A total of 3034 consecutive patients (male 50.4%, mean age 54.6±12.4 years) who had typical or atypical chest pain underwent coronary angiography (CAG) at the cardiovascular center of Korea University Guro Hospital, Seoul, South Korea. Those patients who had less than a 30% fixed stenosis on quantitative coronary angiography (QCA) on diagnostic angiography underwent a subsequent intracoronary Ach provocation test, either via a transradial or transfemoral approach. Patients were excluded if they had one of the following conditions: prior coronary artery bypass graft, prior percutaneous coronary intervention, prior cerebrovascular disease, advanced heart failure (New York Heart Association class III or IV), or serum creatinine ≥3 mg/dL, because these conditions can be major causes of future adverse cardiovascular events and present a bias to CAS. Finally, a total of 1445 patients who had a positive provocation test to different stimulating Ach doses were entered for this analysis. Enrolled patients were divided into two groups according to two different Ach doses: the lower Ach dose group (positive provocation test to 20 µg or 50 µg, n=556 patients) and the higher Ach dose group (positive provocation test to 100 µg, n=860 patients). Clinical and angiographic characteristics during the Ach provocation test were then compared between the two groups.

The first investigations for suspected CAS included typical clinical history, non-invasive stress tests such as a treadmill test, ambulatory electrocardiogram (ECG), and stress echocardiography, with a subsequent invasive angiogram performed for confirmation. CAS was induced by the intracoronary injection of Ach after diagnostic angiography. Nitrates, calcium channel blockers (CCB), beta blockers, angiotensin converting enzyme inhibitors, and other vasodilators or vasoconstrictors were withheld at least 72 hours before CAG. Ach was injected over incremental doses of 20 (A1), 50 (A2), and 100 (A3) µg/min into the left coronary artery over a 1 minute period, with 5 minutes intervals, up to the maximum tolerated dose under continuous monitoring of an ECG and blood pressure measurement. Angiography was repeated after each Ach dose until a significant vasoconstriction (70%) response was obtained. Intracoronary infusion with 0.2 mg nitroglycerin (NTG) was administered after completing the Ach provocation test. Angiography was then performed 2 minutes later. If focal or diffuse significant vasoconstriction of coronary arteries was induced with any dose of Ach by visual assessment, any further Ach infusion was ceased. End systolic images for each segment of the left coronary artery were chosen according to the corresponding points on the electrocardiographic trace (QRS onset or end of T wave) and analyzed using the appropriate QCA system of the catheterization laboratory (FD-20, Phillips, Amsterdam, the Netherlands). The coronary artery diameters were measured with QCA before and after the administration of Ach at the site that showed the greatest changes following drug administration. Reference diameter was measured at the proximal and distal portion of each artery before and after the intracoronary Ach infusion, and the mean reference diameter was used to assess the extent of diameter narrowing. During the CAG and Ach provocation test, significant CAS was defined as focal or diffuse severe transient luminal narrowing (>70%) by visual assessment with or without chest pain, or ischemic ECG change such as ST-T segment elevation, depression (≥1 mm), or T wave inversion. Previously, we have published our data with Korean criteria in several international peer-reviewed journals.7)8) The normal coronary appearance was defined as less than 20% luminal narrowing on coronary angiogram, as measured with QCA. Myocardial bridge (MB) was considered when the characteristic phasic systolic compression of the coronary artery had a >30% decrease in diameter on the angiogram after intracoronary NTG infusion, usually in anterior-posterior cranial projection or right anterior oblique cranial projection. Multi-vessel spasm (MVS) was defined as significant CAS of ≥2 major epicardial coronary arteries. The presences of a baseline spasm was defined as focal or diffuse narrowing more than 30% in diameter on the angiogram before the Ach provocation test was applied, as compared with the final angiogram after intracoronary NTG infusion. Diffuse CAS was defined as significant CAS site length ≥30 mm.

