Short QT Syndrome

Overview

Short QT syndrome is a rare and dangerous inherited disease affecting the heart's electrical system. In this condition, the heart muscle's contraction and relaxation cycle is completed faster than normal. The measurement called the QT interval on an electrocardiogram (ECG) is shorter than normal.

The QT interval represents the time it takes for the lower chambers of the heart (ventricles) to become electrically activated and then return to a resting state. The normal QT interval varies with heart rate, but the corrected QT (QTc) value is generally between 350-450 milliseconds. In short QT syndrome, this value drops below 330 milliseconds.

A short QT interval causes the ventricles to relax too early. This creates instability in the heart's electrical system and sets the stage for dangerous rhythm disorders. Lethal arrhythmias such as ventricular fibrillation or ventricular tachycardia can develop.

Short QT syndrome can lead to sudden cardiac arrest at any age. Sudden death can occur even in young and apparently healthy individuals. If there is a family history of unexplained sudden deaths, this syndrome should come to mind.

Short QT syndrome shows autosomal dominant inheritance. This means it can be passed from an affected parent to a child with a 50 percent probability. Sometimes, however, it can also arise from new mutations.

Early diagnosis and appropriate treatment are life-saving. An implantable cardioverter defibrillator (ICD) is the most effective method for preventing sudden death.

Symptoms

The symptoms of short QT syndrome vary greatly from person to person. Some people experience no symptoms and the condition is discovered by chance. In others, serious symptoms are seen.

The most common symptoms are:

• Fainting (syncope). This is the most common symptom. Lack of blood flow to the brain due to sudden rhythm disturbance leads to loss of consciousness. Fainting can occur during exercise, at rest, or during sleep.
• Heart palpitations. Rapid and irregular heartbeats are felt. This is usually a sign of ventricular tachycardia or atrial fibrillation episodes.
• Seizure-like episodes. Convulsions may be seen during fainting. This is sometimes confused with epilepsy.
• Sudden cardiac arrest. This is the most serious situation. The heart suddenly stops and without emergency intervention it is fatal. This can appear as the first symptom in short QT syndrome.
• Atrial fibrillation. Irregular rhythm develops in the upper chambers of the heart. In short QT syndrome, atrial fibrillation can be seen at a young age and run in families.
• There may be no symptoms. In some people the syndrome is asymptomatic. It is noticed by chance on a routine ECG or during family screening.

Symptoms usually begin in young adulthood but can appear at any age. In infants it can cause sudden infant death syndrome (SIDS).

When to See a Doctor

Be sure to see a doctor in the following situations:

• If you have experienced unexplained fainting, cardiological evaluation is important.
• If fainting develops together with palpitations, call emergency services immediately.
• If there is a family history of unexplained sudden death at a young age, see a cardiologist and have family screening done.
• In families with a history of sudden infant death syndrome (SIDS), siblings should be screened.

Causes and Risk Factors

Short QT syndrome is a genetic disease. It develops due to mutations in genes encoding ion channels in the heart muscle.

Risk factors:

• Family history. If there is short QT syndrome or unexplained sudden death in the family, the risk is high.
• Sudden death at a young age. Sudden death histories especially under age 40 should raise suspicion.
• Unexplained fainting. Recurrent fainting in young and healthy individuals can be a sign of short QT syndrome.
• Atrial fibrillation. Atrial fibrillation at a young age (under 40) that runs in families can be associated with short QT.

Complications

If left untreated, short QT syndrome leads to serious complications.

• Sudden cardiac arrest and sudden death. This is the most serious complication. Development of ventricular fibrillation stops the heart and without emergency intervention it is fatal. Sudden death can occur at any age in short QT syndrome.
• Recurrent fainting. Frequent fainting leads to injuries and severe decline in quality of life.
• Atrial fibrillation. Atrial fibrillation can develop at a young age. This increases stroke risk.
• Ventricular tachycardia. Rapid and dangerous ventricular rhythm disorders develop.
• Sudden infant death syndrome (SIDS). In infants, short QT syndrome can cause SIDS.
• Psychological problems. Fear of sudden death can lead to anxiety and depression.

Diagnosis

Short QT syndrome is diagnosed with electrocardiogram (ECG) and genetic testing.

