Whether saline-induced hyperemia captures exercise-induced coronary flow regulation remains unknown.

To describe absolute coronary flow (Q) and microvascular resistance (Rμ) adaptation during exercise in participants with Angina with Non-Obstructive Coronary Arteries (ANOCA). To explore correlations between saline and exercise-derived Coronary Flow Reserve (CFR) and Microvascular Resistance Reserve (MRR).

Rμ, Q, CFR and MRR were assessed in the left anterior descending artery using continuous thermodilution with saline infusion at 10 mL/min (rest), 20 mL/min (hyperemia) and finally at 10 mL/min infusion rate during stress testing with a dedicated supine cycling ergometer. Incremental workload of 30 watts every two minutes was applied. A CFRsaline<2.5 cutoff was used to identify coronary microvascular dysfunction (CMD). A minimal sample size of 29 participants was required to detect a hypothesized Spearman coefficient correlation r=0.5 between CFRsaline and CFRexercise using a 80% power and 5% significance level test.

CFRsaline-defined CMD was observed in 53.3% of the participants (16/30). During cycling, these patients had a lower ability to increase Q (7 [30.5;103.0] versus 21 [5.8;45.0] mL/min/30watts, P=0.01) due to a lower reduction of Rμ (-109 [32;286] versus -202 [102;379] WU/30watts, P<0.01) as compared with the normal CFRsaline group. In the overall population, CFRsaline and CFRexercise were 2.70±0.90 and 2.85±1.54 respectively, with an agreement classification of 83.3%. A good correlation between saline and exercise techniques for both CFR (r=0.73, P<0.0001) and MRR (r=0.76, P<0.0001) was observed (Fig. 1). Among participants with normal CFRsaline, 28.7% (4/14) had impaired CFRexercise<2.5 at peak of exercise due to a moderate and late decrease of Rμ.

Saline-induced hyperemia provided a valid surrogate for exercise physiology independently of the absolute level of CFR and MRR, although exercise provided more granularity to evaluate adaptation among participants with exercise related CMD.