Brugada Syndrome

Brugada syndrome (BrS) is a heritable cardiac channelopathy characterised by distinctive ST-segment changes in the right precordial electrocardiogram leads (V1–V3) and an elevated risk of ventricular fibrillation (VF) and sudden cardiac death (SCD). First described by the Brugada brothers in 1992, the syndrome has since become recognised as one of the most important causes of structurally normal-heart SCD, particularly in young males of Southeast Asian descent.

Brugada syndrome accounts for approximately 20% of sudden unexplained death syndrome (SUDS) cases and up to 12–20% of SCD cases in individuals with structurally normal hearts at autopsy. The estimated worldwide prevalence of the Brugada ECG pattern is 0.1–0.5% in Western populations, rising to 1–5% in Southeast Asian countries. In Australia, the condition is encountered across all ethnic backgrounds, though the highest prevalence of the diagnostic ECG pattern is observed in individuals of Southeast Asian and Polynesian heritage. Australian data suggest the prevalence of a diagnostic Type 1 pattern in the general Australian population is approximately 0.12–0.4%, consistent with international estimates.

The male-to-female ratio for clinical diagnosis is approximately 8–10:1, likely reflecting hormonal modulation of the transient outward potassium current (I_to) and differences in right ventricular outflow tract (RVOT) electrophysiology. The median age at diagnosis is 35–45 years, though the condition can present at any age, including infancy.

Inheritance Pattern

Brugada syndrome is inherited in an autosomal dominant pattern with incomplete penetrance and variable expressivity. This means that approximately 50% of first-degree relatives of an affected individual will carry the pathogenic variant, but not all carriers will manifest the clinical phenotype. Male predominance in clinical expression is well established.

SCN5A and the Cardiac Sodium Channel

Mutations in the SCN5A gene (chromosome 3p21) encoding the α-subunit of the cardiac voltage-gated sodium channel (Na_v1.5) account for approximately 20–30% of clinically diagnosed Brugada syndrome cases. Over 300 SCN5A mutations have been identified, predominantly missense mutations leading to loss-of-function of the sodium current (I_Na).

Loss of I_Na produces the Brugada phenotype through the repolarisation hypothesis and the depolarisation hypothesis:

• Repolarisation hypothesis: Reduced I_Na in the RVOT epicardium unmasks the transient outward potassium current (I_to), creating a transmural voltage gradient between epicardium and endocardium during phase 1 of the action potential. This produces the characteristic ST elevation and creates a substrate for phase 2 re-entry, which can degenerate into VF.
• Depolarisation hypothesis: Reduced I_Na causes conduction delay in the RVOT, resulting in delayed activation and ST-segment elevation through partial right bundle branch block-like effects. Slowed conduction creates a substrate for re-entrant arrhythmias.
• Both mechanisms may coexist, with the RVOT being the critical anatomical region due to its naturally high I_to density and heterogeneous expression of ion channels.

Additional Gene Loci

Mutations in other genes encoding ion channel subunits and regulatory proteins have been implicated in smaller subsets of BrS:

In approximately 60–70% of BrS cases, no pathogenic variant is identified on current genetic testing panels. Genetic testing, when performed, should include at minimum SCN5A; expanded panels may include the additional loci listed above. Genetic testing is available through major Australian genetic testing laboratories (e.g., Sonic Genetics, Victorian Clinical Genetics Services) and is Medicare-rebatable under MBS item 73307 where clinical criteria are met.

Genotype-Phenotype Correlations

SCN5A-positive patients tend to exhibit greater PR prolongation, more conduction abnormalities, and a higher rate of atrial fibrillation than SCN5A-negative patients.

Triggers and Modulators

The Brugada ECG pattern and arrhythmic events are often unmasked or exacerbated by:

• Fever: The most common trigger; fever ≥38°C increases I_to density and further reduces I_Na, widening the transmural gradient.
• Drugs: Sodium-channel blockers, tricyclic antidepressants, lithium, cocaine, anaesthetic agents (propofol, bupivacaine), and others listed at www.brugadadrugs.org.
• Vagal stimulation: Increased vagal tone during sleep (nocturnal predominance of events), postprandial states, and alcohol excess.
• Hypokalaemia, hyperkalaemia, and hypothermia.

ECG Criteria

The diagnostic criteria for Brugada syndrome are centred on the morphology of the ST segment in the right precordial leads V1–V3, ideally recorded from the 2nd, 3rd, and 4th intercostal spaces (high V1–V3 positions) in addition to standard positions.

Diagnostic Criteria (Brugada Consensus, 2013)

A diagnosis of Brugada syndrome requires a Type 1 ECG pattern (spontaneous or drug-induced) plus at least one of the following:

• Documented ventricular fibrillation or polymorphic ventricular tachycardia
• Self-terminating polymorphic VT or VF
• A family history of SCD (<45 years) in a first-degree relative
• Type 1 ECG pattern in family members
• Arrhythmic syncope (nocturnal agonal respiration)
• Inducibility of VT/VF on electrophysiology study

Pharmacological Provocation Testing

When a Type 2 or Type 3 ECG pattern is identified, a sodium-channel blocker challenge may unmask a Type 1 pattern. Testing must be performed in a monitored setting with continuous ECG and haemodynamic monitoring, with defibrillation capability immediately available.

ECG Modifiers

• Record ECGs in multiple right precordial positions (V1–V3 at 2nd, 3rd, and 4th intercostal spaces) to increase diagnostic yield.
• Repeat ECGs during febrile episodes and at different times of day (nocturnal vagal predominance may unmask pattern).
• Signal-averaged ECG (SAECG) may reveal late potentials, particularly in SCN5A-positive patients.
• Baseline PR prolongation and QRS widening are more common in SCN5A carriers.

