Atrial Hypertrophy

The P-wave represents the wave of depolarization that spreads from the sino atrial node,throughout the atria, and is usually 0.08 to 0.1 seconds (80-100 ms) in duration. Right atrial depolarization forms the initial portion of the P-wave. The left atrial depolarization forms the terminal portion of the P-wave. The normal P-wave axis falls between + 45 o and + 60 o . P-wave in normal individuals is upright in I, II, aVl and aVf. In lead III, it could be upright or negative. In the right precordial leads (V1 and sometimes V2) the P-wave is biphasic with an initial

positive deflection followed by a later negative one. In the remaining chest leads, normal P-waves (Ta-wave) produces low amplitude signals and are always upright. Atrial repolarisation coincides with normal QRS wave; hence atrial repolarisation normally does not manifest on a surface ECG. However, in complete heart block Ta waves may be seen on PR-segment as short deflections just beyond the P-waves with polarity opposite to that of P-wave. P-wave abnormalities occur in atrial enlargement and arrhythmias. The following cartoon shows patterns of atrial enlargement in lead II and lead V1.

Right and left atrial hypertrophy in lead II and VI

Left Atrial Enlargement (LAE)
Diagnostic Criteria
 

• The terminal portion of the P-wave in lead V1 must be one small box wide by one small box (0.04second x 0.04mv) deep or larger to qualify as left atrial enlargement.

• This force can be calculated by multiplying the time in seconds by the depth in millimeters. If this product is more negative than -0.04, LAE is present.

• A notched broad based P-wave in leads I and II with a duration of 0.12 milliseconds or more is called “P mitrale”.

• LAE can shift the P-wave axis to +15 o or less.

• Comparision of ECG abnormalities to echocardiographic criteria for left atrial enlargement demonstrates limited sensitivity but high specificity for the ECG criteria.

Common Causes of LA Enlargement
• Valvular Disease

— Mitral stenosis

— Mitral regurgitation

• Decreased Left Ventricular Compliance

— Longstanding hypertension

— Hypertrophic cardiomyopathy

— Aortic stenosis

— Aortic regurgitation

— Infiltrative heart disease

— Restrictive Cardiomyopathy

• All of these conditions increase either pressure or volume loading on the atria leading to enlargement and/or hypertrophy.

Cartoon showing the pattern of P-wave in lead II in left atrial enlargement

Right Atrial Enlargement (RAE)

Diagnostic Criteria

• The P-wave in leads II, II and aVF is peaked with a height greater than 2.5mm. “P pulmonale”.

• The P-wave axis is +75 or greater.

• The positive aspect of the P-wave in lead V1 or V2 is >1.5mm in height.

Differential Diagnosis

• Valvular Disease

— Tricuspid stenosis

— Tricuspid regurgitation

• Pulmonary Hypertension

— COPD

— Pulmonary emboli

— Interstitial lung disease

— Sleep apnea

— Mitral valve disease with pulmonary hypertension

— Restrictive cardiomyopathy

• Congenital Heart Disease

— Ebstein’s anomal

— Tricuspid atresia

— Pulmonary atresia

Cartoon showing the pattern of P-wave in right atrial enlargement

Biatrial Enlargement
Diagnostic Criteria

Because the P-wave is composed of distinct right and left atrial components, the diagnosis of biatrial enlargement is simply made by looking for the criteria for both right and left atrial enlargement.

• A large biphasic P-wave in lead V1 with the initial component greater than 1.5mm in height and the terminal component at least 1mm in depth and 0.04 sec in duration.

• A P-wave amplitude of >2.5mm and duration of >0.12 seconds in the limb leads II.