Absolute Coronary Blood Flow Measured by Continuous Thermodilution in Patients With Ischemia and Nonobstructive Disease

Abstract

Background: Intracoronary continuous thermodilution is a novel technique to quantify absolute coronary flow (Q) and resistance (R) and has potential advantages over current methods such as coronary flow reserve (CFR) and index of microvascular resistance (IMR). However, no data are available in patients with ischemia and nonobstructive coronary artery disease (INOCA).

Objectives: This study aimed to assess the relationship of Q and R with the established CFR/IMR in INOCA patients, to explore the potential of absolute Q, and to predict self-reported angina.

Methods: Consecutive INOCA patients (n = 84; 87% women; mean age 56 ± 8 years) underwent coronary function testing, including acetylcholine (ACH) provocation testing, adenosine (ADE) testing (CFR/IMR), and continuous thermodilution (absolute Q and R) with saline-induced hyperemia.

Results: ACH testing was abnormal (ACH+) in 87%, and ADE testing (ADE+) in 38%. The median absolute Q was 198 ml/min, and the median absolute R was 416 WU. The absolute R was higher in patients with ADE+ versus ADE- (495 WU vs. 375 WU; p = 0.04) but did not differ between patients with ACH+ versus ACH- (421 WU vs. 409 WU; p = 0.74). Low Q and high R were associated with severe angina (odds ratio: 3.09; 95% confidence interval: 1.16 to 8.28; p = 0.03; and odds ratio: 2.60; 95% confidence interval: 0.99 to 6.81; p = 0.05), respectively.

Conclusions: In this study, absolute R was higher in patients with abnormal CFR/IMR, whereas both Q and R were unrelated to coronary vasospasm. Q and R were associated with angina, although their exact predictive value should be determined in larger studies.

Keywords: INOCA; absolute coronary blood flow; acetylcholine; adenosine; coronary function test; coronary physiology.