A 58-year-old man with a history of anterior wall myocardial infarction 6 months ago presents with recurrent episodes of sustained ventricular tachycardia. What is the most common site of origin of reentrant ventricular tachycardia in post-infarction patients?

Explanation

## Origin of Post-Infarction Ventricular Tachycardia **Key Point:** The subendocardial border zone (surviving myocardium adjacent to the infarct scar) is the most common site of reentry in post-MI ventricular tachycardia. This region contains areas of slow conduction and unidirectional block, which are prerequisites for reentrant circuits. ### Pathophysiology of the Border Zone 1. **Scar formation** — Dense fibrosis in the central infarct zone 2. **Surviving myocardial islands** — Interspersed viable cells within or adjacent to scar 3. **Altered conduction** — Fibrosis causes slow, discontinuous propagation 4. **Unidirectional block** — Allows reentry to occur 5. **Electrolyte disturbances** — Abnormal automaticity and triggered activity ### Mechanism of Reentry The border zone creates a substrate where: - Impulses travel slowly through fibrotic tissue - Anatomical or functional obstacles permit unidirectional conduction block - The impulse re-enters previously depolarized tissue after the refractory period ends - This creates a self-perpetuating circuit → sustained VT **High-Yield:** Post-infarction VT is almost always reentrant (not automatic), and the scar border zone is the anatomical substrate in >90% of cases. **Clinical Pearl:** Mapping studies during electrophysiology procedures consistently identify the subendocardial border zone as the critical isthmus for reentry in post-MI patients. This is why catheter ablation targets this region. ### Why Other Sites Are Less Common | Site | Frequency | Context | |------|-----------|----------| | Subendocardial border zone | Most common (>90%) | Post-MI reentry | | Papillary muscle | Rare | Structural abnormality, not post-MI | | RVOT | Idiopathic VT (no structural disease) | Automatic focus, not post-MI | | Ventricular septum at His | Very rare | Congenital or infiltrative disease | **Mnemonic:** **SCAR BORDER** — Surviving myocardium At Conduction-slowed Reentry zone = BORDER zone is the substrate.