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[″ + kardia, heart, + gramma, something written]
ABBR: ECG A record of the electrical activity of the heart, consisting of waves called P, Q, R, S, T, and sometimes U. The first, or P, wave is caused by the depolarization of the atria, whose electrical changes in turn cause atrial contraction. The Q, R, and S waves (QRS complex) correspond to depolarization of ventricular muscle. The T wave corresponds to ventricular repolarization. The electrocardiogram gives important information concerning the spread of electricity to the different parts of the heart and is used to diagnose rhythm and conduction disturbances, myocardial infarction or ischemia, chamber enlargement, and metabolic disorders, among others.