Long QT syndrome (LQTS)

February 8, 2017

Long QT syndrome (LQTS) is a disorder of the heart’s electrical activity. It can cause sudden, uncontrollable, dangerous arrhythmias (ah-RITH-me-ahs) in response to exercise or stress. Arrhythmias are problems with the rate or rhythm of the heartbeat.

People who have LQTS also can have arrhythmias for no known reason. However, not everyone who has LQTS has dangerous heart rhythms. When they do occur, though, they can be fatal.

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 and then recharge. It is translated to the time it takes for the heart muscle to contract and then recover.

LQTS occurs as the result of a defect in the ion channels, causing a delay in the time it takes for the electrical system to recharge after each heartbeat. When the Q-T interval is longer than normal, it increases the risk for torsade de pointes, a life-threatening form of ventricular tachycardia. LQTS is rare. The prevalence is about 1 in 5,000 persons in the Untied States.

Long QT syndrome can cause temporary loss of consciousness and cardiac arrest, as well as sudden death — which, unfortunately, is sometimes the first symptom of untreated LQTS.


LQTS can be congenital (present at birth) or acquired (developed under certain conditions).

Congenital LQTS is related to an inherited genetic defect. Thirteen genes have been associated with the disorder, but mutations on three of them account for most cases. Because the gene abnormalities are present at birth, congenital LQTS often is diagnosed in childhood, sometimes as early as one or two years old. Risk of arrhythmia is related to a patient’s particular gene defect. For instance, people with a mild genetic abnormality might not experience symptoms unless exposed to a trigger, such as an LQTS-inducing drug.

Congenital LQTS manifests in different ways, depending on the particular gene affected. In patients with long QT syndrome type 1 (LQTS1), arrhythmia is commonly triggered by exercise, especially swimming. Patients with LQTS2 may experience arrhythmia after being startled, such as by a loud telephone ring. For those with LQTS3, arrhythmia is usually triggered at night during sleep.

Acquired LQTS usually is caused by certain commonly prescribed medications that can lengthen the QT interval, triggering dangerous arrhythmias in some patients. Among several classes of drugs that can induce this disorder, those at highest risk include medications for cardiac arrhythmias; drugs used to treat psychiatric illness; and antibiotics, particularly those in the quinolone and macrolide families. An extensively used pain reliever called methadone, and some cold medications also may cause a prolonged QT interval.

Acquired LQTS also can occur due to an electrolyte disturbance, such as low potassium caused by severe diarrhea or vomiting.

Risk Factors

People who may have a higher risk of inherited or acquired long QT syndrome may include –

  • Children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures, or a history of cardiac arrest
  • Family members of children, teenagers and young adults with unexplained fainting, unexplained near drownings or other accidents, unexplained seizures, or a history of cardiac arrest
  • First-degree relatives of people with known long QT syndrome
  • People taking medications known to cause prolonged QT intervals
  • People with low potassium, magnesium or calcium blood levels — such as those with the eating disorder anorexia nervosa

Long QT syndrome often goes undiagnosed or is misdiagnosed as a seizure disorder, such as epilepsy. However, long QT syndrome might be responsible for some otherwise unexplained deaths in children and young adults. For example, an unexplained drowning of a young person might be the first clue to inherited long QT syndrome in a family.


Major Signs and Symptoms

If people have long QT syndrome (LQTS), they can have sudden and dangerous arrhythmias (abnormal heart rhythms). Signs and symptoms of LQTS-related arrhythmias often first occur during childhood and include –

  • Unexplained fainting. This happens because the heart isn’t pumping enough blood to the brain. Fainting may occur during physical or emotional stress. Fluttering feelings in the chest may occur before fainting.
  • Unexplained drowning or near drowning. This may be due to fainting while swimming.
  • Unexplained sudden cardiac arrest (SCA) or death. SCA is a condition in which the heart suddenly stops beating for no obvious reason. People who have SCA die within minutes unless they receive treatment. In about 1 out of 10 people who have LQTS, SCA or sudden death is the first sign of the disorder.

