• Typical symptoms of acute coronary syndrome (ACS) include chest pressure, heaviness, burning, or dyspnea that is left-sided or retrosternal.
• Features that make ACS more likely include radiation to both arms, radiation to the left arm, radiation to the right arm, radiation to the neck or jaw, pain similar to prior ischemia, worsening with exertion, associated diaphoresis, or associated dyspnea.
• Features that make ACS less likely include pain that is pleuritic or associated with syncope.
• While these characteristics can be helpful in determining the likelihood of ACS, patients often present with atypical symptoms, and none of these are adequate to rule-in or rule-out ACS.

A number of cardiac and non-cardiac diseases can cause chest pain or symptoms that mimic angina. A few don’t-miss conditions are listed below:

• Vital signs.
• Targeted history and physical exam.
• 12-lead ECG.
• Telemetry.
• Labs: cardiac troponin, CBC, BMP, PT/PTT (CK-MB is not useful given contemporary troponin assays).
• Chest x-ray.
• Consider additional testing or imaging depending on the clinical scenario.

Acute coronary syndrome is defined as an atherothrombotic plaque rupture event leading to myocardial infarction. In the evaluation of findings suspicious for ACS, clinicians should consider and exclude other causes of the patient’s symptoms or troponin elevation that may mimic ACS while initiating management for possible ACS.

Diagnosis of STE-ACS:

• New ST-segment elevation at the J-point in 2 contiguous leads meeting the following criteria:
  • In V2-V3:
    • ≥1.5 mm for women.
    • ≥2 mm for men ≥40 years.
    • ≥2.5 mm for men <40 years.
  • In all other leads, ≥1 mm.
• New or “presumably new” left bundle-branch block (LBBB) has been considered an STE-ACS equivalent, but is not diagnostic of MI in isolation. Many cases of “presumably new” LBBB are due to lack of recent and/or prior ECG. Most patients with new or presumably new LBBB do not have ACS, but those who do may be a high-risk subgroup. In one study of 892 patients admitted with an initial diagnosis of STE-ACS, 36 patients (4%) had new or presumably new LBBB. Of those 36 patients, 14 (39%) had a final diagnosis of ACS and 5 (14%) were found to have coronary artery occlusion consistent with an STE-ACS equivalent.
• See the modified Sgarbossa criteria below for diagnosis of MI in the presence of known LBBB.
• If there are ST changes in the inferior distribution (II, III, aVF) obtain right-sided leads and look for ≥1 mm ST-elevation in V4R to evaluate for right ventricular ST-elevation MI.
• If there are ST-depressions in the anterior leads (V1-V3) or R>S in V1, obtain posterior leads and look for ST-elevation in V7-V9 to rule out posterior ST-elevation MI.

Diagnosis of MI in the presence of known LBBB:

• Modified Sgarbossa criteria (any of the following):
  • ST-segment elevation ≥1 mm in the same direction as the QRS complex (concordant) in any lead.
  • ST-segment depression ≥1 mm in any of leads V1-V3.
  • ST-segment elevation or depression discordant with the QRS complex of ≥1 mm AND with a magnitude ≥25% of the QRS complex.
• The modified Sgarbossa criteria has a sensitivity of 91% and specificity of 90% for the diagnosis of acute MI.

Diagnosis of NSTE-ACS:

• Ischemic symptoms that are due to atherothrombotic plaque rupture coronary artery disease associated with elevated cardiac troponin in the absence of ST-segment elevation on ECG.
• ECG findings can include ST-segment depression, T-wave inversion, Q-waves, non-specific ST-T changes, or the ECG can appear normal in NSTE-ACS.
• Specific ECG findings suggestive of NSTE-ACS include:
  • New horizontal or down-sloping ST-segment depression ≥0.5 mm in 2 contiguous leads.
  • T-wave inversion >1 mm in 2 contiguous leads with prominent R wave or R/S ratio >1.

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