A simple, readily available method for risk stratification of patients with unstable angina and non-ST elevation myocardial infarction

Abstract

The rationale for risk stratification of patients with unstable angina and non-ST elevation myocardial infarction (MI) includes the identification of patients at higher risk of recurrent events after index presentation to enable clinicians to triage patients to the most appropriate level of care in the inpatient or outpatient setting, and optimize the use of medications, revascularization options, and length of stay. Prior studies have shown that a variety of variables predict risk of clinical events, including the following: clinical criteria such as age and history of coronary artery disease1,2 ; ST-segment changes on admission electrocardiogram or Holter monitor3,4 ; detection of serum cardiac markers such as creatine kinase, creatine kinase- MB fraction, myoglobin, or cardiac-specific troponins5‐11 ; detection in the serum of other biochemical markers such as fibrinogen and C-reactive protein,12,13 and nuclear imaging modalities. 14 Detailed statistical models have been created that integrate these variables noted above in a number of trials. 15,16 A more detailed risk score for the Thrombolysis In Myocardial Infarction (TIMI) 11B cohort has been developed.17 This risk score requires 7 predictor variables, several of which may not be known at patient presentation, and is subject to patient recall and may require time to obtain. We tested a simple risk stratification scheme using age, ST deviation on the admission electrocardiogram, and the detection of elevated levels of serum cardiac markers, and evaluated its clinical usefulness in TIMI 11B, a large contemporary trial of patients presenting with unstable angina and non-ST elevation MI. ••• TIMI 11B, a multicenter, international, randomized, double-blind, placebo-controlled phase III trial of enoxaparin versus unfractionated heparin for unstable angina and non-ST elevation MI has been previously reported.18 All patients were required to have ischemic discomfort of at least 5 minutes at rest within 24 hours before randomization. At the start of the trial, patients were eligible if they had either a documented history of coronary artery disease, with a history of an abnormal angiogram, prior MI, coronary artery bypass surgery, or percutaneous transluminal coronary angioplasty, ST deviation, or elevated serum cardiac markers. Elevated cardiac-specific troponins were allowable as inclusion criteria per the study protocol; however, during the period of enrollment of patients, creatine kinase and creatine kinase-MB fraction were the predominant biomarkers used for routine clinical purposes at the participating sites. After about 40% of the target enrollment, the inclusion criteria were modified to focus on higher risk patients by requiring that all patients have either ST deviation or positive cardiac markers.