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Percutaneous left atrial appendage (LAA) closure technology is a novel therapeutic strategy for stroke prevention in patients with atrial fibrillation. The histopathologic response following mechanical LAA closure with the next generation WATCHMAN (WM) FLX device (Boston Scientific Corporation, Marlborough, MA) has not been previously reported. This study evaluated the safety and healing response of the WM FLX as compared to the WM device in the canine model up to 90 days.
Implantation of the WM FLX device (n=6) and WM (n=6) in the canine LAA was performed to evaluate the histologic healing response at 45 and 90 days. Gross examination included device integrity, positioning within the LAA, strut penetration of the LAA and healing. The devices and surrounding LAA were embedded in methyl methacrylate plastic, sawed into longitudinal sections, ground using Exakt Linear Grinding technology, polished, and stained with toluidine blue and basic fuchsin stains. All sections were examined by light microscopy for inflammation, thrombus, neointima, endothelialization, and device sealing of the LAA. In addition, myocardium was evaluated for thromboemboli.
The WM FLX and WM devices were well positioned within the LAA orifice with slight differences related to variable LAA anatomy. There was no evidence of perforation of the LAA in any device. The WM FLX showed a similar and appropriate healing response when compared to WM at 45 and 90 days. Endocardial tissue growth with endothelialization was essentially complete in all devices with the exception of single animal from WM at 90 days in which there was minimal thrombus associated with slight protrusion of the device into the left atrium. Inflammation was minimal and consisted of chronic inflammation with rare multinucleated giant cells localized near the polyester cover. The superior and inferior aspects of the devices were contiguous with the left atrial wall with the exception of a single WM at 90 days exhibiting slight protrusion from the ostium. There was no evidence of myocardial infarction or thromboembolism in any animal and there was no compression or thrombosis of the underlying left circumflex coronary artery.
All closure devices were appropriately positioned within the LAA with conformation to variable left atrial anatomy. Healing by endothelialized endocardial tissue growth was essentially complete by 90 days in both WM FLX and WM with histologic features similar to those previously reported for WM and other larger cardiac devices.