New or presumed new left bundle branch block is STEMI-equivalent.

New or presumed new left bundle branch block is STEMI-equivalent.

• A. True
• B. False
• C. Not specified
• D. Only with chest pain

Answer: (A)

A new or presumed new left bundle branch block is treated as STEMI-equivalent because a new LBBB distorts the ECG in a way that makes true ST-elevation MI patterns hard to read. In the setting of acute chest pain or other ischemic symptoms, a new LBBB can indicate an acute coronary occlusion, so the safest course is to activate the STEMI pathway and pursue emergent reperfusion (PCI or thrombolysis) without waiting for classic ST elevations. If the block is known to be chronic and unchanged, it wouldn’t automatically be treated the same way, but “new or presumed new” reflects the scenario where MI could be present, warranting rapid reperfusion.

A new or presumed new left bundle branch block is treated as STEMI-equivalent because a new LBBB distorts the ECG in a way that makes true ST-elevation MI patterns hard to read. In the setting of acute chest pain or other ischemic symptoms, a new LBBB can indicate an acute coronary occlusion, so the safest course is to activate the STEMI pathway and pursue emergent reperfusion (PCI or thrombolysis) without waiting for classic ST elevations. If the block is known to be chronic and unchanged, it wouldn’t automatically be treated the same way, but “new or presumed new” reflects the scenario where MI could be present, warranting rapid reperfusion.