A prolonged QT interval is an irregular heart rhythm that can be seen on an electrocardiogram (ECG or EKG) . It reflects a disturbance in how the hearts bottom chambers (ventricles) send signals. In a prolonged QT interval, it takes longer than usual for the heart to recharge between beats. Long QT syndrome (LQTS) is a heart signaling disorder that can cause fast, chaotic heartbeats (arrhythmias) . It can be congenital or acquired. Congenital LQTS is caused by genetic mutations that affect the ion channels in the heart, while acquired LQTS is the result of conditions, medications, or events that prolong the QT interval. A QTc greater than 440 ms in men or greater than 460 ms in women is considered prolonged, and a QTc greater than 500 is associated with an increased risk of torsade de pointes, a life-threatening form of ventricular tachycardia.

To diagnose LQTS, healthcare providers can measure the QT interval on an EKG. If the QT interval is longer than 450 milliseconds, a person may have LQTS. Treatment for LQTS may include lifestyle changes, medications, and surgery or other procedures. People with LQTS should avoid drugs that could cause prolonged QT intervals and let their healthcare provider know about all the medications and supplements they take, even those bought without a prescription. Regular health checkups and good communication with healthcare providers may help prevent health conditions that lead to some types of acquired LQTS.