Author + information
- Received December 2, 2014
- Revision received January 22, 2015
- Accepted February 5, 2015
- Published online April 1, 2015.
- Nina C. Wunderlich, MD∗,
- Roy Beigel, MD†,‡,
- Martin J. Swaans, MD, PhD§,
- Siew Yen Ho, MD‖ and
- Robert J. Siegel, MD†∗ ()
- ∗Cardiovascular Center Darmstadt, Darmstadt, Germany
- †The Heart Institute, Cedars-Sinai Medical Center, Los Angeles, California
- ‡The Heart Institute, Sheba Medical Center, and the Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel
- §Department of Cardiology, St. Antonius Hospital, Nieuwegein, the Netherlands
- ‖Cardiac Morphology Unit, Royal Brompton Hospital, London, United Kingdom
- ↵∗Reprint requests and correspondence:
Dr. Robert J. Siegel, Cedars Sinai Medical Center, 127 South San Vicente Boulevard, Suite A3600, Los Angeles, California 90048.
Percutaneous left atrial appendage (LAA) exclusion is an evolving treatment to prevent embolic events in patients with nonvalvular atrial fibrillation. In the past few years multiple percutaneous devices have been developed to exclude the LAA from the body of the left atrium and thus from the systemic circulation. Two- and 3-dimensional transesophageal echocardiography (TEE) is used to assess the LAA anatomy and its suitability for percutaneous closure to select the type and size of the closure device and to guide the device implantation procedure in conjunction with fluoroscopy. In addition, 2- and 3-dimensional TEE is also used to assess the effectiveness of device implantation acutely and on subsequent follow-up examination. Knowledge of the implantation options that are currently available along with their specific characteristics is essential for choosing the appropriate device for a given patient with a specific LAA anatomy. We present the currently available LAA exclusion devices and the echocardiographic imaging approaches for evaluation of the LAA before, during, and after LAA occlusion.
The left atrial appendage (LAA) is a tubular, blind-ended pouch attached to the main body of the left atrium (LA). It is the source of cerebral thromboembolism in approximately 90% of patients with nonvalvular atrial fibrillation (AF) (1,2).
LAA occlusion or exclusion to prevent embolism in patients with nonvalvular AF by implanting a percutaneously delivered device to exclude the LAA cavity from the systemic circulation has evolved since the first implantation of an LAA occlusion device in 2001 (3). Currently there are 3 devices (Figure 1) available for percutaneous implantation within the LAA and one suture-based technology to occlude the LAA (Figure 2). European guidelines for management of AF now recommend that percutaneous LAA closure may be considered in high stroke risk patients with contraindications for long-term oral anticoagulation (class IIb indication, level of evidence B) (4).
Transesophageal echocardiography (TEE) is the main imaging modality used to assess LAA anatomy, aid in the selection of a suitable device and size, and identify anatomic contraindications. Two-dimensional (2D) and 3-dimensional (3D) TEE are used in conjunction with fluoroscopy to guide the procedure, evaluate results after device placement, and monitor for complications. In this review, we focus on current echocardiographic imaging approaches for the evaluation of the LAA before, during, and after LAA occlusion, and on the different imaging aspects in regard to the currently available devices.
Current Devices for Percutaneous LAA Occlusion or Exclusion
As shown in the Central Illustration, as well as in Figures 1 and 2, knowledge of the different devices and their characteristics is important for optimal patient selection and successful guidance of an LAA closure procedure. All LAA closure devices described in this review are available for clinical use in Europe. In the United States, the endoluminally implanted devices can only be used as part of a clinical trial. The LAA occluder device (Watchman device, Boston Scientific, Natick, Massachusetts) received FDA approval very recently in March 2015. The LAA ligation device (LARIAT suture device, SentreHEART, Inc., Redwood City, California) is approved by the Food and Drug Administration for suture placement and knot tying in surgical applications; however, it is not approved specifically for treatment of stroke prevention in patients with AF.
