QRS interval



Associate Editor-In-Chief:

Duration
The precordial leads are approximately 0.01 or 0.02 seconds longer than the standard leads.

Definitions of Low Voltage:

 * If the total amplitude above and below the isoelectric line is < 5 mm in all 3 standard leads.
 * An average voltage in the limb leads of < 5 mm with an average of < 10 mm in the chest leads (1).
 * Should be at least 5 mm in V1 and V6, 7 mm in V2 and V5 and 9 mm in V3 and V4.

Differential diagnosis of low voltage:

 * Diffuse Coronary artery disease
 * Congestive heart failure
 * Pericardial effusion (See also Diseases of the Pericardium)
 * Myxedema
 * Amyloidosis
 * Emphysema
 * Obesity

Definition of maximal voltage:
Can be up to 20 to 30 mm in lead 2 and can be up to 25 to 30 mmm in the precordial leads.

Additional resources

 * ECGpedia: Course for interpretation of ECG
 * The whole ECG - A basic ECG primer
 * 12-lead ECG library
 * Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
 * ECG information from Children's Hospital Heart Center, Seattle
 * ECG Challenge from the ACC D2B Initiative
 * National Heart, Lung, and Blood Institute, Diseases and Conditions Index
 * A history of electrocardiography
 * EKG Interpretations in infants and children