Electrocardiography is a rapid, non-invasive investigation that provides essential information about heart rhythm, conduction and acute ischaemia. For students and junior clinicians, a dependable, repeatable method for reading a 12‑lead tracing reduces errors and speeds diagnosis. This article provides a practical checklist, common patterns and learning resources so you can confidently link tracing findings to clinical decisions.
Start with quality and context
Always check technical factors first: correct lead placement, paper speed (usually 25 mm/s) and calibration. Note the clinical presentation: chest pain, syncope, palpitations, or monitoring in the peri‑operative/critical care setting. Correlate the tracing with vitals and bedside tests such as troponin when ischemia is suspected. See our Clinical Examination Guide for integrating ECG interpretation into a full assessment.
Stepwise checklist
- Rate: Quick estimate using 300 / large boxes between R waves; confirm precisely if irregular.
- Rhythm: Are P waves present and regular? Identify sinus rhythm, atrial fibrillation, flutter, or paced rhythms.
- Intervals: Measure PR (120–200 ms), QRS (<120 ms) and QTc (Bazett or Fredericia correction).
- Axis and voltages: Use leads I and aVF to evaluate frontal plane axis; assess low voltage or signs of chamber enlargement.
- ST‑T changes: Look for regional ST elevation or depression, reciprocal changes, and T wave inversion patterns.
- Compare: Old tracings are invaluable—document changes from baseline.
Key patterns and immediate actions
Recognising a few high‑yield patterns helps time-sensitive decisions. For example, focal ST elevation with chest pain requires immediate reperfusion pathways; diffuse ST elevation with PR depression suggests pericarditis; a new wide QRS with hypotension may indicate ventricular tachycardia and requires urgent intervention.
High-yield examples
- Acute coronary syndrome: Regional ST elevation ± reciprocal changes—seek cardiology and follow local reperfusion protocol.
- Atrial fibrillation: Irregularly irregular rhythm without clear P waves—assess rate, anticoagulation need, and cause.
- Bundle branch block: Wide QRS, different morphologies in V1–V6 that affect ischaemia interpretation.
Learning and resources
Practice with multiple tracings and cases. Authoritative resources include the European Society of Cardiology and the American Heart Association. Our Question Bank contains ECG cases to test pattern recognition and clinical reasoning.
Reporting tips
- State the rhythm, rate, and the main abnormality (include measurements where relevant).
- Note if comparison with a prior tracing is available and whether changes are acute.
- When uncertain, request cardiology review — clinical correlation is essential.
Consistent use of a checklist, deliberate practice, and case-based learning will make ECG interpretation faster and more reliable in both exams and clinical care.