FCPS Paediatrics TOACS · Long QT Syndrome (LQTS)

✅ Candidate's answer:
• ECG findings:
  - Prolonged QT interval – QT length >0.44 seconds in children.
  - QTc (corrected QT) > 0.46 seconds – calculated using Bazett formula: QTc = QT / √(RR interval).
  - T wave abnormalities – broad-based, low-amplitude, notched T waves (LQT2), or long ST segment (LQT3).
• Normal QTc values:
  - Children: <0.44 seconds (440 ms).
  - Adolescents: <0.45 seconds (450 ms).
  - Borderline: 0.44-0.46 seconds.
  - Prolonged: >0.46 seconds (460 ms).
• Calculation: Measure QT interval from the beginning of the QRS to the end of the T wave. Use the longest QT in any lead (usually V2-V4).
• If QTc is >0.46 seconds, LQTS should be suspected.

✅ Candidate's answer:

Type	Gene	Ion Channel	Triggers	ECG Pattern
LQT1	KCNQ1	I_Ks (potassium)	Exercise / swimming	Broad-based T-wave
LQT2	KCNH2 (HERG)	I_Kr (potassium)	Emotion / auditory (alarm, phone)	Low-amplitude, notched T-waves
LQT3	SCN5A	I_Na (sodium) – gain of function	Sleep / rest	Long ST segment

• LQT1: Most common (40-50%) – exercise-induced syncope/cardiac arrest. Swimming is a classic trigger.
• LQT2: 30-40% – auditory triggers (alarm, phone, sudden noise), emotional stress, postpartum.
• LQT3: 5-10% – rest/sleep-related (high risk of death during sleep).
• Other types: LQT4-13 (rare).
• Jervell and Lange-Nielsen: LQT + sensorineural deafness (KCNQ1, KCNE1) – autosomal recessive.
• Andersen-Tawil: LQT + periodic paralysis + dysmorphic features (KCNJ2).
• Timothy syndrome: LQT + syndactyly + ASD (CACNA1C).

✅ Candidate's answer:
• The Schwartz score is a clinical diagnostic tool for Long QT Syndrome. Points are assigned based on ECG parameters, clinical history, and family history.
• Scoring system:
  - ECG (QTc):
    - ≥ 480 ms: 3 points
    - 460-479 ms: 2 points
    - 450-459 ms (male): 1 point
  - Clinical history:
    - Torsades de Pointes: 2 points
    - Syncope (with stress): 2 points
    - Syncope (without stress): 1 point
  - Family history:
    - First-degree relative with LQTS: 1 point
    - Sudden death < 30 years: 1 point
• Interpretation:
  - ≥ 4 points: High probability (diagnosis of LQTS).
  - 3 points: Intermediate probability (consider genetic testing).
  - ≤ 2 points: Low probability.
• Used in conjunction with genetic testing – not all LQTS patients have a positive genetic test (negative in ~25% of cases).

✅ Candidate's answer:
• Acute management of TdP with a pulse (stable):
  1️⃣ Magnesium sulfate: 25-50 mg/kg IV bolus over 15-30 minutes (max 2 g). This is the first-line treatment even if serum Mg is normal.
  2️⃣ Correct electrolytes:
    - Potassium: Target K+ > 4.5 mEq/L (IV potassium supplementation).
  3️⃣ Discontinue all QT-prolonging drugs – check for any medications that may have precipitated TdP.
  4️⃣ If heart rate is slow: Use isoproterenol or atrial pacing to increase heart rate (overdrive pacing).
  5️⃣ Lidocaine: May be used in refractory TdP.
• Pulseless TdP (cardiac arrest):
  - Follow PALS algorithm:
    - Defibrillation: 2 J/kg (if pulseless VT), then 4 J/kg.
    - Epinephrine: 0.01 mg/kg IV/IO every 3-5 minutes.
    - Amiodarone: 5 mg/kg IV for refractory VT/VF (caution in LQTS – may prolong QT further; consider lidocaine instead).
    - Magnesium: 25-50 mg/kg IV in pulseless arrest (when TdP suspected).

