Short QT syndrome is a disorder that causes electrical dysfunction in the heart. It is a genetic disorder marked by the abnormal shortening of the QT intervals on an electrocardiogram. Each heartbeat is divided into several phases and each is assigned a letter: P, Q, R, S and T. The QT interval refers to the time it takes for the heart’s ventricles to contract and relax. A short QT is an abnormally short interval between Q and T.
What is an electrocardiogram?
It is a test that records the heart’s electrical activity over a given period of time. It identifies the speed at which the heart is beating (heart rate), whether it is beating normally (heart rhythm) and the effectiveness of the heart muscle. An electrocardiogram is also called an ECG or EKG.
Consequences
Short QT syndrome is a disorder that can have several serious consequences for heart health:
Heart arrhythmias:
- Atrial fibrillation : a rapid, irregular heart rhythm in the atria (upper heart chambers) that can impair the heart’s ability to pump blood.
- Ventricular fibrillation : a potentially fatal arrhythmia in which the ventricles (lower chambers of the heart) beat rapidly and erratically and can impair blood flow from the heart to the rest of the body.
- Syncope: individuals with short QT syndrome may faint unexpectedly due to a sudden decrease in blood flow to the brain.
- Sudden cardiac death: Short QT significantly increases the risk of sudden cardiac death, especially if arrhythmias are not detected and treated quickly. Sudden cardiac death can occur at any time, even in young and apparently healthy individuals.
Causes
There is no predominant triggering factor; incidents can occur at rest or during physical exertion. Short QT syndrome is primarily caused by genetic factors. Several genetic mutations have been identified as being responsible for this disorder. These mutations generally affect ion channels, which act as gateways in the cells, controlling the passage of ions such as calcium, potassium and sodium, which are essential for maintaining heart rhythm.
Research is still underway to determine if any other mutations are involved in short QT syndrome.
Symptoms
Symptoms of short QT syndrome can vary based on the severity of the condition and are sometimes absent until severe arrhythmia occurs. These are the main symptoms associated with short QT:
- Palpitations: a sensation of rapid or irregular heartbeats.
- Syncope: sudden fainting without warning, often due to cardiac arrhythmias.
- Sudden cardiac arrest: in the most severe cases, short QT can lead to sudden cardiac arrest, sometimes without prior symptoms. This can be triggered in particular by physical exertion or stressful situations.
Some people with short QT may have no symptoms before arrhythmia occurs.
Diagnosis
The diagnosis is based on analysis of an electrocardiogram, along with the measurement of the QT interval and QTc, a heart-rate corrected QT interval. Although we do not know the exact limits for the duration of a short QT interval, people with short QT syndrome currently have a QT interval between 325 and 220ms.
Other studies can also be performed:
- Medical and family history: to identify history of sudden death or heart disease in the family.
- Genetic tests: to identify specific mutations associated with short QT.
It is also important that the patient informs their immediate relatives (parents, siblings and children) of the existence of short QT syndrome. They can do this personally or give written consent for the doctor to share the information. This is a little-known condition that appears to be inherited with a 50% chance of transmission in each pregnancy.
Treatment
Treatment options for short QT are limited. They focus primarily on preventing severe arrhythmias. These are some of the key approaches:
- An implantable cardioverter-defibrillator (ICD) is often considered to be the preferred treatment for patients with short QT syndrome, particularly those who have experienced severe cardiac events or are at high risk. The ICD constantly monitors the heart rate and can deliver shocks to restore a normal rhythm in case of arrhythmia.
- Antiarrhythmic medication: this type of medication works by altering the heart’s electrical properties to restore a normal rhythm.
- Monitoring and follow-up: it is essential for diagnosed patients to be monitored by a specialized cardiologist on a regular basis. This includes regular ECGs and assessments to track the progression of the condition and the effectiveness of the treatment.
The choice of treatment depends on several factors, including the severity of the condition, the symptoms present, and the patient’s medical history. A personalized approach is crucial for effectively managing short QT.
Important information
Due to an increased risk of arrhythmia, people with short QT may have a lower tolerance for intense exercise, leading them to limit their everyday physical and sports activities.
Reviewed and approved by Frédéric Sacher, Professor, MD, PhD, Cardiologist at Bordeaux University Hospital (CHU)
