Key Points
- Clinical Context: Abnormal ECGs must be interpreted within the patient’s presentation. Not all abnormalities are life-threatening, and high-risk conditions can still appear subtle or even “normal.”
- Serial Monitoring: Single ECGs are insufficient in many high-risk cases. Repeat ECGs, obtain adjunctive tests, and closely observe evolving symptoms.
- Documentation: Record both abnormal findings and key negatives. Tie findings directly to the presenting complaint and management decisions.
- Customized Interpretation: Tailor your analysis to the clinical scenario (e.g., chest pain, syncope, dyspnea).
- Computer Limitations: Automated interpretation frequently misses early ischemia and subtle abnormalities. Always confirm with your own interpretation.
Computer ECG interpretation tends to be poor at detecting early signs of ischemia. This example was interpreted as normal but missed subtle inferior ST elevation and early reciprocal ST depression and T wave inversions in aVL in a patient with evolving STEMI. Presented by Dr. Mattu in the March 20, 2022 Workout (link in related).
Abnormal STAT ECG Findings:
Heart Rate:
- Tachycardia (>100 bpm, adults): Distinguish physiologic (fever, pain, hypovolemia) vs. arrhythmic (SVT, VT, AFib).
- Bradycardia (<60 bpm, adults): Consider AV block, medications, ischemia, or electrolyte disorders.
- Pediatrics: Recognize normal age-based heart rate ranges to avoid overcalling abnormality:
- Neonates (0-1 month): 90-180 bpm
- Infants (1 month-1 year): 100-160 bpm
- Toddlers (1-3 years): 90-150 bpm
- Preschoolers (3-5 years): 80-140 bpm
- School-aged (6-12 years): 70-120 bpm
- Adolescents (13-18 years): 60-100 bpm
- QTc abnormalities in children carry similar arrhythmogenic risks as adults.
Rhythm:
- Irregular Rhythms: Consider atrial fibrillation/flutter; crucial to document clearly in stroke evaluations.
- Ectopy: Evaluate significance of premature atrial or ventricular complexes, considering clinical context.
Axis Deviation:
- Left Axis Deviation (LAD): Suggestive of LVH, left anterior fascicular block, or inferior MI.
- Right Axis Deviation (RAD): Indicates right ventricular strain (PE, COPD, pulmonary hypertension), sodium channel blocker toxicity, or hyperkalemia.
Intervals:
- PR Interval:
- Prolonged >200 ms = AV block.
- Short <120 ms = pre-excitation (e.g., WPW).
- QRS Duration:
- Wide (>120 ms): Suggests bundle branch blocks, ventricular rhythms, hyperkalemia, sodium-channel blocker toxicity.
- QTc Interval:
- Prolonged (>500 ms): Significant risk for Torsades de Pointes.
- Short (<350 ms): Risk factor for ventricular arrhythmias and sudden cardiac death.
Waveform Morphology:
- Q Waves: Pathologic if >1 small box wide (≥40 ms) or >1/3 height of R wave, indicating prior MI.
- Poor R Wave Progression: Suggests prior anterior MI or cardiomyopathy.
ST Segment:
- Elevation: OMI/STEMI → emergent reperfusion.
- Depression: Indicates ischemia; clinical correlation required. Depression in V1-V3 may be from Posterior STEMI.
T Waves:
- Inversion: May represent ischemia, especially if dynamic or correlating with symptoms.
- Peaked T Waves: Suggestive of acute hyperkalemia; absence reassuring in ESRD patients.
Common Pitfalls in Abnormal ECG Interpretation:
- Hidden Ischemia: A normal or subtle ECG does not exclude ACS. Repeat if suspicion remains.
- Lead Misplacement:
- High V1/V2 → false anterior MI or RBBB.
- Limb reversal → abnormal axis mimicking pathology.
- Normal Variants:
- Early repolarization (young adults) mimics STEMI.
- Juvenile T-wave inversions (esp. III, aVF, V1–V3 in young females).
- Computer Overreliance: Machines miss early ischemia and subtle findings.
Key Clinical Scenarios & Documentation Examples:
- Chest Pain: “No STEMI/equivalent criteria. No dynamic ischemic changes.”
- Stroke Evaluation: “No atrial fibrillation/flutter present.”
- Dyspnea/PE concern: “No right heart strain (no RAD, S1Q3T3, or T-wave inversion in right precordials).”
- Syncope: “No arrhythmia, AV block, QT prolongation, Brugada pattern, or ischemic changes.”
- ESRD/Hyperkalemia: “T-wave morphology assessed—no peaked T waves, QRS not widened.”
KEY CLINICAL PEARLS:
- A normal ECG does not rule out ischemia or other high-risk pathology.
- Always interpret in clinical context and obtain serial tracings if concern remains.
- Avoid overcalling benign variants but remain vigilant for subtle ischemic changes.
- Careful documentation of both abnormal and absent findings supports sound decision-making and medicolegal protection.
Related Topics & Recommendations:
