Expansion
Rate, rhythm, axis, intervals, then the waves in every lead
Expansion
0. Details: patient, date, time, calibration (10 mm per mV) and paper speed (25 mm per second), and whether an old ECG is available.
- Rate: 300 divided by the number of large squares between R waves. If irregular, count the QRS complexes on the rhythm strip and multiply by 6
- Rhythm: regular or irregular, and is there a P wave before every QRS and a QRS after every P
- Axis: normal, left or right, using leads I and aVF
- P wave: over 2.5 mm tall is right atrial enlargement (P pulmonale), over 120 ms wide or bifid is left atrial enlargement (P mitrale)
- PR interval: normal 120 to 200 ms, being 3 to 5 small squares
- QRS: width (over 120 ms is broad), height for voltage criteria, Q waves, and R wave progression across the chest leads
- ST segment: elevation or depression, and in which territory
- T waves: inversion, peaking, flattening
- QT interval, corrected for rate
- Extras: U waves, delta waves, epsilon waves, J waves
Rate landmarks on the large squares: 300, 150, 100, 75, 60, 50.
Then ask the two questions that matter: is this an acute problem needing immediate action, and does it explain the patient’s symptoms.
A normal ECG does not exclude acute coronary syndrome, and up to a third of patients with myocardial infarction have a non-diagnostic initial ECG, which is why serial tracings and posterior leads are used.