When the Clot Runs Deep: Tackling High Thrombus Burden in Primary Percutaneous Coronary Intervention.

High intracoronary thrombus burden complicates a significant proportion of ST-segment elevation myocardial infarctions (STEMI) managed with primary percutaneous coronary intervention (PCI), and remains a major determinant of procedural complexity, microvascular obstruction, and adverse outcomes. Restoration of epicardial coronary flow alone does not ensure adequate myocardial reperfusion, as distal embolization and no-reflow may occur despite technically successful PCI. Effective management requires an understanding of the dynamic interplay between thrombus burden, culprit plaque morphology, coronary flow, and procedural strategy. Although angiography remains the initial imaging modality, it frequently underestimates thrombus burden and provides limited information regarding the underlying lesion. Intravascular imaging offers complementary insights into thrombus composition, plaque morphology, vessel architecture, and lesion severity, facilitating tailored therapeutic decision-making. Pharmacological treatment integrates potent antiplatelet and anticoagulant therapies, with selective use of intracoronary fibrinolytics and vasodilators in appropriate patients. Mechanical adjuncts, including aspiration thrombectomy, excimer laser coronary angioplasty, and emerging thrombus-modifying technologies, may be beneficial in selected cases, although routine use has not consistently improved clinical outcomes. This review summarizes the contemporary evidence on the pathophysiology, assessment, and management of high thrombus burden in STEMI, highlights the complementary roles of angiography and intravascular imaging, and proposes a practical algorithm for individualized management based on coronary flow, thrombus characteristics, and culprit lesion morphology.