Question: Wisconsin Subscriber Answer: ICD-9 includes the following definition with 426.82 (bold added for emphasis): "Condition characterized by recurrent syncope, malignant arrythmias, and sudden death; characteristic prolonged Q-T interval on electrocardiogram." The QT interval is "the time elapsing from the beginning of the QRS complex [represents ventricular depolarization] to the end of the T wave in an electrocardiogram, representing the total duration of electrical activity of the ventricles," according to the American Heritage Medical Dictionary. The QT interval length depends on the patient's heart rate, so in documentation, the QT interval is usually corrected for the heart rate and denoted as "QTc." Long QT syndrome affects the heart's electrical system and can be a harbinger of impending cardiac arrest.