Diagnosed with Long QT Syndrome: What to Know?

Long QT syndrome (LQTS) is a rare genetic conduction disorder. As a result, the ventricles in the heart take longer to pump and recover than expected. This can lead to uncontrollably fast heart rates and rhythms — symptoms range from “nothing to worry about” to relatively minor to fatal.

LQTS may be harmless and never a concern, or it can cause fainting, seizures, and sudden cardiac death in an otherwise healthy person.

LQTS occurs in approximately 1 in every 2,000 live births.

LQTS affects all ethnic groups and both males and females. However, women with LQTS are more likely to faint or die suddenly during menstruation and soon after giving birth.

Normal, healthy heart function

Ionized (electrically charged) electrolytes enter and exit the heart muscles through pores called ion channels. The movement of these electrical ions (potassium, calcium, sodium, and magnesium) cause your heart to pump.

An electrocardiogram (ECG) detects, measures, and records this electrical activity in the heart. On an ECG, five separate "waves" represent the movement of electrical impulses through your heart.

These waves are named P, Q, R, S, and T.

  • The P wave shows the impulses moving through the top part of the heart, the atria.
  • The QRS waves together show the impulses moving through the lower part of the heart, the ventricles.
  • The T wave shows the impulses preparing to fire again.

Long QT syndrome occurs when the impulses take longer than usual to move from the Q wave to the T wave.

What happens to the body?

In a person with LQTS, the ion channels allowing the movement of electrolytes may not work well, or there may not be enough of them. As a result, the ion pathways in the ventricles take longer to recharge, potentially disrupting the heart's electrical activity and causing dangerous arrhythmias or uncontrollably fast heart rates.

LQTS leaves a person at risk of sudden, life-threatening changes in their cardiac rhythm. One such condition is ventricular fibrillation (VF). This abnormal heart rhythm fails to supply blood to the rest of the body. Immediate medical attention is needed.

Several factors can trigger these changes in a person with LQTS, including fear, excitement, and physical activity. However, these events may also occur while a person is resting or sleeping.

What causes LQTS?

LQTS is often an inherited genetic condition. An inherited gene mutation resulting in this congenital heart defect accounts for approximately 75% of cases. However, the condition may also develop later in life.

Several different factors may trigger LQTS:

  • Low levels of electrolytes in the heart: sodium, calcium, potassium, and magnesium.
  • Sudden loud noises, mainly while resting.
  • Exercise, especially swimming.
  • Certain medications.
  • Strenuous activities.
  • Sleeping or resting.
  • Thyroid conditions.
  • Extreme emotions.

Should I be screened for risk factors?

If someone in your family has LQTS, you or your child may have inherited the condition. Your family members may not even be aware they have LQTS, as it often goes undiagnosed. Talk to your doctor if you or someone in your family has had unexplained episodes, such as:

  • Fainting.
  • Seizures.
  • Drowning or near drowning.
  • Sudden death.

Certain conditions may put you at greater risk of developing LQTS or triggering an episode:

Certain heart conditions, including cardiomyopathy (thick heart muscle) or certain congenital heart defects.

Medical conditions that cause low potassium, calcium, or magnesium in the blood, such as:

  • Eating disorders.
  • Thyroid disorders.
  • Serious diarrhea or vomiting.

Medications that affect how your ion channels work, such as certain:

  • Antibiotics.
  • Antihistamines.
  • Antidepressants.

Knowing the symptoms

Some people do not have any symptoms; this is called silent LQTS.

Symptoms of inherited LQTS usually start during childhood — it is rare for symptoms to begin after 40. Symptoms may include:

  • Slow heart rate.
  • Heart palpitations.
  • Noisy gasping during sleep.
  • Frequent light-headedness or feeling you are going to faint.
  • Seizures caused by a lack of oxygen to the brain during the episodes.
  • Frequent fainting can occur at any age but often appears in pre-teens through the 20s. Fainting while swimming may lead to drowning or a near drowning episode.

Some people may develop abnormal heart rhythms, known as arrhythmias, which can result in sudden cardiac arrest and premature death. The first symptom in 1 out of every ten people with LQTS is cardiac arrest.

Cardiac arrest is a life-threatening emergency that can lead to death if not treated immediately. Also, cardiac arrest can be triggered by a heart attack or heart failure. A person experiencing cardiac arrest, also known as sudden cardiac death, will lose consciousness and stop breathing. Someone in cardiac arrest will die within minutes if not treated.

If you see someone in cardiac arrest:

  • Call 9-1-1
  • Get an AED (Automated External Defibrillator) if available.
  • Begin CPR.
  • Stay with the person until advanced medical help arrives.

Males and females both develop LQTS, but the chances of events differ between males and females.

Males are more likely to have episodes during childhood through puberty.

Females are more likely to have episodes after puberty, childbirth, and menopause.

How is LQTS diagnosed?

Your doctor will ask about your medical history, your family's medical history, your symptoms, and what medications you take. Then, they will run an ECG on you to check your heart rhythm. If the ECG indicates LQTS, they may run more tests, including blood tests to check your electrolyte and thyroid levels.

You may need to wear a Holter monitor — a wearable device for monitoring your heart rate. A Holter monitor tracks your heart rhythm using electrodes and electrical leads, much like an EKG. You may have to wear the device for several days. Additionally, your doctor may order a stress test to see what is happening with your heart while exercising.

Reducing the risks and treatment options

Unfortunately, scientists have yet to discover a cure for LQTS. Therefore, treatment centers around preventing arrhythmias and associated symptoms and lowering your risk for life-threatening complications.

Treatments may include medication or lifestyle changes such as:

  • Avoiding strenuous exercise.
  • Avoiding stressful or emotional situations.
  • Avoiding sudden loud noises, such as phones and alarm clocks.
  • Frequent blood draws to monitor your electrolyte levels and adjusting your diet to keep them balanced.

Patients may need a pacemaker or an implantable cardioverter-defibrillator (ICD) implanted just under the skin near the heart to monitor rhythm. A pacemaker keeps your heart rate above a certain level by sending electrical impulses if you are prone to low heart rates. An ICD can shock your heart back into a normal rhythm if it starts to beat very quickly.

Some situations may require surgery to cut the nerves sending the electrical impulses causing dangerous heart rhythms.


LQTS is a life-long condition, but the risk of developing life-threatening heart rhythms decreases with age.

Especially in males, the QT length may return to normal after puberty, lowering the risk of fainting, arrhythmias, or sudden death. Luckily, risks usually drop even further for men over 40.

A congenital heart defect usually causes long QT syndrome. The pores in the heart that allow electrolytes to flow through and create the electrical impulses that pump the heart do not develop correctly.

Some people never have symptoms of LQTS, but others will develop symptoms such as heart palpitations, fainting, or seizures.

In a small percentage of people, the heart will go into an extremely fast or uncontrollable rhythm, leading to sudden cardiac arrest. Sudden cardiac arrest is a medical emergency. Call 9-1-1, get an AED, and do CPR until an ambulance arrives.

Schedule a consultation with your doctor if you think you or your child may have LQTS. This is especially important if someone in your immediate family has experienced a drowning or near drowning episode.

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