Murray law-based angiography-derived assessment of coronary microcirculatory resistance in myocardial ischemia and non-obstructive coronary arteries.

Background: The current European Society of Cardiology guidelines suggest invasive coronary function testing (CFT) for patients with suspected ischemia and non-obstructive coronary arteries (INOCA). We aimed to investigate the diagnostic yield of a novel Murray law-based coronary angiography derived assessment of coronary microcirculatory resistance in patients with INOCA.

Methods: This is a prospective, investigator-driven, registry including consecutive patients with INOCA undergoing CFT. The index of microvascular resistance (IMR) and coronary flow reserve (CFR) were determined via bolus thermodilution. Absolute flow (Q) and resistance (R) were assessed by continuous thermodilution. Measurements of angiography-derived resistance (μR) were performed in a centralized, independent, corelab, blinded to clinical data and invasive functional tests results.

Results: Out of 141 patients with suspected INOCA undergoing CFT, 118 patients were included in the final analysis. A positive linear correlation was found between μR and R (R = 0.36, p < 0.001). The discriminatory potential of μR was acceptable, using R ≥ 500 and IMR ≥25 as reference (AUC 0.675, p = 0.001 and AUC 0.639, p = 0.010, respectively). Notably, a μR of ≤145 had a negative predictive value of >99 %, and a μR ≥ 500 a positive predictive value of 88 %.

Conclusions: Murray law-based angiography-derived assessment of coronary microcirculatory resistance in patients with INOCA is a feasible method and is especially helpful for the screening of coronary microvascular dysfunction. Although refinements of this technique are warranted, it may contribute to a wider application of guideline recommendations for the diagnosis and management of patients with microvascular angina in clinical practice.