Cycling coupled to intra-coronary thermodilution to evaluate angina with non-obstructive coronary artery disease

Abstract BACKGOUND Patients with Angina and Non-Obstructive Coronary Artery disease (ANOCA) face misdiagnosis and inadequate treatment. A new continuous thermodilution method enables assessment of absolute coronary blood flow (Q) and microvascular resistance (Rµ). The effectiveness of saline-induced hyperemia in capturing exercise-induced coronary flow regulation remains unknown. OBJECTIVE To describe Q and Rµ adaptation during exercise and to explore the correlation between Coronary Flow Reserve (CFR) derived from saline and exercise-induced hyperemia, as well as Microvascular Resistance Reserve (MRR). Methods Q, Rµ, CFR and MRR were first assessed using continuous thermodilution with saline infusion at 10 mL/min (rest) and 20 mL/min (hyperemia) in the left anterior descending artery, followed by subsequent stress testing using a dedicated supine cycling ergometer. The microvascular parameters were assessed during incremental workload of 30 watts every two minutes. CFRsaline<2.5 was considered the cutoff for coronary microvascular dysfunction. 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. Results Coronary microvascular dysfunction was observed in 53.3% of the participants with suspected ANOCA (16 out of 30). During cycling, participants with coronary microvascular dysfunction had a lower reduction in Rµ (-109 [32; 286] versus -202 [102; 379] WU per 30 watts, p<0.01) and a lower ability to increase coronary flow (7 [30.5; 103.0] versus 21 [5.8; 45.0] mL/min per 30 watts, p=0.01) compared with those without coronary microvascular dysfunction. In the overall population, average CFRsaline and CFRexercise were 2.70±0.90 and 2.85±1.54, respectively (p=0.46) with an agreement classification of 83.3%. A good correlation between the two techniques was observed for both CFR (Spearman coefficient r=0.73, p<0.0001) and MRR (r=0.76, p<0.0001). Monitoring of CFR and Rµ during exercise unmasked functional coronary microvascular dysfunction priorly labeled as normal by saline induced hyperemia in 13.3% of the study population. These individuals had a moderate and late decrease of Rµ during the early stages of exercise, with a plateau up to 75% of their theoretical workload. Conclusion Participants with coronary microvascular dysfunction demonstrated compromised CFR due to impaired reduction of Rµ during physical workload. 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 hemodynamic adaptation among participants with functional dysfunction.