Although this P wave abnormality often occurs in the setting of left atrial hypertrophy, it is a manifestation of prolonged intraatrial conduction and may occur in patients with left atrial fibrosis due to a variety of causes, including, but not limited to, left atrial hypertrophy. The ECG shown here is from an elderly patients with no obvious cardiac disease. The broad notched P wave, seen best in lead II, probably reflects an intraatrial conduction disturbance due to atrial fibrosis.