Pseudoaneurysm formation in a subset of patients with small intestinal submucosa biologic patches after carotid endarterectomy

Background The carotid artery is frequently patched after carotid endarterectomy (CEA) to minimize the risks of early postoperative thrombosis and late recurrent stenosis. The small intestinal submucosa (SIS) patch is a biologic vascular patch derived from porcine small intestine. It is composed primarily of cell-free collagen and other extracellular matrix constituents that act as a scaffold for host cell deposition. Methods In May 2001, we began an investigational trial of SIS patches in 76 patients undergoing patch angioplasty of the carotid artery after CEA. Results No adverse events related to the patches were observed in the first 69 patients implanted with an SIS patch. However, in late 2002, seven patients were found to have asymptomatic pseudoaneurysms (PSA) by duplex imaging ≤10 weeks after their CEAs. The trial was immediately suspended. The PSAs were treated by surgical resection with vein grafting in two patients and placement of covered endoluminal stents in four patients. One patient is being followed as the PSA is small and has remained stable. Histopathologic examination of the SIS patch explanted from one of the surgically treated patients demonstrated the presence of actin-positive myofibroblasts or smooth muscle cells. Extensive mechanical testing of the SIS material from the two material lots associated with PSAs demonstrated thinner and more variable physical characteristics compared with control device lots. Conclusions Biologic patches that undergo active remodeling in the carotid artery require greater thickness than was anticipated to decrease wall stress and suture hole elongation. Patches exceeding this minimum thickness will be required to ensure the safety of new SIS patch designs for vascular operations.