Short Q-T Syndrome (SQTS)
What is short Q-T syndrome (SQTS)?
Short Q-T syndrome is a rare genetic type of abnormal heart rhythm that was discovered in 1999.
The electrical activity of the heart is produced by the flow of ions (electrically charged particles of sodium, calcium, potassium, and chloride) in and out of the cells of the heart. Tiny ion channels control this flow. The Q-T interval is the section on the electrocardiogram (ECG) that represents the time it takes for the electrical system to fire an impulse through the ventricles (lower chambers of the heart) and then recharge. It is translated to the time it takes for the heart muscle to contract and then recover.
If you have SQTS, your heart beats at a normal rate, but the time it takes to recover (the Q-T interval) is much shorter. Another difference in patients with SQTS is that the Q-T interval does not change as the speed of the heartbeat changes. In healthy people, the Q-T interval gets longer when the heart beats slower and shorter when the heart beats faster.
What causes SQTS?
Short Q-T syndrome is a congenital defect, which means it is present at birth. The condition is inherited from at least one parent. The defect changes the way the heart’s ion channels function (called a channelopathy).
So far, scientists have found several different defects that can occur in five different genes related to the potassium channels. However, in most cases, the gene is not identified. Research is being done to identify other genes.
What problems does SQTS cause?
When there is abnormal electrical activity in the heart, the heart muscle discharges and recharges faster than normal. This can cause three types of abnormal heart rhythms ─ atrial fibrillation, ventricular tachycardia and ventricular fibrillation. If you have SQTS, you can have one or more of these.
- Atrial fibrillation is an abnormal heart rhythm that starts in the atria (the heart’s upper chambers). Some people with SQTS have occasional atrial fibrillation, while the problem can be almost constant for others.
- Ventricular tachycardia is a very fast regular rhythm in the ventricles (the heart’s lower chambers).
- Ventricular fibrillation is a very fast abnormal rate causing the ventricles to flutter or quiver. It causes sudden cardiac death.
Symptoms & Diagnosis
What are the symptoms of SQTS?
The majority of patients with SQTS have symptoms. The most common symptoms are:
- Heart pounding (palpitations)
- Fainting (syncope)
- Sudden cardiac death (may be the first symptom for some patients)
- Atrial fibrillation
If SQTS causes atrial fibrillation, other symptoms may include shortness of breath, dizziness, fatigue and chest discomfort. Some people with SQTS never have symptoms or problems related to the condition. But, it is important for anyone who knows they have SQTS to see a doctor for regular care to prevent sudden cardiac death or cardiac arrest.
How is SQTS diagnosed?
The first steps to determine if your symptoms are related to SQTS include a complete medical and family history and an electrocardiogram (ECG). Your doctor will check the ECG for a short Q-T interval. However, a single short Q-T interval does not necessarily mean you have SGTS. This is one of the reasons it is important to provide a complete medical and family history1.
Your doctor may evaluate you for SQTS if you:
- Survived sudden cardiac death
- Have a history of polymorphic ventricular tachycardia or ventricular fibrillation without a known cause
- Have a history of unexplained syncope
- Are young and have atrial fibrillation
- Have family members diagnosed with SQTS
- Have family members who died from sudden cardiac death
Your doctor will likely perform some diagnostic tests to check for SQTS. These may include:
- Resting 12-lead ECG: This is the first step in checking for SQTS.
- 24-hour ambulatory monitoring: This device records your heart rate and heartbeat during a normal day.
- Exercise stress testing: Measures how well your heart functions as you walk on treadmill or ride an exercise bike.
- Electrophysiology (EP) study: Electrodes are placed directly on the heart muscle to record the heart’s electrical activity. This test is used very selectively in patients whose diagnosis is unclear even after other tests are done.
- Other tests, such as blood and lab work, may be done to rule out other causes of a short Q-T interval.
Genetic testing is recommended for patients who have ECG results and a family/medical history that strongly indicates a diagnosis of SQTS. Genetic testing can be used to confirm the diagnosis. If you do have SQTS, your family members should have genetic testing for the condition and get any needed medical care.
What treatments are available for patients with SQTS?
Implantable cardioverter defibrillator (ICD)
If you have SQTS and a history of sudden cardiac death or ventricular arrhythmias; or if you have a family history of these conditions, you are at high risk of future sudden cardiac death. Your doctor will likely recommend that you get an implanted cardiac defibrillator (ICD) to prevent sudden cardiac death.
There are many medications available to help regulate your heart rhythm. Doctors are working to determine which medications are best to treat patients with SQTS.
What is the outlook for people with short QT syndrome?
There is not a lot of available information about SQTS; however, researchers and doctors continue to learn more. The sooner you are diagnosed with and start treatment for SQTS, the less likely you are to have serious symptoms, including sudden cardiac death and cardiac arrest. It is important for first-degree relatives of patients diagnosed with SQTS to be evaluated for the condition. The evaluation should include a screening, ECG and genetic testing.
What kind of physician diagnoses and treats patients with SQTS?
If you are at risk for SQTS or have been diagnosed with SQTS, you should be evaluated and treated by an experienced team that includes several different types of specialists. This approach helps ensure that patients with SQTS get the best possible care. The team should include the following:
- Electrophysiologist - A doctor who specializes in diagnosing and treating patients with heart rhythm problems.
- Geneticist - A doctor who studies genetic patterns to identify gene defects in patients that can cause problems.
- Primary care physician - The patient’s usual general doctor who can provide general follow-up care and monitor medications.
Story Credit: http://my.clevelandclinic.org/health/articles/short-qt-syndrome