Long QT syndrome could make for fast, chaotic heartbeats

DEAR MAYO CLINIC: My son was diagnosed recently with long QT syndrome after a scary fainting spell. What do I need to know to keep him healthy? Also, I have tested negative, but my doctor still suggests I take beta blockers and avoid certain medications. Why would this be necessary? Should I tell other family members to be tested?

Long QT syndrome (LQTS) is a genetic abnormality in the heart's electrical system. The condition is one of many genetic heart rhythm disorders. Of these, LQTS is the most common, affecting as many as 1 in 2,000 people.

In patients who have this syndrome, the heart works perfectly as a muscle and a pump, but its built-in electrical system has a glitch, causing it to recharge itself too slowly and inefficiently in preparation for the next beat. This glitch can make the heart vulnerable to fast, chaotic heartbeats that may trigger a sudden fainting spell, a sudden faint followed by a generalized seizure, or even cardiac arrest that can result in sudden death.

Many patients with LQTS have no symptoms and never know they have the condition. But there are warning signs that someone has LQTS, and knowing those signs is extremely important. Such warning signs include a prior sudden fainting spell that occurred with minimal warning, especially if during exercise, excitement, or when startled, and a family history of unexpected, unexplained sudden deaths involving a young relative. And, if sudden cardiac arrest occurs, the only thing that can prevent sudden death is a rapid external shock from an automatic external defibrillator (AED).

The most common triggers for long QT patients are exercise, excitement or any activity that causes an adrenaline rush. For example, being caught off guard or startled by a loud sound, such as the sudden ringing of a phone or an alarm, can be triggers.


Because LQTS is a genetic disease, if one person has it, every family member is potentially vulnerable. Once the disease is diagnosed, the person's relatives — children, siblings and parents — need to be evaluated carefully. Since your son has been diagnosed, you and your husband and other children should be tested. But, if your son's LQTS has been diagnosed clinically and genetically confirmed, then a sibling or parent who has never exhibited symptoms, has normal cardiac tests, and tests negative for the affected child's LQTS disease-causing mutation does not need to be treated. However, a cardiologist with experience in LQTS should review your situation.

The good news is that the condition is manageable. Eating and sleeping well, along with a diet rich in potassium, helps. Certain medications, including some antibiotics, antidepressants, and psychiatric drugs, should be avoided. Ask your son's physician for a complete list.

While beta blockers are very effective in preventing these "electrical attacks," some patients do not tolerate this medication or need additional protection. For these individuals, there are some alternatives. Implanting a small defibrillator that will shock the heart's rhythm back to normal, if needed, may make sense. The implant is surgically placed in the chest to monitor electrical activity. If the heart exhibits a life-threatening change in rhythm, the defibrillator delivers an electrical shock to restore the heart's normal rhythm.

A relatively new alternative to implanting a defibrillator is videoscopic denervation therapy — removing a chain of nerves along the left side of the spine. Mayo Clinic can perform this procedure using minimally invasive surgery. Denervation helps reduce the chances that adrenaline-related triggers will ignite the LQTS heart. Although this treatment reduces the risk of a future event significantly, it should not be viewed as a surgical cure for the disease.

The current best screening tool for LQTS, the 12-lead electrocardiogram, is not foolproof. In the meantime, understanding, respecting, and acting upon the warning signs are extremely important.

In any consideration of long QT syndrome, the answers to these two questions may help prevent a sudden death:

Have you ever fainted suddenly, unexpectedly, with minimal warning during exercise or immediately after an auditory stimulus like an alarm clock?

Has anyone in your family died suddenly and unexpectedly before age 50?


Sudden, unexplainable death in someone under 50 is worth looking into. In studying autopsies of these patients, a genetic heart abnormality is found in about 25 to 35 percent. Many of those tragedies had clear-cut yes answers to one of the two questions. If they were known to have LQTS, a personalized treatment program might have been life-saving. — Michael J. Ackerman, M.D., Ph.D., Pediatric Cardiology, Mayo Clinic, Rochester.

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