1. Definition and Epidemiology

Brugada syndrome (BrS) is a rare, inherited primary electrical disorder characterized by a distinctive electrocardiographic (ECG) pattern—classically coved-type ST-segment elevation in right precordial leads (V1–V3)—and an increased risk of sudden cardiac death (SCD) due to polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF), often during rest or sleep. The underlying structural heart is typically normal on echocardiography, cardiac MRI, and histopathology.

• Epidemiology:
  • Prevalence: ~1–5 per 10,000 in most populations; up to 12–50 per 10,000 in Southeast Asia (especially Thailand and Japan).
  • Male predilection: Male-to-female ratio of ~8:1 for symptomatic cases; males present earlier and more severely.
  • Age of onset: Symptomatic events most common between 30–50 years, though arrhythmic events have been reported in children and elderly.
• Genetics:
  • Inheritance is predominantly autosomal dominant with incomplete penetrance (~20–40% in carriers).
  • SCN5A loss-of-function mutations account for ~20–30% of clinical cases and up to 5–10% of de novo cases. This gene encodes the α-subunit of the cardiac sodium channel Na_v1.5, critical for phase 0 depolarization.
  • Other implicated genes (collectively explain <10% overall):
    • CACNA1C, CACNB2b (L-type calcium channel subunits)
    • SCN1B–SCN3B, SCN10A (sodium channel β-subunits and Na_v1.7)
    • AKAP9, FARP2, SLMAP, ZNF101 (involved in ion channel anchoring/expression regulation)
  • Recent genome-wide association studies (GWAS) suggest polygenic contributions and modifier effects influencing penetrance and phenotype expressivity.

2. Pathophysiology: The “Transmural Voltage Gradient” Hypothesis

BrS arises from an imbalance between inward (Na⁺, Ca²⁺) and outward (I_to, I_Kr) currents during early repolarization, particularly in the right ventricular outflow tract (RVOT) epicardium.

• Key mechanisms:
  • Reduced sodium channel function → attenuated phase 1 repolarization → accentuation of the transient outward potassium current (I_to) → accentuated transmural voltage gradient.
  • This creates a substrate for phase 2 reentry and spontaneous VF, especially under conditions that further suppress I_Na (e.g., fever, sodium channel-blocking drugs).
• Regional vulnerability: Epicardial cells in the RVOT may exhibit action potential alternans and conduction block, promoting re-entry.

3. Clinical Presentation

Many patients are asymptomatic until their first manifestation is SCD. Symptomatic presentations include:

Note: Females may present with bradycardia, atrioventricular block, or seizures rather than classic VF.

4. ECG Diagnosis & Classification

Brugada ECG patterns are dynamic and may be concealed (spontaneously or only unmasked by provocation).

Diagnostic ECG Patterns (Brugada Pattern)

Classified by the ESC 2022 Guidelines and HRS/EHRA/APHRS 2022 Consensus Statement:

✅ Key diagnostic criterion for Brugada syndrome (not just pattern):
Type 1 ECG (spontaneous or drug-induced) PLUS at least one of the following:

• Documented VF or polymorphic VT
• History of syncope suggestive of arrhythmia
• Nocturnal agonal respiration
• Family history of SCD <45 years
• Family member with diagnostic Type 1 ECG (esp. first-degree relative)

Provocative Testing

Sodium channel blockers (e.g., ajmaline, flecainide, procainamide) are used to unmask Type 1 pattern in suspected cases.

• Flecainide challenge (preferred over ajmaline in US due to availability):
  • IV infusion (1–2 mg/kg over 10 min) under continuous monitoring.
  • Sensitivity ~60–85%; specificity >98% when Type 1 appears.
  • Contraindications: LVEF <45%, structural heart disease, prior arrhythmia with drug, known sodium channelopathy (e.g., Long QT type 3).

🚨 Safety note: Provocative testing should be performed in a monitored setting with resuscitation equipment available.

5. Risk Stratification

SCD risk varies markedly; not all Type 1 carriers require ICD. Key risk factors:

Electrophysiology Study (EPS) Role

• Historically used for risk stratification: programed electrical stimulation (PES) to induce VF.
• Current evidence (e.g., FRENCH Brugada Registry, 2021 update; Brugada Syndrome Risk Stratification Trial subanalysis):
  • Non-inducibility does NOT rule out high risk—many SCD cases occur in non inducible patients.
  • Inducibility adds modest predictive value, especially in asymptomatic Type 1 carriers with spontaneous ECG.
• ESC 2022 Guidelines: EPS is optional and should be individualized (Class IIb indication); not routinely recommended for risk stratification.

