LAA occlusion involves placing an endovascular device — Watchman, Amplatzer plug, or Lariat — to seal off the left atrial appendage in patients with atrial fibrillation who are at high risk for stroke but cannot tolerate long-term anticoagulation.
1 Preprocedural sizing
Contrast-enhanced, ECG-gated Cardiac CT is highly accurate for measuring:
- The LAA ostium
- The neck (where the device anchors)
- The lobar length
CT-derived measurements for selecting the correct Watchman device size are reported to be 100% accurate.
2 Anatomic relationships
CT establishes the spatial relationship between the LAA and surrounding structures:
- The proximal left circumflex artery (LCx) — helps demarcate the boundary of the LAA neck. Crossing or compressing it is a known complication.
- The interatrial septum — guides the required transseptal puncture.
3 Ruling out thrombus
CT is used to definitively rule out a preexisting LAA thrombus — an absolute contraindication for the occlusion procedure.
4 Post-procedural CT follow-up
After implant, CT is highly effective for confirming correct device positioning, ruling out device embolization, assessing peridevice seal, and detecting device-related thrombus. CT is actually more sensitive than TEE for peridevice leaks.
Contrast opacification distal to the device — the hallmark finding requiring precise terminology:
A visible gap or channel of contrast along the device border that creates communication between the left atrium and the distal LAA. On CT, defined by an LAA Hounsfield unit value > 100 HU and/or an LAA/left atrium HU ratio ≥ 0.25. PDL implies the device does not fully fill the LAA ostium.
Contrast opacification distal to the device without a visible gap along the device border. This reflects incomplete endothelialization of the device fabric — the occluder fits the LAA ostium correctly, but the membrane surface has not yet been fully covered by endothelium, allowing contrast to pass through microscopic fabric pores. EIS is distinct from PDL and implies correct device sizing with an immature device surface.
5 Hypoattenuation thickening & device-related thrombus
Hypoattenuation thickening (HAT) refers to hypoattenuated material on the atrial face of the device — a finding separate from contrast distal to the device. HAT exists on a spectrum from benign healing to clinically significant thrombus:
| HAT grade | CT appearance | Clinical significance |
|---|---|---|
| Low-grade | Thin, smooth hypoattenuation ≤ 4 mm | Likely physiologic endothelialization / device healing |
| High-grade | Thick, irregular hypoattenuation > 4 mm or mobile | Device-related thrombus (DRT) — warrants anticoagulation consideration |
HAT is graded on the atrial surface and is conceptually distinct from LAA contrast filling (PDL/EIS). A patient can have DRT (high-grade HAT) without any contrast distal to the device, and vice versa.
Device-related thrombus (DRT) — high-grade HAT — carries clinical risk: systemic embolism has been reported. Management typically involves anticoagulation and serial CT or TEE follow-up until resolution.
References
- Korsholm K, Iriart X, Saw J, et al. Position Statement on Cardiac Computed Tomography Following Left Atrial Appendage Occlusion. JACC Cardiovasc Interv. 2024;17(15):1747–1764. doi:10.1016/j.jcin.2024.04.050
- Korsholm K, Jensen JM, Nørgaard BL, et al. Peridevice Leak Following Amplatzer Left Atrial Appendage Occlusion: Cardiac Computed Tomography Classification and Clinical Outcomes. JACC Cardiovasc Interv. 2021;14(1):83–93. doi:10.1016/j.jcin.2020.10.034
- Duan Z, Shi G, Wang B, et al. Cardiac Computed Tomography Angiography for Assessment of Endothelial Insufficiency of Left Atrial Appendage Disc-like Occluder. J Cardiovasc Electrophysiol. 2024;35(3):389–398. doi:10.1111/jce.16176
- Iriart X, Blanc G, Bouteiller XP, et al. Clinical Implications of CT-detected Hypoattenuation Thickening on Left Atrial Appendage Occlusion Devices. Radiology. 2023;308(3):e230462. doi:10.1148/radiol.230462
- Alkhouli M, Alarouri H, Kramer A, et al. Device-Related Thrombus After Left Atrial Appendage Occlusion: Clinical Impact, Predictors, Classification, and Management. JACC Cardiovasc Interv. 2023;16(22):2695–2707. doi:10.1016/j.jcin.2023.10.046