✅ Candidate's answer:
• Beta-blockers are the cornerstone of therapy for congenital LQTS (especially LQT1 and LQT2). They reduce the risk of cardiac events (syncope, TdP, SCD) by:
  - Reducing sympathetic tone and preventing arrhythmias triggered by exercise/emotion.
  - Shortening the QT interval in some patients.
• Preferred beta-blockers:
  - Propranolol (1-3 mg/kg/day divided TID) – non-selective, lipid-soluble, good CNS penetration. Preferred for LQT1 and LQT2.
  - Nadolol (1-2 mg/kg/day once daily) – long-acting, once-daily dosing, excellent for compliance.
  - Atenolol (1-2 mg/kg/day) – cardioselective, but less effective in LQT2 and LQT3.
• Propranolol is preferred because it is non-selective and has been shown to be more effective in LQT1 and LQT2.
• Beta-blockers are less effective in LQT3 – may need ICD placement.
• Compliance: Lifelong therapy – do not stop abruptly (risk of rebound arrhythmias).

✅ Candidate's answer:
• ICD is indicated for:
  1️⃣ Cardiac arrest survivors (aborted SCD) – secondary prevention.
  2️⃣ Recurrent syncope despite optimal beta-blocker therapy.
  3️⃣ High-risk genotypes: LQT3 (SCN5A) – higher risk of SCD; Jervell and Lange-Nielsen (high risk).
  4️⃣ QTc > 550 ms (especially in LQT1 and LQT2).
  5️⃣ Family history of SCD despite beta-blockers.
  6️⃣ Non-compliance with beta-blockers – ICD as backup.
• ICD implantation in children: Technical challenges (size, lead complications, battery life). Usually placed in older children/adolescents. Left-sided subcutaneous ICD (S-ICD) is an option in older children.
• Shared decision-making: Discuss with family the risks and benefits.

✅ Candidate's answer:
• Avoid QT-prolonging drugs – consult CredibleMeds list; especially macrolides, fluoroquinolones, antihistamines, psychotropics, antiarrhythmics.
• Avoid electrolyte disturbances: Prevent diarrhea/vomiting, treat hypokalemia/hypomagnesemia aggressively.
• Exercise restrictions (depending on genotype):
  - LQT1: Avoid competitive swimming, high-intensity exercise, and extreme physical exertion. Non-competitive exercise is allowed with precautions.
  - LQT2: Avoid sudden loud noises (alarms, phone ringtones, loud speakers).
  - LQT3: Avoid sleep deprivation and drugs that prolong QT during rest.
• General: Avoid dehydration (maintain fluid intake), treat fever promptly (fever can prolong QT in some LQT types).
• School: Inform teachers and coaches – child may need to take breaks during PE.
• Emergency plan: Family should know CPR and how to use an AED (if available).

✅ Candidate's answer:
• QT-prolonging drugs to avoid in LQTS patients:
  - Antibiotics: Macrolides (erythromycin, clarithromycin, azithromycin – lower risk), fluoroquinolones (ciprofloxacin, levofloxacin).
  - Antiarrhythmics: Class IA (quinidine, procainamide), Class III (sotalol, amiodarone – lower risk).
  - Psychotropics: Antipsychotics (haloperidol, risperidone), antidepressants (tricyclics, SSRIs – lower risk).
  - Antihistamines: Terfenadine, astemizole (withdrawn).
  - GI motility: Cisapride (withdrawn).
  - Antifungals: Fluconazole, ketoconazole, itraconazole.
  - Others: Ondansetron (anti-emetic), methadone, donepezil.
• Resources: CredibleMeds.org – comprehensive list of QT-prolonging drugs.
• Clinical pearl: Always check for drug interactions – many drugs prolong QT and increase risk of TdP.

✅ Candidate's answer:
• Family screening is essential because LQTS is inherited in an autosomal dominant pattern (except Jervell and Lange-Nielsen – autosomal recessive).
• First-degree relatives (parents, siblings) should undergo:
  - ECG screening – multiple ECGs (QTc may vary).
  - Exercise stress test – QT prolongation may be unmasked during exercise.
  - Holter monitoring – to detect QT prolongation at night.
  - Genetic testing (if a pathogenic variant is identified in the proband).
• Genetic testing in the proband: Identify the specific mutation (LQT1, LQT2, LQT3, etc.). If found, predictive testing is offered to at-risk relatives.
• If no mutation found: Clinical diagnosis is based on the Schwartz score (ECG findings, clinical history, family history).
• Genetic counseling: 50% risk for each child of an affected parent. Penetrance is variable – some carriers are asymptomatic.

