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: QRS Duration by 12-Lead Electrocardiography

Published: August 9, 2026Updated: August 16, 2026

: This test measures the QRS duration on a 12-lead electrocardiogram (ECG), which reflects how long the electrical signal takes to travel through the ventricles of the heart.

Quick summary

[": QRS duration helps show whether the heart's electrical signal is moving through the ventricles normally or is delayed."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
9950-7
Short code
QRS dur L-AVL
Synonyms
QRS dur L-AVL
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

: What This Test Measures

: A 12-lead ECG records the heart's electrical activity from several viewpoints. The QRS duration is the time, measured in milliseconds, from the start of the QRS complex to its end, representing ventricular depolarization.

: How the Test Is Done

: Small electrodes are placed on the chest and limbs and connected to an ECG machine, which records the tracing in a few minutes. The test is painless and does not require needles or sedation.

: Why It May Be Ordered

: Doctors use QRS duration to evaluate the heart's electrical conduction, to check for bundle branch block or other conduction delays, and to monitor conditions or treatments that can affect the heartbeat.

: What Results Mean

: A QRS duration within the expected range generally indicates normal ventricular conduction. A longer duration may suggest delayed conduction through the ventricles. Your clinician interprets the result together with your symptoms, other ECG findings, and medical history.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

: QRS Duration

Frequently asked questions

: Does this test hurt?
: No. A 12-lead ECG is painless; you may feel only the slight stickiness of the electrodes on your skin.
: Do I need to prepare for the test?
: Usually no special preparation is needed. You may be asked to lie still and breathe normally during the recording, and your care team will tell you if any other instructions apply.
: Can I interpret my QRS duration result on my own?
: It is best not to. QRS duration must be interpreted along with the rest of the ECG, your symptoms, and your medical history, so discuss your results with your healthcare provider.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy