Significant Response to Lower Acetylcholine Dose Is Associated with Worse Clinical and Angiographic Characteristics in Patients with Vasospastic Angina

Background and Objectives: The intracoronary injection of acetylcholine (Ach) has been shown to induce coronary spasms in patients with variant angina. Clinical significance and angiographic characteristics of patients with a significant response to lower Ach dosages are as-yet non-clarified compared with patients responding to higher Ach doses. Subjects and Methods: A total of 3034 consecutive patients underwent coronary angiography with Ach provocation tests from January 2004 to August 2010. Ach was injected in incremental doses of 20, 50, 100 mu g into the left coronary artery. Significant coronary artery spasm was defined as focal or diffuse severe transient luminal narrowing (> 70%) with/without chest pain or ST-T change on the electrocardiogram (ECG). We compared the clinical and angiographic characteristics of patients who responded to a lower Ach dose (20 or 50 mu g, n= 556) to those that responded to a higher Ach dose (100 mu g, n= 860). Results: The baseline clinical and procedural characteristics are well balanced between the two groups, except diabetes was higher in the lower Ach dose group and there were differences in medication history. After adjusting for confounding factors, the lower Ach dose group showed more frequent temporary ST elevation and atrioventricular block on the ECG. Furthermore, the group of patients who responded to the lower Ach dose was associated with a higher incidence of baseline and severe spasm than those who responded to a higher Ach dose. Conclusion: Patients with a significant response to a lower Ach dose were associated with more frequent ST elevation, baseline spasm, and more severe spasm compared with those who responded to a higher Ach dose, suggesting more intensive medical therapy with close clinical follow-up is required for those patients.