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A single assay result and ECG finding may rule out MI in EDs

High-sensitivity assays for cardiac troponin T concentration below the limit of detection in combination with a nonischemic ECG can quickly and safely rule out acute myocardial infarction in patients presenting to the ED with possible emergency acute coronary syndrome, according to recent data published in Annals of Internal Medicine

“A single [high-sensitivity assay for cardiac troponin T (hs-cTnT)] measurement below the limit of detection or the limit of blank may rule out [acute] MI]… [however], the underpinning evidence presented was from a small number of studies, some of which were affected by laboratory calibration errors resulting in hs-cTnT concentrations that were lower than the true concentrations,” John W. Pickering, PhD, from Christchurch Hospital, University of Otago Christchurch and Christchurch Heart Institute in New Zealand, and colleagues wrote. “If findings can be validated across multiple studies that are free of these limitations, this approach could enable safe discharge of many more patients than in current practice.”

Researchers assessed the ability of a single hs-cTnT concentration below the limit of detection (less than 0.005 μg/L) and a nonischemic ECG to rule out acute MI in adults presenting to the ED with chest pain.

Using data collected from EMBASE and MEDLINE between Jan. 1, 2008 to Dec. 14, 2016, they selected cohort studies involving adults presenting to the ED with possible acute coronary syndrome where an ECG and hs-cTnT measurements were taken and acute MI outcomes adjudicated during initial hospitalization. They used data provided by investigators of the previous studies on the number of low-risk patients and the number who had acute MI during hospitalization or a major adverse cardiac event or death within 30 days by risk classification: low risk or not low risk.

Out of 9,241 patients in the 11 cohort studies evaluated, Pickering and colleagues classified 2,825 (30.6%) as low-risk. Of these low-risk patients, 14 (0.5%) had acute MI. The results showed that in most settings, patients assessed for acute coronary syndrome with hs-cTnT below the limit of detection and a nonischemic ECG had very low risk for acute MI or major adverse cardiac events within 30 days. Researchers found that in individual studies, the sensitivity of the risk classification for acute MI ranged from 87.5% to 100% and pooled estimated sensitivity was 98.7% (95% CI, 96.6-99.5). For 30-day major adverse cardiac events, sensitivity ranged from 87.9% to 100% and pooled sensitivity was 98% (95% CI, 94.7-99.3). No deaths occurred among low-risk patients.

“Acute myocardial infarction may be ruled out in a substantial proportion of patients after only one blood draw,” Pickering and colleagues wrote. “At this time, we do not recommend a single-blood draw strategy in patients presenting within 3 hours of symptom onset. Because the strategy had considerable heterogeneity of sensitivity among sites, it should not be used without careful additional clinical assessment to identify patients with a high likelihood of underlying critical coronary stenosis.” – by Savannah Demko

Disclosure: Pickering reports grants from the Emergency Care Foundation, Canterbury Medical Research Foundation and Canterbury District Health Board. Please see the full study for a complete list of all authors’ relevant financial disclosures.