Overview
Definition:
Long QT syndrome (LQTS) is a disorder of cardiac repolarization characterized by a prolonged QT interval on the electrocardiogram, predisposing individuals to potentially life-threatening ventricular arrhythmias, specifically torsades de pointes (TdP)
It can be congenital (genetic) or acquired.
Epidemiology:
Congenital LQTS (cLQTS) affects approximately 1 in 2,000 to 1 in 5,000 individuals
The incidence of acquired LQTS is higher, largely driven by drug-induced QT prolongation
It is a significant cause of sudden cardiac death (SCD) in young, otherwise healthy individuals
Certain genetic subtypes are more prevalent in specific populations.
Clinical Significance:
LQTS represents a critical medical condition in pediatrics due to its association with syncope, seizures, and sudden cardiac death
Early diagnosis, appropriate risk stratification, and timely management, including the judicious use of beta-blockers and careful sports counseling, are paramount to preventing adverse events and improving long-term outcomes for affected children.
Clinical Presentation
Symptoms:
Syncope, often triggered by exercise, emotional stress, or auditory stimuli
Seizures, which may be mistaken for epilepsy
Palpitations
Presyncope
Sudden cardiac arrest (rarely the first presentation)
Asymptomatic individuals with a prolonged QT interval identified incidentally.
Signs:
A prolonged corrected QT interval (QTc) on ECG, typically >460 ms in males and >480 ms in females, though thresholds can vary
Bradycardia, especially during sleep
Other findings may be non-specific or related to the underlying cause of acquired LQTS.
Diagnostic Criteria:
The clinical diagnosis of LQTS is based on a combination of ECG findings (QTc duration, T-wave morphology, presence of U waves), clinical history (syncope, SCD in relatives), and genetic testing
The Schwartz score or similar risk stratification tools are often used
For example, a QTc > 480 ms with syncope scores highly
Genetic testing confirms specific gene mutations in cLQTS.
Diagnostic Approach
History Taking:
Detailed family history of syncope, arrhythmias, SCD, or unexplained deaths at a young age
Personal history of syncope, near-drowning, or seizures, noting triggers (exercise, emotion, sleep, auditory)
Medications and electrolyte status in suspected acquired LQTS
History of hearing loss in Jervell and Lange-Nielsen syndrome.
Physical Examination:
General physical examination focusing on neurological status and signs of underlying conditions
Auscultation for murmurs
Assess for congenital anomalies
A resting 12-lead ECG is crucial for measuring the QT interval and assessing T-wave morphology
Holter monitoring can capture intermittent arrhythmias.
Investigations:
Resting 12-lead ECG: measure QTc, evaluate T-wave morphology (e.g., broad biphasic T waves in LQTS1, flattened T waves in LQTS2)
Stress testing (with caution and appropriate monitoring): can unmask QT prolongation or provoke arrhythmias
Holter monitoring: assess for arrhythmias and QT variability
Echocardiography: to rule out structural heart disease
Genetic testing: for specific LQTS-associated genes (KCNQ1, KCNH2, SCN5A, etc.) in suspected cLQTS
Serum electrolytes (potassium, magnesium, calcium) to rule out acquired causes.
Management
Initial Management:
For acquired LQTS, identify and discontinue offending agents (drugs, electrolyte imbalances)
Correct electrolyte abnormalities
Immediate risk stratification for symptomatic patients
In cases of torsades de pointes with hemodynamic compromise, defibrillation is indicated.
Medical Management:
Beta-blockers (e.g., propranolol, nadolol) are the cornerstone of therapy for symptomatic cLQTS, particularly LQTS1 and LQTS2
Dosing is weight-based and titrated to reduce symptoms and arrhythmia burden
For LQTS3, sodium channel blockers may be considered in select cases
Magnesium infusion can be used acutely for TdP.
Surgical Management:
Implantable cardioverter-defibrillator (ICD) implantation is indicated for high-risk patients with cLQTS, including those with a history of syncope despite beta-blocker therapy, aborted SCD, or very prolonged QTc
Left cardiac sympathetic denervation (LCSD) is an adjunct therapy for refractory cases or intolerance to beta-blockers.
