An electrocardiograph (ECG) is a study of the magnitude of the heart’s electrical potential, which is measured by placing 10 electrodes on the patient’s limbs and surface of the chest to monitor 12 electrical vectors (‘leads’). Leads are designated frontal leads (I, II and III), limb leads (aVR, aVL and aVF) and chest leads (V1, V2, V3, V4, V5 and V6).

ECG waves are designated P, Q, R, S and T:

Complexes of more than one wave are designated by unspaced letters. Intervals between waves can be designated either by unspaced letters, as for complexes, or by an unspaced en dash. Include the word complex or interval: