Unstable angina in the context of high-sensitive troponins: Still a marker of high risk? A comparison of outcomes with adjudicated type 1 myocardial infarction

Abstract

Background: Unstable angina (UA), considered historically a marker of high risk, has rarely been studied in the high sensitive troponin era. We sought to characterise this population and determine short- and medium-term outcomes for UA and compared this to both patients with musculoskeletal chest pain and adjudicated type 1 MI (NSTEMI).

Method: We conducted a post-hoc analysis of 2 prospective cohort studies of suspected acute coronary syndrome in 2 hospitals in the northwest of England. (n = 3018) We used a dedicated symptom score to diagnose unstable angina. Type 1 MI (NSTEMI) was diagnosed by independent physician adjudication according to 3rd universal definition of MI. Follow-up was 100% complete for all patients to 1 year.

Results: 185 (6.1%) and 249 (8.3%) were adjudicated as suffering from UA and NSTEMI respectively. We restricted our analysis of UA to 158 (5.2%) patients with UA with high sensitive troponin T (Roche Elecsys) ≤14 ng/L (≤99th percentile). Compared to the NSTEMI population, the UA cohort were younger (59 vs 74, p < 0.002), had a lower incidence of hypertension (56.3% vs 69.1%, p = 0.009), had significantly lower composite risk scores and had fewer ECG abnormalities (ST depression >1 mm, 5.1% vs 15.6%, p = 0.001, T wave flattened, biphasic or inverted 24.1% vs 47.8%, p < 0.0001). Subsequent Type 1 MI to 30 days and 1 year in the UA cohort was 1.9% and 1.9% respectively compared to 0.8% and 2.4% in the index type 1 MI (NSTEMI cohort) respectively. However, compared to patients presenting with musculoskeletal chest pain (n = 468) there was a significantly greater incidence of subsequent MI and coronary revascularisation in patients with unstable angina. All cause death at 30 days and 1 year was 0.0% and 0.6% (n = 1) for UA patients and 2.8% (n = 7) and 16.1% (n = 40) for the NSTEMI cohort respectively.

Conclusion: UA, defined objectively by a symptom score and absence of myocyte necrosis, is still prevalent as an entity, with a risk of subsequent MI and urgent or emergency coronary revascularisation. However, mortality is >10-fold lower when compared to NSTEMI, indicating a less severe pathology in terms of atherosclerosis or plaque burden, and implying the need for a different management strategy to that of NSTEMI.

Keywords: Acute coronary syndrome; High sensitive troponins; Unstable angina.