6. Management: Evidence-Based Approach

A. Lifestyle & Triggers

All patients must avoid:

• Fever (>38.5°C): Aggressive antipyresis (acetaminophen, cooling) is critical—fever accounts for ~20% of arrhythmic events.
• Drugs that block sodium channels:
  • High risk: Class I antiarrhythmics (flecainide, propafenone), cocaine, alcohol excess, tricyclic antidepressants, lithium, bupivacaine.
  • Full list: www.brugadadrugs.org (maintained by European Heart Rhythm Association).
• Heavy alcohol ingestion and fasting/starvation (autonomic shift toward vagal tone).

B. Pharmacotherapy

C. Device Therapy

• Primary prevention ICD:
  • Class I indication for:
    ▪ Symptomatic patients (SCA, syncope, nocturnal agonal respiration)
    ▪ Spontaneous Type 1 ECG with inducible VF during EPS (selective use; consider patient factors)
  • Shared decision-making essential due to high complication rates: lead fractures (~5–10% at 5 years), inappropriate shocks (up to 25%), infection (3–7%). Especially challenging in young, active patients.
• ICD alternatives in select cases:
  • Subcutaneous ICD (S-ICD): Preferred if no need for pacing (e.g., no bradycardia, AV block). Avoids transvenous lead complications. Recent data (PREPARE-Brugada subanalysis) supports efficacy.
  • Implantable loop recorders (ILR) may be considered in very low-risk asymptomatic Type 1 carriers for monitoring (e.g., family history+, spontaneous ECG+).

D. Catheter Ablation

• Target: Epicardial substrate in RVOT—requires pericardial access (via subxiphoid approach).
• Evidence (CARTO Brugada Registry, JACC 2023):
  • Acute success >95% (elimination of Type 1 ECG).
  • Long-term freedom from arrhythmia: ~70–80% at 3 years.
  • Indications:
    ▪ Recurrent ICD shocks (Class IIa)
    ▪ Symptomatic patients refusing/poor candidates for ICD
    ▪ Fever-induced VF in high-risk pediatric/young adults

7. Family Screening & Genetic Counseling

• First-degree relatives: Clinical screening (ECG ± sodium channel blocker challenge) recommended regardless of genetics.
• Genetic testing:
  • Offered to probands; positive result enables cascade testing.
  • Negative test does not rule out BrS due to low diagnostic yield.
  • Variants of uncertain significance (VUS) require careful interpretation—avoid overdiagnosis.

8. Special Populations

• Fever in children/young adults: “Brugada-first-symptom” is common—ECG should be obtained acutely and followed up.
• Pregnancy: Low arrhythmia risk, but fever must be aggressively treated; ICD management requires multidisciplinary care.
• Athletes: BrS not a contraindication to sports if low-risk—but high-intensity endurance may unmask ECG changes.

Conclusion

Brugada syndrome is a life-threatening channelopathy requiring nuanced diagnosis, risk stratification, and management. While the Type 1 ECG pattern is necessary for diagnosis, clinical context determines risk. ICD remains cornerstone for secondary prevention, but emerging modalities (ablation, quinidine) offer valuable alternatives. Precision medicine approaches—including genotype-guided risk prediction—are evolving but not yet standard. Close collaboration with inherited arrhythmia centers and adherence to ESC/HRS guidelines are essential.

References

1. Priori SG, et al. 2022 ESC Guidelines for the management of patients with ventricular arrhythmias. Eur Heart J. 2023;44(6):417–528.
2. Zeerleder S, et al. Brugada Syndrome: A 20-Year Review. Circulation. 2021;143(19):1872–1885.
3. Barc J, et al. The Brugada Syndrome: From Genetics to Clinical Practice. JACC Clin Electrophysiol. 2020;6(8):871–885.
4. Nagashima M, et al. Epicardial Ablation for Brugada Syndrome: Long-Term Outcomes. J Am Coll Cardiol. 2023;81(12):1165–1176.
5. Mazariego K, et al. Flecainide Challenge in Diagnosing Brugada Syndrome: A Systematic Review. Heart Rhythm. 2022;19(5):734–742.

For real-time drug safety updates: www.brugadadrugs.org