Signal-averaged electrocardiogram
Signal-averaged electrocardiography (SAECG) is a special electrocardiographic technique, in which multiple electric signals from the heart are averaged to remove interference and reveal small variations in the QRS complex, usually the so-called "late potentials". These may represent a predisposition towards potentially dangerous ventricular tachyarrhythmias.
Source: Wikipedia — Signal-averaged electrocardiogram (CC BY-SA 4.0)