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Background Left atrial appendage (LAA) thrombus is a high-consequence finding linked to cardioembolic stroke risk, and its exclusion is key to achieve safe rhythm-control in atrial fibrillation. However, incomplete early-phase LAA opacification on coronary CT coronary angiography (CTCA) often reflects circulatory stasis rather than true thrombus, risking false-positive reporting without a structured confirmatory step.Purpose To describe a pragmatic HHFT protocol for LAA thrombus assessment using Canon PRISM CTCA with rapid delayed confirmation, designed to support consistent reporting and downstream stroke-avoidance decision-making (figure 1).Summary of content In routine CCTA, if an LAA filling defect is identified on the initial angiographic phase, a targeted, limited z-coverage delayed confirmation acquisition is performed approximately 30-seconds later (HHFT PRISM protocol parameters pending). LAA findings are then categorised as: (i) likely slow flow (defect resolves or substantially improves on the delayed confirmation), (ii) suspicious for thrombus (defect persists), or (iii) indeterminate (artefact or inadequate opacification). Persistent or indeterminate findings allow escalation depending on clinical context. This approach mirrors published delayed-phase principles in which persistence on later imaging supports thrombus while resolution supports stasis.Conclusion A standardised short-delay confirmation LAA re-scan step on Canon PRISM CT has allowed better characterisation of LAA filling in support of stroke team pathways. An apparent LAA filling defect on early-phase CCTA most commonly represents:A. True thrombusB. Circulatory stasis/slow contrast mixingC. Left atrial tumourD. Mitral regurgitationE. Previous MIAbstract 20 Figure 1(Correct answer: B)