The P wave is produced by atrial depolarization. This wave is best visualized in lead II and normally does not exceed 3mm. in height (0.3mV) or 3mm horizontally (0.12 sec). The P wave is upright in all leads except aVR.
The P wave is
1. Absent in atrial fibrillation, nodal rhythm, sinoatrial block and hyperkalemia.
2. Wide and notched (P-mitral) in left atrial enlargement.
3. Tall and peaked (P-pulmonale) in right atrial enlargement.
Causes of atrial enlargement:
1. Mitral or Tricuspid stenosis.
2. Secondary to pulmonary hypertension.
3. Secondary to cor pulmonale.
4. Secondary to ventricular hypertrophy.
5. Lutembacher’s syndrome (MS and ADS).
6. Left atrial myxoma.
7. Cor triatrium.