As a medical professional with expertise in cardiology, I can provide you with information on what is considered a prolonged QT interval. A prolonged QT interval is a condition where the time between the start of the Q wave and the end of the T wave in the heart's electrical cycle, as measured on an electrocardiogram (ECG), is longer than usual. This interval represents the time the ventricles take to depolarize and then repolarize, which is a critical part of the heart's rhythm. Under normal circumstances, the QT interval varies based on factors such as age, gender, and heart rate. However, a universally accepted cutoff for a prolonged QT interval is not straightforward due to these variables. Generally, a QT interval that is greater than 450 milliseconds (ms) in males and 460 ms in females is considered prolonged in adults at a heart rate of 60 beats per minute (bpm). For children, the threshold is typically lower. It's important to note that the QT interval can be corrected (QTc) for heart rate using various formulas to standardize it to a heart rate of 60 bpm, which makes it more comparable across different individuals and conditions. read more >>

Long QT syndrome is a heart rhythm disorder that can cause serious irregular heart rhythms (arrhythmias). ... In long QT syndrome, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance, which often can be seen on an electrocardiogram (ECG), is called a prolonged QT interval.read more >>