FCPS Paediatrics TOACS · Sick Sinus Syndrome

✅ Candidate's answer:
• ECG findings:
  - Sinus bradycardia – heart rate <60 bpm for age (45 bpm in this adolescent).
  - Sinus pauses – >2-3 seconds, indicating sinus node dysfunction.
  - Alternating tachycardia – episodes of atrial tachycardia or atrial flutter (tachy-brady syndrome).
  - Variable PR intervals – may indicate AV node involvement.
  - Junctional escape beats – may be present during sinus pauses.
• Diagnosis: Sick Sinus Syndrome (SSS) – also known as tachy-brady syndrome.
• Tachy-brady pattern: Alternating episodes of bradycardia (sinus bradycardia, pauses) and tachycardia (atrial arrhythmias such as atrial flutter, atrial fibrillation, or SVT). This is a hallmark of sick sinus syndrome.

✅ Candidate's answer:
• Causes of Sick Sinus Syndrome in children:
  1️⃣ Post-surgical congenital heart disease: Most common cause in children.
    - Fontan procedure (any type – lateral tunnel, extracardiac conduit).
    - Mustard or Senning procedure (atrial switch for d-TGA) – high incidence of sinus node dysfunction due to atrial suture lines.
    - Repaired ASD – sinus node damage during surgery.
    - Repaired VSD – less common.
  2️⃣ Cardiomyopathy: Dilated cardiomyopathy, hypertrophic cardiomyopathy.
  3️⃣ Channelopathies: SCN5A mutations (progressive cardiac conduction disease, Brugada syndrome, LQTS3).
  4️⃣ Drugs: Beta-blockers, calcium channel blockers, digoxin, antiarrhythmics.
  5️⃣ Infiltrative diseases: Myocarditis, sarcoidosis (rare).
  6️⃣ Genetic: NKX2-5 mutations (ASD + AV block + SSS).
  7️⃣ Idiopathic: Primary sinus node dysfunction (rare).
• Most common associated CHD: Fontan, Mustard, and Senning procedures – up to 50% of patients develop SSS over time.

✅ Candidate's answer:
• Why SSS occurs after Fontan:
  - Surgical injury: The sinus node is located near the superior vena cava (SVC) – atrial cannulation and suture lines can damage the sinus node or its blood supply.
  - Hemodynamic changes: Elevated central venous pressure, atrial stretch, and chronic volume/pressure overload can affect sinus node function.
  - Atrial scarring: Fibrosis from prior surgeries creates a substrate for reentry and sinus node dysfunction.
  - Time-dependent: SSS is a progressive complication; incidence increases with time post-Fontan.
• Incidence:
  - At 10 years post-Fontan: ~20-30% of patients develop SSS or atrial arrhythmias.
  - At 20 years: ~40-50% develop SSS or tachyarrhythmias.
  - Fontan type: Lateral tunnel and extracardiac Fontan have similar rates of SSS.
• Impact: SSS increases the risk of thromboembolism, heart failure, and Fontan failure.

✅ Candidate's answer:
• Symptoms of SSS:
  - Bradycardia-related symptoms:
    - Syncope or near-syncope (due to prolonged pauses).
    - Dizziness, lightheadedness.
    - Fatigue, exercise intolerance (heart rate fails to increase with activity).
    - Heart failure symptoms (if severe bradycardia leads to low cardiac output).
  - Tachycardia-related symptoms:
    - Palpitations (atrial flutter, SVT, atrial fibrillation).
    - Chest discomfort.
  - Variable symptoms: "Tachy-brady" pattern – episodes of palpitations alternating with dizziness/syncope.
• In children:
  - Often presents with fatigue and exercise intolerance (decreased heart rate response).
  - Syncope (especially during exertion or emotional stress).
  - Palpitations – may be described as "racing heart."
  - May be asymptomatic (incidental ECG finding) – but needs evaluation.

✅ Candidate's answer:
• Diagnosis of SSS:
  1️⃣ ECG: Sinus bradycardia, sinus pauses (>2-3 seconds), sinus arrest, junctional escape rhythm.
  2️⃣ Holter monitoring (24-48 hrs): Essential to capture episodic bradycardia, pauses, and tachyarrhythmias. Detects the "tachy-brady" pattern.
  3️⃣ Exercise stress test: Assesses heart rate response to exercise – failure to increase heart rate (chronotropic incompetence) is a sign of SSS.
  4️⃣ Ambulatory rhythm monitoring: For infrequent symptoms (event monitor, implantable loop recorder).
  5️⃣ Echocardiogram: To exclude structural heart disease, assess ventricular function, and evaluate for Fontan complications.
• Role of Holter: Detects pauses >3 seconds, atrial arrhythmias, and the relationship between symptoms and rhythm.
• Role of exercise testing: Chronotropic incompetence (HR fails to reach 80% of predicted max) is a marker of sinus node dysfunction.

✅ Candidate's answer:
• Acute management of symptomatic bradycardia/pauses:
  1️⃣ Atropine: 0.02 mg/kg IV (max 0.5 mg) – may improve heart rate if vagal-mediated.
  2️⃣ Isoproterenol: Infusion (0.05-1 mcg/kg/min) – increases heart rate temporarily.
  3️⃣ Temporary transcutaneous or transvenous pacing: If symptomatic (syncope, hypotension, heart failure).
  4️⃣ Treat underlying cause: Correct electrolyte abnormalities, adjust medications (beta-blockers, digoxin).
• If the patient has atrial tachycardia with rapid ventricular rate:
  - Rate control: Beta-blockers (esmolol, metoprolol), digoxin (avoid in WPW).
  - Anticoagulation: If atrial flutter or atrial fibrillation >48 hours, consider TEE-guided cardioversion or anticoagulation (warfarin, DOAC) for 3-4 weeks.
  - Elective cardioversion: If unstable or refractory.
• Pacemaker: For persistent symptomatic bradycardia.

✅ Candidate's answer:
• Indications for pacemaker in SSS (AHA/ACC guidelines):
  1️⃣ Symptomatic bradycardia – syncope, near-syncope, dizziness, exercise intolerance directly attributable to bradycardia.
  2️⃣ Sinus pauses >3 seconds with symptoms (or >5 seconds even asymptomatic).
  3️⃣ Chronotropic incompetence – failure to increase heart rate with exercise causing symptoms.
  4️⃣ Tachy-brady syndrome – if treatment of tachycardia (ablation, antiarrhythmics) is needed, pacing may be required to prevent bradycardia.
  5️⃣ Post-surgical SSS (Fontan, Mustard) – if symptomatic and no reversible cause.
  6️⃣ Asymptomatic patients with high-grade block – no pacemaker indicated unless symptoms.
• Pacemaker type: DDDR (dual-chamber rate-responsive) is preferred to maintain AV synchrony and improve exercise tolerance.
• In Fontan patients: Epicardial leads often needed; rate-responsive pacing important.

✅ Candidate's answer:
• Atrial flutter/fibrillation in SSS (Fontan patients):
  - High risk of thromboembolism – due to stagnant flow, atrial stasis, and intracardiac shunts (fenestrations).
  - Anticoagulation indicated if:
    - Atrial flutter/fibrillation >48 hours duration.
    - Prior thromboembolism.
    - Fenestrated Fontan – higher risk of paradoxical embolism.
    - Mechanical valve or prior stroke.
• Anticoagulation options:
  - Warfarin: Target INR 2-3 (for Fontan patients).
  - DOACs (Direct oral anticoagulants): Apixaban, rivaroxaban – emerging use in adult congenital heart disease, but limited pediatric data.
  - Heparin/LMWH: For acute anticoagulation or bridging.
  - Aspirin: Not sufficient for atrial arrhythmias in Fontan patients.
• Cardioversion: If atrial flutter, may need TEE-guided cardioversion if duration >48 hours.

✅ Candidate's answer:
• Rate control for atrial tachyarrhythmias:
  1️⃣ Beta-blockers: Metoprolol, atenolol, or propranolol – first-line for rate control and to reduce symptoms.
  2️⃣ Digoxin: Can be used for rate control in atrial flutter, but avoid in WPW.
  3️⃣ Calcium channel blockers: Verapamil or diltiazem – for rate control (avoid in WPW).
  4️⃣ Class Ic antiarrhythmics: Flecainide – for rhythm control in atrial flutter (caution in structural heart disease).
  5️⃣ Class III antiarrhythmics: Amiodarone or sotalol – for rhythm control (reserve for refractory cases).
• Rhythm control vs rate control:
  - Rate control: Preferred if asymptomatic or well-tolerated.
  - Rhythm control: If symptoms are severe, consider catheter ablation of atrial flutter.
• Ablation: For atrial flutter (cavotricuspid isthmus-dependent or intra-atrial reentry) – can reduce arrhythmia burden.

