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Key Points

  • An abnormal ECG obtained in an acute or emergent setting will suggest a variety of conditions, but the clinical context determines its relevance. ECG findings must be interpreted in conjunction with the patient’s clinical presentation.
  • Not all abnormal ECG findings indicate a life-threatening condition. Conversely, some severe conditions may present with subtle or even normal ECG findings.
  • Serial ECGs, additional testing, and close clinical monitoring are often necessary, especially in high-risk patients, to avoid missing critical diagnoses.
  • Proper documentation of both the presence and absence of specific ECG findings can guide clinical decision-making and demonstrate comprehensive consideration of potential diagnoses.
  • Customization of ECG interpretation is essential to correlate specific ECG abnormalities with the patient’s symptoms and clinical scenario.

Findings on an Abnormal ECG:

Heart Rate:

  • Tachycardia: >100 bpm, consider unstable tachyarrhythmias and differentiate between compensatory sinus tachycardias for stressors or illness.
  • Bradycardia: <60 bpm, assess for unstable bradyarrhythmias and heart block.

Rhythm:

  • Irregular Rhythm: Could indicate atrial fibrillation or flutter. Document if absent, especially in stroke evaluation.
  • Ectopy: Presence of premature atrial or ventricular contractions may be benign or indicate underlying pathology.

Axis Deviation:

  • Left Axis Deviation (LAD): Can suggest left anterior fascicular block or LVH. 
  • Right Axis Deviation (RAD): Seen in right heart strain, pulmonary embolism, or COPD. 

PR Interval:

  • Prolonged PR Interval: May suggest conduction abnormality; significant in syncope evaluation.
  • Short PR Interval: Consider pre-excitation syndromes like WPW.

QRS Complex:

  • Wide QRS (>120 ms): Consider bundle branch blocks, ventricular rhythms, hyperkalemia, sodium channel blocker toxicity, etc.
  • Poor R Wave Progression: May indicate anterior MI or old myocardial infarction.

ST Segment:

  • Elevation: Sign of acute occlusion MI. Absence of ST elevation in chest pain should be noted to indicate non-STEMI considerations.
  • Depression: Could indicate ischemia, particularly in reciprocal leads or during exertion.

QT Interval:

  • Prolonged QTc: (>500 ms) Increases risk of Torsades de Pointes. Document normal QTc in syncope to rule out this concern.

T Waves:

  • Inverted T Waves: May indicate ischemia, especially if dynamic. 
  • Peaked T Waves: Consider hyperkalemia, especially in ESRD. Absence suggests normal potassium levels.

Abnormal ECG Pitfalls:

  • Hidden Ischemia: A normal or non-diagnostic ECG does not exclude ischemia, particularly in high-risk patients.
  • Lead Misplacement: Incorrect lead placement can mimic or obscure true abnormalities.
  • Normal Variants: Understand common benign variants to avoid misdiagnosis.

KEY CLINICAL PEARLS:

  • Don't Rely Solely on Computer Interpretations:
    • Always review the ECG yourself, and never trust the ECGs computer interpretation of "Normal ECG"
    • Computers can still miss early signs of ischemia and other life-threatening condition, correlated ECGs clnically!
  • Lead Misplacement Pitfalls:
    • Precordial Leads: V1 and V2 placed too high can mimic anterior MI or RBBB
    • Limb Leads: Reversed leads can alter the axis and create false pathology
  • Normal Variants to Recognize:
    • Early Repolarization: Common in young, healthy people; can look like ST elevation but is harmless
    • Benign T Wave Inversion: Often seen in leads III and aVF, especially in young females
  • Watch for Hidden Ischemia:
    • A normal ECG doesn't rule out ischemia. Consider serial ECGs and further testing if clinical suspicion is high