Endoluminal LAA closure devices
LAA occluder device
The LAA occluder device (Figure 1A) is a self-expanding system with a nitinol frame covered with a permeable 160 μm polyethylene terephthalate fabric on the LA side of the device. Ten active fixation hooks are placed around the circumference. There are more data on outcomes available on the LAA occluder device than on any other LAA occlusion system. Randomized studies with the LAA occluder device (PROTECT-AF [WATCHMAN Left Atrial Appendage System for Embolic PROTECTion in Patients With Atrial Fibrillation] trial; n = 707; 463 device/244 control) confirmed noninferiority for LAA occlusion compared with oral warfarin therapy with regard to the primary composite endpoint of stroke, cardiovascular or unexplained death, and all-cause death (5–7). After 3.8 years of follow-up among PROTECT-AF patients, percutaneous LAA closure met criteria for both noninferiority and superiority, compared with warfarin, for preventing the combined outcome of stroke, systemic embolism, and cardiovascular death, as well as superiority for cardiovascular and all-cause mortality (8).
In the randomized PREVAIL (Evaluation of the Watchman LAA Closure Device in Patients With Atrial Fibrillation Versus Long Term Warfarin Therapy) trial (n = 407; 269 device/138 control), a continuum of the PROTECT-AF trial, LAA occlusion was noninferior to warfarin for ischemic stroke prevention or systemic embolism >7 days post-procedure. Although noninferiority was not achieved for overall efficacy, event rates were low and numerically comparable in both treatment arms (device implantation vs. chronic warfarin therapy) (9). Registry data on 610 patients have also been published (10–12).
First Generation LAA Plug
The first generation LAA plug (Amplatzer Cardiac Plug, St. Jude Medical, Inc., St. Paul, Minnesota) (Figure 1B) device is designed to occlude the full cross-sectional area of the LAA orifice. The device is made of a flexible braided nitinol mesh and has 2 major components: a distal lobe with 6 pairs of hooks attached and a proximal disc to cover the ostium. A central waist constitutes an articulating, compliant connection between the disc and the lobe. Nonrandomized trials with the first generation LAA plug demonstrate feasibility, effectiveness in reducing thromboembolic cerebral events, and a high rate of technical success (13–16). Data on nearly 2,000 first generation LAA plug patients are published. Most of them were implanted in Europe, 20 in Asia, and 52 in Canada (10,13–17). A second-generation LAA plug (AMPLATZER Amulet LAA occluder, St. Jude Medical, St. Paul, Minnesota) is also being tested in clinical trials (18). The second generation LAA plug allows for larger LAAs to be treated. This device design has a slightly larger disc than the first generation LAA plug to better occlude the LAA ostium. The waist and the lobe are longer compared with the first generation LAA plug and the number of stabilizing wires surrounding the device body is increased for improved device flexibility and stability.
Flexible LAA occlusion device
The flexible LAA occlusion device (Coherex WaveCrest, Coherex Medical, Inc., Salt Lake City, Utah) (Figure 1C) was approved for use in Europe in September 2013. This umbrella-shaped device consists of a nitinol frame with 20 anchoring points. An occlusive, nonthrombogenic expanded polytetrafluoroethylene membrane covers the LA side of the device. A polymer foam around the device faces the LAA side. Preliminary clinical experience with the flexible LAA occlusion device (n = 63) demonstrated high closure rates of 97% and a good safety profile (19).
Epicardial approach for LAA ligation
Figure 2 shows the LAA ligation device. This device is designed to occlude the LAA percutaneously using a suture. The percutaneous catheter-based LAA ligation using the LAA ligation device has been shown to be feasible and effective in humans and complete closure of the LAA has been achieved in observational studies and 1 retrospective multicenter study in the United States (n = 277 with successful device implantation) (20–23).
Imaging Modalities and General Imaging Aspects in Procedure Planning
As described in Table 1 and shown in Figure 3, it is useful to divide the LAA anatomically into 3 regions: 1) the ostium; 2) the neck; and 3) the lobar region. There is broad variability in LAA morphology, a fact that complicates adequate evaluation (24). LAA ostium diameters range from 10 to 40 mm, its length from 16 to 51 mm, with volumes from 0.7 to 19.2 ml. On postmortem evaluation it was demonstrated that LAA from patients with AF have 3 times the volume of those who were in sinus rhythm (25). Patients with chronic AF frequently have LAA remodeling in which there is dilation, stretching, and reduction in pectinate muscle volume, as well as endocardial fibroelastosis (25).
