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 Table of Contents  
REVIEW ARTICLE
Year : 2017  |  Volume : 2  |  Issue : 1  |  Page : 22-28

Evolution of left atrial appendage exclusion


Department of Cardiovascular Diseases, Mayo Clinic Hospital, Arizona, Phoenix, AZ, USA

Date of Web Publication19-Jun-2017

Correspondence Address:
Dan Sorajja
Division of Cardiovascular Diseases, Mayo Clinic Hospital, 5777 E Mayo Boulevard, Phoenix, AZ, 85054
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2352-4197.208457

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  Abstract 

Atrial fibrillation is independently associated with an increased risk of thromboembolic stroke. While anticoagulants decrease this risk, they also carry a substantial risk of bleeding. Most left atrial thrombi arise from the left atrial appendage (LAA), which has led to several investigations into surgical and percutaneous methods of LAA exclusion for stroke reduction. The PubMed database was queried, and over 400 articles were considered for inclusion in this review. Of the surgical methods of LAA exclusion, complete excision is the most effective. Other methods, including ligation and stapling, may be incomplete and associated with left atrial thrombus formation. Surgical LAA exclusion has been commonly performed during mitral valve surgery although it has not been shown to prevent stroke in many retrospective studies. In patients unable to take warfarin, several percutaneous LAA exclusion devices have been studied, including the PLAATO system, Amplatzer Cardiac Plug (ACP), Watchman device, and Lariat. Both the ACP and Watchman have shown a significant stroke reduction and improved procedural safety with greater experience. The Lariat ligates the LAA using a combined endocardial and epicardial approach but is currently associated with substantial procedural risks. With better patient selection for the different options of LAA exclusion, thromboembolic stroke protection can be maximized with fewer complication risks.

Keywords: Atrial fibrillation, exclusion, left atrial appendage, occlusion, stroke


How to cite this article:
Abrich VA, Sorajja D. Evolution of left atrial appendage exclusion. Int J Heart Rhythm 2017;2:22-8

How to cite this URL:
Abrich VA, Sorajja D. Evolution of left atrial appendage exclusion. Int J Heart Rhythm [serial online] 2017 [cited 2017 Nov 19];2:22-8. Available from: http://www.ijhronline.org/text.asp?2017/2/1/22/208457


  Introduction Top


Atrial fibrillation (AF) was first found to independently increase the risk of stroke by 4.8-fold, based on data from the Framingham study in 1991.[1] The mechanism is widely accepted to be related to stasis of blood in the left atrium, which predisposes to thrombus formation and resultant systemic embolization to the cerebral circulation.[2] The majority of left atrial thrombi have been found to originate in the left atrial appendage (LAA), which accounts for 91% of thrombi in nonvalvular AF and 57% of thrombi in rheumatic AF.[3] The risk of stroke can be calculated based on the CHA2 DS2–VASc score.[4] Anticoagulation with warfarin was found to decrease this stroke risk by 64%.[5] Novel oral anticoagulants, such as dabigatran, rivaroxaban, and apixaban, are even more effective than warfarin at reducing the risk of ischemic stroke and have a better safety profile. Compared to warfarin, together they are associated with an 18% reduction in stroke or systemic embolism, 9% reduction in mortality, and 49% reduction in hemorrhagic stroke.[6] Not surprisingly, the administration of warfarin and novel oral anticoagulants has emerged as first-line therapy in the management of AF.[7] Unfortunately, anticoagulants are inherently associated with risks of bleeding, which may be substantial and occasionally life-threatening.[2] As such, exclusion of the LAA has been investigated as an alternative to anticoagulation for reducing the stroke risk associated with AF. In this review, the different modalities of LAA exclusion will be covered, ranging from surgical exclusion during cardiac surgery to the use of dedicated percutaneous occlusion devices.


