This tool calculates the absolute QT duration and the heart-rate corrected QTc interval using Bazett's formula.
Accurate assessment of the QT interval is essential for identifying potential risks for cardiac arrhythmias.
Absolute QT Interval:
0 ms
Corrected QT (QTc) (ms):
Note: Normal QTc is typically <440ms for men and <460ms for women. Values exceeding these ranges may warrant further clinical investigation.
The QT interval represents the total time for ventricular depolarization and repolarization, reflecting the electrical activity from the start of the QRS complex to the end of the T wave.
The most common correction formula used in clinical practice is the Bazett Formula: QTc = QT / √RR
Consider an ECG recorded at a paper speed of 25 mm/s where the QT interval is measured as 10 small boxes and the patient's heart rate is 60 BPM.
Paper speed determines how many milliseconds each small box represents. At 25 mm/s, one small box is 40ms, while at 50 mm/s, it is only 20ms.
A normal QTc interval is generally under 440ms. Values above 450-470ms are often considered prolonged and may indicate an increased risk of arrhythmias.
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