Important aspects for LAA occlusion include the correct sizing of the landing zone diameters for the selected device and the measurement of the depth and orientation of the main anchoring lobe and the number and origin of additional lobes. In >50% of patients, 2 or more lobes are present (26,27).
Because of the substantial variations in LAA anatomy that impact device selection and efficacy, as detailed in Table 1, an accurate assessment of anatomic LAA characteristics is crucial before an LAA closure procedure. LAA imaging modalities used include transthoracic echocardiography (TTE), TEE, multidetector computed tomography (MDCT), and cardiac magnetic resonance (CMR).
Before an LAA closure procedure, 2D and 3D TTE is used to evaluate LA dimensions and volumes (28,29) and left ventricular function (a risk factor for thromboembolism ), and to exclude contraindications for LAA closure (e.g., patients with valvular AF) or significant valve disease requiring surgery or patients with a left ventricular thrombus or a mechanical heart valve who require chronic anticoagulation.
Pre-procedure TEE is the main imaging modality because the LAA cannot be definitively assessed by TTE. The close relationship of the esophagus and the LA allows detailed imaging of the LAA in most patients (31). Among other things TEE is used to exclude thrombi in the LA and LAA (32). 3D TEE is helpful in differentiating a thrombus from LAA pectinate muscles (33). In case there is uncertainty about the presence of a clot, the use of ultrasound contrast is helpful to identify these thrombi (34). Pre-procedure TEE is also used to exclude other sources of embolism, such as cardiac masses and thrombi (3D TEE has shown to be more accurate compared with 2D TEE in characterizing diameters, types, surface features, mobility, and sites of intracardiac masses, and spatial relationship to surrounding structures [35–38]) as well as aortic arch atheroma. If an LA/LAA thrombus is diagnosed, anticoagulant therapy should be given until the thrombus has resolved by TEE before proceeding to implantation of an LAA occlusion device.
A careful multiplane 2D TEE analysis (0° to 180°) (39) improves the understanding of complex LAA morphologies. Slight rotations of the probe are useful to assess all lobes adequately and to depict additional lobes. 3D TEE provides a more detailed assessment and quantitative analysis of the LAA orifice area compared with 2D TEE (40,41).
MDCT and CMR
Although TEE is the most widely used imaging modality for LAA evaluation, MDCT and CMR are emerging imaging techniques for the pre- and post-procedural assessment of thrombus formation, LAA anatomy and function, device assessment, and the detection of complications post-procedure, which can provide complementary or additional information regarding the LAA.
MDCT acquires 3D volumetric data sets of the entire heart, which can be reconstructed by using numerous planes at different points in time during the cardiac cycle thus providing accurate assessment of LAA anatomy. MDCT accurately depicts the morphology of the LAA ostium, the perimeter of the LAA orifice, and the angle of the first LAA bend. Measurement of the LAA ostial perimeter is the most reproducible parameter for sizing an LAA occluder rather than the measurement of its maximum diameter (42,43). MDCT has a 100% sensitivity for excluding LAA thrombi (44). However, it has a high rate of false positive tests and poor interobserver variability (45).
Different LAA morphologies were described recently by the use of MDCT to categorize the various LAA shapes: windsock, cactus, cauliflower, and chicken wing (46,47), but the impact of these different morphologies on procedural outcome after LAA closure is unknown. Limitations of MDCT include ionizing radiation, a lower temporal resolution than TEE, and it cannot be performed during device deployment.