  Methods Top


We queried the PubMed database for articles that contained the search phrases “left atrial appendage occlusion” and “left atrial appendage exclusion” and reviewed more than 400 abstracts for inclusion in this review. Publication dates of included articles ranged from July 02, 1949 to February 01, 2016. We chose to include randomized controlled trials, case–control studies, and case series dealing with the topics of surgical or percutaneous LAA exclusion. A particular focus was placed on cerebrovascular event outcomes and procedural safety. Articles were saved and organized using EndNote X4 software (Thomson Reuters, Philadelphia, Pennsylvania). Reported event rates were normalized to adjusted annual event rates.

Surgical Exclusion

Surgical LAA exclusion was first performed concomitantly during surgery for mitral stenosis.[8],[9] Although this procedure has been shown to be safe, its implementation depends on the surgeon and institution.[3] Surgical LAA exclusion is now indicated in patients with AF undergoing cardiac surgery for other primary indications, according to current management guidelines for AF.[7] Successful LAA exclusion is confirmed by transesophageal echocardiography (TEE), with overall success rates among studies varying from 40% to 90%.[10],[11],[12],[13],[14] Common methods of LAA exclusion include complete excision of the LAA (45%–83% success rate), exclusion through ligation (23%–90% success rate), and exclusion through stapling (0%–72% success rate) [Figure 1]. Left atrial thrombus or spontaneous echo contrast has been documented in up to 50% of patients with incomplete exclusion following ligation or stapling and in up to 17% of patients following complete excision of the LAA. More recently, surgical LAA exclusion with an epicardial clip system (Atriclip, AtriCure, Inc., Cincinnati, Ohio) has been associated with a 100% successful closure rate during open heart surgery and with a 71% successful closure rate during minithoracotomy [Figure 2].[15],[16]
Figure 1: Stapled excision of the left atrial appendage. (a) The stapler is loaded with pericardial strips. (b) The left atrial appendage is excised, and area beneath the buttressed staple line is examined (From Gillinov AM, et al. Stapled excision of the left atrial appendage. J Thorac CV Surg 2005;129 (3):679-680. Used with permission).

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Figure 2: Atriclip for exclusion of the left atrial appendage (From Salzberg SP, et al. left atrial appendage clip occlusion: Early clinical results. J Thorac Cardiovasc Surg 2010; 139:1269-74. Used with permission). (a) Reusable Miltex deployment tool. LAA clip is loaded onto the jaws of this tool. (b) LAA mobilized within the clip (1) near the pulmonary veins (2) and pulmonary artery (3) with operator's hand (4) mobilizing the heart.

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The effectiveness of surgical LAA exclusion during cardiac surgery for reducing the risk of stroke has been evaluated in multiple retrospective studies, with mostly disappointing results. Surgical LAA exclusion done concomitantly with mitral valve surgery has been studied in multiple heterogeneous series comprising between 50 and 812 patients.[13],[16],[17],[18],[19] In these studies, the prevalence of AF ranged from 61.3% to 85.9%, with LAA exclusion being performed in 27.9%–100% of patients. Adjusted annual cerebrovascular event rates in these patients were 0.6%–3.4% during mean follow-up periods of 3.6–5.8 years.[13],[16],[17],[19] LAA exclusion was not found to prevent stroke in most of these studies;[13],[17],[18],[19] however, one study found the absence of LAA exclusion to be a predictor of embolic events.[16] Interestingly, another study that included patients who underwent either mitral valve or coronary artery bypass graft (CABG) surgery showed that surgical LAA exclusion prevented postoperative cerebrovascular events for patients with CHA2 DS2–VASc scores of two or less.[17]

Aside from mitral valve surgery, surgical LAA exclusion is routinely performed during the Maze procedure for surgical ablation of AF.[20] In a study of 265 patients undergoing the Maze procedure, the adjusted, annual cerebrovascular event rate was 0.3% during a mean follow-up of 3.6 years. In other studies, the Maze procedure has been associated with successful LAA closure, and its omission was a predictor of late stroke occurrence.[10],[18] Isolated, thoracoscopic LAA exclusion has also been investigated: one small series of 15 patients undergoing isolated LAA exclusion through ligation or stapling had an annual adjusted stroke rate of 0% during a mean follow-up of 1.3 years, whereas another small series of thirty patients undergoing complete LAA excision had an annual adjusted stroke rate of 3.8% during a mean follow-up of 3.5 years.[21],[22]

More recently, interest has grown for performing LAA exclusion concomitantly during CABG surgery. The safety and efficacy of this practice were prospectively evaluated in the Left Atrial Appendage Occlusion Study (LAAOS) I and II, two small, randomized pilot studies comprising 77 and 51 patients, respectively.[15],[23] Adjusted annual stroke rates in the LAA occlusion arms were 3.6% for LAAOS I and 3.8% for LAAOS II during mean follow-up periods of 13 months and 12 months, respectively. In comparison, the adjusted annual stroke rates for the non-LAA occlusion arms were 0% for LAAOS I and 12.0% for LAAOS II. These studies paved the way for LAAOS III, an ongoing multicenter, randomized controlled trial. LAAOS III is recruiting 4700 patients with AF undergoing CABG, who will be randomized to LAA exclusion versus no LAA exclusion.[24] The primary outcome of stroke or systemic embolism will be analyzed at a mean follow-up of 4 years. This will be the largest study to date to determine whether or not surgical LAA exclusion reduces the risk of stroke in patients with AF.


  Percutaneous Exclusion Top


Percutaneous LAA exclusion devices were developed to provide thromboembolic protection in patients with AF who have contraindications to anticoagulation, embolic events while taking anticoagulants, or intolerance to anticoagulants [Table 1].[25] The first device developed was the percutaneous LAA transcatheter occlusion system (PLAATO, ev3 Inc., Plymouth, Minnesota, USA); however, its development was discontinued by the manufacturer in 2007 because of financial reasons. The device consisted of a self-expanding nitinol cage that was covered by a nonpermeable, polytetrafluoroethylene membrane designed to promote endothelialization,[26] and patients who had the device implanted were required to take aspirin [Figure 3]a.[25] The PLAATO system was evaluated in multiple series comprising between 15 and 180 patients.[26],[27],[28],[29],[30],[31] Success rates for acute closure varied from 90% to 100%. Periprocedural complications reported in these studies included a 0.6%–1.4% incidence of device embolization [28],[29] as well as a 1.6%–6.7% incidence of pericardial effusion.[26],[27],[28],[29],[30],[31] Adjusted annual cerebrovascular event rates were 0%–5.5% during mean follow-up periods between 9.8 and 45 months.[27],[28],[29],[30],[31] The PLAATO device was associated with a 65% reduction in stroke risk relative to the predicted risk of stroke based on the CHADS2 score.[27],[28]
Table 1: Comparison between different percutaneous methods of left atrial appendage exclusion

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Figure 3: Percutaneous exclusion of the left atrial appendage. (a) PLAATO System; (b) Amplatzer Cardiac Plug; (c) Watchman; (d) Lariat Suture Delivery Device (From Patel TK, Yancy CW, Knight BP. Left atrial appendage exclusion for stroke prevention in atrial fibrillation. Cardiol Res Pract 2012; Article ID 610827, 2012. doi: 10.1155/2012/610827. Used with permission).

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The Amplatzer septal occluder (St. Jude Medical, St. Paul, Minnesota, USA), originally designed for closing atrial septal defects, was the next percutaneous device that was tested for occluding the LAA; the device was used in a series of 16 patients, in which one of these patients had device embolization [Figure 3]b.[32] The Amplatzer septal occluder was subsequently adapted for LAA occlusion as the Amplatzer Cardiac Plug (ACP, St. Jude Medical). The ACP consists of a lobe connected to a disc; the lobe anchors the device in the neck of the LAA, and the disc covers the LAA orifice.[25] After the device is implanted, dual antiplatelet therapy (aspirin and clopidogrel) is administered for 1–6 months, after which aspirin alone is prescribed. Success rates for acute closure varied from 95% to 98% in multiple series comprising between 20 and 137 patients.[33],[34],[35],[36] Periprocedural complications reported in these studies included pericardial effusion (1.7%–3.5% incidence),[33],[34],[35],[36],[37] device embolization (0%–1.9% incidence),[33],[34],[35],[36],[37] coronary artery embolism (0.7%–5% incidence),[33],[34] and cerebrovascular events (1.9%–2.5% incidence).[33],[35],[37] One study showed a 14.2% incidence of thrombi with the ACP although all thrombi resolved after treatment with enoxaparin.[36] During mean follow-up periods ranging from 12.7 to 21 months, adjusted annual cerebrovascular event rates were 0%–1.7%.[34],[35],[36] A second generation device, the Amplatzer Amulet (St. Jude Medical) has been shown to have comparable efficacy to the ACP but with fewer peridevice leaks.[38]

The Watchman (Boston Scientific Corporation, Natick, Massachusetts) was the next percutaneous LAA occlusion device to be developed [Figure 3]c. It consists of a nitinol cage with a row of fixation barbs around the surface, which are covered by a permeable polymeric membrane.[25] Unlike previous percutaneous devices, the Watchman was evaluated in a randomized controlled trial. PROTECT AF (Watchman Left Atrial Appendage System for Embolic Protection in Patients With Atrial Fibrillation) was a multicenter, unblinded clinical trial that randomized 707 patients in a 2:1 ratio to two arms: the device versus warfarin.[39] The successful implantation rate was 88%. Patients who had the Watchman implanted were required to take warfarin with aspirin for the first 45 days after the implant, followed by dual antiplatelet therapy for 4.5 months, and then aspirin alone thereafter. At a mean follow-up of 3.8 years, the Watchman was superior to warfarin, demonstrating a 40% reduction in the primary composite endpoint of stroke, systemic embolism, and cardiovascular death. This reduction was mainly driven by reductions in the incidence of hemorrhagic stroke (0.6% in the device arm, 4.0% in the warfarin arm) and cardiovascular death (3.7% in the device arm, 9.0% in the warfarin arm). Although no significant difference in the incidence of ischemic stroke was shown in the trial (5.2% in the device arm, 4.1% in the warfarin arm), a meta-analysis of 2406 trial and registry patients later showed the Watchman to be associated with a small increase in ischemic strokes offset by a relatively larger reduction in hemorrhagic strokes.[40]

Procedure-related complications in PROTECT AF occurred in the device arm within the first 7 days and included pericardial effusion with tamponade (4.8% incidence), ischemic stroke (1.3% incidence), and device embolization (0.6% incidence).[39] Improved procedure-related outcomes have since been shown in the subsequent randomized PREVAIL (Watchman Left Atrial Appendage Closure Device in Patients with Atrial Fibrillation Versus Long-Term Warfarin Therapy) trial, as well as the Continued Access Protocol and EWOLUTION registries, mitigating initial safety concerns [Table 2]. With improved operator experience over a learning curve, successful device implantation rates were higher (95%–98.5%), whereas periprocedural complication rates were lower than those observed in the PROTECT AF trial. These included serious pericardial effusions (0.5%–2.2% incidence), device embolization (0%–0.5% incidence), and ischemic stroke (0%–0.4% incidence).[41],[42],[43] Moreover, alternative blood thinner regimens after implantation have been investigated. Replacement of warfarin during the first 45 days after device deployment with novel oral anticoagulants and dual antiplatelet therapy has been shown to be safe and effective.[44],[45],[46] Nevertheless, device thrombosis has been documented in patients with clopidogrel resistance.[47]
Table 2: Procedural complications following Watchman implantation

