## Clinical Context The patient presents with a wide complex tachycardia in the setting of prior MI with features suggestive of ventricular tachycardia (VT): syncope, haemodynamic instability, and ECG findings consistent with VT (left axis deviation, precordial concordance). The substrate is likely a re-entrant circuit in the scarred myocardium. ## Investigation Rationale **Key Point:** Electrophysiology (EP) study with programmed ventricular stimulation is the gold standard investigation for diagnosis and risk stratification of sustained ventricular arrhythmias post-MI. ### Role of Each Investigation | Investigation | Role in VT Diagnosis | Utility | |---|---|---| | **EP Study + PVS** | Diagnostic + therapeutic | Confirms VT, maps substrate, guides ablation | | **Cardiac MRI** | Structural assessment | Identifies scar burden and location; prognostic but not diagnostic | | **Echocardiography** | Functional assessment | Assesses LV function; does not diagnose arrhythmia | | **Holter monitor** | Screening tool | Detects arrhythmias but cannot confirm VT mechanism in acute setting | **High-Yield:** In a haemodynamically unstable patient with suspected VT, EP study allows: 1. Induction of VT with programmed stimulation (diagnostic criterion) 2. Mapping of the re-entrant circuit 3. Immediate therapeutic ablation if VT is induced 4. Risk stratification for ICD implantation **Clinical Pearl:** The ECG findings (left axis deviation, precordial concordance) are highly specific for VT originating from the inferior or apical wall, often in a scar post-MI. EP study will confirm the diagnosis and identify the critical isthmus for ablation. **Warning:** Do not confuse diagnostic confirmation with structural assessment. Echocardiography and cardiac MRI assess the substrate (scar, LV dysfunction) but do NOT confirm the diagnosis of VT itself — only EP study with induction can do that.
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