Although experience is limited, CMR is an alternative noninvasive imaging modality in pre- and post-procedural LAA assessment to accurately visualize LAA size and function, and to detect thrombi in patients with AF with effectiveness comparable with TEE (48–52). LAA devices are typically made from metals that include nitinol, titanium, titanium alloy, MP35N, 316L stainless steel, and 304V stainless steel. At 1.5-T, only devices made from 304V stainless steel displayed weakly ferromagnetic qualities. The LAA occluder device has been tested and findings indicate that this device can be safely used at 3.0-T (53). In post-procedural evaluation contrast-enhanced CMR is feasible to confirm occluder placement and to detect residual peridevice leaks (54).
Advantages of CMR include no radiation exposure or need for iodinated contrast. However, limitations include the lower spatial resolution, prolonged examination times, the dependence on the ability to perform adequate breath holds, and limited ability to use CMR in patients with implanted pacemakers or defibrillators or during the device implantation procedure.
Specific Imaging Aspects in Pre-Procedure Planning
Device sizing for endoluminal occlusion devices
Device sizing is of paramount importance to ensure a stable device position and optimal sealing of the LAA. Undersizing of the device has the potential risk of device migration or embolization and may favor peridevice leakage. Oversizing of the device should also be avoided because this may cause cardiac perforation, pericardial effusion, and cardiac tamponade (11,55,56).
To avoid undersizing, the measurements for device selection should be performed when the LAA size is largest, namely at the end of ventricular systole and under normal LA filling conditions. To accurately define ostium diameters, landing zone diameters and LAA depth measurements should be obtained pre-procedurally in different echocardiographic views and intraprocedurally also with the addition of fluoroscopy.
As shown in Figure 4, when 2D TEE is used (left panel), the required measurements are obtained by rotating the TEE transducer array through at least 4 different mid-esophageal planes (typically at ∼0°, ∼45°, ∼90°, and ∼135°). Because the LAA orifice is most commonly oval in shape (26) larger orifice diameters can often be found on 120° to 135° planes rather than at 45° or 90° (57).
Figure 4 (right panel) provides an additional example of real-time (RT) 3D TEE of the LAA. Several studies validate that RT 3D TEE more accurately assesses the true LAA orifice size. RT 3D TEE was found to be closely related to CT measurements (40,41), whereas 2D TEE tends to underestimate the LAA orifice area (40,41,58,59).
The choice of an appropriate occlusion device depends on accurate measurements of the landing zone diameters. To achieve a secure and stable device position, the size of the occlusion device is usually selected to be a few millimeters larger in diameter than the measurements of the landing zone (Table 2). The maximum length of the anchoring lobe has to be measured in addition (in the expected axis of the device) to ensure that this lobe has enough space to accommodate the selected device. As illustrated in Figure 4 and Table 2, different device designs require different measurements because the different endoluminal occluder systems vary slightly.
The angle between the ostium, the neck, and the main anchoring lobe should be evaluated because it can influence the choice of the puncture site and/or the curve of the delivery sheath. The number and origin of additional LAA lobes also needs to be assessed.
Specific LAA morphologies
Because some LAA morphologies are more challenging for device closure than others, LAA anatomy should be adequately defined before any planned procedure. A secondary lobe originating close to the ostium can pose problems, because it may not be covered after device deployment. Two large lobes of a similar size separated by a large rim in between them may cause problems if the remaining proximal portion of the LAA is too short to accommodate a device.
A cone-shaped LAA is characterized by progressive reduction in dimensions from its orifice to its distal tip. A major concern with this morphology is that compressive forces transmitted by the distal LAA wall onto the closure device are more pronounced than in the proximal LAA, which can result in compressive forces that would push the device out of the LAA toward the orifice and into the LA. The risk of device migration or embolization is therefore increased in these patients. Moreover, this may be further aggravated by the lack of trabeculations in the LAA landing zone region. When an LAA plug device is used, it has to be taken into consideration that the ostium diameter is considerably larger than the landing zone diameter in such morphologies. Consequently, the disc may be too small to seal the ostium adequately in some patients. Finding a suitable LAA plug size can be challenging in these patients.
A chicken wing LAA morphology, characterized by an early (<20 mm from the ostium) and severe bend, is one of the most difficult anatomic variations for LAA closure. Specific implantation techniques may be necessary to achieve LAA occlusion in these cases (60). We have found that the chicken wing morphology is generally best evaluated using the long axis TEE planes (120° to 135°).