The diagnostic process typically includes:

• Electrocardiogram (ECG). This is the foundation of diagnosis. The corrected QT (QTc) interval is measured. If the QTc value is below 330 milliseconds, short QT syndrome is considered. A short QTc alone does not always mean disease, however; it must be evaluated together with clinical findings.
• Holter monitor. Twenty-four hour ECG recording is obtained. QT interval variability and rhythm disorders are investigated.
• Exercise test. How the QT interval changes during and after exercise is monitored. In short QT syndrome, the QT interval does not lengthen sufficiently with exercise.
• Electrophysiology study. The heart's electrical properties are examined in detail via cardiac catheterization. Inducibility of ventricular fibrillation is tested. This test helps with risk assessment.
• Genetic testing. Genes associated with short QT syndrome are searched for mutations. Genetic testing confirms the diagnosis and enables family screening. The absence of a mutation on genetic testing does not rule out the syndrome, however.
• Family screening. First-degree relatives (parents, siblings, children) should be screened with ECG. If a genetic mutation is known, genetic testing is performed on family members.
• Echocardiography. The structure of the heart is assessed. Structural heart disease is ruled out.
• Blood tests. Electrolyte levels (especially calcium and potassium) are checked. Electrolyte imbalances can shorten the QT interval and must be ruled out.

Treatment

Treatment for short QT syndrome aims to prevent sudden death. The treatment decision is made based on symptoms, family history, and risk assessment.

Treatment options include:

Implantable cardioverter defibrillator (ICD). This is the most effective treatment for preventing sudden death. The ICD is surgically placed below the chest. It continuously monitors heart rhythm. When it detects ventricular fibrillation or dangerous ventricular tachycardia, it automatically delivers an electrical shock and saves lives.

Who is the ICD recommended for:

• People who have survived sudden cardiac arrest (strongest indication)
• Those who have experienced unexplained fainting
• Those with a family history of sudden death and a very short QTc (for example <320 ms)
• Those identified as high risk on electrophysiology study

Medication. Quinidine can lengthen the QT interval and reduce the risk of rhythm disorders. It has side effects, however, and is not effective in every patient. Medication is usually given in addition to an ICD. Beta blockers may be beneficial in some patients.

Avoidance of risk factors. High-intensity competitive sports may be restricted. Excessive alcohol consumption and stimulant substances should be avoided. Medications that shorten the QT interval (some antibiotics, antiarrhythmics) should not be used.

Maintenance of electrolyte balance. Potassium and calcium levels should be kept in the normal range.

Family screening and genetic counseling. Family members should be screened and risk assessment performed. Genetic counseling should be given to people planning to have children in the future.

Living with Short QT Syndrome

Being diagnosed with short QT syndrome can be frightening. With appropriate treatment and follow-up, however, most people can lead normal lives.

If you have short QT syndrome, pay attention to the following:

• If you have an ICD, maintain it. Attend regular cardiology appointments. The ICD battery must be replaced after years. If your ICD delivers a shock, be sure to notify your doctor.
• Use your medications regularly. Use quinidine or other recommended medications according to your doctor's instructions.
• Consult before taking new medication. Some medications can further shorten the QT interval or increase the risk of rhythm disorders. Consult your cardiologist before starting a new medication.
• Maintain your electrolyte balance. Your potassium and calcium levels should be checked regularly. Notify your doctor if you experience vomiting, diarrhea, or excessive sweating.
• Inform your family. Tell your relatives about the syndrome. Explain what they should do if you faint. Have them receive CPR training.
• Have your family members screened. Your first-degree relatives should undergo cardiological evaluation. Early diagnosis saves lives.
• Get psychological support. Living with the risk of sudden death can be stressful. Get psychological support if needed.
• Wear a medical bracelet. Wear a medical bracelet or necklace indicating you have short QT syndrome. It informs the healthcare team in emergencies.
• Consult about sports restrictions. High-intensity competitive sports are generally not recommended. Light to moderate exercise is safe for most people, however. Discuss with your cardiologist.
• Consult if you are planning pregnancy. Pregnancy is usually safe in short QT syndrome but requires close monitoring.

Preparing for Your Appointment

What you can do:

• When did fainting episodes occur and what were they like?
• Do you experience heart palpitations?
• Is there a family history of sudden death? Who and how old were they?
• List all medications and supplements you are taking.
• Bring your previous ECG records.
• Write your questions down in advance.

Questions you can ask your doctor:

• Is the diagnosis of short QT syndrome certain?
• What is my risk of sudden death?
• Do I need an ICD?
• Is medication an option?
• Should I have genetic testing?
• Should my family be screened?
• Can I exercise?
• Is pregnancy safe?
• What is my life expectancy?

Your doctor may ask you:

• Have you experienced fainting?
• Do you have palpitations?
• Is there a family history of sudden death?
• What medications are you taking?
• Do you do high-intensity sports?
• Is there drug use?