Atrial fibrillation is the most common arrhythmia worldwide and is a major risk factor for embolic stroke. In this article, the authors describe the crucial role of two- and three-dimensional transesophageal echocardiography in the pre- and postprocedural assessment and intraprocedural guidance of percutaneous left atrial appendage (LAA) occlusion procedures. Although recent advances have been made in the field of systemic anticoagulation with the novel oral anticoagulants, these medications come with a significant risk for bleeding and are contraindicated in many patients. Because thromboembolism in atrial fibrillation typically arises from thrombi originating in the LAA, surgical and percutaneous LAA exclusion/occlusion techniques have been devised as alternatives to systemic anticoagulation. Currently, surgical LAA exclusion is typically performed as an adjunct to other cardiac surgical procedures, which limits the number of eligible patients. Recently, several percutaneously delivered devices for LAA exclusion from the systemic circulation have been developed, some of which have been shown in clinical trials to reduce the risk for thromboembolism. These devices use an either purely endocardial LAA occlusion approach, such as the Watchman and Amulet procedures, or both an endocardial and a pericardial (epicardial) approach, such as the Lariat procedure. In the Watchman and Amulet procedures, a transseptally delivered structure composed of nitinol is placed in the LAA orifice, thereby excluding the LAA from the systemic circulation. In the Lariat procedure, a magnet link is created between a transseptally delivered endocardial wire and epicardially delivered pericardial wire, followed by epicardial suture ligation of the LAA.
Highlights
- •
The LAA is the most common site of thrombus formation in nonvalvular atrial fibrillation.
- •
In nonvalvular atrial fibrillation, percutaneous LAA occlusion/exclusion is an alternative method of thromboembolism prevention for patients who are either ineligible for or too high risk to receive systemic anticoagulation therapy.
- •
2D/3D transesophageal echocardiography has a critical role in all percutaneous LAA occlusion/exclusion procedures, including screening for eligibility, device sizing, intraprocedural guidance, and postprocedural follow up.
- •
The most commonly used percutaneous LAA occlusion/exclusion devices worldwide include the Watchman, Amulet, and Lariat.
Attention ASE Members:
Visit www.aseuniversity.org to earn free continuing medical education credit through an online activity related to this article. Certificates are available for immediate access upon successful completion of the activity. Nonmembers will need to join the ASE to access this great member benefit!
LAA Anatomy
Detailed knowledge of LAA anatomy is essential for successful percutaneous LAA closure procedures. The LAA is a complex “fingerlike” projection from the anterolateral portion of the left atrium. Internally, it begins with an orifice that is typically ovoid and thus has a major and a minor orifice diameter. This orifice opens to its neck region, then its body, and ultimately ends in its apex ( Figure 2 ).
The anatomic definition of LAA “orifice” is typically different from the “orifice” defined as the landing zone for various LAA occluder devices. This is addressed in detail with each individual occluder device description below.
The LAA orifice is separated from the left-sided pulmonary veins by the ligament of Marshall (also referred to as the left lateral or “Coumadin” ridge). The LAA may contain one or more lobes, defined as protrusions from its main body.
Anatomic variants of the LAA are well described and include the windsock, the broccoli (or cauliflower), the cactus, and the chicken wing ( Figure 3 ). Of the known LAA variants, the chicken-wing morphology is the most common. However, it is also known to cause the greatest procedural difficulty with regard to LAA occlusion/exclusion. This is due to its broad width and shallow depth, which create a difficult situation regardless of the type of device used.
LAA anatomy is typically established during the screening process using gated cardiac computed tomographic angiography. It may also be confirmed using both intraprocedural TEE and fluoroscopy.
Correspondence of Fluoroscopic and Transesophageal Echocardiographic Views of the LAA
It is important that a common language be developed between interventionalists, who are typically most familiar with fluoroscopy, and echocardiographers performing intraprocedural TEE.
