Lead II: the rhythm strip

Lead II looks from the right arm toward the left leg, almost straight down the heart's normal axis, so every wave is upright and clean. It is the canonical teaching and rhythm lead: learn the normal P-QRS-T here first.

• P wave: upright, rounded; < 2.5 mm tall and < 120 ms wide (atrial depolarization).
• PR interval: 120–200 ms, the time from atrial to ventricular activation.
• QRS: a small septal q, a dominant R, ≤ 110 ms wide (ventricular depolarization).
• QT: rate-dependent (Bazett); QTc < ~450 ms. T wave upright and slightly asymmetric.