Long QT syndrome is a rhythm in which the QT interval, which is the amount of time it takes for the ventricles to contract and then relax, is longer than normal. The normal range, at 60 beats per minute is .30 – .46 seconds. In the example below, the QT interval is .56 with a heart rate of 79 beats per minute. In this case the QT interval corrected due to the faster rate (vs 60 beats per minute) is .64 seconds.
Long QT syndrome can be a result of drug effects or electrolyte abnormalities. In addition, it can also be an inherited trait. In any case, determining the underlying cause is necessary before appropriate treatment can be determined.