Who Should be Screened for the Long QT Syndrome?

The Long QT syndrome should be considered in any otherwise healthy child or young adult who:-

a) Experiences syncopal (loss of consciousness) or near syncopal spells, principally during physical exertion or emotional distress - particularly in cases where the events are repetitive.

NOTE: Episodes occurring during emotional stress are somewhat less specific because vasovagal (the common faint) episodes may also occur during emotional excitement. However, it's unusual for the common faint to occur during physical activity.

b) Has a family history of unexplained sudden death in otherwise healthy young persons

NOTE: Some of the conditions which should be questioned are unexplained death during swimming, death during seizures, a family history of 'seizure' disorders and other unexplained deaths.

The Screening Process

The Resting Electrocardiogram:
This test will detect a number of individuals with the Long QT Syndrome. However, the QT interval is sometimes very modestly prolonged, and occasionally even normal in individuals with the Syndrome. Therefore, the resting electrocardiogram, while very helpful in many patients is not always accurate in diagnosing Long QT Syndrome. Further information can be obtained by evaluating several electrocardiograms (ECG's) on family members. Since this is a genetic condition in most cases, a child suspected of having the Long QT Syndrome would most likely have a parent with the syndrome, and very likely siblings with the syndrome as well. Therefore, evaluation of the ECG'S of the parent and siblings of a suspected Long QT patient can also assist in making a diagnosis.

The Exercise (Stress) Electrocardiogram:
QT intervals that are somewhat borderline or even normal at rest may become distinctly abnormal during exercise, clarifying the diagnosis or clarifying that the patient does not have the LONG QT Syndrome if the QT remains normal. An exercise test which allows the individual to exercise for 10 to 15 minutes without achieving a heart rate more than 150-160 beats per minute works best for this process. The standard treadmill test which is used for detecting coronary artery disease is not optimal for the evaluation of suspected Long QT patients. The reason is that the workload is too hard and occurs too fast, so the individual tends to achieve a fast heart rate rather early in the exercise. Talk to the physician regarding a lower effort and a more protracted exercise test. The ECG's are then evaluated for the behaviour of the QT interval at each stage of exercise and particularly important, just after exercise in the early recovery. The QT interval is prolonged and/or prolongs even further during and immediately following exercise in Long QT patients.

Dr. Robert Hamilton, M.D., F.R.C.P Electrophysiologist at the Hospital for Sick Children in Toronto, Canada