What Is Short QT Syndrome?

Overview

Short QT syndrome (SQTS) is a rare, life-threatening, inheritable condition of the heart characterised by abnormal short QT intervals on the electrocardiogram (ECG) and manifested by atrial and ventricular arrhythmias (irregular heartbeats).

Short QT Syndrome is a sporadic or autosomal dominant disorder (will be passed onto offspring) accompanied by increased cardiac repolarization.¹

Causes of short qt syndrome

As in other inherited arrhythmogenic diseases, several mutations have occurred in SQTS that affect the function of ions required to generate the cardiac action potential. These mutations cause either hyperfunction of the delayed rectifier potassium current or hypofunction of the calcium current, resulting in a shortening of the repolarization period and an increase in transmural dispersion of repolarization featuring the three periods: short QT interval, short atrial and ventricular effective refractory periods and hence making it more susceptible to atrial and ventricular fibrillation.²

SQTS is a “channelopathy” caused by changes in genes (mutations) encoding proteins forming potassium or calcium ion channels on the cardiac and neuronal cell membranes that are essential for the heart’s electro-mechanical function. The severity of the disease varies from one sibling to another. SQTS may be diagnosed in children if they show clear cardiac symptoms or if there is any suspected family history.

While assuming SQTS to be inheritable, cases in which a familiar history is absent may be due to spontaneous mutation during embryonic development.

SQTS is a genetic disease caused by mutations in multiple genes and occurs when a single copy of a non- or hyper-working gene is inherited from either parent. However, follow-up of patients with SQTS showed that only 20 to 30% may be explained by mutations in genes encoding potassium or calcium channels.

Genetic alterations encoding calcium or sodium channels have not been demonstrated to be a clear diagnosis of SQTS. 

Acquired SQTS is associated with hypercalcemia, hyperkalaemia, acidosis, etc.

Signs and symptoms of short qt syndrome

The most frequent and common clinical presentation of SQTS is cardiac arrest.

Syncope was the first presenting symptom in 24% of cases; up to 31% of patients referred to palpitations, and atrial fibrillation was present in more than 80% of them despite their young age.

Atrial fibrillation is one of the main findings of SQTS, and therefore, it is a preferred choice in the management of young patients with lone atrial fibrillation.

Men with idiopathic ventricular fibrillation show a shorter QT. Although it usually occurs in adults (median age 30 years), the presentation of age ranges from a few months to the sixth decade of life. In Short Qt Syndrome, there are no triggers that take place at rest or exercise.

Management and treatment for short qt syndrome

When you visit your cardiologist, your doctor could recommend: 

Implantable cardioverter defibrillator (ICD) -  It delivers an electric shock to your heart when it senses an irregular heartbeat.

Insertion of an implantable cardioverter-defibrillator is considered secondary prophylaxis (preventative measure) in a patient with Short QT Syndrome. However, primary prophylaxis is controversial and lacks sufficient data. Studies have shown that the insertion of an implantable cardioverter defibrillator saved many lives in patients with cardiac arrest and syncope. No shocks were delivered to patients without a history of either syncope or cardiac arrest.

Medications- Currently, quinidine is the only drug of choice. Alternatively, medicines like flecainide or ibutilide, propafenone, amiodarone, sotalol or beta-blockers such as metoprolol or carvedilol may also be recommended.⁴

Diagnosis of short qt syndrome

Short QT syndrome is a rare, life-threatening disease. Genetic screening is very important in the diagnosis of SQTS.

Establishing a definition of short QT syndrome (SQTS), including its symptomatology and QT-interval duration, is still a work in progress.

The role of genetic testing is limited in SQTS, as most patients who show symptoms might have an unknown genetic cause. 

Risk factors

Risk stratification is the main challenge in clinical assessment because Short Qt is a rare channelopathy. The only predictor of cardiac arrest in a patient with SQTS is the family history or previous cardiac arrest. 

Complications

An implantable cardiac defibrillator is considered the most effective measure in short QT syndrome. Inappropriate shock is a common complication observed in patients with ICD.

FAQs

How can I prevent short qt syndrome?

Prevention is not possible in short Qt syndrome, since it is caused by a genetic mutation.

Consult a cardiologist if you have an SQTS history. A cardiologist would then monitor the condition of your heart health to help reduce complications such as cardiac death. 

What is the difference between short qt syndrome and long sq syndrome?

Short QT syndrome is an irregularly short QT interval, under 0.34 seconds, whereas long Qt syndrome is an irregularly long QT interval that exists over 0.45 seconds. To prevent complications, understanding QT interval is very important.⁵

How common is short qt syndrome?

The prevalence and prognosis may vary. SQTS can lead to sudden cardiac death. It is estimated that people with short QT syndrome have a 40% chance of sudden cardiac death by the age of 40, with the highest risk between ages 0 to 1 and 20 to 40 years old.

SQTS occurring in newborn to 1-year-old kids is known as sudden infant death syndrome. Because short QT syndrome is rare, researchers are still studying how short QT syndrome affects life expectancy.⁶

When should I see a doctor?

It is high time to visit your doctor or cardiologist when you have a family history of short QT syndrome, you notice palpitations or fatigue, or you have irregular heartbeats.

Summary

Short qt syndrome is a rare condition caused by a genetic mutation. It affects the electrical activity of the heart and can lead to life-threatening arrhythmias (abnormal heart rhythms).. The syndrome is to be monitored and treated with medications to prevent serious complications and sudden death. While there is no cure for this condition, early diagnosis and treatment can help reduce the risk of complications such as sudden cardiac death.

Bhashwati Deb Barma

Bachelor of Physiotherapy,M.S., Ramaiah Medical College, India

Bhashwati is a Physiotherapist with a firm grasp of Paediatric physiotherapy and is currently working with special children in the community.

She has 6 years of experience working in hospitals and non-profit organizations set up. As a writer by passion, she is putting up her practical and academic knowledge into her articles.

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