Early ‘Rule-In’ Diagnosis of Acute Myocardial Infarction 4 h Post Admission for Rapid Risk Stratification by Creatine Kinase Increment (Creatine Kinase Change)

Abstract

The use of creatine kinase (CK) measurement on admission, CK at 4 h, percentage CK change and electrocardiography (ECG) were compared for early risk stratification in the diagnosis of acute myocardial infarction (AMI). A total of 248 patients (median age 62 years, range 26–84) were studied (187 men, 61 women) of whom 118 had a final diagnosis of AMI. Median time to presentation was 3·92 h (range 0–11·17 h). Overall, the admission ECG had a sensitivity of 72·6% [95% confidence interval (CI) 64·6–80·7] with specificity of 88·9% (CI 83·4–94·4); 4 h CK change had a sensitivity of 100% (CI 96·1–100) with a specificity of 90·4% (CI 83·5–95·1). After excluding those with contraindication to anti-thrombotic therapy there were 109 patients with an uncertain initial diagnosis. In this group, admission CK had a sensitivity of 37·5% (CI 18·8–59·4) with a specificity of 94% (CI 86·8–98·1); 4 h ECG had a sensitivity of 43·8% (CI 19·8–70·1) with specificity of 97·4% (CI 86·5–99·9%); 4 h CK had a sensitivity of 79·2% (CI 57·8–92·9) with a specificity of 96·5% (CI 90–99·3); 4 h CK increment had a sensitivity of 100% (CI 85·8–100) with a specificity of 94% (CI 86·8–98·1). The admission ECG remains the investigation of choice for early ‘rule-in’ diagnosis of AMI for thrombolysis. Admission measurement of CK offers a small advantage in the patient with an uncertain diagnosis but the overall benefit is low. A strategy of admission ECG plus serial testing allows diagnosis to be complete by 4 h for accurate risk stratification. Whether this can be used for selection for therapeutic options (thrombolytic, anti-coagulation, anti-platelet or anti-anginal agents) requires further clinical trials.