From the Guidelines
Normal Corrected QT (QTc) Interval
A normal QTc interval is generally considered to be less than 450 ms in men and less than 460 ms in women.
- Prolongation of the QTc interval can be a concern with certain medications, such as quinidine, sotalol, and dofetilide, which can increase the risk of torsades de pointes 1.
- In clinical practice, a QTc interval above 500 milliseconds is typically considered abnormal and may warrant further evaluation or adjustment of medications 1.
- The upper limit of normal for QTc intervals is suggested to be 450 ms in men and 460 ms in women on baseline ECG evaluation 1.
- It's also important to note that QTc prolongation above 500 ms and a change from baseline of more than 60 ms are considered to be of particular concern because torsades de pointes rarely occurs when QTc is less than 500 ms 1.
- The American Heart Association recommends that a QTc over the 99th percentile should be considered abnormally prolonged, with approximate 99th percentile QTc values for otherwise healthy postpubertal individuals being 470 ms for males and 480 ms for females 1.
- Normal limits proposed in different studies vary to a certain extent, depending on the characteristics of the study population and particularly on the type of QT-adjustment function used, but practical compromise for the evaluation of QT-interval prolongation and shortening in adult men and women are: prolonged QT: women, 460 ms or longer; men, longer than 450 ms 1.
From the FDA Drug Label
If the QTc is greater than 440 msec (500 msec in patients with ventricular conduction abnormalities), TIKOSYN is contraindicated.
If at any time after the second dose of TIKOSYN is given the QTc is greater than 500 msec (550 msec in patients with ventricular conduction abnormalities), TIKOSYN should be discontinued.
If QTc exceeds 500 milliseconds (550 msec in patients with ventricular conduction abnormalities), TIKOSYN therapy should be discontinued and patients should be carefully monitored until QTc returns to baseline levels.
A normal Corrected QT (QTc) interval is not explicitly defined in the label, but it can be inferred that a QTc interval of less than or equal to 440 msec (or 500 msec in patients with ventricular conduction abnormalities) is considered acceptable for initiating TIKOSYN therapy 2.
From the Research
Normal Corrected QT (QTc) Interval
The normal Corrected QT (QTc) interval is a topic of interest in the medical field, particularly in relation to the effects of certain medications on the heart.
- The study 3 provides some insight into the normal QTc interval in children, where the median baseline QTc was found to be 410 milliseconds, with a range of 350-450 milliseconds.
- This suggests that a normal QTc interval may be around 410 milliseconds, but it can vary between 350-450 milliseconds.
- It is also worth noting that a QTc interval of 450 milliseconds or more is considered increased, as seen in two patients in the study 3 who showed a QTc increase ≥450 milliseconds after taking domperidone.