Aortic versus distal pressure for derivation of hyperaemic microvascular resistance: From the ILIAS registry

Background: In patients with angina and non-obstructive coronary arteries (ANOCA), intracoronary function testing typically involves assessing the minimal microvascular resistance. This can be derived from the coronary flow and the distal pressure (Pd) during maximal hyperaemia. Theoretically, in ANOCA patients, resistance and pressure have minimal impact along the epicardial vessel, suggesting the possibility of deriving hyperaemic microvascular resistance (HMR) using aortic pressure (Pa) instead of Pd, but this has not been studied previously. Methods and results: Data from the ILIAS registry, a global multicentre registry pooling lesion-level coronary pressure and flow data, were used to compare HMR calculated with Pa versus Pd. A total of N = 1321 evaluated vessels were included. The study population consisted predominantly of men (68 %) with a mean age of 62 ± 10 years, and stable anginal symptoms (93 %). The overall correlation between HMR calculated with Pa and with Pd was good (Pearson's correlation coefficient: 0.84, p ≤0.005). The Bland-Altman plot showed a mean difference between HMR based on Pa and Pd of 0.53 (limits of agreements ±1.35). An adjusted Bland-Altman showed that the difference between HMR based on Pa and Pd was significantly related to the functional severity of the epicardial lesion (R² = 0.71, coef.: −4.5, p < 0.005). In patients with a FFR >0.80 there were no considerable outliers, and with a FFR <0.80 outliers increased significantly. Conclusions: In ANOCA patients, defined by a FFR above 0.80, HMR can be accurately measured with aortic pressure instead of distal pressure. However, in patients with a FFR below 0.80, there is a significant difference between HMR measured with Pa and Pd.