Low voltage limb leads only:
Defined as peak-to-peak QRS voltage < 5 mm in all limb leads.

Low voltage limb and precordial leads:
Defined as peak-to-peak QRS voltage < 5 mm in all limb leads and < 10 mm in all precordial leads.

Differential diagnosis:
Primary myocardial causes include multiple or massive infarction(s), infiltrative diseases such as amyloidosis, sarcoidosis, or hemochromatosis, and myxedema.

Extracardiac causes:
Pericardial effusion, COPD, pleural effusion, obesity, anasarca and subcutaneous emphysema. When there is COPD, expect to see low voltage in the limb leads, as well as in leads V5 and V6.

The classical pattern of pulmonary disease (COPD):
If the amplitude of the P wave in lead If approaches that of the QRS complex in lead II, think of COPD. This pattern occurs because of tall P waves due to increased right atrial pressure with concomitant low QRS voltage due to COPD.

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