Hypertension was defined as either systolic or diastolic elevation of blood pressure ≥140/90 mm Hg or ongoing antihypertensive pharmacological treatment. Dyslipidemia was defined as a total cholesterol level ≥200 mg/dL or current treatment with lipid-lowering drugs. Current smoking was defined as active smoking within the past 12 months. Diabetes mellitus was defined as a fasting blood glucose level ≥126 mg/dL, or any use of hypoglycemic agents or insulin. In the present study, if a patient's past history, medical records, present symptoms, or medical examination results accorded with one of the following criteria, the patients were diagnosed with peripheral artery disease: 1) Claudication symptoms with ankle brachial indices <0.90; 2) Claudication symptoms with findings of a significant lesion (≥70% diameter stenosis) in a peripheral artery by a doppler ultrasound, computed tomographic angiography, magnetic resonance angiography, or invasive angiography; 3) Symptomatic carotid, subclavian arterial disease (≥70% diameter stenosis) documented by image studies including computed tomographic angiography, magnetic resonance angiography, or invasive angiography. Insignificant coronary artery disease was defined as a ≤20% diameter stenosis in coronary arteries documented by image studies including computed tomographic angiography, magnetic resonance angiography, or invasive angiography.

All statistical analyses were performed using Statistical Package for the Social Sciences (SPSS) 17.0 (SPSS Inc., Chicago, IL, USA). For continuous variables, differences between the two groups were evaluated by an unpaired t-test or Mann-Whitney rank sum test. For discrete variables, differences were expressed as counts and percentages and analyzed with a χ² or Fisher's exact test between the groups, as appropriate. Multivariate logistic regression analysis, which included baseline confounding factors, was used for assessing the independent predictors for significant CAS. A two-tailed p of <0.05 was considered to be statistically significant. Data were expressed as mean±standard deviations.

This study has several obvious limitations. First, in the guidelines for diagnosis and treatment of patients with vasospastic angina (Japanese Coronary Association 2008), CAS is defined as the "transient, total, or sub-total occlusion (>90% stenosis) of a coronary artery with a sign/symptoms of myocardial ischemia (anginal pain and ischemic ST changes).20) However, we considered patient safety and convenience in real world practice, thus, we did not wait until subtotal or total occlusion through maximal Ach stimuli. We considered safety to be more important when performing an Ach provocation test on the outpatient clinic base. Therefore, in our study, significant CAS was defined as focal or diffuse severe transient luminal narrowing (>70%) with or without chest pain, or ischemic ECG change, such as ST-T segment elevation, depression (≥1 mm), or T wave inversion. This might have resulted in a significant risk of false (+) findings, if >70% diffuse coronary spasm is regarded as a (+) result due to differences of diagnostic criteria. Second, the limitations of our study include the observational retrospective design, which lacks randomization and may inadvertently introduce a selection bias. Third, even though we minimized the confounding effects from the baseline biases with multivariate logistic analysis, it is possible that some potential confounders may have impacted on our results. However, we tested CAS in a relatively larger study population, which is helpful in minimizing any confounding effects from the baseline biases. Fourth, the Ach provocation test was not performed in the early morning. It was usually performed around noon. The circadian variation of coronary spasms may21) be the reason why the positive provocation rate for CAS was higher in our study than that observed in previous reporting.22) Fifth, because we enrolled all patients who had chest pain (without concern about typical or atypical chest pain), without significant coronary artery stenosis, the typical expected (+) rate of spasm may have been higher in this study. Therefore, we enrolled only >70% diffuse coronary spasm patients, as this is not currently regarded as variant angina.

The sixth limitation is the study population, in which there may have been present a bias toward those who had undergone the Ach provocation tests. Ach provocation tests were performed to document significant CAS for the diagnosis of variant angina. Thus, this study was not designed to evaluate the degree of endothelial dysfunction in patients with variant angina.

In conclusions, the present study found that patients with vasospastic angina documented by a lower Ach dose provocation test have a higher incidence of transient ST elevation, baseline spasm, and more severe spasms than patients who responded to a higher dose of Ach. Therefore, in the real clinical world, patients with significant CAS documented by a lower Ach dose would require more aggressive and intensive medical therapy and careful clinical follow-up would be required for this particular subset of patients.