Left Atrial Appendage Obliteration - Pathology review

J Am Coll Cardiol Intv, 2010; 3:870-877

Left Atrial Appendage Obliteration

Mechanisms of Healing and Intracardiac Integration

Robert S. Schwartz, MD, David R. Holmes, MD, Robert A. Van Tassel, MD, Robert Hauser, MD, Timothy D. Henry, MD, Michael Mooney, MD, Ray Matthews, MD, Shephal Doshi, MD, Russell M. Jones, BS, Renu Virmani, MD

Objectives: The objectives of this study were: 1) to delineate the temporal course of histopathologic healing as the left atrial appendage (LAA) is obliterated by a mechanical device; and 2) to compare this process with other intravascular and intracardiac implanted technologies.

Background: Intracardiac device healing is incompletely understood. We thus studied the histopathology of device-based LAA obliteration.

Methods: Nine dog hearts were examined over time after LAA device placement and results were compared with human hearts with prior LAA obliteration using the same device.

Results: At 3 days in dogs, atrial surfaces were covered by fibrin, which sealed gaps between the LA wall and the device and filled the LA appendage cavity. At 45 days, endothelial cells covered the endocardial surface with underlying smooth muscle cells that sealed the device-LA interface. Regions with prior thrombus were replaced by endocardium surrounding the device membrane. Disorganized thrombus remained in the LAA body and at the periphery near the appendage walls. Mild inflammation was observed as thrombus resorbed. By 90 days, a complete endocardial lining covered the former LAA ostium. Organizing thrombus had become connective tissue, with no residual inflammation. The human necropsy hearts had similar findings. In these 4 hearts (139, 200, 480, and 852 days after implant), the ostial fabric membrane was covered with endocardium. The appendage surface contained organizing thrombus with minimal inflammation. Organizing fibrous tissue was inside the LAA cavity, prominent near the atrial wall. The LAA interior contained organizing thrombus.

Conclusions: This intracardiac device integration study delineated healing stages of early thrombus deposition, thrombus organization, inflammation and granulation tissue, final healing by connective tissue, and endocardialization without inflammation. These observations may yield insight into cellular healing processes in other cardiac devices.

Figure 1 Composite Images of the LAA and Obliteration

(A) Post-mortem dog heart (no device implanted), showing the exterior view of the left atrial appendage (LAA). (B) Diagrammatic view of the Watchman LAA obliteration method. Metal struts with anchoring hooks secure the device within the body of the appendage cavity. A fabric membrane filter covers the atrial surface of the device, preventing thrombi from escaping into the left atrial chamber. A center hub is used to connect the device to the catheter delivery system. (C) Dog autopsy specimen 28 days after Watchman implant showing a cross-sectional cutaway view of the Watchman device. The fabric membrane is covered with a fine layer of endocardium, and the metal struts are shown holding the device in place. Pectinate muscles internal to the LAA cavity are labeled. (D) Dog autopsy specimen showing a view of the former LAA ostium, now completely obliterated by the endocardium-covered fabric membrane. This view is from the left atrial cavity, where it is clear that thrombi potentially residing the left atrial appendage body could no longer escape into the left atrium and systemic circulation.

There are multiple other images of this device with pathologic specimens from Dog heart and Human heart at different times after implanation. Longest one, after 852 days after implantation.