Typical Presentations

• Sudden cardiac arrest (SCA) / VF: Approximately 4–12% of BrS patients present with aborted SCA as the first manifestation.
• Syncope: Arrhythmic syncope, often nocturnal or occurring at rest, is the most common symptomatic presentation. Nocturnal agonal respiration (gasping during sleep reported by bed partner) is a key historical feature.
• Palpitations: May reflect atrial fibrillation (present in 10–20% of BrS patients) or ventricular ectopy.
• Asymptomatic ECG detection: An increasing proportion of patients are identified incidentally or through family screening.
• SIDS / SUADS: BrS has been implicated in sudden infant death syndrome and sudden unexplained death in the young.

Differential Diagnosis

The Type 1 ECG pattern must be distinguished from other causes of right precordial ST elevation:

• Right bundle branch block (RBBB) — typically without coved ST morphology
• Acute anterior STEMI / coronary vasospasm
• Arrhythmogenic right ventricular cardiomyopathy (ARVC)
• Right ventricular hypertrophy / acute right heart strain (e.g., pulmonary embolism)
• Early repolarisation pattern
• Pericarditis / myocarditis
• Hyperkalaemia, hypothermia
• Duchenne muscular dystrophy
• Mechanical mediastinal compression (thymoma, mediastinal haematoma)

An echocardiogram and cardiac MRI should be performed to exclude structural heart disease (especially ARVC) before confirming a BrS diagnosis.

Formal Diagnostic Criteria (2023 HRS/EHRA/APHRS Expert Consensus)

The following investigations are recommended in the workup of suspected Brugada syndrome:

Risk stratification in Brugada syndrome remains challenging and is an area of active research. The following framework is based on the 2022 ESC and 2023 HRS/EHRA/APHRS guidelines:

Key Risk Factors

1. Implantable Cardioverter-Defibrillator (ICD)

The ICD remains the cornerstone of sudden cardiac death prevention in Brugada syndrome. It is the only intervention with proven mortality benefit in high-risk patients.

Australian considerations: ICD implantation is performed at all major tertiary cardiac centres and is covered under standard hospital funding. Single-chamber ICD (VVI) is preferred in young patients to minimise lead-related complications and tricuspid valve interference. Subcutaneous ICD (S-ICD) may be considered to avoid transvenous lead complications in younger patients without pacing indications. Post-implantation, regular device clinic follow-up is essential (typically 3–6 monthly).

2. Quinidine

Quinidine is the primary pharmacological therapy for Brugada syndrome. It blocks the transient outward potassium current (I_to), thereby reducing the transmural voltage gradient that underlies the Brugada ECG pattern and arrhythmogenesis.

Indications for quinidine:

• Adjunctive therapy in patients with recurrent appropriate ICD shocks (VF storm)
• Primary therapy in patients who refuse ICD implantation or are not candidates
• Asymptomatic patients with spontaneous Type 1 ECG and additional risk factors (consideration)
• Treatment and prevention of atrial fibrillation in BrS patients
• Children with BrS and arrhythmic events (paediatric dosing under specialist supervision)

3. Catheter Ablation

Epicardial catheter ablation of the arrhythmogenic substrate in the right ventricular outflow tract (RVOT) has emerged as an effective intervention for Brugada syndrome, particularly in patients with recurrent VT/VF despite ICD and quinidine therapy.

Procedural details:

• Approach: Combined epicardial (percutaneous subxiphoid) and endocardial mapping and ablation.
• Target: Low-voltage fractionated electrograms, late potentials, and broad duration electrograms predominantly in the RVOT epicardium.
• Endpoint: Elimination of abnormal electrograms, normalisation of the Type 1 ECG pattern, and non-inducibility of VT/VF at post-ablation PES.
• Australian availability: Performed at major specialised EP centres (e.g., Alfred Hospital Melbourne, RPAH Sydney, Royal Adelaide Hospital, Prince Charles Hospital Brisbane). Referral to a high-volume BrS ablation centre is recommended.

Indications for catheter ablation:

• VF storm or recurrent appropriate ICD shocks despite quinidine therapy
• Quinidine intolerance or contraindication with recurrent VT/VF
• Consideration as first-line therapy in high-volume centres with demonstrated expertise

4. General Measures and Trigger Avoidance

5. Other Pharmacological Considerations

• Cardiology follow-up: Annual review with an electrophysiologist or specialised inherited arrhythmia clinic. More frequent review if symptomatic, post-ICD implantation, or on quinidine therapy.
• ECG surveillance: Serial 12-lead ECGs at each clinic visit. Repeat ECG during any febrile illness. High V1–V3 recording recommended.
• ICD management: Device clinic review every 3–6 months. Interrogation for appropriate/inappropriate shocks, arrhythmia burden, and battery status. Consider remote monitoring.
• Quinidine therapy monitoring: Serum quinidine levels (target 2–5 µg/mL), renal function, LFTs, FBC at baseline and every 6–12 months. ECG for QTc monitoring.
• Family screening: First-degree relatives should have baseline and serial ECGs. Genetic testing of the index case facilitates targeted cascade testing in relatives. Repeat ECG screening of genotype-negative relatives during adolescence and early adulthood.
• Psychological support: Diagnosis of an inheritable SCD syndrome has significant psychosocial impact. Screen for anxiety and depression; referral to psychology/counselling services as needed. Driver's licence implications (Australasian Fitness to Drive guidelines — private licence generally unrestricted if ICD implanted and asymptomatic; commercial licence restrictions apply).

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