Stanford Center for Inherited Cardiovascular Disease

Long QT Syndrome

The Long QT syndrome is a disorder that affects the recovery of the electrical state of the heart after each heart beat and is associated with sudden death. Ion channels are responsible for healthy flow of electrical signals that control the heart beat. A genetic abnormality in the potassium ion channels or exposure to certain medications in some patients can lead to a dangerous heart rhythm called “Torsades de Pointes”. Patients who experience Torsades de Pointes can have dizziness, syncope (passing out), or even sudden death.Long Qt ECG

The heart muscle itself is not abnormal, so patients can be asymptomatic until their first episode of Torsades de Pointes. Although imaging studies, such as cardiac ultrasounds, are typically normal, patients with Long QT Syndrome have a characteristic “stretching” of one of the intervals that is measured on the electrocardiogram (ECG) that leads to the diagnosis. This “stretching” can come and go, which often makes the diagnosis of Long QT difficult to make. Repeating the ECG at different time points is often necessary to help make the diagnosis. Patients with Long QT Syndrome can be placed on medications, such as beta-blockers, which can decrease the risks of sudden death. However, patients who have had repeated episodes of passing out or who had near sudden death experiences will often need an internal cardiac defibrillator.

There are over 10 genes that have been linked to the Long QT Syndrome. The numbering system used in Long QT Syndrome refers to the gene affected. For example, Long QT 1 refers to a mutation in the potassium ion channel KCNQ1. Most, but not all, long QT syndromes are passed on in a dominant manner. In the minority of patients with associated deafness, the syndrome is passed on in a recessive manner. Commercial testing for long QT syndrome is able to identify approximately 75% of the known mutations.

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