Long QT interval is a condition that affects the heart’s electrical rhythm, which can lead to potentially life threatening arrhythmia.

Behind the pumping action of the heart is an electrical conduction system. Specialized muscle cells in the heart’s walls send signals to the rest of the heart to ensure that the heart beats at a steady, consistent rate.

Long QT syndrome (LQTS) is a problem with the heart’s electrical conduction system that may prevent the heart from pumping properly, leading to palpitations, blackouts, seizures, and life threatening arrhythmias.

This article explores long QT syndrome, its symptoms, times, causes, and more.

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An electrocardiogram (EKG) is a device that maps the electrical signals that move through the heart as it beats and relaxes.

Each heartbeat cycle has five electrical waves: P, Q, R, S, and T. The QT interval is the electrical activity between the Q and T waves.

It represents the time it takes the ventricles or lower heart chambers to relax or the time it takes for the heart’s electrical system to send an impulse through the ventricles.

Generally, this takes about one-third of each heartbeat cycle. In LQTS, the interval lasts longer than usual, which reflects an extended duration or prolongation of the recovery phase of the ventricles.

Learn more about QT prolongation.

Some individuals with LQTS may not experience any symptoms. This is known as silent LQTS.

Fainting or syncope is the most common symptom of LQTS, affecting 50% of those with a genetic variant. It often occurs during exercise or times of high emotions.

Other common symptoms include:

Sudden death is the first sign of LQTS in 10 to 15% of individuals. Cardiac arrest involves a heart that suddenly stops beating. It can cause a person to die within minutes unless they receive immediate treatment.

Certain types of LQTS may also present with non-cardiac symptoms. These include:

  • hearing loss
  • skeletal abnormalities, such as short stature and scoliosis
  • immune dysfunction
  • cognitive issues, such as problems with learning, behavior, and memory

LQTS has two types, inherited and acquired.


LQTS happens due to problems in the opening and closure processes of the ion channels in the heart. Any disturbance in these channels can lead to LQTS.

Mutations in the genes coding for these channels can lead to the condition. So far, there are different subtypes of LQTS associated with 15 autosomal dominant and two autosomal recessive genes. Autosomal means that the gene is located on one of the numbered non-sex chromosomes.

The most common is the KCNQ1 gene, responsible for LQTS type 1. Other types of inherited LQTS include:

  • LQTS type 2, 3, 4, and 5
  • Jervell and Lange-Nielsen syndrome
  • Romano-Ward syndrome
  • Timothy syndrome


A person may also develop LQTS during their lifetime. Acquired causes are relatively more common than inherited forms.

Any electrolyte disturbance can cause QT interval prolongation. This may include:

Certain medications can also cause prolonged QT syndrome:

The QT interval duration depends heavily on the electrical activity of the ventricles. This largely depends on the movement of charged potassium and sodium ions in and out of the heart cell walls.

Any disturbance in these ion channels can lead to excess positive ions inside the cell, causing QT interval prolongation.

The following factors may increase a person’s risk of LQTS:

  • having a family history of LQTS or a family member has experienced unexplained seizures or fainting, drowning or near drowning, or unexplained sudden death
  • having a heart condition, such as congenital heart defects and cardiomyopathy
  • taking certain medications that can affect the heart’s ion channels, such as antibiotics, antidepressants, or antihistamines
  • having certain medical conditions, such as thyroid disorders, eating disorders, or serious diarrhea and vomiting

LQTS is also more common in people assigned female at birth.

A longer QT interval increases the risk of life threatening arrhythmias. Treatment aims to shorten these intervals. Treatment may include medications, devices, or surgery to improve electrolyte levels and shorten a person’s QT interval.


Most people with LQTS, even those without symptoms, require medications like beta-blockers. However, some medications may prolong the Qtc intervals. If this happens, discontinuation of the medication under the guidance of a healthcare professional is important.


People with frequent or severe symptoms may require extra help to manage the rhythm of the heart. Doctors implant the device under the skin of the chest and have wires pass down into the heart to monitor the rhythm.

An implantable automatic cardioverter-defibrillator (ICD) detects life threatening arrhythmias and sends a shock to the heart to prevent sudden death. Doctors recommend this to high risk individuals, including those previously resuscitated from cardiac arrest


Some people with LQTS may need a left cardiac sympathetic denervation (LCSD) or sympathectomy. This minimally invasive procedure involves cutting some autonomic nerves to reduce the frequency of arrhythmic events.

When the QT interval is longer than usual, it can cause irregular heart rhythms like ventricular tachycardia and a life threatening arrhythmia called torsades de pointes (TdP).

The treatments may also cause side effects. For example, implanting devices may cause bleeding, infection, or collapsed lung.

LCSD has a small risk of the following side effects:

  • left-sided dryness
  • facial flushing
  • sweating or hyperhidrosis
  • different hand temperature
  • permanent eye drooping or ptosis

It is not possible to prevent inherited LQTS. However, a person can prevent triggers or conditions that cause acquired LQTS.

The following lifestyle changes may help reduce a person’s risk of fainting and sudden cardiac death associated with LQTS:

  • avoiding swimming alone
  • avoiding strenuous activities and exercises, including competitive sports
  • avoiding startling sounds
  • avoiding stressful situations and managing emotions
  • rehydrating, especially after an illness
  • taking potassium supplements and increasing intake of potassium-rich foods like vegetables and bananas.
  • discussing with a doctor before taking new medications or supplements or making any other changes to your treatment plan.

The following are questions people frequently ask about long QT syndrome.

What triggers long QT types?

Genetic modifications can lead to inherited forms of long QT syndrome. While acquired forms happen secondary to electrolyte imbalances and certain medications.

Emotional stress, sudden and startling loud noises, and strenuous exercise may trigger long QT syndrome symptoms.

How serious is long QT syndrome?

Long QT syndrome is a potentially fatal condition that may lead to sudden death due to cardiac arrest.

Long QT syndrome presents as an abnormally long QT interval on an EKG, which can increase a person’s risk of abnormal heart rhythms and sudden cardiac death.

Treatment may include medications, implantable devices, or surgery to help reduce the risk of arrhythmias. Lifestyle changes like avoiding stress and strenuous activities may help relieve symptoms.