Overview
Definition:
Prolonged QT syndrome (LQTS) is a disorder of cardiac repolarization, characterized by a prolonged QT interval on the electrocardiogram
This can lead to life-threatening ventricular arrhythmias, such as Torsades de Pointes, which may manifest with symptoms mimicking seizures, including syncope and generalized tonic-clonic movements
Differentiating these from true epileptic seizures is crucial for appropriate management.
Epidemiology:
Congenital LQTS affects approximately 1 in 2,000 to 1 in 30,000 individuals
Acquired LQTS is more common and can be caused by medications, electrolyte imbalances, or cardiac conditions
Pediatric syncope is a common presentation, with seizures being a significant differential diagnosis
Identifying LQTS as a cause of syncope-like episodes is vital for preventing sudden cardiac death.
Clinical Significance:
Misdiagnosis can lead to delayed or incorrect treatment
Unrecognized LQTS can result in recurrent syncope, neurological injury from falls, and importantly, sudden cardiac death
Prompt and accurate differentiation is essential for initiating life-saving cardiac management and preventing neurological sequelae.
Clinical Presentation
Symptoms:
Syncope, often precipitated by emotional stress, exercise, or auditory stimuli
Seizure-like activity, including tonic-clonic movements, eye deviation, and altered consciousness
Palpitations
Family history of sudden unexplained death or syncope
Absence of post-ictal confusion typically seen in seizures
Prodromal symptoms may be absent or minimal.
Signs:
Bradycardia or irregular heart rhythm
Hypotension
Neurological examination may be normal or show transient focal deficits if related to hypoperfusion
Physical findings during a witnessed event may include opisthotonos, myoclonus, or apnea, mimicking an epileptic seizure
Documenting the event with video-EEG and ECG is invaluable.
Diagnostic Criteria:
Prolonged QT interval on ECG (corrected QT [QTc] > 450-460 ms in males, > 470-480 ms in females)
Presence of Torsades de Pointes
Clinical criteria including syncope or seizures, congenital LQTS gene mutations, or family history
Absence of a clear epileptic origin on EEG is supportive of a cardiac cause.
Diagnostic Approach
History Taking:
Detailed history of the event: precipitating factors, duration, specific movements, witness accounts of any cyanosis or irregular breathing
Past medical history, especially cardiac or neurological conditions
Family history of syncope, seizures, arrhythmias, or sudden unexplained death
Review of all medications, including new prescriptions or over-the-counter drugs known to prolong the QT interval
Electrolyte balance history.
Physical Examination:
Comprehensive cardiovascular examination, assessing for murmurs, gallops, and peripheral pulses
Neurological examination to assess for focal deficits, cranial nerve palsies, and reflexes
Careful examination for any dysmorphic features suggestive of congenital syndromes (e.g., Romano-Ward, Jervell and Lange-Nielsen syndromes).
Investigations:
Electrocardiogram (ECG): Essential for measuring QT interval and detecting arrhythmias
Serial ECGs may be needed
Holter monitoring: To capture intermittent arrhythmias
Cardiac MRI: To rule out structural heart disease
Echocardiogram: To assess cardiac function and rule out structural abnormalities
Electroencephalogram (EEG): Crucial to differentiate from true seizures
normal EEG during or between events is highly suggestive of a non-epileptic origin
Genetic testing: For confirmation of specific LQTS subtypes and genetic counseling.
Differential Diagnosis:
Epileptic seizures: Differentiated by EEG findings and typical post-ictal state
Vasovagal syncope: Usually characterized by prodromal symptoms and less frequent seizure-like activity
Orthostatic hypotension: Less likely to present with typical LQTS-related movements
Other channelopathies or arrhythmias
Psychogenic non-epileptic seizures (PNES): May mimic both syncope and seizures but often lack ECG abnormalities and have distinct behavioral patterns.
Management
Initial Management:
Immediate resuscitation if cardiorespiratory arrest occurs
Continuous ECG and vital sign monitoring
Withdrawal of offending medications known to prolong QT
Correction of electrolyte imbalances (hypokalemia, hypomagnesemia, hypocalcemia).
Medical Management:
Beta-blockers: Propranolol or nadolol are first-line agents for most LQTS types to reduce adrenergic stimulation and catecholamine-induced arrhythmias
Specific drug dosages vary by LQTS type and patient age
e.g., Propranolol 2-4 mg/kg/day divided q6-8h
Sodium channel blockers (e.g., flecainide) may be considered for specific LQTS types
Avoid QT-prolonging medications
Magnesium sulfate infusion for Torsades de Pointes.
Surgical Management:
Implantable cardioverter-defibrillator (ICD): Indicated for patients with recurrent syncope or documented life-threatening ventricular arrhythmias despite optimal medical therapy
Left cardiac sympathetic denervation (LCSD): A surgical option for refractory LQTS, particularly in symptomatic individuals who are not candidates for ICD or have failed medical therapy.
Supportive Care:
Patient and family education on LQTS, triggers to avoid, and emergency management
Regular follow-up with a pediatric cardiologist and neurologist
Development of an emergency action plan
Counseling regarding genetic implications for family members.
Complications
Early Complications:
Sudden cardiac death (SCD)
Recurrent syncope or near-syncope
Neurological injury secondary to syncope (e.g., falls, head trauma).
Late Complications:
Chronic arrhythmias
Malfunction or inappropriate shocks from ICD
Post-denervation syndrome following LCSD
Psychological impact of living with a life-threatening condition.
Prevention Strategies:
Strict adherence to beta-blocker therapy
Regular ECG and clinical monitoring
Genetic counseling and screening of at-risk family members
Avoidance of known QT-prolonging drugs and triggers
Prompt treatment of electrolyte imbalances.
Prognosis
Factors Affecting Prognosis:
Specific LQTS genotype
Severity of QT prolongation
History of syncope or aborted SCD
Adherence to medical therapy
Presence of trigger factors
Family history of SCD.
Outcomes:
With appropriate management, including beta-blockers and avoidance of triggers, many individuals with LQTS can live normal or near-normal lives
Patients with high-risk genotypes or a history of SCD have a poorer prognosis and often require ICD implantation
Risk of SCD is significantly reduced with effective treatment.
Follow Up:
Regular cardiology and neurology follow-up is essential
Annual or biannual ECGs and clinical assessments
Holter monitoring as indicated
ICD checks if applicable
Education for patients and families on recognizing warning signs and seeking immediate medical attention.
Key Points
Exam Focus:
Differentiating cardiac syncope from epileptic seizures is critical
LQTS predisposes to Torsades de Pointes, a polymorphic VT
Beta-blockers are the mainstay of medical therapy for most LQTS types
Avoidance of QT-prolonging drugs is paramount
ICD implantation for high-risk patients.
Clinical Pearls:
Always consider LQTS in a child with recurrent syncope or seizure-like activity, especially if triggered by exercise, stress, or auditory stimuli
A family history of unexplained sudden death in young individuals should raise suspicion for LQTS
Video-EEG and ECG correlation are key for diagnosis
Drug-induced LQTS is a common and preventable cause.
Common Mistakes:
Treating LQTS-induced seizure-like activity with antiepileptic drugs without ruling out a cardiac cause
Failing to recognize QT prolongation on ECG
Prescribing QT-prolonging medications in patients with known or suspected LQTS
Inadequate follow-up and monitoring of patients with LQTS.