Reducing missed ACS


Patients with Acute Coronary Syndrome (ACS) are discharged from the Emergency Department with missed diagnosis at a relatively low rate. But because ACS is a leading cause of death, this translates into a major medico-legal concern for Emergency Physicians. While it is impossible to reduce the miss rate to zero without admitting every patient, many cases of missed ACS are preventable.


A medico-legal review from nearly 30 years ago found typical features of patients with missed ACS:

So the solution is not to get cardiac enzymes or admit everyone, but to not ignore the possibility of ACS in young patients with “atypical” symptoms, and to closely scrutinize the ECG. These findings have continued in the literature since then:

There are three medical errors that emerge from the literature: not considering “atypical” symptoms as potential ACS, not interpreting the ECG correctly, and discharging patients with unstable angina. A review of the literature suggests assumptions behind these errors, which if corrected can hopefully reduce the rate of missed ACS:



With chest pain rules, chest pain protocols and chest pain units, ACS has often been reduced to Acute Chest pain Syndrome. But chest pain is only one of the cardinal symptoms of ACS (the other being dyspnea, nausea/vomiting, weakness, sweating, or jaw/arm pain), and chest pain is absent in many cases of ACS. ACS without chest pain has often been described as “atypical” as though it is rare or benign, but these are dangerous assumptions.

Historically women have been labelled as having “atypical” symptoms of ACS, but this is only if we consider “typical” symptoms as classic chest pain described by the majority of previously healthy middle aged men with ACS–a historical bias reflecting who was initially the focus for cardiovascular research. But this assumption that ACS patients have chest pain breaks down if we consider the full range of patients, including women and elderly patients. If this is taken into account, ACS without chest pain is more common in young women then in young men, but happens in both sexes and at an increasing frequency (with decreasing sex differences) over the age spectrum

As the authors concluded: “our goal should be to standardize ACS symptom presentation and to elucidate the full range of ACS and MI symptoms considering the substantial overlap of symptoms among women and men rather than use conventional terms such as ‘typical’ and ‘atypical’ angina.”



ACS is a dynamic process but the ECG is only a brief and partial snapshot of this process.

With nearly half of initial ECGs being nondiagnostic, including some which progressed from normal to STEMI, it’s essential to get serial ECGs and compare with prior ECGs. But ECGs don’t make the diagnosis on their own, they have to be interpreted:

  • Missed opportunities for reperfusion therapy for ST-segment elevation myocardial infarction: results of the Emergency Department Quality in Myocardial Infarction (EDQMI) study. Am Heart J 2008. Prospective multicentre trial of 2215 patients with AMI, including 460 with STEMI
    • 22% did not receive reperfusion, a third of which had STEMI that was not identified

As with the initial literature summarized, there are many cases of missed ACS where the ECG did show changes but it was not recognized. ECG interpretation is a life-long skill that requires constant work–and thankfully there are a number of experts in the field who constantly share their lessons



Under the pressure to see patients quickly and not use hospital resources, it’s common for non-STEMI patients with potential ACS to be stratified by troponin: troponin positive (NSTEMI) gets admitted, while troponin negative gets discharged. But the latter group includes some high risk patients with unstable angina who should get admitted despite normal bloodwork. Fortunately there’s been the development and validation of the HEART score–a 10-point score based on common clinical variables, which differentiates those at low risk of MACE (score 0-3) from those at  higher risk (>3 points):

Screen Shot 2018-07-14 at 1.23.02 PM

Like all clinical decision rules the HEART score has its limitations. The history is based on suspicious chest pain, which as discussed is only a subset of ACS patients. The ECG interpretation is user dependent. Risk factors are based on conventional factors but there are others, eg HIV, SLE, etc. And the low risk group is not no risk. But at least it provides a framework for risk stratifying patients to help providers safely discharge those at low risk while advocating for admitting those at those at high risk.

In summary, we run the risk of missing ACS if we dismiss “atypical” symptoms instead of considering all the symptoms, look at only one ECG snapshot instead of comparing to an old and a repeat ECG, and assume all troponin negative patients are automatically safe for discharge. Instead, to reduce ACS think of A.C.S.:

  • All symptoms of ACS, not just chest pain
  • Cardiogram comparison and interpretation
  • Stratify using the HEART score.


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