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
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