Atrial fibrillation (AF) accounts for the majority of cardioembolic strokes, especially in elderly individuals. Although anticoagulation reduces the risk of embolic stroke, a significant proportion of AF patients have relative or absolute contraindications to anticoagulation. Patients with high bleeding risk are also the patients at highest risk of stroke with AF.
Imaging studies have previously documented that >90% of embolic strokes in nonvalvular AF originate from the left atrial appendage (LAA). This might be secondary to specific anatomy of pectinate muscles, as well as inflammation and fibrosis involving the LAA. This therefore makes therapies targeted at LAA occlusion (LAAO) appealing. LAAO is currently covered by Centers for Medicare & Medicaid Services (CMS) as an alternative for stroke prevention in patients with an elevated stroke risk (CHADS2 ≥2 or CHA2DS2-VaSc score ≥3) who have the appropriate rationale for avoiding long-term oral anticoagulation after a shared decision-making process. This chapter will primarily focus on the Watchman, which is currently the only Food and Drug Administration (FDA)–approved endocardial LAAO device.
Left atrial appendage occlusion devices
The Watchman (Boston Scientific, Natick, MA) is the only percutaneous device ( Fig. 22.1 ) approved by the FDA for LAAO in United States. The PROTECT AF (Left Atrial Appendage System for Embolic Protection in Patients with Atrial Fibrillation) trial demonstrated that patients with nonvalvular AF and an additional risk factor for stroke ( n = 707) had similar rates of stroke and cardiovascular death after Watchman compared with warfarin. The PREVAIL (Prospective Randomized Evaluation of the Watchman LAA Closure Device in Patients with Atrial Fibrillation Versus Long-Term Warfarin Therapy) trial also showed noninferiority to warfarin.
The improving procedural success and safety have been replicated in real-world clinical practice with low rates of cardiac tamponade (≈1%), procedural strokes (<0.1%), and mortality (<0.1%).
Some of the other percutaneous devices available in Europe include an Amplatzer Cardiac Plug (ACP) or its newer iteration, the Amulet device (St. Jude Medical, Little Canada, MA), and the WaveCrest (Coherex Medical, Salt Lake City, UT). The largest available literature on the ACP ( n = 1047) demonstrated an annual stroke risk of 2.3% (59% lower than expected based on patient risk scores). The Amulet is reported to have a lower rate of periprocedural leaks than the ACP and a lower risk of dislodgment. The Amplatzer Amulet LAA Occluder Investigational Device Exemption (IDE) trial has been initiated in the United States to demonstrate its noninferiority to the Watchman.
Alternatively, epicardial approaches for LAAO may be considered in patients who cannot tolerate any anticoagulation or do not have suitable LAA anatomy for endocardial occlusion. The Lariat is a suturelike device that is inserted with a combination of endocardial and epicardial approaches and has high procedural success for LAA occlusion. There have been procedural safety concerns with the Lariat due to possible LAA perforation and tamponade requiring urgent cardiac surgery. The Aegis (Aegis Medical, Vancouver, Canada) allows for exclusively epicardial LAAO and has thus far been studied primarily in canine models. Both open and minimally invasive thoracoscopic surgical techniques have also been employed for LAAO. Data on surgical techniques have been limited, with incomplete closure a concern with earlier strategies. Newer devices such as the AtriCure AtriClip system promise to offer superior rates of effective occlusion.
AHA recommendations
The current European Society of Cardiology (ESC) and American Heart Association (AHA)/American College of Cardiology guidelines suggest that surgical excision of the LAA may be considered in patients undergoing cardiac surgery or thoracoscopic AF surgery (grade IIB). LAA occlusion devices are not currently included in the AHA or ESC guidelines.
Patient selection
The national coverage determination requires the following criteria:
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CHADS 2 score ≥2 or CHA 2 DS 2 -VASc score of ≥3
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Documented evidence of a formal shared decision-making process between the patient and a noninterventional physician using evidence-based decision-making tools on oral anticoagulants
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Suitable for short-term warfarin, but deemed unable to take long-term oral anticoagulation
These patients could be those with prior non-life-threatening bleeding events, those with high HAS-BLED scores (typically >3), those with a history of coronary artery disease on dual antiplatelet therapy, and patients with end-stage renal disease (creatinine clearance <15 to 30 mL/min). Bleeding issues in such patients are of significant concern. The current recommendations for the Watchman device require at least 45 days of warfarin post–device implantation followed by 4.5 months of clopidogrel and lifelong aspirin (if the residual leak on follow-up transesophageal echocardiogram [TEE] at 45 days is <5 mm). Registry data have documented excellent safety and efficacy of LAAO in these patients.
Patients with contraindications to even short-term anticoagulation were recently evaluated in a nonrandomized ASA Plavix Feasibility Study With Watchman Left Atrial Appendage Closure Technology (ASAP). The authors achieved a 64% relative risk reduction with the Watchman device compared with historically expected rates of ischemic stroke in patients with a mean CHADS 2 score of 2.8 when treated with antiplatelet therapy alone.
Preprocedural planning
TEE is important to document absence of LAA thrombi and to determine the size and shape of the LAA. The acceptable LAA ostium size should be >17 mm and <31 mm for the Watchman procedure. The LAA ostium should be measured in at least four TEE views: 0 degrees from the left circumflex coronary artery to a point 2 cm from tip of the left upper pulmonary vein (LUPV) limbus and 45, 90, and 135 degrees from the mitral valve (MV) annulus to a point 2 cm from the tip of LUPV limbus. The LAA usable length should be measured next from the ostium to the back wall along the neck axis. The usable LAA length should be equal to or greater than the largest ostium diameter.
The LAA anatomy ( Fig. 22.2 ) is highly variable, and its shape, number of lobes, presence of pectinate muscles, etc. can be characterized on TEE. Although the shape of the LAA can be described using terms such as “chicken wing” or “broccoli,” the only things that are really important are whether we have an adequate landing zone and whether the device will fully exclude the LAA without extruding into the left atrium (LA).
Procedure
The Watchman is a semispherical nitinol frame partially coated with a polyethylene terephthalate fabric cap ( Fig. 22.1 ). The polyethylene terephthalate fabric serves as a 160-micron filter that faces into the body of the LA and creates a permeable membrane to block thrombus embolization while providing a scaffold over which endothelialization can occur. The base is anchored into the LAA by 10 fixation barbs. The device is available in five different sizes: 21, 24, 27, 30, and 33 mm. The Watchman Transseptal Access Sheath is available in double, single, and anterior curves (14F outer diameter, 12F inner diameter, and a 75-cm working length).
The most important step of the LAAO procedure is a good transseptal location. In most cases, this is mid-inferior and posterior on the interatrial septum guided by TEE ( Fig. 22.3 ). This is because the LAA is an anteriorly directed structure with its ostium perpendicular to this axis. A mid-inferior and posterior puncture site allows the delivery sheath to be safely advanced as deep as possible within the LAA for coaxial device deployment. An anterior puncture will place the sheath out of the LAA plane, whereas a superior puncture could result in noncoaxial sheath orientation or obstruction from the LUPV limbus/ “coumadin ridge.” However, mid instead of posterior location might be more suitable for a LAA with a predominant posterior lobe for more direct vector orientation. Likewise, a prominent LUPV limbus might prevent the device sheath from turning anteriorly into the LAA. In such cases, a more mid rather than posterior transseptal puncture in this circumstance will allow easier access to the LAA.
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