The Long-QT Syndrome

The ancient Greeks already knew that not all problems can be solved by ruler and compass alone.

Similarly to the problem of squaring the circle,the diagnosis of a the long-qt or the Brugada syndrome is often not possible with ECG, ruler and compass alone.Since there can be large difficulties to identify the long-QT syndrome solely from measurement of the QT-interval duration on 12-lead ECGs, the role of gene tests to discover this disease is important. Several studies investigating the phenotype of patients with the long-QT syndrome demonstrated that a normal QT-interval (even when corrected for the heart rhythm, QTc) can often not conclusively exclude this disease. Clinical diagnosis with measurement of QTc may be uncertain in as many as 50% of family members of a patient having the disease. Thus, in a substantial proportion of relatives from long-QT syndrome families, molecular diagnosis is the most informative method.

Our new long-QT gene test completes the diagnosis of long-QT syndrome by the full analysis of five genes

Due to the enormous heterogeneity of the molecular basis of this disease, comprehensive screening for the long-QT syndrome is difficult and can only be performed in specialized laboratories. Today, these gene test are, however, today commercially available, for example at the diagene laboratories inc. in Reinach, Switzerland.

The Long QT Syndrome

The long QT syndrome is a hereditary disorder of the electrical rhythm system of the heart. The patients with long-QT syndrome may have fainting, seizures, and abnormal, very fast heartbeats or no symptoms until an often severe arrhythmia occurs that can lead to death. Most of the deaths can be prevented with early diagnosis and treatmentt of long-QT syndrome. Hence, identification of members from families with known hereditary arrhythmia syndromes such as long-QT and Brugada syndrome is crucial (family tracing). This concept is also another example how gene tests and early treatment can prevent severe complications of a inherited disease (protective medicine). Long-QT usually affects children or young adults.

The electrical signal that stimulates the contraction of the heart muscle can be recorded on an electrocardiogram (ECG). A characteristic wave can be deduced; the different parts of this waveform are designated by letters (P, Q, R, S, and T). The interval between Q and T represents the time for electrical activation and inactivation of the ventricles. Patients with long-QT syndrome are susceptible to an abnormally rapid heart rhythm (arrhythmia) which can dramatically disturb the normal function of the heart and lead to death. A specific, very dangerous ECG pattern called "torsade des pointes" can then occur. The early beginning of the treatment, for example by using beta-blockers, in specific cases surgical procedures or implantable defibrillators, prevents patients from sudden death.

What is the QT interval? Every heartbeat is started by an electrical signal that tells the heart muscle to contract. The electrical signal causes the waves that can be shown on an ECG, na-med P, Q, R, S, T, and U. The time from the beginning of the Q wave to the end of the T wave is called QT interval. This QT interval represents the time needed by the heart muscle cells to recharge beffore the next beat. Patients with long QT syndrome have an unusual long QT interval. When the ion channels that control the electrical activity of the heart don't function proper-ly, a long QT syndrome may result.