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

Mnemonic

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

• Electrolytes (Hyperkalemia)
• Left Bundle Branch Block
• Early Repolarization
• Ventricular Hypertrophy (Left)
• Aneurysm (Ventricular)
• Thailand (Brugada Syndrome)
• Inflammation (Pericarditis)
• Osborne (J) Waves (hypothermia)
• Non-Ischemic Vasospasm

ELEVATION

Electrolytes (Hyperkalemia)

• T waves are peaked without any concave-down (tombstone) ST elevation
• T waves of hyperkalemia should be tall, symmetrical, pointed, and narrow
• Untreated hyperkalemia will progress to a sinuventricular rhythm or a sine wave

Left Bundle Branch Block

• 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

Early Repolarization

• 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

Ventricular Hypertrophy (Left Ventricular Hypertrophy)

• 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

Aneurysm (Ventricular Aneurysm)

• 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

Thailand (Brugada Syndrome)

• 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)

Inflammation (Pericarditis)

• 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

Osborn (J) wave

• 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

Non-Ischemic Vasospasm

• 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

See Also

• ST-Elevation Myocardial Infarction (STEMI)
• ST segment elevation
• STEMI equivalents