Right and Left Atrial Abnormalities

(NB: ˇ§Atrial abnormalityˇ¨ is a term being used increasingly in place of ˇ§atrial enlargementˇ¨, ˇ§atrial dilatationˇ¨ or ˇ§atrial hypertrophyˇ¨.)

Look for signs of atrial abnormalities in leads in which the P wave is most prominent: usually lead II, but also leads III, aVF, and V1.

In sinus rhythm the right atrial depolarization wave (brown) precedes that of the left atrium (blue) and the combined depolarization waves, the P wave, is less than 120 ms wide and less than 2.5 mm high.
In right atrial abnormality, right atrial depolarization lasts longer than normal and its wave extends to the end of left atrial depolarization. Although the amplitude of the right atrial depolarization current remains unchanged, its peak now falls on top of that of the left atrial depolarization wave. As a result, the combined waves of right and left atrial depolarization, the P wave, is taller than normal (taller than 2.5 mm) but its width remains within 120 ms.
In left atrial abnormality left atrial depolarization lasts longer than normal but its amplitude remains unchanged. Therefore, the height of the resultant P wave remains within normal limits but its duration is longer than120 ms. A notch (broken line) near its peak may or may not be present.
A biphasic P wave in V1 is another sign suggesting atrial abnormality. In right atrial abnormality, the initial positive portion of the biphasic P wave is larger than the terminal negative portion.
A biphasic P wave in V1, with its terminal negative deflection more than 40 ms wide and more than 1 mm deep is another ECG sign of left atrial abnormality.

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