New LBBB as STEMI Equivalent — EECC MCQ

Correct answer: D — Acute MI presenting with new LBBB — the Sgarbossa criteria (or modified Smith criteria) should be applied to identify STEMI-equivalent patterns in the presence of LBBB; emergent angiography may be needed

New LBBB in the setting of chest pain or syncope with troponin rise should be treated as a potential STEMI equivalent. The 2023 ESC ACS Guidelines state that new LBBB (not known to be pre-existing) with clinical presentation suggestive of ongoing myocardial ischaemia should be managed as STEMI. The Sgarbossa criteria help identify MI in LBBB: (1) concordant ST elevation ≥1 mm in leads with positive QRS (highly specific); (2) concordant ST depression ≥1 mm in V1-V3; (3) discordant ST elevation ≥5 mm (low specificity — Smith modification uses a ratio of ST elevation to S wave depth ≥0.25 for better accuracy). In this patient: new LBBB + syncope + troponin rise + hypotension → urgent angiography is indicated. However, NOT all new LBBB is MI — it can also represent progression of conduction disease in HFrEF, and clinical context must guide the decision.

Reference: ESC (2023): ACS Guidelines; Sgarbossa/Modified Smith Criteria