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An "abnormal" QTc in males is a QTc above 450 ms; and, in females, above 470 ms. [17] If there is not a very high or low heart rate, the upper limits of QT can roughly be estimated by taking QT = QTc at a heart rate of 60 beats per minute (bpm), and subtracting 0.02 s from QT for every 10 bpm increase in heart rate.
MDCalc was founded by two emergency physicians, Graham Walker, MD, and Joseph Habboushe, MD, MBA, [5] and provides over 500 medical calculators and other clinical decision-support tools. [6] The MDCalc.com website was launched in 2005. [5] In 2016, MDCalc launched an iOS app, [7] followed by an Android app in 2017. [8]
Corrected QT interval (QTc) The QT interval is measured from the beginning of the QRS complex to the end of the T wave. Acceptable ranges vary with heart rate, so it must be corrected to the QTc by dividing by the square root of the RR interval. A prolonged QTc interval is a risk factor for ventricular tachyarrhythmias and sudden death.
A medical calculator is a type of medical computer software, whose purpose is to allow easy calculation of various scores and indices, presenting the user with a friendly interface that hides the complexity of the formulas.
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The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females. LQTS is suggested if the QTc is longer than these cutoffs. However, as 5% of normal people also fall into this category, some suggest cutoffs of 470 and 480 ms for males and females respectively, corresponding with the 99th centiles of normal values.
The value for a normal QT interval is similar in males and females from birth up to adolescence. During infancy, a normal QTc is defined as 400 ± 20 milliseconds. Before puberty, the 99th percentile of QTc values is 460 milliseconds. After puberty, this value increases to 470 milliseconds in males and 480 milliseconds in females. [citation needed]
The JT interval is used to estimate the QTc for patients with a baseline intraventricular conduction defect. But no one talks about an ST interval (or JT interval) in common practice. I'd like to see more references to prove this measurement is notable.