A prolonged QT interval indicates an abnormality detected on an ECG.

On an electrocardiogram (ECG), each heartbeat is mapped with five different waves, namely, P, Q, R, S, and T, wherein alphabets Q through T correspond to the heart cells’ recharging or repolarizing after a muscle contraction.

A prolonged QT interval indicates an abnormality detected on an ECG. This abnormality reflects a disturbance in the conduction of electricity in the lower chamber (ventricles) of the heart.

What is long QT syndrome?

Long QT syndrome (LQTS) is a rare disorder detected on the electrocardiogram, which represents the time taken by the heart muscle (ventricles) to contract and then recover.

The electrical activity of the heart is produced by the influx and outflux of electrically charged ions such as charged particles of sodium, calcium, potassium, and chloride. This chemical process within the muscle cells is the reason for the heart’s contraction for pumping out blood.

LQTS is a result of a defect in these ion channels, which causes a delay in the time taken for the electrical system of the heart to recharge after each heartbeat (in normal conditions, the QT interval is about a third of each heartbeat cycle).

It is also known as:

• LQTS
• Jervell and Lange-Nielsen syndrome
• Romano-Ward syndrome

What causes LQTS?

Long QT syndrome (LQTS) is typically referred to as a corrected QT interval that exceeds 440 ms in men and 460 ms in women on a resting electrocardiogram.

Multiple factors have been implicated in causing prolonged QT intervals, including:

• Acquired: It is triggered by
  • Medications such as antihistamines, decongestants, diuretics, antibiotics, antidepressants, cholesterol-lowering, and some diabetes medicines.
  • Events such as extreme emotions, surprise, and a slow heart rate during sleep.
• Congenital or genetic:
  • Children with genetic mutation or inheritance of abnormal gene codes for the ion channels may be diagnosed early in infancy due to a seizure episode.
  • Boys by the age of 15 years are more prone than girls to have a dangerous cardiac episode caused by LQTS.
  • Some people with mild LQTS may not show any symptoms although they may have family members who have LQTS.

Depending on the type of ion channel abnormalities, LQTS is classified into LQT1, LQT2, LQT3, LQT4, and LQT5. People with LQT3 have the highest risk of life-threatening arrhythmias.

What are the risks and triggers of LQTS?

People at risk of LQTS include:

• Children who are born deaf
• Blood relatives of family members detected with LQTS (first-degree relative)
• Children who have unexplained sudden death or syncope in family members
• People already diagnosed with LQTS who take medications known to prolong the QT interval

Certain factors can trigger the condition, including:

• Electrolyte imbalance:
  • Hypokalemia (potassium deficiency)
  • Hypomagnesaemia (magnesium deficiency)
  • Hypocalcemia (calcium deficiency)
• Malnutrition
• Hypothyroidism
• History of a stroke or heart disease (heart failure, heart attack, left ventricular hypertrophy, or bradycardia)
• Certain medications

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What are the symptoms of LQTS?

Most of the time, people with Long QT syndrome do not show any symptoms. It is detected on an electrocardiogram done for any other reason.

Some people may present with symptoms that first appear during the early teen years including:

• Palpitations (fluttering in the chest)
• Seizure-like activity (caused by lack of blood flow to the brain)
• Syncope (dizziness or fainting episode)
• Sudden cardiac arrest

What is the significance of QT prolongation?

Long QT syndrome has gained clinical importance because prolongation of this interval can predispose to a potentially fatal ventricular arrhythmia known as torsades de pointes (a life-threatening form of ventricular tachycardia).

In this, the ventricles beat very fast (more than 200 times per minute) and irregularly, resulting in a sudden drop in blood pressure that may persist, leading to ventricular fibrillation and sudden cardiac death.

Is QT prolongation serious?

Long QT syndrome (LQTS) increases the risk of abnormal heart rhythms, including the life-threatening arrhythmia torsades de pointes, which may result in syncope (fainting) or sudden cardiac death.

Fortunately, LQTS is a rare medical condition that can be passed on from generation to generation.

The risk of having an abnormal heart rhythm that may lead to fainting or sudden cardiac arrest may never go away. However, it may lessen with age.

How is LQTS treated?

Long QT syndrome is a lifelong condition, and its treatment may depend on the type and severity of symptoms:

• Avoiding triggering factors such as intense exercise and swimming, taking triggering medications, and treatment of any underlying disease or deficiency
• Medications such as beta-blockers and antiarrhythmic (medications that control the heart rhythm)
• Inserting a pacemaker or an implantable cardioverter–defibrillator