✅ Candidate's answer:
• Cardiac syncope (LQTS/TdP):
  - Trigger: Exercise, emotion, loud noise, drugs.
  - Prodrome: Palpitations, dizziness, chest pain (less common).
  - During episode: Brief myoclonic jerks or stiffening (due to cerebral hypoperfusion), no post-ictal confusion (rapid recovery).
  - Recovery: Spontaneous, usually within 1-2 minutes.
• Seizure (epileptic):
  - Trigger: Often spontaneous, no specific trigger.
  - Prodrome: Aura (visual, olfactory) in some.
  - During episode: Tonic-clonic movements, cyanosis, tongue biting, incontinence.
  - Post-ictal: Confusion, lethargy, headache (lasting minutes to hours).
• Key feature: Normal ECG in seizure vs prolonged QT in LQTS.
• Diagnostic approach: ECG, Holter, echocardiogram, EEG (if suspicion of seizures).

✅ Candidate's answer:
• Hypokalemia (K+ < 3.5): Prolongs the QT interval and causes prominent U waves and ST depression. Increases the risk of TdP, especially in patients with LQTS.
• Hypocalcemia (Ca < 8.5): Prolongs the QT interval by prolonging the ST segment (the plateau phase of repolarization).
• Hyperkalemia (K+ > 5.5): Causes peaked (tented) T waves, wide QRS, and ultimately sine wave pattern (not primarily QT prolongation).
• Hypercalcemia: Shortens the QT interval.
• Clinical pearl: In LQTS patients, maintain K+ > 4.5 mEq/L and Mg > 2.0 mg/dL to reduce arrhythmia risk. Treat diarrhea/vomiting aggressively.

✅ Candidate's answer:
• Jervell and Lange-Nielsen (JLN) syndrome:
  - Autosomal recessive inheritance.
  - Associated with congenital sensorineural deafness.
  - Mutations: KCNQ1 (most common) or KCNE1 – both affect the I_Ks potassium channel.
  - Prognosis: High risk of sudden cardiac death (SCD) – more severe than Romano-Ward. ICD is often indicated early.
  - Treatment: Beta-blockers + ICD. Cochlear implants for deafness.
• Romano-Ward syndrome:
  - Autosomal dominant inheritance.
  - No deafness.
  - Mutations: KCNQ1, KCNH2, SCN5A, etc.
  - Less severe than JLN – but still carries risk of SCD.
• Clinical pearl: Any child with LQTS and deafness should be suspected of having JLN syndrome and requires aggressive management (ICD).

✅ Candidate's answer:
• Prognosis depends on:
  - Genotype: LQT1 and LQT2 have better outcomes with beta-blockers; LQT3 has higher risk of SCD, especially during sleep.
  - QTc length: QTc > 550 ms → higher risk.
  - Age at presentation: Syncope in childhood (especially < 10 years) → higher risk.
  - Gender: LQT2 – females have higher risk; LQT1 – males have higher risk before puberty.
• With treatment (beta-blockers):
  - Risk of SCD is reduced from ~50% (untreated) to < 5% with beta-blockers.
  - Patients with ICD: Risk of SCD is < 1% per year.
• Lifelong follow-up: Annual ECG, Holter, exercise stress test. Adjust beta-blocker doses with growth.
• Psychosocial support: Address anxiety about sudden death; encourage participation in age-appropriate activities with restrictions.

✅ Candidate's structured answer:
• “Your child has a condition called Long QT Syndrome – a rare, inherited heart rhythm disorder. It causes the heart to take a little longer to recharge between beats, which can lead to dangerous heart rhythms.”
• “The good news is that we have excellent treatments to prevent these dangerous rhythms. Your child will need to take a medication called a beta-blocker – it slows the heart and reduces the risk of these episodes.”
• “We will also test other family members (parents, siblings) because this condition can run in families. If they are at risk, we can start treatment early.”
• “Your child will need to avoid certain medications that can make the condition worse – we will give you a list. He or she should also avoid high-intensity sports or extreme exercise, but can still play and enjoy normal childhood with some precautions.”
• “It is very important that you never stop the medication without consulting us – sudden stopping can cause a rebound effect.”
• “We will see your child regularly (every 6-12 months) to adjust medications and monitor the heart. Most children with this condition live long, healthy lives with proper treatment.”