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Subsequent to the Watchman, the Lariat Suture Delivery Device (SentreHeart, Inc., Redwood City, California) was developed [Figure 3]d. The Lariat incorporates an epicardial approach to exclude the LAA. To deploy the Lariat, the operator accesses the pericardial space and guides a snare and suture to the base of the LAA over a rail comprised a set of magnet-tipped epicardial and endocardial guidewires, thus ligating the LAA.[48] Following the procedure, antiplatelet and anticoagulant therapy regimens are heterogeneous among patients, consisting of aspirin monotherapy, dual antiplatelet therapy, or oral anticoagulation.[49],[50],[51],[52] Successful closure rates have been reported to range from 93% to 96% in multiple series comprising between 27 and 154 patients.[49],[50],[51],[52] Procedural complications in these studies included LAA perforation (0.6%–9.8% incidence),[49],[50],[51],[52] pericardial effusions (1.1%–43.9% incidence),[49],[50],[51],[52] and pericarditis (2.2%–22% incidence).[49],[50],[52] One study reported a 3.7% incidence of periprocedural stroke [52] while another study reported a 4.8% incidence of left atrial thrombi.[51] The adjusted annual ischemic cerebrovascular event rates ranged from 0% to 4.2% during mean follow-up periods of four to 12 months.[49],[50],[51]

In addition to safety and ischemic events, the effect of percutaneous LAA exclusion on atrial electrical activity is also a subject of interest. Necrosis of the LAA after ligation with the Lariat has been reported to decrease the duration, amplitude, and dispersion of the P wave on the electrocardiogram, which may represent reverse electrical atrial remodeling.[53] However, the combination of pulmonary vein isolation and LAA closure did not show a reduction in AF after 2 years in a small randomized trial of 89 patients.[54] In fact, the short-term burden of postprocedure AF was higher in those patients who underwent the combination procedure. Nevertheless, the recently approved aMAZE trial (Percutaneous Alternative to the Maze Procedure for the Treatment of Persistent or Long-standing Persistent Atrial Fibrillation) will prospectively gauge the efficacy of the Lariat in conjunction with pulmonary vein isolation for maintenance of sinus rhythm in a larger cohort of approximately 600 patients with AF, with stroke being a secondary endpoint.[55]


  Imaging Top


Imaging studies are important for confirming correct device placement and for checking for peridevice leaks. TEE has been used in most studies of percutaneous devices; however, advanced three-dimensional imaging with multidetector computed tomography (MDCT) has become an important adjunct. Compared with TEE, MDCT can provide more accurate data for sizing and for optimal placement of percutaneous occlusion devices, which can reduce procedural complications and the occurrence of peridevice leakage.[56],[57] Moreover, MDCT has revealed substantial heterogeneity of the LAA and its ostium, allowing for several distinct morphological classifications that have implications on patient selection and procedural planning.[58] Cardiac magnetic resonance and real-time three-dimensional TEE have emerged as alternatives to MDCT.[59],[60] Recently, three-dimensional printing of a patient's LAA from a CT image has helped plan the implantation of a Watchman device, which may have interesting implications as the technology becomes more widely available in hospitals.[61]


  Conclusion Top


LAA exclusion has evolved over the past several decades from being a procedure only performed concomitantly during cardiac surgery to now including several dedicated percutaneous procedure options intended to replace anticoagulation for the treatment of patients with AF. With most surgical data being retrospective, the results of the ongoing LAAOS III will more definitively determine the benefit of surgical LAA exclusion. Of the percutaneous devices, the Watchman is currently the only one the US Food and Drug Administration approved after it showed clinical benefit in randomized controlled trials.[62] Eligible patients must have a CHA2 DS2–VASc score ≥3 and a contraindication for long-term anticoagulation although they should be able to take warfarin for the short-term.[63] Whereas implantation of the Watchman has fewer complications with improved operator experience, the Lariat is still associated with substantial procedural safety concerns. The routine deployment of the Lariat during pulmonary vein isolation procedures will depend on the efficacy and safety results from the ongoing aMAZE trial.[55] With better patient selection for the different options of LAA exclusion, thromboembolic stroke protection for patients with AF can be maximized with fewer complication risks.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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