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Maximum Standard Deviation of ECG Intervals (Heart Rate Variability Analysis)

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

This test measures how much your heart’s electrical signals vary over time, assessed from your ECG. It helps evaluate how well your autonomic nervous system controls your heart rate.

Quick summary

["Assesses heart rate variability, a key measure of autonomic nervous system function."]

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

Key facts at a glance

LOINC
91546-2
Short code
ST Deviation Max EKG
Synonyms
ST Deviation Max EKG
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

The test analyzes the standard deviation of your heart’s intervals (the time between consecutive heartbeats) recorded during an ECG. A higher variability typically reflects better heart health and stress resilience, while lower variability may indicate conditions like autonomic dysfunction or heart disease.

Why It’s Done

Your healthcare provider may order this test to check for autonomic nervous system issues, such as those linked to diabetes, heart disease, or neurological disorders. It can also help monitor long-term heart health, especially in patients with known cardiovascular risks.

How It’s Performed

You’ll lie down or sit comfortably while electrodes are attached to your chest. A machine records your heart’s electrical activity for a set period. The test captures natural heartbeats without additional stimulation.

What to Expect Before the Test

No special preparation is needed. Wear loose clothing, remove jewelry from your wrists or chest, and avoid caffeine or nicotine for 1–2 hours before the test if instructed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

ECG Variability Max SD

Frequently asked questions

How long does this test take?
The ECG recording itself takes about 5–15 minutes, but the full analysis of your heart’s variability may take additional time for your provider to review results.
What does a low standard deviation of ECG intervals mean?
A lower standard deviation suggests your heart’s rhythm may be less adaptable to changes, which could indicate autonomic nervous system dysfunction or increased cardiovascular risk. Your doctor will discuss this with you based on your full clinical picture.
Can I eat or drink before this test?
No restrictions apply, but avoid caffeine or nicotine for 1–2 hours before testing if advised by your provider, as they can temporarily affect heart rate variability.
  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