Missed ACS is a common source of medico-legal cases. In the Canadian Medical Protective Association’s 2010 article Delay in diagnosis of ACS, they identified 292 ACS related medico-legal cases in the previous decade, and identified common problems: “incomplete history, delay in testing, incomplete testing, and misinterpretation of diagnostic tests.

What’s the scale of the problem? In the New England Journal of Medicine’s 2000 study Missed diagnoses of Acute Cardiac Ischemia in the Emergency Department, the authors prospectively collected charts on 10,000 patients across 10 hospitals in the early 1990s, 17% of whom had AMI/UA. They found

• 889 patients with AMI, 2.1% discharged with misdiagnosis of noncardiac chest pain, pulmonary condition, or stable angina; there was an 11% disagreement on STE on the ECG interpreted by blinded cardiologist.
• 966 unstable angina, 2.3% discharged with misdiagnosis of stable angina, atypical chest pain.
• Risk factors for misdiagnosis included: women less than 55, non-white, shortness of breath, nondiagnostic ECG.

There are also issues with suboptimal treatment, according to the American Heart Journal 2008 study Missed opportunities for reperfusion therapy for ST-segment elevation myocardial infarction: Results of the Emergency Department Quality in Myocardial Infarction (EDQMI) study. Looking at more than 2000 patients presenting to five Emergency Departments in the US in the early 2000s, 22% STEMI patients did not receive reperfusion. The reasons

• STE not identified
• LBBB not documented as new or old
• withheld for inappropriate reason: intermittent/prolonged/resolved pain

Given that the ECG is central to the diagnosis of ACS and that it’s a skill subject to individual variation, it’s not surprising that (mis)reading ECG is a major factor in missed ACS. There are two issues here

1. interpreting STE that exists, including its differential (eg BER, LVH, aneurysm, pericarditis)

• Errors in Emergency Physician Interpretation of ST-segment Elevation in Emergency Department Chest Pain Patients. Acad Emerg Med 2000;7:1256-1260. Retrospective review chest pain patients 200 with STE: 6% misinterpreted–including LVA believed to be AMI, BER believed to be AMI or pericarditis, STE believed to be BER, LVH
• Disagreement in the interpretation of electrocardiographic ST segment elevation: a source of error for emergency physicians? Am J Emerg Med 2004; 22: pp. 65. EP Discrepancy on quarter of ECGs with STE, especially if minor elevation and no reciprocal changes
• Differentiating ST-elevation myocardial infarction from nonischemic ST-elevation in patients with chest pain. Am J Cardiol 2011; 108(8): pp. 1096-1101. There was a wide variation in interventional cardiologists in differentiate STEMI from nonischemic STE 

   

  2. STE equivalents

• Pitfalls in diagnosing ST elevation among patients with acute myocardial infarct. J Electrophys 2001;46(6):653-659. 35% had STD precordial leads, more than half of whom had angio lesions compatible with inferolateral STEMI equiv (left circ, ramus intermedius, rca).
• Novel patterns of ischemia and STEMI equivalents. Card Clinics 2012;30(4):591-599. Patterns include: STE in aVR as a sign of L main;, tall R wave in V1 as a sign of posterior STE; De Winter T (anterior STD + tall T wave) as a sign of early critical LAD; Wellens sign (anterior biphasic or deep T wave inversion) as a sign of LAD disease; and Sgarbosa criteria for LBBB + STE
• Common pitfalls in the interpretation of electrocardiograms from patients with acute coronary syndromes with narrow QRS: a consensus report. J of Electrocard 2012; 45(5): 463-375

The latter provides a thorough overview of high risk ischemic signs

1. STD V1-4: posterior STEMI (LCX) –> 15 lead ECG
2. prominent T waves: early subendocardial
3. STD V1-4 + tall T (deWinter T): evolving STEMI
4. V1-3 flip T: LAD subocclusion
5. V1-4 deep T wave inversion (Wellens): LAD subocclusion
6. STE aVL/I without STD V1-2: anteriolat STEMI
7. STE aVL/I _ diffuse STD: left main/3VD occlusion

Lessons

1. consider ACS, including in young patients, with chest/arm pain, SOB, tired/weak, epigastric pain/dyspepsia
2. carefully read the ECG, including 15 lead and serial ECG
3. consider the differential for ST changes
   1. STE = ELEVATIONS: Electrolyte (hyperK), LBBB, Early repol, Ventricular hypertrophy, Aneurysm, Thrombus (MI), Inflammation (pericarditis), Osborne waves, Non-occlusive vasospasm, Sudden death (Brugada)
   2. STD = DEPRESSED: Dilated CMO, Enlarged ventricle, Potassium loss, Reciprocal change, Embolism, Subendocardial, Shock, Encephalon bleed, Digoxin
   3. Early R-wave = R-WAVED: RBBB, WPW, ACS (posterior), Ventricle hypert (RVH), Electrode, Dystrophy
   4. T wave inversion = FLIPPED: Fascicles (BBB), LVH, Ischemia, Pulmonary embolism, Pediatric, Encephalon bleed, Digoxin

You can use the HEARTS approach to ECG to look for signs of ischemia in every area: