Left Atrial Appendage Closure
Thomas A. Dewland
Randall J. Lee
INTRODUCTION
For decades, clinicians have recognized the association between atrial fibrillation (AF) and thromboembolic stroke.1 This risk has traditionally been mitigated through oral anticoagulant therapy.2,3,4 A sizeable proportion of patients, however, are poor candidates for long-term anticoagulation because of an elevated bleeding risk. While data from contemporary clinical trials suggest that the yearly risk of major bleeding on anticoagulation is approximately 2% to 4% per year,3,5,6 this risk is likely higher in certain patient populations with more severe comorbidities compared with carefully selected trial participants. Concern for bleeding complications has prompted the development of alternative therapies to mitigate AF-associated stroke risk.
The left atrial appendage (LAA) plays a central role in the pathogenesis of AF-associated stroke.7,8 The reduction in mechanical atrial function and LAA contractility that accompanies AF frequently results in a substantial decrease in appendage blood flow velocity. In addition to other factors including inflammation and endothelial dysfunction,9 this stasis increases the propensity for thrombus formation; approximately, 90% of the thrombi that develop secondary to AF originate in the LAA.7 This finding, coupled with the clinical need for non-pharmacologic stroke prevention strategies, has led to the development of invasive techniques to anatomically eliminate this vulnerable LAA substrate through mechanical closure.
Several techniques currently exist for LAA closure. Broadly, these techniques can be classified as percutaneous versus surgical. Percutaneous closure is typically performed via a transseptal puncture using femoral venous access, with some techniques also requiring percutaneous subxiphoid epicardial access. Surgical LAA closure typically utilizes either a lateral thoracotomy, lateral thoracoscopic, or median sternotomy approach. Various terms are indiscriminately used in the literature to describe mechanical LAA interventions, including appendage closure, occlusion, exclusion, ligation, and removal. Closure is a general term for the methods described in this chapter. Occlusion specifically refers to the use of an endocardial device to seal the appendage, although exclusion/ligation describes closure via an external ligature. Only open surgical techniques can effectively remove or excise LAA tissue.
Currently, the Watchman device (Boston Scientific, Natick, MA, USA) is the only LAA closure system approved by the US Food and Drug Administration (FDA) for AF-associated stroke prevention. Two randomized trials have compared this therapy to warfarin.10,11 Collectively, these trials suggest that Watchman implantation is noninferior to warfarin for AF stroke prevention.
Additional devices that utilize a conceptually similar approach and implant technique have been developed, including the Amplatzer Cardiac Plug (Abbott Laboratories, Chicago, IL, USA), and WaveCrest LAA Occlusion System (Coherex Medical, Salt Lake City, UT, USA), but none have received FDA approval as of early 2021. The LARIAT device (SentreHEART, Redwood City, CA, USA) is an alternative approach that uses a suture-based epicardial ligation system that is delivered with simultaneous left atrial endocardial and percutaneous subxiphoid epicardial access. This technology has notably not been evaluated with regard to AF stroke prevention in a prospective, randomized clinical trial. Several open surgical techniques have also been developed for LAA closure, including oversewing the appendage or placement of a mechanical clip on the epicardial surface near the appendage ostium (AtriClip [AtriCure, Mason, OH, USA]).
INDICATIONS
In general, LAA closure is indicated for individuals with an elevated risk of AF-associated thromboembolic stroke and a compelling reason to discontinue or avoid long-term anticoagulant therapy. The threshold used to define an appropriate “elevated risk” will continue to evolve as the long-term efficacy of the LAA closure is better defined and advances in implant technology, technique, and experience influence procedural safety. The CHA2DS2-VASc score is the guideline-recommended clinical scoring system used to estimate annual stroke risk among nonanticoagulated patients with AF,12 and this scoring system plays a central role in defining LAA closure candidacy. While the initial clinical trials evaluating the efficacy of Watchman therapy relative to warfarin enrolled individuals with different minimum stroke risk profiles (including a CHADS2 score ≥1 for PROTECT AF [PROTECTion in Patients With Atrial Fibrillation]),10,11 current US Medicare and private insurer reimbursement protocols only cover Watchman implantation for individuals with a CHADS2 score greater than or equal to 2 or a CHA2DS2-VASc score greater than or equal to 3. The stroke risk threshold to justify alternative, non-FDA-approved LAA closure techniques is not defined, although an absolute stroke risk similar to or higher than that used for the Watchman
device is likely appropriate. Because surgical LAA closure can be accomplished with minimal additional risk or procedural length during open cardiac surgery performed for other indications, current surgical guidelines indicate that it is reasonable to surgically close the LAA in all patients with a history of AF at the time of their concomitant open surgical procedure, regardless of thromboembolic risk.13
device is likely appropriate. Because surgical LAA closure can be accomplished with minimal additional risk or procedural length during open cardiac surgery performed for other indications, current surgical guidelines indicate that it is reasonable to surgically close the LAA in all patients with a history of AF at the time of their concomitant open surgical procedure, regardless of thromboembolic risk.13
In addition to having an elevated AF stroke risk, current candidates for LAA closure should also be identified by their treating clinicians as poor long-term candidates for anticoagulation. Explicit criteria to establish poor anticoagulation candidacy have not been rigorously defined. A prior history of clinically significant bleeding is the main justification for LAA closure, although closure can be considered among individuals who have occupations or hobbies that confer an elevated risk of traumatic bleeding or are at high risk of bleeding due to medical comorbidities (eg, thrombocytopenia or frequent mechanical falls with resultant head trauma).
ANATOMIC CONSIDERATIONS
The growth and clinical adoption of LAA closure have resulted in renewed interest in appendage anatomy. The internal orifice of the LAA is typically ovoid, although a minority of patients will demonstrate more complex, alternative morphologies.14 A defined neck usually extends from this orifice, beyond which the body/dominant lobe of the appendage extends and gives rise to a variable number of secondary lobes. Several terms have been used to describe the anatomy of the main appendage body. In general, most appendages demonstrate one of the following four patterns, listed in order of decreasing prevalence: (1) chicken wing, characterized by a sharp bend in the dominant lobe in its proximal or middle portion; (2) cactus, with multiple branches arising from the dominant lobe; (3) windsock, with a relatively straight dominant lobe; or (4) cauliflower, distinguished by complex branching of multiple lobes without a dominant central lobe.15
The Watchman device currently comes in five sizes (21, 24, 27, 30, and 33 mm), and individuals with an appendage ostium that is less than 17 mm or greater than 31 mm are not currently candidates for closure with this device. As the Watchman device is circular, it may prove difficult or impossible to circumferentially occlude appendages with severely eccentric ostial shapes. Ostial width should be measured using transesophageal echocardiography (TEE); the distance between the left circumflex coronary artery/mitral valve annulus and a point 2 cm from the tip of the left upper pulmonary vein/LAA ridge should be assessed at 0, 45, 90, and 135° transducer angles (Figure 48.1). The device is considered “square” in its dimensions, as the length of the device is identical to the maximal ostial diameter. For this reason, appendages with ostial diameters that substantially exceed the depth of the dominant lobe, as is more commonly seen in a chicken wing and cauliflower morphologies, can be particularly challenging to safely and successfully close. Device size selection must therefore incorporate maximal ostial width, appendage depth, and overall appendage anatomy. The device should be compressed between 8% and 20% once successfully implanted to mitigate the risk of embolization. To achieve adequate compression, a device diameter of 5 to 7 mm larger than the maximally measured ostial diameter is typically chosen, provided the appendage depth is also adequate.
 FIGURE 48.1 Measurement of left atrial appendage ostial width by transesophageal echocardiogram. Ostial appendage width should be measured using a transesophageal echocardiogram; the distance between the left circumflex coronary artery/mitral valve annulus (A) and a point 2 cm from the tip of the left upper pulmonary vein/LAA ridge (B) should be assessed. LAA, left atrial appendage. |
The next-generation Watchman FLX device, approved, and currently available overcomes some of the limitations of the previous generation Watchman device. The Watchman FLX comes in five sizes (20, 24, 27, 31, and 35 mm) for ostia measuring 15 to 32 mm, allowing closure of both smaller and larger LAA ostia compared with the current Watchman device. Additionally, because of the redesign of the profile and fixation struts of the Watchman FLX, only 10 mm of LAA depth is required, making the device more amenable to LAA morphologies where the ostium width is greater than the depth of the dominant lobe.
The LARIAT snare is 50 mm in diameter, and attempted closure is not safe when the maximal appendage diameter exceeds this dimension. Some individuals with ostial diameters too large to be closed with a Watchman device (>31 mm) may be candidates for this technique. Because of technical aspects of LARIAT implant, the LAA cannot be closed when the distal tip of the appendage is posteriorly directed or when it lies behind the pulmonary artery.
FUNDAMENTALS OF LEFT ATRIAL APPENDAGE CLOSURE
Preprocedure
It should be emphasized that Watchman LAA closure is best considered as a treatment strategy rather than a single invasive procedure for stroke reduction. Patients who receive this device require postimplant TEE imaging and months of anticoagulation or antiplatelet therapy to prevent thrombus formation during implant endothelialization. Before proceeding with device implantation, it is crucial that patients understand this postprocedure regimen. Detailed counseling and thoughtful
patient selection are especially important with respect to the postprocedure anticoagulation regimen, as the very nature of Watchman candidacy implies a heightened risk of bleeding complication. If a patient is determined to have an absolute contraindication to anticoagulant or antiplatelet therapy, remaining closure options include percutaneous LAA ligation or open surgical closure.
patient selection are especially important with respect to the postprocedure anticoagulation regimen, as the very nature of Watchman candidacy implies a heightened risk of bleeding complication. If a patient is determined to have an absolute contraindication to anticoagulant or antiplatelet therapy, remaining closure options include percutaneous LAA ligation or open surgical closure.
Intraprocedure
Transseptal puncture location is critically important for the success of the procedure. Because of the anterior and superior orientation of the dominant lobe in most appendages, puncture of the fossa ovalis in an inferior and posterior location is necessary to allow for catheter manipulation and coaxial orientation of the delivery sheath and appendage (Figure 48.2). In cases where it is difficult to place the delivery sheath into an appropriate lobe, repeat transseptal access should be considered, especially if review of the initial attempt suggests a lower or more posterior puncture can be safely obtained.
The operator should have a complete understanding of the appendage anatomy before selecting and deploying the device. This will require the integration of both the TEE and fluoroscopic images. These imaging modalities are complementary and, when used together, will ensure adequate device sizing. As echocardiographic measurements can underestimate the ostial diameter and depth of the appendage, careful attention to fluoroscopic assessment of these dimensions is important. In addition to using the depth measurement markers on the access sheath, fluoroscopic estimation of LAA ostial diameter can be quickly performed by remembering that the access sheath is approximately 5 mm in width. Many patients presenting for this procedure will have had a prior contrast-enhanced chest computed tomographic (CT) scan for unrelated clinical care; these studies should also be reviewed. In some cases, three dimensional (3D) reconstruction of appendage anatomy may be possible, which gives the operator further insight into the often-complex structure of the appendage.
 FIGURE 48.2 Transesophageal echocardiogram-guided transseptal puncture. Because of the anterior and superior orientation of the dominant lobe in most appendages, puncture of the fossa ovalis in an inferior and posterior location is necessary to allow for catheter manipulation and coaxial orientation of the delivery sheath and appendage. Bicaval (left) and short-axis (right) transesophageal echocardiographic views are helpful for guiding the puncture. AoV, aortic valve; IVC, inferior vena cava; SVC, superior vena cava. |
CLINICAL APPLICATIONS
Watchman Methodology
Most patients undergo a preprocedure screening TEE in the weeks before implant to confirm that appendage anatomy is appropriate for closure. The necessity of this preprocedure imaging is debatable, as a TEE is also performed at the time of device implantation. Omitting this preprocedure TEE may improve patient convenience, reduce overall healthcare costs, and slightly diminish patient risk. On the other hand, obtaining a screening TEE allows for the early identification of patients with anatomy that is either difficult or not feasible to close. This allows for more tailored preprocedure patient counseling, discussion of alternative closure techniques if necessary, more efficient patient flow in the procedure laboratory, and avoidance of preprocedure anticoagulation in high-risk patients who cannot be treated with a Watchman device.
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