✅ Candidate's answer:
• Catheter ablation is an adjunctive therapy for SSS – it does not cure SSS but can treat associated tachyarrhythmias.
• Indications for ablation in SSS:
  1️⃣ Atrial flutter (cavotricuspid isthmus-dependent): Highly effective (>90% success).
  2️⃣ Atrial fibrillation: Pulmonary vein isolation may reduce episodes (limited pediatric data).
  3️⃣ SVT (WPW, AVNRT): If associated with palpitations.
  4️⃣ Recurrent tachycardia despite medical therapy – especially if causing symptoms or Fontan failure.
• Important: Ablation may exacerbate bradycardia – often pacemaker is needed after ablation (since bradycardia may become more pronounced).
• In Fontan patients: Ablation of atrial flutter is often performed to reduce arrhythmia burden and improve Fontan hemodynamics.

✅ Candidate's answer:
• Genetic mutations associated with SSS:
  1️⃣ SCN5A: Causes progressive cardiac conduction disease (Lenègre disease), Brugada syndrome, LQTS3, and SSS.
  2️⃣ HCN4: Mutations in the pacemaker channel – cause familial SSS.
  3️⃣ NKX2-5: ASD + AV block + SSS.
  4️⃣ MYH6: Atrial septal defects and sinus node dysfunction.
  5️⃣ GATA4: Congenital heart disease and sinus node dysfunction.
  6️⃣ TBX5 (Holt-Oram): ASD, upper limb anomalies, and conduction disease.
• Clinical implications: Genetic testing is indicated in patients with SSS and a family history of conduction disease, sudden death, or syndromic features. Cascade screening for family members.

✅ Candidate's answer:
• Complications of untreated SSS:
  1️⃣ Syncope and falls – due to prolonged pauses → injury.
  2️⃣ Heart failure – due to bradycardia (low cardiac output) and tachyarrhythmias.
  3️⃣ Thromboembolism – atrial arrhythmias → clot formation → stroke or systemic embolism.
  4️⃣ Fontan failure – in patients with single ventricle, arrhythmias can lead to protein-losing enteropathy, plastic bronchitis, and heart failure.
  5️⃣ Sudden death – rare but can occur with severe bradycardia or if atrial fibrillation degenerates to VF (with WPW).
  6️⃣ Progression of arrhythmias – SSS is a progressive disease; bradycardia and tachyarrhythmias worsen over time.

✅ Candidate's answer:
• Sports participation in SSS (AHA/ACC guidelines):
  - Symptomatic SSS: No competitive sports until evaluated and treated.
  - With pacemaker: Can participate in low-to-moderate intensity non-contact sports (swimming, jogging, tennis, golf).
  - Avoid competitive sports if patient has:
    - Uncontrolled atrial arrhythmias.
    - Hemodynamically significant pauses (even with pacemaker).
  - With Fontan: Avoid contact sports – risk of chest trauma and Fontan failure.
  - Shared decision-making: Discuss risks and benefits. Most patients can lead active lives with proper management.

✅ Candidate's structured answer:
• “You have a condition called Sick Sinus Syndrome – the natural pacemaker of the heart (the sinus node) is not working properly. Sometimes it beats too slowly, and sometimes it beats too fast – this is called 'tachy-brady' syndrome.”
• “This condition is commonly seen in patients who have had the Fontan procedure, and it is a known long-term complication. We have excellent treatments to manage it.”
• “For the slow heart rate, you may need a pacemaker – a small device that will help your heart beat at a normal rate. For the fast heart rate, we may use medications (beta-blockers) or consider a procedure called ablation to stop the fast rhythms.”
• “You will need to take blood thinners (anticoagulation) to prevent stroke, because the fast rhythms can lead to clot formation.”
• “You should avoid competitive sports but can still lead an active life with low-to-moderate intensity activities. We will follow you regularly in the cardiology clinic.”
• “We will help you transition to adult cardiology care when the time comes. You are not alone – we will support you every step of the way.”