A 38-year-old woman with Brugada syndrome (diagnosed by genetic testing) presents with recurrent episodes of ventricular fibrillation. To assess the risk of future arrhythmias and guide ICD implantation decisions, which investigation provides the most specific electrophysiological information?

## Investigation of Choice for Brugada Syndrome Risk Stratification **Key Point:** Electrophysiological study (EPS) with programmed ventricular stimulation is the most specific investigation for assessing arrhythmia inducibility and guiding ICD implantation in Brugada syndrome. ### Brugada Syndrome Pathophysiology Brugada syndrome is caused by mutations in **SCN5A** (sodium channel gene, similar to LQT3) or other genes affecting the Na^+^ channel function. This results in: 1. **Loss of function of L-type Na^+^ channels** → reduced inward Na^+^ current during phase 0 2. **Unopposed outward K^+^ current** in the epicardium (due to Ito channel) → phase 1 "spike-and-dome" morphology 3. **Transmural voltage gradient** → ST-segment elevation in V1–V3 (Brugada ECG pattern) 4. **Reentry substrate** → ventricular fibrillation risk ### Why EPS is the Gold Standard for Risk Stratification **High-Yield:** Programmed ventricular stimulation (PVS) assesses: - **Inducibility of ventricular fibrillation** with one or two extrastimuli - **Refractory period properties** of the ventricle - **Substrate vulnerability** to reentry | Finding | Clinical Significance | | --- | --- | | Inducible VF with ≤2 extrastimuli | High risk; ICD indicated | | Non-inducible VF | Lower risk; medical management may suffice | | Inducibility with 3+ extrastimuli | Intermediate risk; shared decision-making | **Clinical Pearl:** Patients with: - **Spontaneous Type 1 Brugada ECG pattern** + **inducible VF on EPS** → **ICD strongly recommended** - **Asymptomatic with Type 1 pattern** + **non-inducible on EPS** → **ICD deferred, close monitoring** - **Symptomatic (syncope/VF)** → **ICD indicated regardless of EPS result** ### Mechanism: How EPS Identifies Arrhythmia Risk Programmed stimulation reproduces the reentrant circuit that underlies ventricular fibrillation in Brugada syndrome. The ability to induce VF with minimal extrastimuli indicates a vulnerable substrate and predicts future spontaneous arrhythmias. **Mnemonic:** **EPS = Electrophysiological Substrate** (directly assesses the reentry circuit) ## Why Other Investigations Are Insufficient **Holter monitoring** documents spontaneous arrhythmias but does not provoke the substrate or predict future risk in asymptomatic patients. **Stress testing** does not reliably induce VF in Brugada syndrome and may be dangerous; it is not used for risk assessment. **Cardiac CTA** is used for structural imaging but provides no electrophysiological information about arrhythmia substrate or inducibility.