What to Know About Long QT Syndrome (LQTS)

A Common Cause of Sudden Death in Young People

Long QT syndrome is a medical condition that causes abnormal electrical conduction in the heart. When graphed on an electrocardiogram (EKG or ECG) each heartbeat has five distinct waves: P, Q, R, S, and T. Long QT refers to a longer space between the Q and T waves. This space is also known as the QT interval.

This long QT interval can cause no symptoms at all or serious symptoms, including fainting, seizure, and death. This article will discuss long QT syndrome symptoms, causes, and treatments. It will also cover risk factors and screening options.

A young person wearing a Holter monitor to detect heart arrhythmia such as long QT syndrome

Su Arslanoglu / Getty Images

What Does Long QT Syndrome Feel Like?

Long QT syndrome may have no symptoms. However, it can feel like:

  • Palpitations or fluttering in the chest
  • Lightheadedness
  • Fainting

When long QT syndrome causes a fatal arrhythmia (abnormal rhythm of heartbeats), the person has symptoms that lead to them collapsing and cause sudden cardiac death.

Long QT Syndrome Types

Long QT syndrome is either acquired at some point during life or is an inherited condition that you are born with.

Inherited Long QT Syndrome

Inherited long QT syndrome is diagnosed in people who were born with the condition. People who have inherited long QT syndrome typically have one of the following three subtypes:

  • Long QT syndrome type 1: Potassium ion channels (receptors in the heart) do not properly work, which causes irregular electrical heart activity. Torsades de pointes, a potentially fatal heart arrhythmia, is more common in this subtype, but the arrhythmia is more likely to stop without treatment, making it less fatal. Long QT syndrome type 1 is most commonly triggered by exercise.
  • Long QT syndrome type 2: This subtype occurs when there is insufficient potassium ion activity in the heart. This causes heart arrhythmia and is often triggered by emotional stress and loud noises.
  • Long QT syndrome type 3: Not enough sodium moving through the ion channels can cause this long QT subtype. It is most often triggered during sleep, when the heart rate is slow.

Acquired Long QT Syndrome

Acquired long QT syndrome is diagnosed in people who develop the condition later in life. It is usually brought on by another condition, a medication, or an event that causes the QT interval to lengthen. Women are more likely than men to develop acquired long QT syndrome.

If a medication or condition is identified as the cause, stopping or correcting it may resolve the symptoms.

Terms

In this article, the terms for sex or gender from the sources cited are used. These generally relate to anatomical or chromosomal characteristics at birth. Verywell recognizes that people may have a gender identity that differs from the source's use of the terms.

What Are the Symptoms of Long QT Syndrome?

Symptoms of long QT syndrome can be brought on by exercise, emotional distress, or when sleeping. The symptoms tend to start during childhood and rarely start after the age of 40.

The symptoms of long QT syndrome are:

Some people who have long QT syndrome do not have any symptoms at all. These people may learn they have the condition only after being evaluated for other conditions.

One in 10 people with long QT syndrome discover they have the syndrome after they have a sudden cardiac arrest. Sudden cardiac arrest is a medical condition in which the heart stops beating due to an arrhythmia. It is fatal unless treatment is received immediately.

What Causes Long QT Syndrome?

Long QT syndrome is caused by not enough ion channels in the heart muscle or ion channels that do not work properly.

Ion channels in the heart open and close to let sodium, calcium, and potassium move in and out of the heart cells. This is part of how the heart creates electrical activity. When the ion channels do not work correctly or if there are not enough of them then the heart's electrical activity can become irregular and cause a heart arrhythmia.

Up to 75% of people diagnosed with long QT syndrome have inherited the condition. Other people will have acquired the condition from a medication or another medical condition.

Risk Factors for Long QT Syndrome

The risk factors for long QT syndrome include:

  • Family history: People who have a family history of long QT syndrome or sudden cardiac death are at higher risk of developing the condition.
  • Sex: Women are more likely than men to develop long QT syndrome.
  • Electrolyte imbalances: These include medical conditions that cause low electrolyte levels like diarrhea and vomiting.
  • Heart conditions: People with cardiomyopathy (disease of the heart muscle) or congenital (present at birth) heart defects are at greater risk of long QT syndrome.
  • Medications: Certain medications change how heart ion channels work, increasing the risk of long QT syndrome. These include some antibiotics, antidepressants, antihistamines, antifungals, and antiarrhythmics.

