Myocardial Infarction in a Patient With Left Bundle Branch Pacing

BACKGROUND: A pacing rhythm can delay the diagnosis of acute myocardial infarction. CASE SUMMARY: A patient with chest pain and left bundle branch pacing (LBBP) was admitted to the emergency department. His subsequent electrocardiogram did not show dynamic ST-segment changes but a decrease in QRS amplitude in the anterior wall. Emergency angiography showed total occlusion of the proximal left anterior descending artery. DISCUSSION: This case highlights that in patients with chest pain and LBBP: 1) dynamic ST-segment changes may be absent even in the setting of total coronary occlusion; 2) dynamic QRS amplitude reduction can be a critical sign of ongoing myocardial ischemia and infarction; and 3) emergency angiography is warranted when angina cannot be relieved despite drug therapy, even if ST-T changes are absent. TAKE-HOME MESSAGES: In patients with chest pain and LBBP, a dynamic decrease in QRS amplitude should be considered as significant as ST-segment deviation. Emergency coronary angiography is crucial for timely intervention, especially when patients' symptoms persist.