Other Signs and Symptoms – Often, people who have LQTS 3 develop an abnormal heart rhythm during sleep. This may cause noisy gasping while sleeping.

Silent Long QT Syndrome – Sometimes long QT syndrome doesn’t cause any signs or symptoms. This is called silent LQTS. For this reason, doctors often advise family members of people who have LQTS to be tested for the disorder, even if they have no symptoms.


Sometimes, prolonged QT intervals in people with long QT syndrome never cause problems. However, physical or emotional stress might “trip up” a heart susceptible to prolonged QT intervals. This can cause the heart’s rhythm to spin out of control, triggering life-threatening, irregular heart rhythms (arrhythmias) including –

  • Torsades de pointes — ‘twisting of the points‘ – This arrhythmia is characterized by the heart’s two lower chambers (ventricles) beating fast, making the waves on an ECG monitor look twisted.
  • Ventricular fibrillation – This condition causes the ventricles to beat so fast that the heart quivers and effectively ceases pumping blood.


LQTS is a treatable condition and the doctor may prescribe medication, surgery or recommend lifestyle changes.

Medication – Beta-blockers are the most commonly prescribed medication and they work by slowing the heart rate by reducing the effect of adrenaline on the heart. It is important to discuss with the doctor the medications that work best for some and to follow instructions carefully.

Surgery – In certain circumstances, some may be required to have surgery on nerves that regulate the heartbeat or they may need an implantable cardioverter defibrillator (ICD) if LQTS causes abnormal heart rhythms.

Lifestyle – If properly treated and controlled, many people with LQTS require very few changes to their normal lifestyle. However, a diagnosis of LQTS may require the patient to make some adjustments to their lifestyle. For instance certain sports or activities increase the risk of fainting or more serious events in patients with LQTS. It is important for the patient to discuss this matter with their cardiologist to determine how best to live a healthy, active lifestyle while minimizing the risk of further complications.

Alternative Treatment

Potassium – Potassium is a mineral that is found in the body. It is derived from the diet and is important for cardiac health. Potassium supplements may improve the heart’s recharging system and may be helpful for people with certain forms of LQTS. If the potassium content in the blood rises, the action potential shortens. It is believed that increasing potassium concentration could minimize the occurrence of arrhythmias. Potassium supplements tend to work best in LQT2, because the HERG (human ether-a-go-go-related gene) potassium channel in the heart is especially sensitive to potassium concentration.

Magnesium – Intravenous magnesium has been reported to reduce the incidence of atrial fibrillation and cardiac arrhythmia.

Aconite – The toxic effects associated with aconitine (a poisonous alkaloid and the active principle of aconite) limit its ability to be used to treat arrhythmia.

Corydalis – Early evidence suggests certain compounds found in corydalis may be of benefit for arrhythmia.

L-carnitine – L-carnitine, or acetyl-L-carnitine, is an amino acid found in the body. L-carnitine has been reported to be beneficial in maintaining a healthy heart. Although preliminary results are promising, well-designed and reported clinical trials investigating the effect of L-carnitine on arrhythmia are lacking.

Omega-3 fatty acids – There is evidence from multiple clinical studies supporting the intake of omega-3 fatty acid (also known as fish oil) supplements for a healthy heart. Fish oil supplements have been reported to lower triglycerides and reduce the risk of death, heart attack, and stroke in people with known heart disease. Fish oil may also slow the buildup of atherosclerotic plaques (hardening of the arteries) and lower blood pressure slightly.

Traditional Chinese medicine – Traditional Chinese medicine (TCM) is a broad term encompassing many different methods and traditions of healing, such as acupuncture, herbal medicines, cupping, and moxibustion. They share a common heritage of technique or theory rooted in ancient Chinese philosophy (Taoism) and dating back over 5,000 years. TCM herb combinations have been used to stabilize arrhythmias after viral myocarditis (inflammation of the heart).


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