A 64-year-old man develops an anterior STEMI. He is taken for primary PCI at 90 minutes. Post-procedure, angiography shows TIMI-3 flow, but his ECG shows persistent ST elevation and he develops new right bundle branch block with QRS duration 140 ms. What does this ECG finding indicate?
- A Reperfusion injury with ventricular aneurysm formation
- B Extension of infarct to involve the right ventricle
- C Acute pericarditis complicating STEMI
- D New RBBB suggests proximal LAD occlusion with extensive septal necrosis ✓
Explanation
New right bundle branch block (RBBB) complicating anterior STEMI indicates extensive septal involvement because the right bundle is supplied by the proximal LAD (septal perforators). This implies a proximal LAD territory infarct with large myocardial mass at risk and is associated with increased mortality compared to anterior MI without conduction defect. Right ventricular infarction complicates right coronary artery occlusion and presents with ST elevation in V4R; it does not cause RBBB as a primary ECG change. Persistent ST elevation post-PCI can indicate ventricular aneurysm but not specifically when RBBB is the new finding.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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