What are the diagnostic criteria for Brugada syndrome?

Diagnostic Criteria for Brugada Syndrome

The diagnosis of Brugada syndrome requires the presence of a Type 1 Brugada ECG pattern, characterized by coved ST-segment elevation ≥2 mm followed by a negative T-wave in leads V1-V3, either occurring spontaneously or induced by sodium channel blockers. 1

ECG Patterns in Brugada Syndrome

Type 1 (Diagnostic) Pattern

• Coved ST-segment elevation ≥2 mm (0.2 mV) in leads V1-V3
• Followed by a negative T-wave
• Downsloping ST-segment with STJ/ST80 ratio >1 (Corrado index)
• Only the Type 1 pattern is considered diagnostic 2

Non-Diagnostic Patterns

• Type 2: "Saddleback" morphology with high takeoff (≥2 mm) ST-segment elevation, remaining ≥1 mm above baseline, followed by a biphasic or positive T-wave
• Type 3: Either coved or saddleback morphology with J-point elevation ≥2 mm but terminal portion of ST-segment <1 mm 2

Diagnostic Approach

1. ECG Evaluation:

   • Examine right precordial leads (V1-V3) for characteristic patterns
   • If Type 1 pattern is not clear but suspected:
     • Confirm correct lead placement
     • Repeat ECG if necessary
     • Perform high precordial lead ECG (V1 and V2 placed in 2nd or 3rd intercostal space) 2

2. Sodium Channel Blocker Challenge:

   • Indicated when Brugada syndrome is suspected but Type 1 pattern is not present spontaneously
   • Agents used: flecainide, ajmaline, or procainamide
   • Test is positive if Type 1 pattern appears during drug administration
   • Should be terminated if ventricular arrhythmias, marked QRS widening, or Type 1 pattern develops 2

3. Differentiation from Early Repolarization:

   • Use the "Corrado index" to differentiate Type 1 Brugada pattern from athlete's early repolarization
   • Measure ST elevation at J-point (STJ) and 80ms after (ST80)
   • Type 1 Brugada: STJ/ST80 ratio >1 (downsloping ST-segment)
   • Early repolarization: STJ/ST80 ratio <1 (upsloping ST-segment) 2

Important Diagnostic Considerations

• Lead V3 alone is not diagnostic in any ECG 3
• Type 1 pattern may be present in only one right precordial lead (V1 or V2) in 38% of cases 3
• Spontaneous Type 1 pattern carries worse prognosis than drug-induced pattern 1, 4
• ECG changes may be dynamic and intermittent, requiring repeated ECGs 2
• Fever can unmask or accentuate the Brugada ECG pattern 2, 1

Additional Diagnostic Features

• QRS complex fractionation (seen in a minority of patients)
• Prolonged PR interval (>200 ms)
• QRS prolongation in V2 (≥120 ms)
• Absence of structural heart disease 5

Risk Stratification Markers

• Spontaneous (vs. drug-induced) Type 1 ECG pattern
• History of syncope or aborted cardiac arrest
• Male gender (>90% of diagnosed cases)
• Family history of sudden cardiac death (controversial)
• Markers of increased heterogeneity of ventricular repolarization 1, 5, 6, 4

Clinical Pitfalls and Caveats

• The definition of Brugada ECG has evolved since its initial description; not all patients with Brugada ECG have Brugada syndrome 7
• Consider potential factors that may accentuate Brugada-like ECG patterns:
  • Hyperkalaemia
  • Fever (requires aggressive management)
  • Medications with sodium ion channel blocking properties
  • Excessive alcohol intake
  • Cocaine use 2, 1
• ST elevation is typically less pronounced in females 5
• The presence of right bundle branch block can complicate diagnosis 2

By following these diagnostic criteria and considerations, clinicians can accurately diagnose Brugada syndrome and identify patients at risk for sudden cardiac death who may benefit from preventive interventions such as ICD implantation.