Sinus P wave
 Duration <120 ms.
      - First portion for depolarization of the RA wall.
      - Late portion for depolarization of the LA and inferior RA wall.
      - The negative late portion of V1 should be < 50 ms.
      - First portion directs anteriorly, leftward and inferiorly.
      - Late portion directs posteriorly (LA activation) and inferiorly.
      - Axis on frontal plane (P wave axis) is about +45 to +60 degree, with the range of +0 to +75 degree.
      - In limb leads, the normal sinus P wave is seldomly exceeded 0.2 mV or 25% of normal QRS amplitude.
      - In V1, the first positive portion should have < 0.15 mV amplitude and the negative late portion should have < 0.1 sec. duration.
Sinus P wave
        - is upright in lead I, II, aVL and aVF, inverted in lead aVR.
        - in lead III may be upright, biphasic (about 7%) or inverted.
        - in first portion of V1 is upright and inverted in late portion.
There are wide range in variation of sinus P wave since several factors may effect the P wave. These include: Anatomic cardiac position to the anterior chest wall; state of autonomic influence; intra and/or interatrial conduction abnormality; atrial pressure and/or volume load; atrial/atria diseases; electrode positioning (precordial lead).

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