Stroke prevention in AF presents significant challenges as well as opportunities. Current treatment strategies with systemic anticoagulation, while effective, are fraught with limitations involving poor compliance, intolerance, and inconvenience. While newer oral anticoagulants overcome many of these limitations, all anticoagulants suffer from an unavoidable lifelong commitment to medication and elevated bleeding risk.
Given that the LAA is the source of thromboembolism in the vast majority of patients with AF and stroke, a newer paradigm of targeting the LAA has naturally evolved. Several strategies are available, although surgical LAA removal will likely not have a large role as a stand-alone procedure due to its significant morbidity. The minimally invasive strategies involve foreign body occlusion of the LAA ostium and pericardial suture ligation of the LAA base.
Several questions remain regarding LAA exclusion. Aside from the PLAATO device, which is no longer available, the information regarding long-term durability of percutaneous LAA exclusion is not yet available. Even after acute procedural success, there is commonly a small diverticulum or “beak” left behind at the LAA ostium. In light of the surgical data that incomplete closure is worse than no closure at all [26
], there are concerns about the thrombogenicity of this unnatural diverticulum.
The data also highlight that success rates are operator and experience dependent. As every new procedure necessarily involves a learning curve, the hope is that the second- and third- generation data with LAA exclusion will show improving procedural success rates with decreasing complication rates. The WATCHMAN experience has already demonstrated this.
The ultimate dominance of one percutaneous technique over the rest is unlikely. A more likely outcome is that device selection will be tailored to patient characteristics. For instance, prior cardiac surgery or pericardial adhesions would make endocardial occlusion devices more feasible than the LARIAT system. On the other hand, an absolute contraindication to antiplatelet drugs or oral anticoagulation makes the LARIAT system more attractive as it appears to have no requirement for postprocedure anticoagulation. Similarly, a patient deemed at high risk for infection may benefit from the LARIAT system given its lack of endovascular hardware.
An even larger issue is the selection of appropriate candidates for these devices. Current focus has been on patients with intolerance or contraindications to warfarin. Whether these devices will be offered as an equal (or preferred) alternative to anticoagulation remains to be seen. PROTECT AF confirmed the non-inferiority of LAA exclusion to warfarin, but superiority data is still lacking. In addition, all LAA exclusion trials excluded patients with valvular AF or with prosthetic valves; the role of LAA exclusion in these patients is unknown. Finally, to date the comparison arm for these devices has only been warfarin. As some of the newer anticoagulants have reduced bleeding risk compared with warfarin, it is possible that the benefit of mechanical LAA exclusion would diminish in head-to-head trials against the newer agents.
The ultimate goal of LAA exclusion is to replace the lifelong need for anticoagulation with a single procedure associated with a small upfront risk and tremendous long-term benefit. This paradigm rests on the assumption that thromboembolism in AF is due solely to the anatomic presence of the LAA. However, data suggests that AF is associated with a systemic hypercoagulable state which may contribute to stroke risk in an independent and meaningful way [39
]. This argues against discontinuation of anticoagulation, regardless of the patency of the LAA. Larger and longer-term studies will help shed light on this important question.
Despite the remaining challenges, LAA exclusion represents a promising alternative to systemic anticoagulation for the prevention of stroke in patients with AF. Already, studies have established that LAA exclusion is a viable option in patients with intolerance or contraindications to anticoagulation. Whether LAA exclusion is a superior strategy to anticoagulation in all AF patients remains to be seen. In addition, whether mechanical LAA exclusion reduces risk of stroke over the long term will require further clinical trials.