Long QT syndrome (LQTS)

Long QT syndrome (LQTS) is an inherited heart rhythm disorder affecting approximately 1 in 2500 people. LQTS is caused by mutations in genes that regulate the electrical activity in the heart. People with LQTS may experience palpitations, syncope (fainting), or even sudden death.

The name of the condition is based on the EKG pattern present in the majority of individuals with the condition. The QT interval on an EKG represents the time when the heart is relaxing after each heart beat. In people with LQTS, this interval is typically longer than normal. When the QT interval is prolonged, there is an increased risk for a dangerous heart rhythm.

Diagnosing LQTS can be difficult because individuals with the condition do not always have abnormal EKGs and QT prolongation can be intermittent. In fact, about a quarter of people with LQTS have normal EKGs and those with a long QT interval on one EKG may have normal EKGs at other times.

Treatment for LQTS is recommended for people with prior symptoms as well as young people without prior symptoms. Medications (beta-blockers) reduce the risk for syncope and sudden death in individuals with LQTS. Most of the time LQTS can be effectively treated with medication but if a person continues to have symptoms while taking medication, an internal cardioverter defibrillator (ICD) might be recommended. With appropriate treatment, people with LQTS can live long, healthy lives.

Genetics

The abnormal heart rhythms in LQTS are due to genetic differences in the electrical system that controls the heart rhythm. Many LQTS genes have been discovered and mutations in these genes are responsible for about three quarters of families with the condition. We expect to identify more genes responsible for LQTS as our knowledge in cardiac genetics improves over time.

Most often, LQTS is inherited in an autosomal dominant manner. This means that each child of a parent with LQTS has a 50% chance of inheriting the genetic mutation associated with the condition. The genetic mutation does not skip generations. However, the condition may appear to skip generations because some people carry the genetic mutation for LQTS but have a normal EKG and no symptoms. Even if a person with the genetic mutation does not have symptoms or an abnormal EKG, they can still pass the gene mutation to their children and their children could develop symptoms. The chance of inheriting the gene mutation is the same for men and women. Many people who inherit the genetic mutation will never have any health problems related to long QT syndrome.

There is a far less common form of LQTS that follows an autosomal recessive inheritance pattern and is associated with other physical and medical problems. In this pattern, the condition is due to two gene mutations, one that has been inherited from each parent. The siblings of an individual with autosomal recessive CPVT each have a 25% chance of having the condition.

Genetic testing can help establish a diagnosis of LQTS, be useful in medical management, and help family members determine their risk for the condition.

Family members

Since LQTS syndrome is a genetic condition, the family members of someone who has the condition may be at risk of developing the abnormal heart rhythms. Close relatives (parents, siblings, and children) of someone with LQTS should be evaluated for the condition by consulting a cardiologist familiar with LQTS.

Electrophysiologists are cardiologists who are experts in abnormal heart rhythms. Appointments can be made with the electrophysiologists at UCSF by calling (415) 353-2554.

Precautions

Individual recommendations should be made with the help of a cardiologist. Individuals with LQTS are often advised to avoid medications that prolong the QT interval. Such medications can bring out arrhythmias and can even cause cardiac arrest. A list of medications to avoid is maintained at https://www.sads.org.uk/drugs-to-avoid/. Additionally, people with LQTS should stay hydrated since dehydration can also provoke abnormal heart rhythms. It is a good idea for people with LQTS to wear a medical alert necklace or bracelet.

Dangerous heart rhythms are sometimes associated with specific triggers in LQTS. There are different types of LQTS and certain event triggers have been associated with the different types. Sometimes individuals with LQTS are advised to avoid certain triggers such as exercise, particularly swimming, sudden loud noise, and extreme emotion depending upon their past symptoms and the type of LQTS they have.

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