[Form fruste of long QT syndrome].

The long QT syndrome (LQTS) is an inherited disorder associated with recurrent syncope and sudden death from ventricular arrhythmias. It is characterized by a prolonged QT interval on the ECG. A case is discussed in which a patient presented with recurrent syncopal episodes on exertion associated with a slightly prolonged QT interval. Family history revealed an increased incidence of sudden deaths in two generations. Some reports on similar patients suggest that there may be a forme fruste of the long QT syndrome. The additional diagnostic values of exercise stress test, Valsalva maneuver and genetic testing are evaluated. After analysis of the patient's and mother's ECGs the diagnosis of a forme fruste of LQTS is made. This case is presented to emphasize the importance of diagnosis of borderline cases of LQTS because of the high risk of sudden death for untreated patients.