By Deborah J. DeWaay, MD, FACP
Associate Professor, Medical University of South Carolina, Charleston, SC
SYNOPSIS: This study strongly suggests that the prognosis for vasospastic angina patients who have suffered a Type II myocardial infarction is worse than traditionally assumed.
SOURCE: Matsue Y, et al. Clinical Features and Prognosis of Type 2 Myocardial Infarction in Vasospastic Angina. Am J Med 2015; 128(4):389-395
Vasospastic angina is defined as the chest pain caused by transient spastic narrowing of coronary vessels. Though a select few cases have reported acute myocardial infarction (MI) and even sudden death, the overall outlook for the majority of patients with vasospastic has been considered good. A 2007 collaboration of leading cardiology organizations produced a classification of five different types of MI. Type II MI describe a troponin I level of greater than the 99th percentile, as well as the presence of vasospastic angina. Despite its classification, there is insubstantial research into the pathology and mechanisms of this particular MI. As such, the authors of this paper aimed to improve understanding of vasospastic angina and Type II MIs by conducting a retrospective analysis of 171 patients admitted to their institution.
Over eight years, each of the 512 patients admitted for chest pain that was secondary to their vasospastic angina were reviewed in this study. The criteria for inclusion used to narrow down the field were: a definite diagnosis of vasospastic angina (following the Guidelines for Diagnosis and Treatment of Patients with Vasospastic Angina for Japanese Circulation Society) and initial troponin presence. The study also excluded patients with prior admissions for heart failure or advanced renal disease, had been diagnosed with Takotsubo cardiomyopathy, or had received coronary revascularization during hospitalization. During admission all patients received echocardiograms, and of the 512 patients, 171 were chosen to be included in the study.
During their initial coronary angiography patients were subject to an acetylcholine provocation test to determine whether or not they had vasospastic angina. Over the course of the eight years, several different tests for troponin I were used, although all tests required a 99th percentile or higher reading to be determined as a “positive” test for vasospastic angina. Angiography readings showing more than 50% luminal narrowing of the coronary artery designated cases of organic coronary stenosis.
A retrospective review of each hospital stay was performed and supplemented by follow-up data obtained from the hospital-affiliated outpatient clinic. Clinical risk scores defined by the Japanese Coronary Spasm Association (JCSA) were calculated to allow prognosis estimation for vasospastic angina. The authors selected study endpoints that included all-cause death and non-fatal MI. The medium follow-up time was 4.4 years.
At baseline the two groups (one group with Type II MI and one group without Type II MI) had similar patient characteristics, except that the group without Type II MI were just under five years older, on average. There were no significant differences between the two groups’ rates of diabetes, dyslipidemia, smoking or hypertension. Ninety-three percent of the patients had definitive acetylcholine provocation tests, and 95.9% were prescribed calcium channel blockers as treatment. Six of the patients received beta-blockers as treatment. Nearly 90% of all patients had ST-segment change concurrent with spontaneous angina.
When judged by the JCSA risk scores, 45.6% of all patients were low-risk, 40.9% were intermediate-risk and 13.5% were high-risk. The Type II MI patient group, in comparison with the all-patients sample, saw 16.7% of patients classified as low-risk, 27.1% deemed intermediate-risk, and 38.5% qualify as high-risk. On average, Type II MI patients had higher JCSA risk scores when contrasted with the non-MI group.
Thirty-two percent of the patients included in the study met the criteria that qualified them as Type II MI patients. During the course of study patients with this form of MI were more likely than their non-MI counterparts to experience a non-fatal MI or a death. The overall survival rate at the 5-year benchmark for vasospastic angina patients was found to be in the 90th percentile. Among Type II MI patients in the study, the five-year survival rate was 84.7%, while the combined, endpoint free survival rate was 71.7%. The mechanism for Type II MI was never fully studied in this analysis and is not included in the final considerations. Prior studies have determined that prognosis worsens with endothelial dysfunction even among patients without coronary artery problems. Moreover, there are already established, independent predictors of worsening prognosis, including microvascular dysfunction, which was not fully accounted for at the outset of this study’s angiogram testing.
As such, this study is characterized by several of its limitations. As a retrospective study of a single institution in Japan, its applicability and therefore generalizability is likely limited. Likewise limiting is that the number of patients and events within the study were relatively low. Furthermore, the follow-up times for patients were short.
Vasospastic angina and Type II MIs, however, are rather uncommon, so the author’s findings still bring relevant information into the light.