LAA assessment for epicardial LAA ligation
When LAA closure with the LAA ligation device is planned a spiral CT has to be obtained to clarify LAA orifice diameters and sizes and LAA orientation and location. Patients with an LAA width >40 mm or in whom the LAA is located under a pulmonary artery (20) are not suitable for suture placement. In patients with 2 large lobes that are pointing in different directions, the placement of the suture loop can be difficult. Patients with prior cardiac surgery or pericarditis also are not suitable for the LAA ligation device procedure because of the high likelihood of residual pericardial adhesions, which would interfere with placement of the LAA ligation device. A TEE pre-LAA ligation device procedure is important to exclude LAA thrombi, and it provides detailed information on the number and orientation of lobes. However, it is not as important for device guidance as TEE is with the implantable LAA occlusion devices (61).
Periprocedural Echocardiographic Assessment
During LAA device implantation (10) echocardiography is the most important imaging modality to support fluoroscopy and is of paramount importance to guide transseptal (TS) puncture, to verify catheter and sheath position in the LAA, to aid device delivery and positioning, to confirm adequate LAA sealing, and to detect complications.
Multiplanar 2D TEE is most commonly used for procedural guidance but intracardiac echocardiography has also been suggested as a feasible alternative imaging solution (62,63). Because the interaction of different moving structures can frequently not be visualized in one single plane, RT 3D TEE facilitates the procedure by providing views where targets (e.g., the LAA), wires, catheters, sheaths, and devices can be observed in one single view and in relation to each other. RT 3D TEE provides more accurate morphological information, facilitates the maneuvering and alignment of devices to the target structures (64), and is recommended for the guidance of LAA closure procedures (65).
Regardless of the device type chosen to occlude the LAA, procedural steps with regard to transcatheter endoluminal LAA closure are similar. The procedure is optimally guided using 2D and 3D TEE in combination. Before the TS puncture LAA clot formation has to be excluded once more, the LAA morphology should be reassessed, and LAA dimension measurements are repeated and combined with angiographic measurements to select the most suitable device type and an appropriately sized device. As illustrated in Figures 5 and 6 the following procedural steps have to be monitored: TS puncture (Online Video 1), positioning of the delivery sheath in the LAA (Online Video 2), and device deployment (Online Video 3).
Assessment of device position immediately post-procedure
Complete occlusion of the LAA and the absence of any alteration of surrounding structures (left upper pulmonary vein or mitral valve) should be confirmed immediately after implantation by the use of fluoroscopy and 2D and 3D TEE (Figure 1). Color-flow Doppler using a low Nyquist limit is used to assess if there is incomplete LAA occlusion and a persistent communication between the LAA cavity and the LA. In some patients complete closure cannot be achieved and a peridevice gap may occur with any of the currently available devices (13,17,19,20,66–68).
There is no consensus as to what constitutes a significant peridevice leak after LAA device occlusion. Because there are data for noninferiority in patients with a residual leak with a jet size ≤5 mm after implantation of a LAA occluder device compared with warfarin therapy in the PROTECT-AF trial (the jet-diameter was measured by 2D TEE with color Doppler in multiple planes; however, absence of a specified Nyquist limit represents a limitation) (5), a peridevice leak ≤5 mm seems to be acceptable and not associated with an increased thromboembolic stroke risk.
Correct device position is of major importance. If an endoluminally implanted occlusion device is placed too deep into the LAA, more proximal originating lobes may be uncovered. For cases in which the device is implanted too proximal in the LAA the occluder may not be adequately compressed by the LAA walls and thus be unstable and it can embolize. Table 3 summarizes criteria for appropriate positioning for different endoluminal devices. A certain amount of device compression is needed with every device. Figure 7 gives an example of the evaluation of device compression after implantation of an LAA occluder device.
After a device is inserted, but before its release from the catheter, gentle traction on the catheter is applied to the device (“tug” test) to demonstrate that the device positioning is stable. The device and the surrounding tissues should move in unison during the tug test.
