Long QT syndrome

Overview

Long QT syndrome (LQTS) is a rare heart rhythm disorder that affects the electrical activity of the heart. It is characterized by a prolonged QT interval on an electrocardiogram (ECG), which reflects delayed repolarization of the heart's ventricles. This delay can lead to episodes of irregular heartbeats (arrhythmias), fainting, seizures, or even sudden cardiac death. LQTS can be inherited (congenital) or acquired later in life due to medications or other medical conditions. With proper diagnosis and management, the risk of serious complications can be significantly reduced.

Causes

Long QT syndrome can be either congenital (inherited) or acquired:

1. Congenital LQTS:

• Caused by mutations in genes that regulate cardiac ion channels (e.g., KCNQ1, KCNH2, SCN5A)

• Inherited in an autosomal dominant or autosomal recessive pattern

• Subtypes include LQT1, LQT2, and LQT3, each with distinct triggers and risks

2. Acquired LQTS:

• Triggered by certain medications (e.g., antiarrhythmics, antibiotics, antipsychotics)

• Electrolyte imbalances such as low potassium, magnesium, or calcium

• Medical conditions like anorexia nervosa, bradycardia, or hypothyroidism

Symptoms

Symptoms of Long QT syndrome may vary, and some individuals remain asymptomatic. When present, symptoms can include:

• Syncope (fainting) – often triggered by exercise, emotional stress, or sudden noises

• Seizures – due to insufficient blood flow to the brain during arrhythmias

• Palpitations – sensation of rapid or irregular heartbeats

• Sudden cardiac arrest – in severe or untreated cases

Symptoms often begin in childhood or adolescence, particularly in congenital forms. Some individuals may only discover the condition through family screening or after a cardiac event.

Diagnosis

Diagnosis of Long QT syndrome involves a combination of clinical evaluation, ECG findings, and genetic testing. Common diagnostic tools include:

• Electrocardiogram (ECG) – measures the QT interval; a corrected QT (QTc) > 450 ms in men and > 460 ms in women is considered prolonged

• Exercise stress test – to observe QT behavior during physical activity

• Holter monitor – continuous ECG recording to detect intermittent abnormalities

• Genetic testing – to identify mutations in known LQTS-associated genes

• Family history – assessment of unexplained sudden deaths or fainting episodes in relatives

Treatment

Treatment for Long QT syndrome aims to prevent life-threatening arrhythmias and manage symptoms. Options include:

• Beta-blockers – first-line therapy to reduce the heart's response to adrenaline and prevent arrhythmias (e.g., propranolol, nadolol)

• Implantable cardioverter-defibrillator (ICD) – used in high-risk individuals or those with a history of cardiac arrest

• Left cardiac sympathetic denervation (LCSD) – a surgical option for patients not responsive to medication

• Medication adjustment – avoiding drugs that prolong the QT interval

• Lifestyle modifications – including avoidance of intense physical exertion, loud noises (in LQT2), and stress triggers

Prognosis

The prognosis for individuals with Long QT syndrome depends on the subtype, presence of symptoms, and adherence to treatment. With appropriate medical management and lifestyle precautions, most people with LQTS can lead normal, active lives. However, untreated or undiagnosed cases can lead to sudden cardiac death, especially in young individuals. Early detection through genetic screening and family history evaluation is essential for reducing risks and improving long-term outcomes.