Cardiac markers for acute myocardial infarction: When should we test?

I read with keen interest the article by Eugene Dagnone and colleagues.1 As the director of a typically overcrowded Canadian emergency department I am constantly searching for clinical tools to avoid admitting patients to hospital and facilitate their safe and expeditious discharge. Patients presenting with chest pain represent a large group who require cautious and time-sensitive evaluation before discharge.

I was disappointed by the methodology used in this study, specifically with regard to the use of the cardiac troponin I (cTnI) enzyme test. The authors stated that “the time profile of cTnI parallels that of the CK MB [creatine kinase and its MB isoenzyme] fraction.” From Table 1 in the article it is evident that 73% of patients enrolled in the intervention group had cTnI evaluated at less than 6 hours after onset of chest pain and 88% at less than 12 hours. It is likely that clinical decision-making would not have been enhanced by results obtained at a time when the sensitivity of the cTnI assay was less than optimal.

Had the study mandated cTnI evaluation at no less than 10 hours after the onset of chest pain, the emergency physician would more reliably have been able to incorporate this test into his or her decision process for admission. I suggest that this modification would very possibly have significantly altered the outcome of the study.

I would encourage the authors or others to undertake further studies utilizing cardiac markers in a time- sensitive manner to evaluate their utility in safely avoiding admissions of patients presenting with chest pain.

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