A 48-year-old woman with no prior cardiac history presents with a single episode of syncope. Holter monitoring captures a 15-second run of monomorphic ventricular tachycardia at 180 bpm, originating from the right ventricular outflow tract (RVOT). Transthoracic echocardiography shows normal LV function and normal RV size. Which investigation is most appropriate to assess the risk of sudden cardiac death and guide management?

Explanation

## Clinical Scenario Analysis The patient presents with: - Idiopathic RVOT-VT (normal LV function, normal RV size) - Monomorphic VT on Holter (single morphology) - Syncope (hemodynamically significant) - Structurally normal heart on echo This is **idiopathic ventricular arrhythmia** (RVOT-VT), which accounts for ~10% of VT cases in structurally normal hearts. ## Investigation of Choice **Key Point:** Electrophysiology study with programmed ventricular stimulation is the gold standard for: 1. **Confirmation** of RVOT origin (12-lead ECG morphology + mapping) 2. **Risk stratification** (inducibility, number of morphologies) 3. **Therapeutic intervention** (radiofrequency ablation) 4. **Assessment of SCD risk** (inducibility of sustained VT) ## Why EP Study Over Alternatives | Investigation | Role | Why NOT First Choice Here | |---|---|---| | Signal-averaged ECG | Detects late potentials (scar-related VT) | Patient has structurally normal heart; SAECG not useful for idiopathic RVOT-VT | | Cardiac MRI RV | Detects RV dysplasia, fibrosis, scar | Echo already normal; MRI may miss subtle RV dysplasia but does NOT confirm diagnosis or guide ablation | | Exercise stress testing + PVS | Assesses exercise-induced VT | Not indicated for resting monomorphic VT; EP study is standard | | **EP study + PVS** | **Induce VT, map RVOT origin, assess inducibility** | **Gold standard for idiopathic VT diagnosis and ablation planning** | ## High-Yield Facts **High-Yield:** Idiopathic RVOT-VT has excellent prognosis with catheter ablation (>95% success rate). EP study is essential to confirm RVOT origin and guide ablation. **Clinical Pearl:** Syncope in the setting of RVOT-VT warrants EP study and ablation, as it indicates hemodynamically significant arrhythmia. Patients with inducible sustained VT have higher SCD risk. **Mnemonic: RVOT-VT FEATURES** — - **R**ight ventricular outflow tract origin - **V**entricle: structurally normal - **O**utflow: monomorphic, catecholamine-sensitive - **T**reatment: ablation (EP study prerequisite) - **V**entricle: idiopathic (no structural disease) - **T**herapy: EP study confirms diagnosis ## Diagnostic Algorithm ```mermaid flowchart TD A[Monomorphic VT + Syncope]:::outcome --> B{Structural heart disease?}:::decision B -->|Yes, scar present| C[EP study for scar-related VT]:::action B -->|No, normal structure| D{RVOT morphology on ECG?}:::decision D -->|Yes| E[EP study to confirm RVOT origin]:::action D -->|No| F[EP study for other idiopathic site]:::action E --> G[Ablation if inducible]:::action F --> G ```