Conquering the ECG - Cardiology Explained - NCBI Bookshelf
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by EA Ashley
The impulse is delayed briefly at the AVN and atrial contraction is completed. ... The rule is: if the wave immediately after the P wave is an upward deflection, it is ... The presence of P waves immediately before every QRS complex indicates sinus .... Does the sum of the S wave in lead V1 (SV1) and the R wave in V6 (RV6) ...

Normal R Wave Progression: Vl Consists of a small R wave and a large S wave, whereas V6 consists of a small Q wave and a large R wave. Since V3 and V4 are located midway between Vl and V6, the QRS complex would be expected to be nearly isoelectric in one of these leads; i.e., the positive and negative deflections will be about equal.
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