1. Introduction
A structured approach to ECG interpretation reduces missed abnormalities. Always interpret the tracing in clinical context and compare with previous ECGs if available.
2. Technical checks
Confirm the patient details, date and time, paper speed and gain. Standard calibration is usually 25 mm per second and 10 mm per mV. Scan quickly for gross artefact, lead misplacement or missing leads before detailed interpretation.
3. Rate, rhythm and axis
Calculate the heart rate and assess whether the rhythm is regular or irregular. Look for P waves and their relationship to the QRS complexes. Determine the frontal plane axis using leads I and aVF, with lead II helping when the axis is borderline.
4. Intervals and wave morphology
Assess P wave morphology, PR interval, QRS duration and morphology, pathological Q waves and QT or QTc interval. Look for chamber enlargement, bundle branch block, pre-excitation and paced complexes.
5. ST segment and T waves
Assess for ST elevation or depression, T wave inversion, hyperacute T waves and U waves. Localise abnormalities by territory and consider reciprocal changes where relevant. Remember that early repolarisation, bundle branch block and ventricular hypertrophy can alter ST and T wave appearance.
6. Summary
Finish with a concise summary that includes the rate, rhythm, axis, conduction intervals and the major abnormality. Correlate the ECG with the clinical picture and state the most likely diagnosis or differential.
Technical checks
Rate and rhythm
Axis
Intervals and morphology
Repolarisation
Pattern recognition
Summary