See quick 12 lead EKG interpretation
The normal p wave is often seen notched, which is likely caused by slightly asynchrony between depolarization of the right and left atrium. However in left atrial enlargement the notched, or bifid, p wave is often marked, in particular in lead II and lead V1, which is where to check for atrial abnormalities (including right atrial enlargement).
The ECG interpretation of left atrial abnormality:
- In lead II: notched p wave ≥ 0.12 sec wide (three small squares, P mitrale)
- In lead V1: a diphasic p wave with predominant terminal negative component ≥ 1 mm deep (one small square) and 0.04 sec wide (one small square)
The second top of the p wave in lead II and the terminal negative p wave deflection in lead V1 represent the left atrial enlargement. A detail from the 12 lead EKG above:
Left atrial enlargement is often caused by left atrial dilatation or hypertrophy due to stenosis of the mitral valve, hence the term p mitrale. Left atrial abnormality may also be caused by left ventricular hypertrophy (LVH) or be due to an intraatrial conduction defect caused by myocardial infarction.
– Mathias
