 25 as established pathological cut-off values. Results: The invasive functional diagnostic procedure allowed patients to be categorized into 4 subgroups: microvascular dysfunction (40%), epicardial vasospasm (17%), mixed disorder (20%), and normal study (23%). No correlation was seen between the Q and the CFR. Using ROC curves, an R > 435 UW was estimated as the optimal cut-off value to identify patients with IMR ≥ 25 with an area under the curve of 0.67 (95%CI, 0.51-0.82; P = .04). Conclusions: The invasive study of vasoreactivity and microcirculation was feasible and safe. Prevalence of vasospasm and microvascular dysfunction in patients with INOCA was high. The CFR/MRI/Q combined study allowed us to unmask a subtype of microvascular dysfunction characterized by an abnormally high coronary flow at baseline. The concordance seen between the microvascular resistance obtained by continuous thermodilution measurements and the reference method was low so future studies are justified to determine the usefulness of this technique.