High-Sensitivity Cardiac Troponin T Measured Twice 1 Hour Apart Can Diagnose and Rule Out Myocardial Infarction in Most Patients with Chest Pain

Cardiac troponin is an important marker of cardiac injury and necrosis that has become increasingly useful in the diagnosis of acute myocardial infarction (MI). While older generation troponin assays could require serial measurements over several hours to provide informative results, newer high-sensitivity troponin tests have shown promise in reducing the time to diagnosis. A recent cohort study derived and validated a clinical algorithm for early diagnosis of acute MI using a high-sensitivity troponin T (hs-cTnT) assay in the emergency department.

A total of 872 patients (median age 64 years) presenting with chest pain were randomly divided into derivation and validation cohorts (436 patients each). Patients with ST-segment elevation myocardial infarction or terminal kidney failure requiring dialysis were excluded prior to randomization. All patients had hs-cTnT assays at presentation and at 1 hour. Patients also had complete clinical assessment including history, physical examination, 12-lead electrocardiography, continuous electrocardiography-monitoring, pulse oximetry, standard blood tests, and chest radiography and additional hs-cTnT assays at 2, 3, and 6 hours after presentation. The reference standard for acute MI diagnosis was adjudication by 2 independent cardiologists using all available medical records to 60-day follow-up.

A 2-part clinical algorithm was developed in the derivation cohort to diagnose or rule out acute MI using the baseline and 1-hour troponin tests. Acute MI is ruled out if the baseline hs-cTnT level is < 12 ng/L AND the absolute change in hs-cTnT level within 1 hour is < 3 ng/L. Acute MI is diagnosed if the baseline hs-cTnT level is ≥ 52 ng/L OR the absolute change in hs-cTnT level within 1 hour is ≥ 5 ng/L. Patients meeting neither set of criteria fall into the "observation zone," requiring continued observation and additional testing.

The incidence of acute MI in the validation cohort was 17%. The algorithm classified 77% of the group:  acute MI was diagnosed in 17% and ruled out in 60%. The remaining 101 patients fell into the observation zone (8 of these patients received final diagnosis of acute MI). For diagnosing acute MI, the algorithm had 97% specificity and 84% positive predictive value.  For ruling out MI, it had 100% sensitivity and 100% negative predictive value (level 1 [likely reliable] evidence). In overall analysis of both cohorts, 30-day survival was 99.8% in patients with MI ruled out, 98.6% in patients in the observation zone, and 95.3% in patients with MI ruled in (p < 0.001 for trend) (Arch Intern Med 2012 Sep 10;172(16):1211).

For more information, see the Cardiac troponin testing topic in DynaMed.

Cochrane Colloquium, September 30^th - October 3^rd, 2012 
Editor-in-Chief Dr. Brian Alper will be presenting at the 20^th Cochrane Collaboration Colloquium held at the Pullman Hotel in Auckland, New Zealand. The topic of the presentation is "Practice-driving evidence: how frequently does it change?"   

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First International Conference on Evidence Based HealthCare (ISEHCON), October 7^th - 8^th, 2012   

Editor-in-Chief Dr. Brian Alper will be leading a workshop at the First International Conference on Evidence Based Healthcare at the India International Centre in New Delhi, India. The topic of the workshop will be "Best Sources for Evidence-Based Literature for Healthcare Practitioners".   

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