Why does S wave decreases from v1 to v6
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ECG precordial leads V1 to V6 S wave decreases R wave progression explanation
The S wave decreases from V1 to V6 because the chest leads progressively move from the right side of the heart toward the left ventricle.
- V1-V2 view the heart from the right anterior chest. Most ventricular depolarization is directed away from these leads, toward the large left ventricle, so they show a small R wave and deep S wave.
- Moving through V3-V4, the lead axis becomes more aligned with the overall ventricular depolarization vector. The R and S waves become similar in size. This is the normal transition zone, usually around V3 or V4.
- V5-V6 overlie the left lateral ventricle. The main depolarization vector travels toward these leads, producing a tall R wave. Therefore, the opposing negative deflection, the S wave, becomes small or may disappear.
So, normal precordial progression is:
V1: small R, deep S → V3/V4: R ≈ S → V5/V6: tall R, small/absent SThis reflects the fact that the left ventricle has much greater muscle mass than the right ventricle and therefore dominates the net QRS vector. A persistent deep S wave in V5-V6 can indicate an abnormality such as right bundle branch block, right ventricular hypertrophy, or abnormal lead placement, but must be interpreted with the full ECG. ECG progression overview
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