Left Atrial Enlargement

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Atrial enlargement can be determined by analyzing the P waves in leads II and V1. The first half of the P wave represents right atrial depolarization, while the second half represents left atrial depolarization. In left atrial enlargement, a P-mitrale, or wide and notched P wave in lead II (greater than 120 ms) can be seen.

 

P wave morphologies for atrial enlargement in leads II and V1.

Examples

ECG Showing Left Atrial Enlargement

Left Atrial Enlargement

Note the deeply inverted P wave in V1 and wide P wave in II, greater than 120ms.
ECG Showing Left Atrial Enlargement

Left Atrial Enlargement

This patient has known hypertrophic cardiomyopathy. Notice the large QRS complexes in V5 and V6 with associated repolarization abnormalities. There are also notched P waves in the inferior leads (i.e., P mitrale appearance) representing left atrial enlargement.
ECG Showing Left Ventricular Hypertrophy

Left Ventricular Hypertrophy

A large QRS complex in aVL (greater than 11 mm) indicates left ventricular hypertrophy. The left axis deviation, slight intraventricular conduction delay, and absent R wave progression across the precordium are all likely explained by left ventricular hypertrophy. The large, downward deflected P wave in V1 and wide P wave in lead II (greater than 120 ms) indicates left atrial enlargement.
ECG Showing Left Ventricular Hypertrophy and Left Atrial Enlargement

Left Ventricular Hypertrophy, Left Atrial Enlargement

The large QRS complexes and asymmetric repolarization abnormalities (i.e., T wave inversions) in the lateral leads are consistent with the "strain" pattern of left ventricular hypertrophy. Additionally, notice that the terminal negative deflection of the P wave in V1 is greater than 1 mm deep and > 40 msec in duration, indicating the presence of left atrial enlargement. This patient was discovered to have severe aortic stenosis.
ECG Showing Left Ventricular Hypertrophy

Left Ventricular Hypertrophy, Left Atrial Enlargement

Classic changes of left ventricular hypertrophy including large QRS complexes, repolarization abnormalities (especially in the inferolateral leads), and discordant ST-segment elevation in the anterior precordial leads (V1 through V3). There is also left atrial enlargement with a wide P wave and a "P-mitrale" appearance in lead II.

References

  1. Wagner GS, Strauss DG. Marriott’s Practical Electrocardiography. 12th ed. Lippincott Williams & Wilkins; 2014.