Detection of complications
Complications may occur at any time during the intervention and during patient follow-up. Figure 8 demonstrates echocardiographic examples of acute and delayed complications of LAA exclusion. The immediate detection of acute complications by echocardiography is of paramount importance to minimize or avoid adverse clinical consequences. Table 4 provides an overview of potential complications, their mechanism and incidence, and prevention and treatment strategies.
Post-Procedural Echocardiographic Follow-Up
TTE is recommended after the intervention before the patient is discharged from the hospital to confirm that no relevant device migration occurred and to exclude the development of a pericardial effusion. TEE is often used for standard echocardiographic follow-up at 1, 3, or 6 and 12 months, then annually (when there is no evidence of device migration or complications after 1 year further surveillance can be done annually by using TTE; in case there is an abnormality that needs clarification, TEE should be performed in addition) to reassess the implanted device for a stable position, migration or embolization, erosion, thrombus formation, and peridevice gaps. Echocardiography is also used to monitor for any interference with neighboring structures, such as the mitral valve, left upper pulmonary vein, and the circumflex coronary artery; but to our knowledge no such cases have been reported to date. The formation of a thrombus or fibrosis within the LAA cavity distal to the occlusion device is a normal finding but careful attention is warranted to evaluate newly developed thrombotic clots either attached to the device or within the LA because this would be an indication for anticoagulation therapy.
Complete closure of the LAA represents one of the major determinants of a successful procedure. Nevertheless, the presence of a peridevice leak is a common finding and there are no data at present that demonstrate that it is associated with an increased risk of stroke (67–69).
Notably it has been shown that intraprocedural leaks can become larger over time and persist for more than 1 year, and new peridevice leakages can also occur during follow-up (66). Consequently, it is important for patients to have serial follow-up echocardiograms. Despite there being no definitive data, it is currently recommended (according to the PROTECT-AF data) that anticoagulation therapy should be continued if there is a persistent peridevice gap >5 mm (5). In some patients with a relevant leak resulting from an uncovered lobe the implantation of a second device is an option to complete LAA closure (70).
During each follow-up atrial septal defect secondary to the TS puncture should be reassessed by the use of TEE (2D or 3D) with and without color Doppler. Saline contrast injections along with a Valsalva maneuver are useful to identify the presence of a right-to-left shunt. These iatrogenic atrial septal defects have a high spontaneous closure rate over time. In one study, only 11% of patients had a persistent atrial septal defect at 6 months and 7% at 12 months after the procedure. Moreover, to date, residual atrial septal defects have not been associated with an increased rate of stroke or systemic embolization during long-term follow-up (71).
LAA device closure is a relatively new, but evolving treatment strategy to prevent embolic events in patients suffering with nonvalvular AF. Echocardiography, using both 2D and 3D TEE, currently represents the most important imaging tool to assess the suitability of the LAA anatomy for the procedure, for selecting the optimal device types and sizes, for guiding the LAA closure procedure in conjunction with fluoroscopy, and for follow-up imaging after device implantation.
For supplemental videos and their legends, please see the online version of this article.
Dr. Wunderlich has received speaker honoraria from St. Jude Medical and Philips Ultrasound. Dr. Swaans is a proctor for Boston Scientific. Dr. Siegel has received educational funding from Philips Ultrasound. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Drs. Wunderlich and Beigel contributed equally to this work.
- Abbreviations and Acronyms
- atrial fibrillation
- cardiac magnetic resonance
- left atrium
- left atrial appendage
- multidetector computed tomography
- real time
- transesophageal echocardiography
- transthoracic echocardiography
- Received December 2, 2014.
- Revision received January 22, 2015.
- Accepted February 5, 2015.
- American College of Cardiology Foundation
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- Current Devices for Percutaneous LAA Occlusion or Exclusion
- Imaging Modalities and General Imaging Aspects in Procedure Planning
- Specific Imaging Aspects in Pre-Procedure Planning
- Periprocedural Echocardiographic Assessment
- Post-Procedural Echocardiographic Follow-Up