Process may be divided into 5 phases -
1) Atrial Depolarization - vector is toward apex; (+) 60 degrees; thus in most leads a (+) P wave.
2) Septal Depolarization - LV --> RV; (+) 150 degrees; may produce a Q wave in some leads (eg. Lead I).
3) Apical & Early LV Depolarization - (+) 60 degrees; R wave.
4) Late LV Depolarization - moves from endocardium to epicardium; goes (-) to (+); vector (+) 60 degrees to final (-) 30 degrees; resultant R or S wave.
5) LV Repolarization - moves from epicardium to endocardium; goes (+) to (-), making T wave upright; vector (+) 30 degrees; longer duration; T wave .
Back to Index