The right anterior oblique caudal view is equivalent to approximately 135° on TEE and typically reveals the major axis of the LAA orifice ( Figure 4 ).
The right anterior oblique cranial view is equivalent to approximately 45° on TEE and typically reveals the minor axis of the LAA orifice ( Figure 5 ).
LAA Anatomy
Detailed knowledge of LAA anatomy is essential for successful percutaneous LAA closure procedures. The LAA is a complex “fingerlike” projection from the anterolateral portion of the left atrium. Internally, it begins with an orifice that is typically ovoid and thus has a major and a minor orifice diameter. This orifice opens to its neck region, then its body, and ultimately ends in its apex ( Figure 2 ).
The anatomic definition of LAA “orifice” is typically different from the “orifice” defined as the landing zone for various LAA occluder devices. This is addressed in detail with each individual occluder device description below.
The LAA orifice is separated from the left-sided pulmonary veins by the ligament of Marshall (also referred to as the left lateral or “Coumadin” ridge). The LAA may contain one or more lobes, defined as protrusions from its main body.
Anatomic variants of the LAA are well described and include the windsock, the broccoli (or cauliflower), the cactus, and the chicken wing ( Figure 3 ). Of the known LAA variants, the chicken-wing morphology is the most common. However, it is also known to cause the greatest procedural difficulty with regard to LAA occlusion/exclusion. This is due to its broad width and shallow depth, which create a difficult situation regardless of the type of device used.
LAA anatomy is typically established during the screening process using gated cardiac computed tomographic angiography. It may also be confirmed using both intraprocedural TEE and fluoroscopy.
Correspondence of Fluoroscopic and Transesophageal Echocardiographic Views of the LAA
It is important that a common language be developed between interventionalists, who are typically most familiar with fluoroscopy, and echocardiographers performing intraprocedural TEE.
The right anterior oblique caudal view is equivalent to approximately 135° on TEE and typically reveals the major axis of the LAA orifice ( Figure 4 ).
The right anterior oblique cranial view is equivalent to approximately 45° on TEE and typically reveals the minor axis of the LAA orifice ( Figure 5 ).
Overview of Percutaneous LAA Occlusion/Exclusion Procedures
Irrespective of the LAA occlusion/exclusion device used, the basic steps are common to all percutaneous LAA occlusion/exclusion procedure. All percutaneous LAA occluder implantation procedures begin with peripheral venous access, which is typically obtained through the right femoral vein. Subsequently, a transseptal puncture is performed to gain access to the left atrium. Thereafter, specific steps for deployments of individual occluder devices are taken.
Transseptal Puncture for Percutaneous LAA Occluders
Overview
After peripheral venous access is obtained, typically through the femoral vein, a transseptal needle delivery catheter and dilator are passed through the inferior vena cava into the right atrium and temporarily placed in the superior vena cava. Thereafter, a transseptal needle is advanced through the delivery catheter.
Using transesophageal echocardiographic guidance, the whole system is then withdrawn from the superior vena cava into the right atrium and positioned against the inferior and posterior portion of the interatrial septum. The deliver catheter is then advanced against the interatrial septum to tent the interatrial septum at an appropriate location. Fluoroscopy and TEE are essential in guiding the proper location of tenting. The needle is then advanced, creating a transseptal puncture.
The inferoposterior puncture position allows the most direct route to the anterolaterally located LAA. This is in contrast to other transseptal procedures such as MitraClip (Abbott Vascular, Abbott Park, IL) implantation and transcatheter mitral valve replacement, which require a superior and posterior transseptal puncture to ensure adequate height above the mitral valve.
Two commonly used transseptal delivery catheters are the Mullins introducer (Medtronic, Minneapolis, MN), and the Agilis steerable introducer (St. Jude Medical). The most commonly used transseptal needle is the Brockenbrough needle (Medtronic), but a radiofrequency needle (Baylis Medical, Montreal, QC, Canada) can be helpful to cross thick, fibrotic, or patched septa. Transseptal catheters and needles are depicted in Figure 6 .