Supportive Care:
Patient and family education regarding triggers, adherence to medication, and emergency protocols
Regular follow-up with a pediatric cardiologist specializing in arrhythmias
Genetic counseling for affected families
Monitoring for drug interactions and side effects of beta-blockers.
Sports Counseling
Risk Assessment:
Sports participation for individuals with LQTS requires a careful, individualized risk assessment
Factors include LQTS genotype, severity of QT prolongation, presence and frequency of symptoms, family history, and response to therapy
The risk of exercise-induced arrhythmias is genotype-dependent.
Recommendations By Genotype:
LQTS1: High risk during exertion and with emotional stress
Generally, participation in low-intensity sports may be considered with strict adherence to beta-blocker therapy and ECG monitoring
High-intensity competitive sports are usually contraindicated
LQTS2: Similar risks to LQTS1, particularly with auditory stimuli and exertion
LQTS3: Lower risk during exertion, but higher risk during sleep/rest
Beta-blockers are less effective, and ICD may be more commonly indicated
Competitive sports often restricted.
General Guidelines:
Participation in organized competitive sports is often restricted or requires careful consideration and close medical supervision
If cleared, patients must remain on optimal beta-blocker therapy, avoid dehydration and electrolyte imbalances, and be educated about recognizing and responding to symptoms
Regular ECG monitoring and stress testing (under supervision) are essential
Absence of symptoms on optimal therapy for a prolonged period is a prerequisite for considering clearance.
Complications
Early Complications:
Torsades de pointes, leading to syncope or sudden cardiac arrest
Drug side effects from beta-blockers (bradycardia, hypotension, bronchospasm, fatigue)..
Late Complications:
Recurrent syncope or seizures despite treatment
Device-related complications if an ICD is implanted (infection, lead malfunction)
Ineffective or poorly tolerated medical therapy leading to persistent risk
Sudden cardiac death.
Prevention Strategies:
Strict adherence to beta-blocker therapy
Avoiding known triggers (certain medications, electrolyte imbalances, intense exercise in susceptible genotypes)
Early identification and management of symptomatic individuals
Appropriate use of ICD in high-risk patients
Genetic screening of at-risk family members.
Prognosis
Factors Affecting Prognosis:
Genotype of LQTS (e.g., LQTS3 generally has a worse prognosis)
Presence and severity of symptoms (syncope, aborted SCD)
Family history of SCD
Response to beta-blocker therapy
Adherence to medical recommendations
Effective ICD function if implanted.
Outcomes:
With appropriate management, including beta-blockers and judicious use of ICDs, the prognosis for individuals with LQTS can be significantly improved, with a marked reduction in the risk of SCD
However, some individuals may still experience breakthrough events or have a less favorable outcome depending on the factors above.
Follow Up:
Lifelong follow-up with a pediatric cardiologist specializing in arrhythmias is essential
This includes regular clinical assessments, ECG monitoring, Holter monitoring, and possibly serial stress testing
Monitoring for medication adherence and side effects is crucial
Genetic counseling and cascade screening of family members are important components of long-term management.
Key Points
Exam Focus:
Recognize LQTS on ECG (prolonged QTc)
Differentiate congenital vs
acquired LQTS
Understand the role of beta-blockers (especially propranolol/nadolol) in cLQTS management
Differentiate management based on LQTS genotype (e.g., exercise trigger in LQTS1 vs
rest trigger in LQTS3)
Indications for ICD and LCSD
Crucial aspects of sports counseling.
Clinical Pearls:
Always check electrolytes (K, Mg, Ca) and review medications in patients with a prolonged QT interval
Family history is critical for diagnosing cLQTS
Syncope in a young person, especially with exercise or an auditory trigger, should raise suspicion for LQTS
Beta-blockers are prophylactic, not acutely corrective for TdP.
Common Mistakes:
Mistaking LQTS for epilepsy or vasovagal syncope
Neglecting family history
Inadequate follow-up and monitoring
Prescribing beta-blockers without proper risk stratification and ongoing assessment
Failing to counsel comprehensively on sports participation based on genotype and risk.