Symptoms of Long QT Syndrome (LQTS)

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Those with Long QT Syndrome (LQTS) are prone to sudden onset dangerous irregularities of heart rate and rhythm and this may lead to arrhythmias and even sudden cardiac death. LQTS is an inherited condition that begins at birth and lasts till death.

Often the symptoms begin during the pre-teen years but sometimes the symptoms may also be seen during childhood.

The symptoms of LQTS usually vary even within families of sufferers. Symptoms may differ depending on whether the person is male or female, their age, and the length of their QT interval. Some people may have a genetic alteration for LQTS but never develop symptoms.

Symptoms of LQTS include unexplained fainting, unexplained seizures and so forth. (1-8)

Unexplained fainting

This may occur due to the fact that a prolonged gap between two heart beats (manifested as the long duration between the QT) is leading to delayed blood supply from the ventricles. This deprives the brain of oxygen and leads to fainting.

Fainting may occur during physical or emotional stress. Sudden noises such as alarm clocks and doorbells can also act as triggers.

Usually there may be no dizziness, blurred vision or sweating or other warnings that are associated with usual fainting spells before the fainting attacks in LQTS.

However, some patients may complain of a fluttering or palpitation in the chest before the fainting spell. Fainting spells may last for a minute or two. These are called syncope.

Unexplained seizures

Sudden fainting spells may often be misdiagnosed as an epileptic seizure.

Unexplained drowning or near drowning

This may be seen in children who have a sudden fainting spell while swimming. This can be fatal.

Sudden cardiac arrest

Sudden cardiac arrest or sudden cardiac death. Sudden cardiac arrest occurs when the heart suddenly stops beating. This may lead to death within minutes unless treated.

People with LQTS have a 1 in 10 risk of sudden cardiac arrest or sudden cardiac death being the first sign of the disorder.

In one in three cases where death results the person appeared quite fit and healthy with no symptoms beforehand.

Symptoms of LQTS 3

Those with LQTS 3 develop an abnormal heart rhythm during sleep or right after waking. This type of LQTS is aggravated by a slow heart rate. These patients may wake up with a noisy gasping while sleeping or may suffer a fainting attack on waking.

Other symptoms of LQTS

Other symptoms of LQTS include dizziness and palpitations.

People who have long QT Syndrome are more likely to develop symptoms one or more of the following characteristics like earlier history of, fainting, seizures, or cardiac arrest, deafness, a QT interval of 0.55 second or longer etc.

Silent Long QT Syndrome

Up to 50% of people with Long QT Syndrome never have any symptoms. In these patients LQTS does not cause any signs or symptoms. This is called silent LQTS. This may be seen in the families of frank sufferers. This is the reason why physicians advise families of the patients to get tested for silent LQTS. These patients may manifest with a sudden cardiac arrest as the first symptom.

Further Reading

Last Updated: May 27, 2023

Dr. Ananya Mandal

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.


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