Most people know that the ECG is only diagnostic of ACS approximately in 50% of cases, and in fact patients presenting with ACS can have an initially completely normal ECG in up to 10% of cases. However, traditional teaching is that if the patient is actively having chest pain or other concerning symptoms, the patient with ACS will nearly always have ECG abnormalities. NOT SO, according to a recent study. Researchers from Davis medical center evaluated patients with presumed ACS and normal ECGs, comparing the prevalence of ACS in patients with active symptoms (e.g. chest pain) during the normal ECG vs. patients that were asymptomatic at the time of the ECG. Cutting to the chase, they found no difference in ther rule-in rate between the two groups. In other words, don't be reassured at all if a patients has a normal ECG during symptoms.
This study supports other studies which continually show that an abnormal ECG is excellent at ruling-in disease, but a normal ECG is poor at ruling-out disease. In the absence of a diagnostic ECG, it's all about the HPI, the HPI, and the HPI. And also...the HPI.
[Turnipsee SD, Trythall WS, Diercks DB, et al. Frequency of acute coronary syndrome in patients with normal electrocardiogram performed during presence or absence of chest pain. Acad Emerg Med 2009;16:495-499.]
