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.

PREVENTABLE MISSED ACS

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

• Litigation against the emergency physician: common features in cases of missed MI. Ann Emerg Med 1989. Review of 65 medico-legal cases of missed MI
  • greater missed if young (a third <40yo), “atypical” (a third painless)
  • ECG performed in only 68% of chest pain patients, 25% of those without chest pain. When performed, ischemia missed in 39%
  • no difference in troponin ordering rates

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:

• Clinical characteristics and natural history of patients with AMI sent home from ER. Am J Cardio 1987. Prospective multicentre investigation of ED patients with chest pain:
  • 4% of MIs missed
  • especially younger, less “typical” symptoms; but had higher mortality rate because of miss
  • 49% of misses could have prevented with closer attention to symptoms and ECG

• Missed diagnoses of acute myocardial infarction in the emergency department: results froma multicentre study. Ann Emerg Med 1993. Multicentre observational and case-control study of 1050 patients with AMI
  • 1,9% missed, 25% had complications
  • 25% had ST elevation, 15% had ST depression, 35% discharged with diagnosis of ischemic heart disease

• Missed diagnoses of acute cardiac ischemia in the emergency department. NEJM 2000. Multicentre prospective trial of 10,689 patients with ACS.
  • 2.1% AMI missed, 2.3% unstable angina discharged; missing ACS doubled the mortality rate
  • more likely missed if women <55yo, non-white, reported shortness of breath, or had normal or nondiagnostic ECG

• Safety and efficiency of emergency department assessment of chest discomfort. CMAJ 2004. Prospective observational trial of 1819 patients with chest pain, including 241 diagnosed with AMI
  • 5.3% missed, of which 5% died
  • 2/3 had abnormal ECG or mild trop elevation

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:

 

1. ACS IS NOT ACUTE CHEST PAIN SYNDROME. CONSIDER ALL SYMPTOMS OF 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.

• Acute coronary syndromes without chest pain, an underdiagnosed and undertreated high-risk group: insights from the Global Registry of Acute Coronary Events. Chest 2004. Prospective multicentre observational study of 20,881 patients with ACS
  • 8% without chest pain, a quarter of whom were initially not considered ACS
    • symptoms: 50% dyspnea, 25% sweat, 25% nausea/vomiting, 20% syncope
  • patients without chest pain: greater elderly, female, hypertensive, diabetic, history of CHF
  • impact on care:
    • patient delay in seeking medical care
    • 25% delay in diagnosis despite no difference in ECG changes
    • 50% less use of PCI; less use of aspirin, beta-blockers and statin on admission and on discharge
    • double the rate of CHF, shock and arrhythmia, and triple the mortality
• Atypical presentation of acute coronary syndrome: a significant independent predictor of in-hospital mortality. J Cardiol 2011. Prospective multicentre observational trial of 6704 patients with ACS
  • 6% had atypical pain (sharp, positional, pleuritic, reproducible, or mainly in the shoulder or arms), 11% had only dyspnea
  • “atypical” presentations were more common in elderly patients with more cardiovascular risk factors
  • mortality rates were 3% for typical, 2.5% for atypical, and 6% for dyspnea
• Significance of atypical symptoms for the diagnosis and management of myocardial infarction in elderly patients admitted to emergency departments. Arch Cardio Dis 2013. Retrospective multicentre study on 255 patients > 75yo with STEMI
  • symptoms:  40% chest pain, 16% faint/fall, 16% dyspnea, 10% GI symptoms, 7% general impairment, 5% delerium
  • “atypical symptoms”: longer delay seeking care, more severe Killip score, longer wait to see physician, less likely to receive reperfusion, higher mortality rate

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

• Time to standardize and broaden the criteria of ACS presentations in women. Can J of Cardiol 2014
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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.”

 

2. ECGs ARE DYNAMIC AND CHALLENGING. COMPARE ECGs AND KEEP LEARNING

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

• Prognostic value of a normal or nonspecific initial electrocardiogram in acute myocardial infarction. JAMA 2001. Multicentre observational study of 391,208 patients with AMI
  • 57% were diagnostic (ST elevation or depression)
  • 35% were nonspecific
  • 8% were normal; of which 18% developed LBBB and 20% developed ST elevation

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

• ECG weekly, with Amal Mattu
• Stephen Smith’s ECG blog

 

3. TROP NEGATIVE DOES NOT RULE OUT ACS. STRATIFY PATIENTS

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):

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.