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.
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.
ECG (Electrocardiogram) waves show the electrical activity of the heart. Here's what they mean.
P wave: It shows when the top chambers (atria) of the heart squeeze to push blood into the bottom chambers (ventricles), that is atrial contraction.
QRS complex: This wave indicates the ventricles contracting to pump blood to the rest of the body (the phase of ventricular depolarization.
T wave: It represents the ventricles resting and getting ready for the next heartbeat. This is the recovery period.
U wave: Sometimes present after the T wave, it represents the repolarization of the papillary muscles or an electrolyte imbalance.
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.
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).
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.
This OTc calculator can be used with a few simple steps.
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).
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.
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.
Fridericia: This is used more commonly for patients with faster heart rates
The Framingham correction based on the Framingham Heart Study
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.
Here are the normal values of the QTc interval.
Adult men: 350 to 450 ms
Adult women: 360 to 460 ms
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.
Genetic disorders (e.g., long QT syndrome)
Medication (e.g., diuretics, antipsychotics, and antibiotics)
Electrolyte abnormalities (e.g., hypokalemia, hypocalcemia and hypomagnesemia)
Other factors that affect QTc interval include the following.
Body mass index (BMI)
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.
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.
Antipsychotics: Haloperidol, ziprasidone, olanzapine, risperidone, quetiapine, thioridazine
Antiarrhythmics: Amiodarone, quinidine, flecainide dofetilide, procainamide
Antidepressants: Amitriptyline, imipramine, citalopram, amitriptyline
Antibiotics: Macrolides, fluoroquinolones
Others: Methadone, sumatriptan, ondansetron, cisapride
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.
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.