Clinical Characteristics and Outcomes of Patients with a Positive Finding for the Coronary Spasm Provocation Test at Low Acetylcholine Doses.

Objective The intracoronary acetylcholine (ACh) provocation test is an invasive standard for diagnosing coronary spastic angina (CSA)/vasospastic angina. Although the guidelines recommend incremental doses of ACh, the clinical relevance of the significant response to lower ACh doses is unclear. Methods From April 2012 to June 2024, 636 patients with no significant epicardial coronary disease undergoing intracoronary ACh provocation testing for the diagnosis of CSA were included. Patients with positive ACh test results were divided into two groups: the low-dose positive group, defined as those who tested positive at the initial dose of ACh in the left and/or right coronary arteries without further dose escalation, and the high-dose positive group, including those who required higher doses for a positive result. The occurrence of intraprocedural adverse events and long-term outcomes was also evaluated. Results Of the 636 patients, 306 (48.1%) were classified as negative, 304 (47.8%) as high-dose positive, and 26 (4.1%) as low-dose positive based on the ACh provocation tests. The baseline characteristics did not differ significantly between the high- and low-dose positive groups. ST-segment elevation on electrocardiography during ACh tests and unstable angina during the follow-up period were more frequent in the low-dose positive group than in the high-dose positive group, while the overall clinical outcomes were similar among the groups. Conclusion Among patients with CSA diagnosed using ACh provocation testing, nearly 10% had a positive diagnosis at a low dose. There may be distinct underlying mechanisms and clinical outcomes depending on the ACh dose required for a positive test result.