STEMI mimics

Background

ST segment elevation is myocardial injury until proven otherwise
- 1mm in two contiguous leads or Left Bundle Branch Block (LBBB) configuration meeting Sgarbossa criteria
When STEMI is unlikely based on symptoms and demographics, consider other etiologies of ST elevation
- Serial EKGs helpful in observing evolution of STEMI pattern
  - Only 72% of patients with STEMI receive diagnosis in first 1.5h [1]

The mnemonic “ELEVATION”, can help you remember STEMI mimics

LBBB as well as any LBBB configuration (ex: RV pacing) can result in ST segment elevation, usually < 5mm
Use Sgarbossa Criteria to determine if there is a concurrent infarct
In addition, may look for Cabrera’s sign or Chapman’s sign if infarct is suspected, though both are specific but poorly sensitive
RBBB does not typically give ST elevation, therefore in cases of RBBB, the usual STEMI rules apply

Normal variant often seen in young athletes
Synonymous with J-point elevation (though not to be confused with a J-wave) i.e. elevation of the point where the QRS usually meets the isoelectric line
Some studies suggest an increased risk of VF in these patients, though the lifetime risk remains unclear
Elevation in this case should be concave and greatest in precordial leads

LVH typically with ‘strain’ pattern
ST elevation should be:
- In V1 - V3 only
- Concave
- Discordant with deep S wave
- Not more than 2 mm elevated

After MI, walls of ventricles can become aneurysmal
- Manifests as persistent ST elevation in territory of old infarct
- Q waves should be present in the leads with persistent ST elevation
Echo is required for the final confirmation
Takotsubo cardiomyopathy (broken heart syndrome) presents similarly

Cardiac sodium channel mutation (usually SCN5A) first described in Thailand in 1992
May be responsible for 4-5% of all sudden cardiac deaths
3 described ECG types:
- Types 1 and 2 more commonly give ST elevation
- Type 3 has “saddle back” appearance without ST elevation
Can be pharmacologically unveiled (ex: antiarrhythmics such as sodium channel blockers), precipitated by illness or fever, or be intermittent (will commonly see an incomplete RBBB pattern)

Diffuse ST elevation
- In acute presentation, there may be PR elevation and ST depression in aVR only, but this is poorly sensitive
PR depression classically taught as EKG sign of pericarditis but may only occur in viral pericarditis
Consider the diagnosis of STEMI in favor of pericarditis when: there is ST depression anywhere (except for V1, aVR), ST elevation height in III>II, there is a convex/horizontal ST elevation morphology, or when there are new Q waves
If predominantly inferior elevation, depression in aVL is very sensitive for STEMI[2]

Hypothermia, usually <30 C is associated with the presence of Osborn J waves
Positive deflections at the J point.
Bradycardia (including AV block) and atrial fibrillation are also common in moderate and severe hypothermia
Hypothermic patients are at risk for VF

True ST elevation, in the sense that the ST elevation pattern is that of an injury current, but has a different mechanism and a different management
Cocaine-induced ST elevation secondary to vasospasm should be treated with benzodiazepines and nitrates as needed
While it is possible to have a STEMI from a ruptured plaque and subsequent clot formation in a patient with cocaine toxicity, it is helpful to risk stratify patients with a suspected STEMI by age, risk-factors, etc
It may be impossible to tell by surface ECG (and therefore without a left heart catheterization) if the ST elevation is due to cocaine toxicity or due to plaque rupture

Riley RF, Newby LK, Don CW, et al. Diagnostic time course, treatment, and in-hospital outcomes for STEMI patients presenting with non-diagnostic initial ECG: A report from the Aheadache mission: lifeline program. Am Heart J. 2013; 165(1):50–56.
Bischof JE, Worrall C, Thompson P, et al. ST depression in lead aVL differentiates inferior ST-elevation myocardial infarction from pericarditis. Am J Emerg Med. 2016; 34(2):149-154.

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