Synopsis
Interpret every 12-lead in a reproducible sequence, identify time-critical patterns and finish with a clinically useful synthesis rather than a list of measurements.
- Start with context: patient, date/time, symptoms and comparison ECG; then verify calibration (usually 25 mm/s and 10 mm/mV), lead placement and artefact.
- RCUK rhythm skeleton: electrical activity, ventricular rate, regularity, narrow/broad QRS, atrial activity, then the P-QRS relationship.
- Rate: regular rhythm about 300 divided by large squares between R waves; irregular rhythm count QRS on a 10-second strip and multiply by 6.
- Rhythm: name atrial and ventricular rhythms separately when needed; do not call 'sinus' unless each P has appropriate morphology and a consistent relationship to QRS.
- Axis: use leads I and aVF as the quick quadrant check, then refine when abnormal; axis is a clue to conduction, hypertrophy or ventricular origin, not a diagnosis alone.
- Intervals: measure PR, QRS and QT/QTc; QRS at least 120 ms is broad in the RCUK tachy algorithm, and NICE treats QTc over 450 ms or under 350 ms as a red flag in TLoC.
- Inspect P waves, QRS morphology/voltage/R-wave progression/pathological Q waves, then ST segments and T waves in anatomical lead groups with reciprocal changes.
- Compare with old and serial ECGs; NICE says a normal resting ECG does not exclude ACS and recommends serial, previous and additional leads when doubt remains.
- Finish with one synthesis: rate + rhythm + axis + intervals + key abnormality + comparison + clinical action.
- Automated interpretation is a prompt, not the final report; NICE requires competent clinician review.