LEAD II — REAL-TIME
P WAVE
Atrial depolarization. Represents electrical activation spreading through the atria. Normal: 80–120 ms duration.
Q WAVE
Septal depolarization. Small negative deflection, initial ventricular activation. Abnormal if >40ms or >25% of R height.
R WAVE
Ventricular depolarization peak. Largest deflection in the QRS complex. Represents ventricular contraction.
S WAVE
Terminal ventricular depolarization. Negative deflection after R wave as activation reaches base of ventricles.
T WAVE
Ventricular repolarization. Asymmetric positive wave following QRS. Inversion may indicate ischemia.
PR INTERVAL
Onset of P to onset of QRS. Reflects AV node conduction. Normal: 120–200 ms. Prolonged = 1st degree AV block.
QT INTERVAL
Ventricular depolarization + repolarization. Corrected QTc >440 ms in men, >460 ms in women = prolonged QT.