Can You Get Screened for Long QT Syndrome?

When someone in the family has been diagnosed with long QT, other family members may want to be screened to see if they are at risk.

Genetic testing looks at genetic markers that can show long QT syndrome. The tests can catch long QT syndrome in 3 of 4 people with the condition. If genetic testing indicates that someone could have long QT syndrome, a healthcare provider may order additional testing, like an EKG.

How Is Long QT Syndrome Diagnosed?

Long QT syndrome is diagnosed using several diagnostic tools. They include:

  • EKG: An EKG looks at the heart's electrical activity. It is the most commonly used test to diagnose long QT syndrome.
  • Holter monitor: A Holter monitor is an EKG monitor worn outside the hospital setting. It monitors a person's EKG for a longer period to catch changes that would normally be missed during a onetime EKG reading.
  • Stress test: This test looks at the heart function during exercise to monitor any changes.
  • Blood test: Blood work can look at electrolyte levels to detect low or high values.

How Is Long QT Syndrome Treated?

Long QT syndrome is treated using a combination of several therapies.

Beta-blockers are a class of medications that prevent the heart from beating too fast. They are a mainstay treatment in people with long QT syndrome.

Electrolyte replacements can help maintain normal levels of potassium, calcium, and sodium, which are necessary for normal electrical activity within the heart.

An implanted pacemaker is a device that generates an electrical pulse when it senses that the heart is beating irregularly or too slowly. In some cases, a pacemaker can also have an internal defibrillator that sends an electrical shock when it senses that the heart rhythm is abnormal.

How to Reduce Your Risk of Cardiac Arrest

People with long QT syndrome should talk to their healthcare provider about ways they can reduce the risk of a cardiac arrest.

The healthcare provider may suggest avoiding activities that can trigger long QT episodes, like exercise, stress, swimming, and loud noises. They may also suggest eating foods high in potassium.

Always make sure to take prescribed medications and contact a healthcare provider if you have symptoms that could indicate that you are having a long QT episode.

How Does Long QT Syndrome Affect Life Expectancy?

Long QT syndrome is typically a condition that someone has to live with for the rest of their life. When left untreated, the risk of sudden cardiac death is high. However, after someone has been diagnosed with long QT syndrome and receives adequate treatment, they can lead a full life.

A 2017 study looked at 166 people diagnosed with long QT syndrome. Seven years after diagnosis, 92% had not had a breakthrough cardiac event (such as fainting, seizure, cardiac arrest, or implanted defibrillator shocks to end defibrillation). While this was a small study, it helps illustrate that, with treatment, most people with long QT syndrome can live without experiencing cardiac events.

When to Contact a Healthcare Provider

Contact a healthcare provider if you experience symptoms of long QT syndrome. If the symptoms include difficulty breathing, seizures, or chest pain, call 911 immediately.

Someone diagnosed with long QT syndrome should have instructions from their healthcare provider on when to call the provider or 911. The instructions will clarify what to do if they feel new symptoms or prolonged symptoms.

Summary

Long QT syndrome is a medical condition caused by abnormal electrical conduction through the heart. This abnormal conduction can go undetected for years or can cause serious symptoms, including a fatal heart arrhythmia. Treatment options include medications and implanted heart devices.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Heart, Lung, and Blood Institute. Long QT syndrome.

  2. Johns Hopkins Medicine. Long QT syndrome (LQTS).

  3. Stanford Medicine. Types of long QT syndrome.

  4. Wilde AAM, Amin AS, Postema PG. Diagnosis, management and therapeutic strategies for congenital long QT syndromeHeart. 2022;108(5):332-338. doi:10.1136/heartjnl-2020-318259

  5. Children's Hospital of Philadelphia. Long QT syndrome.

  6. Rohatgi RK, Sugrue A, Bos JM, et al. Contemporary outcomes in patients with long qt syndromeJournal of the American College of Cardiology. 2017;70(4):453-462. doi:10.1016/j.jacc.2017.05.046

Patty Weasler

By Patty Weasler, RN, BSN
Patty is a registered nurse with over a decade of experience in pediatric critical care. Her passion is writing health and wellness content that anyone can understand and use.