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QTc Calculator

Stay updated on your QTc interval with a reliable and user-friendly calculator.

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Home / Health Insurance / Calculators / Articles / QTc Calculator

An electrocardiogram (ECG) is a common investigation performed to assess the rhythm and functioning of the heart. It is also a part of routine annual checkups. It is a quick and painless procedure in which leads are attached to the body, and a strip is printed out. In an ECG, doctors look at the various waves and intervals to check if the heart is functioning optimally. One of the important measurements in an ECG is the QT interval. And the QTc is the corrected QT interval. Let's understand more about it in detail in this article.

What is a QTc Calculator?
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A QTc Calculator is a statistical model intended to help healthcare providers make better decisions regarding patient healing. Such a calculator calculates the corrected QT interval and helps in decision making regarding prescriptions.

What are the parts of an electrocardiogram?
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ECG (Electrocardiogram) waves show the electrical activity of the heart. Here's what they mean.

An ECG is a routine investigation recommended by doctors during annual checkups. It can also be performed as an emergency procedure after complaints of chest pain. After an ECG is performed, the doctor evaluates if the waves and intervals are normal.

What is the QT interval?
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The QT interval is a very important measurement calculated when an electrocardiogram is performed. It is the segment length from the QRS complex to the T wave’s end. In the ECG, the QT interval is calculated by checking the number of boxes between the points mentioned above. Each small box (1mm distance) denotes 0.04 seconds. This QT interval is particularly important in people with cardiac arrhythmias (irregular heartbeat).

Is the QTc interval the same as the QT interval?
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No. QTc is the corrected QT interval. The duration of the QT interval can fluctuate widely with the heart rate. If a person has a faster heart rate, the ECG waves are closer together and consequently, the QT interval is shorter.

How is the QTc interval calculated?
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This OTc calculator can be used with a few simple steps.

  1. Visit a reliable online website/download app with a OTc interval calculator and enter the QT interval as measured by counting the boxes (in milliseconds).

  2. The heart rate of the patient can be calculated by manually counting the number of beats in one minute or using a monitor. Alternatively, the heart rate can also be calculated from the ECG itself by checking the RR interval. Count the number of small boxes between the highest point (peak) of two R waves. Either the heart rate (in beats per minute) or the RR interval (in milliseconds) can be used in this formula.

  3. Most calculators use the Bazett’s formula to give QTc. Using advanced options, QTc as per other formulae can also be calculated.

The most common  correction used is Bazett’s formula: QTc = QT / √RR

This uses the two parameters described above. Other equations include the following. 

Of these, the Framingham and Fridericia equations were found to give the most accurate estimate of QTc interval, and the subsequent estimate of risk of mortality.

What is the normal value of the QTc interval?
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Here are the normal values of the QTc interval. 

What does an abnormal QTc interval indicate?
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Even in patients who do not have any heart problems, 10-20% may have QTc intervals outside of the normal range.

Prolongation of the QTc interval is a dangerous condition. Particularly, values greater than 500 ms indicate a serious underlying condition and need to be evaluated. Some of the causes of a prolonged QTc interval include the following. 

Other factors that affect QTc interval include the following. 

Any change in QTc interval (whether too long or too short) indicates some defect in heart rhythm and functioning. This can cause cardiac arrhythmias and sudden cardiac death.

Medications that can cause QTc prolongation
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Here is a list of all the medications that can cause QTc prolongation. Combining these medications is very dangerous and can cause a specific arrhythmia known as torsades de pointes that can be fatal. Therefore if you are taking any of these medications make sure to inform your doctor in advance to avoid accidentally combining any of these.

Frequently Asked Questions
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Here’s a list of some FAQs related to the QTc Calculator.


What are the common causes of tachycardia (fast heart rate)?

A heart rate faster than 100 beats per minute is classified as tachycardia. Common causes include fever, consuming too much caffeine, electrolyte imbalance, hypertension, hypotension, anaemia, hyperthyroidism, alcohol use, etc.

What are the common causes of bradycardia?

A heart rate below 60 beats per minute is labelled bradycardia. Common causes include damage to the heart muscle tissue (such as after a heart attack), hypothyroidism, after medication like sedatives, electrolyte imbalance, congenital causes like long QT syndrome, etc.

Disclaimer: The content on this page is generic and shared only for informational and explanatory purposes. Please consult a doctor before making any health-related decisions.