What Is Long QT Syndrome (QT Prolongation)?

Medically Reviewed by Dany Paul Baby, MD on April 19, 2022
4 min read

Long QT syndrome (LQTS) is rare disorder where your heart takes longer than usual to recover after each beat. It affects one in 5,000 people and can raise the risk of “torsades de pointes,” a type of irregular heartbeat that can be deadly. But there are treatments for it. Here’s what you need to know about the condition and how to manage it.

At its most basic level, long QT syndrome is an electrical problem. The heart is powered by the flow of electrically charged particles -- sodium, calcium, potassium, and chloride -- in and out of the cells through tiny channels, or tubes. With LQTS, there’s a glitch that slows down the heart’s ability to recharge. Its name comes from the way this slower rhythm looks on an electrocardiogram (EKG), a test that measure’s the heart’s electrical activity.

Long QT syndrome be inherited or acquired. In other words, it can have root causes in your genes and start at birth, or come later in life due to some other cause.

With inherited LQTS, the genes that help your heart grow give instructions to make too few ion channels, channels that don’t work well, or both. Your heart might beat faster or slower than normal, sometimes during sleep. This can trigger a rhythm that’s hard to control and could be fatal if untreated. People with inherited LQTS should avoid all medications that trigger it.

Acquired LQTS, on the other hand, has various causes. For example, more than 50 medicines could lead to the problem (such as antihistamines, decongestants, diuretics, antibiotics, antidepressants, and cholesterol-lowering drugs). These medicines might also cause symptoms in people who have a genetic basis for LQTS but whose disorder had been “silent.”

Other causes of acquired LQTS include severe diarrhea or vomiting, eating disorders (anorexia nervosa and bulimia), and thyroid disorders that affect the level of minerals in the blood.

Not all people with LQTS have symptoms. The most common are:

  • Fainting that happens with little or no warning (especially when you feel strong emotions or exercise)
  • Fluttering in the chest
  • Seizures (when your brain doesn’t get enough oxygen)

Those symptoms can happen for many reasons. You’ll need to see a doctor to find out what’s going on.

It’s rare, but long QT syndrome can cause sudden death, if your heart doesn’t get back to its normal rhythm on its own or through use of an external defibrillator.

Symptoms of inherited LQTS may start before or shortly after a baby’s birth, during childhood, or in adulthood. Or it may remain “silent.”

If your doctor thinks you may have long QT syndrome, you’ll get various tests in your doctor’s office or at the hospital.

You may get an EKG, which graphs your heart’s electrical rhythm. It can be done while you rest or as part of an exercise stress test. One part of that graph, the QT interval, shows how well your heart’s ventricles, or lower chambers, are beating. Usually, the QT interval lasts about a third of each heartbeat cycle. But with long QT syndrome, this ratio is different.

Your doctor might do genetic tests or check whether certain medicines trigger LQTS. They might also do tests to see if you have electrolyte imbalances in magnesium, potassium, or blood calcium.

You may also need to temporarily wear a device that tracks your heart rhythm as you go about your daily routine. This is done through portable EKGs: Holter monitors can be worn for up to a week and “event monitors” for up to a few months. Sometimes you may need to have a tiny event monitor inserted under your skin to check for abnormal rhythms that don’t happen very often.

Treatment depends on the LQTS type and how severe it is.

For inherited LQTS, your symptoms could be relieved by something as simple as avoiding intense exercise. More severe LQTS might mean you need to take medications called beta-blockers or antiarrhythmic drugs to control your heart’s rhythm. You and your doctor may also consider inserting a pacemaker or implantable cardioverter defibrillator (ICD) that keeps your heart rhythm steady.

For acquired LQTS, you’ll need to stop taking any medications that trigger it and treat related conditions or shortfalls of any electrolytes. As with inherited LQTS, you might also take antiarrhythmic medications or need a pacemaker or ICD.