Once the transseptal puncture of the procedure has been completed, the dilator and sheath are then advanced to avoid left atrial wall injury. A wire is subsequently passed into the left atrium and typically positioned in the left superior pulmonary vein; the dilator and sheath are then removed.
Echocardiographic Guidance of Transseptal Puncture
Although transseptal puncture can be performed with adequate safety using a combination of operator tactile feedback and fluoroscopy, echocardiography (2D TEE, intracardiac echocardiography, and 3D transesophageal biplane imaging) can improve transseptal puncture safety and overall procedural success.
Using 2D and 3D TEE, assessment of the interatrial septum first includes identification of the position, thickness, and mobility of the fossa ovalis. Subsequently, color Doppler imaging is used to assess for baseline patent foramen ovale or atrial septal defect (ASD).
Using biplane imaging of the interatrial septum (anterior-posterior in one plane, superior-inferior in the other) the transseptal needle is guided toward the inferior and posterior portion of the fossa ovalis. After slight needle assembly advancement toward the left atrium, the tenting of the interatrial septum identifies the location of the transseptal needle on echocardiography ( Figure 7 , [CR] available at http://www.onlinejase.com ). It is of utmost importance to do the transseptal puncture in the inferior and posterior aspect of the interatrial septum ( Figure 8 ).
When the echocardiographer provides real-time TEE to an interventionalist, it is useful to label superior, inferior, anterior, and posterior locations on the echocardiographic image.
After transseptal puncture has been performed, 3D TEE using 3D zoom of the interatrial septum may be helpful to confirm that the transseptal puncture has occurred in a favorable location. A step-by-step approach for the production of high-quality views of the interatrial septum by 3D TEE has been previously described using the TUPLE (tilt up, then left) maneuver.
Atrial septal aneurysm and marked lipomatous hypertrophy of the interatrial septum may present anatomic challenges to successful transseptal puncture. The presence of a large atrial septal aneurysm should be communicated to the interventionalist, as excessive advancement of the transseptal needle may lead to perforation of the left atrial free wall. In the presence of lipomatous hypertrophy, it is important to guide the transseptal puncture through the thin central portion of the fossa ovalis rather than the hypertrophied limbs.
Watchman Procedure
Overview
The Watchman is a transseptally delivered, self-expanding nickel titanium device with fixation barbs, covered by a permeable polyester fabric. The device is delivered under fluoroscopic and echocardiographic guidance and is available in five sizes (21, 24, 27, 30, and 33 mm) on the basis of the device diameter on its left atrial side ( Figure 9 ).
The Watchman procedure begins with venous access and transseptal puncture, as described previously. Subsequently, the Watchman 12-Fr delivery system with a pigtail catheter is advanced into the left atrium over the wire and then placed into the LAA. Next, iodinated contrast is injected into the LAA to define its anatomy on fluoroscopy. The Watchman device is then positioned and delivered in the LAA ostium. Finally, the device is released after stability and optimal position are confirmed by both echocardiography and cine fluoroscopy with intravenous contrast. An animated description of the Watchman procedure can be viewed on YouTube: https://www.youtube.com/watch?v=8O2Hba-JQoQ&feature=youtu.be&list=PL63i2jgsqsT_Jzpx5tTAI_rM56xo6JDUj .
Of all percutaneous LAA occluder devices, the Watchman has the most outcomes data, which have demonstrated its noninferiority to chronic warfarin therapy in a randomized trial. Possible procedural complications include pericardial effusion (PEF), device embolization, and procedure-related stroke. After device implantation, patients typically require warfarin therapy for 45 days, followed by dual-antiplatelet therapy (with aspirin and clopidogrel) for 6 months and then aspirin alone for life to prevent clot formation.
Baseline Comprehensive Assessment
All percutaneous LAA occlusion/exclusion devices require comprehensive baseline intraprocedural 2D and 3D TEE. This echocardiographic assessment focuses on establishing the presence or absence of any preexisting intracardiac thrombus (which would lead to procedure cancellation), baseline degree of PEF, as well as anatomic characteristics of the LAA and interatrial septum. The size and position of the LAA body and LAA orifice, the presence or absence of valvular abnormalities, mobile aortic atheroma (>4 mm), and intracardiac shunt are also established.
LAA Sizing Specific to the Watchman
LAA landing zone size and LAA depth are measured during the baseline procedural assessment for the Watchman procedure. On 2D TEE, the LAA is imaged at 0°, 45°, 90°, and 135° ( Figure 10 ). Measurements of the LAA are performed at these imaging angles to determine the maximal diameter of the anticipated landing zone and appendage depth. For the Watchman, the LAA landing zone is measured from the top of the mitral valve annulus or circumflex coronary artery to a point 2 cm below the tip of the left upper pulmonary vein limbus. Depth is measured from the plane of the LAA orifice to the LAA apex.
Because of the tomographic nature of 2D imaging, there is a degree of uncertainty that the 2D transesophageal echocardiographic landing zone diameter measurements are done in the same plane. This limitation can be overcome using multiplanar reconstruction 3D TEE. In multiplanar reconstruction mode, two long axes of the LAA are aligned to visualize the short-axis plane of the LAA, allowing precise measurement of the landing zone diameter ( Figure 11 ).
Once echocardiographic measurements have been performed, the largest LAA landing zone diameter is selected for device sizing. The device is typically oversized compared with the largest measured LAA diameter by 8% to 20%.
LAA Anatomic Exclusion Criteria for the Watchman Device
- •
LAA orifice diameter that is either too small (<16.8 mm) or too large (>30.4 mm).
- •
LAA depth that is too shallow (LAA depth less than largest LAA orifice diameter).
- •
The depth of a secondary LAA lobe (if present) cannot be too close to the LAA orifice (must be >1 cm away), which could lead to an uncovered portion of the LAA.
Other Possible Exclusion Criteria for the Watchman Device
- •
Atrial septal aneurysm excursion distance >15 mm. Atrial septal aneurysm may be considered an indication for anticoagulation even if LAA is excluded.
- •
Large interatrial shunt. This is a semiquantitative criterion; no specific definition for a large shunt on color Doppler or after agitated saline injection is given.
- •
Mobile aortic plaque >4 mm in thickness.
- •
Significant mitral stenosis (mitral valve area < 1.5 cm 2 ).
- •
PEF with thickness > 2 mm.
Echocardiographic Guidance for the Watchman Procedure
After transseptal puncture has been guided by fluoroscopy and echocardiography, the Watchman 12-Fr delivery system with a pigtail catheter is advanced into the left atrium. The delivery system is then guided into the left atrium with both fluoroscopic and 2D or 3D transesophageal echocardiographic guidance. Three-dimensional TEE has the advantage of allowing visualization of the entire lengths of catheters as they traverse the left atrium to reach the LAA.
It also provides clear imaging of the distance between the tip of the guide catheter in the left atrium relative to the atrial septum to prevent accidental transseptal puncture site decannulation back into the right atrium.
After the guide catheter is advanced toward the LAA orifice, a pigtail catheter is threaded through the guide catheter, and contrast angiography is performed to fluoroscopically evaluate the LAA. On 2D and 3D echocardiography, this produces copious amounts of bubbles that obscure imaging.
The guide catheter/pigtail combination is then is navigated such that the corresponding radiopaque marker band for the device size is aligned with the LAA ostium. Once the guide catheter is properly positioned, the pigtail is removed. The Watchman device is then unsheathed slowly but remains attached to the delivery cable. This is observed using 2D and 3D TEE ( Figure 12 , Videos 2 and 3 available at http://www.onlinejase.com ).
