QRS interval

Schematic representation of normal ECG

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Duration

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

Causes of a Wide QRS Interval or a Prolonged QRS Interval

• Bundle branch block

• Left bundle branch block
• Right bundle branch block

• Ventricular tachycardia

Amplitude

Definitions of Low QRS 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.
  
  

Causes of Low QRS 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

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