The electrical impulse is initiated in the sinus node and then activates the right and left atria, generating the P wave. Impulse conduction through the atrioventricular (AV) node and bundle of His, which are small structures, does not generate any ECG activity; this period of "electrical silence" is the PR interval. The first part of the ventricle to be depolarized is the left side of the interventricular septum, producing a small septal Q wave, followed by depolarization of the remainder of the ventricular myocardium, generating the full QRS complex. The T wave represents ventricular repolarization.
Reproduced with permission from: Scarfone RJ, Cho CS. Cardioversion and Defibrillation. In: Textbook of Pediatric Emergency Procedures, 2nd ed, King C, Henretig FM (Eds), Lippincott Williams & Wilkins, Philadelphia 2008. Copyright © 2008 Lippincott Williams & Wilkins.
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