Assessing Anatomy for Left Atrial Appendage Closure
The roles of TEE and CTA in anatomic assessment and device selection for LAA closure.
Left atrial appendage (LAA) closure is now a commercially available alternative means of thromboprophylaxis in atrial fibrillation patients who are not ideal candidates for oral anticoagulation. Although the rate of major procedural complications has significantly improved from 8.7% in the initial prospective study (PROTECT AF) to 4.2% in PREVAIL, there is still a strong incentive to minimize the degree of catheter manipulation in the left atrium and to accurately size occluder devices, thus decreasing opportunities for complications.1,2 Currently, the state-of-the-art imaging modality to evaluate the LAA is transesophageal echocardiography (TEE), the gold standard for anatomic characterization and procedural guidance throughout all of the landmark prospective trials.3
TEE USAGE AND TECHNICAL TIPS
TEE provides high-resolution multiplanar imaging that is especially suitable for evaluating soft tissue. Characterization of the atrial appendage using TEE is performed using four main viewing angles: 0°, 45°, 90°, and 135°.4 From these views, maximal LAA length and width are ascertained, and a device is chosen based on the manufacturer’s sizing guide in the instructions for use.4 The appendage must be at least as deep as the size of the measured ostia to ensure safe implantation, otherwise, the patient will be ineligible. The Watchman device (Boston Scientific Corporation) comes in five sizes (21, 24, 27, 30, and 33 mm), and it is recommended that the selected device achieve 8% to 20% compression. Accurate measurements are important in order to select the appropriate device size based on the maximum LAA diameter. It is generally recommended that preprocedural TEE be performed to ensure anatomic suitability for Watchman implantation and to not bring the patient to the catheterization suite until implantation is relatively ensured, although some centers have chosen to perform anatomic assessment and implantation in the same setting.5
During the procedure, TEE is used to reexamine the appendage under general anesthesia. After excluding thrombus and reconfirming measurements, TEE is particularly useful for directing the trajectory of the transseptal puncture. The fossa is punctured posteriorly and inferiorly, which then facilitates an anterior and superior trajectory. TEE can also direct the posterior and inferior trajectory of the transseptal puncture, as well as confirm the coaxial guide trajectory prior to device delivery (Figure 1). Live surveillance of the device deployment is then used to determine appropriate implantation depth and device stability. If the device appears to be properly placed with respect to the LAA ostia, a “tug test” can be performed, and compression is checked by TEE to assess for device stability. The device should be compressed 8% to 20% to follow manufacturer recommendations prior to releasing. In addition to assisting with deployment, TEE can detect complications early in the case. Identification of pericardial effusions and suboptimal device implantation are vital to procedural safety and to avoid complications, such as device embolization.
LIMITATIONS OF TEE
Although TEE is currently the standard for image guidance for LAA occlusion, it is not without its limitations. Most patients are volume depleted for outpatient TEEs, as they must fast for 6 hours prior to the procedure. The LAA size depends on adequate preloading, and hence, preprocedural outpatient TEE can potentially undersize the true LAA dimensions.6 Another limitation of TEE may be the underappreciation of LAA contractility, especially in sinus rhythm. The LAA dimensions change during the cardiac cycle, and these changes affect sizing, which may not be appreciated by TEE due to insufficient spatial resolution.7,8
APPLICATIONS OF CT
In the search for more comprehensive imaging to provide additional information beyond LAA sizing, CT also has been investigated for evaluating the LAA.9 CT can be performed with cardiac gating with high-resolution scans, providing physicians with excellent image quality and a volumetric, comprehensive data set (Table 1A, Table 1B, and Table 1C). CT has been used to evaluate LAA morphology and the high spatial resolution does perform better than TEE; for instance, CT is more sensitive for detecting postimplantation device leaks.8,10 The promise of a more detailed and comprehensive evaluation of the LAA prompted our center to compare the safety and accuracy of using CT as the primary means for sizing and planning LAA occlusion procedures.
In our pilot study of using CT for LAA occlusion case planning, we learned that CT provides more accurate sizing and improves procedure planning compared to TEE.11 Using CT, we can better measure the appendage, derive coplanar viewing angles, and if available, perform three-dimensional (3D) printing using the CT data (Table 1). Perhaps the most important function is accurate assessment of the morphology and dimensions of the appendage, as CT better appreciates the maximal dimension due to sampling errors made with TEE. Our retrospective series concluded that TEE undersizes the maximal width of the LAA by 2.7 ± 2.2 mm and the length by 4.0 ± 5.8 mm. The ramifications of undersizing are significant; by two-dimensional (2D) TEE maximal width, 62.3% (33/53) of the patients would have received the incorrect initial device and required upsizing to a larger device size intraprocedurally. If not for CT imaging, 12 of 53 patients would have been inappropriately excluded from Watchman implantation either due to width (3/53) or length (9/53) underestimation.11 Multiple device exchanges in the left atrium may increase procedural complications, such as air embolism or catheter-related perforation.
CT imaging also allows the acquisition of additional information via a coplanar viewing angle (Figure 1 and Figure 2). Unlike calcified aortic valves and transcatheter aortic valve replacement, there are no radiographic markers to help delineate the coplanar view.12 Usually, when performing angiography, imaging angles are changed to minimize foreshortening and overlap of other angiographically overlapped structures, most notably in coronary angiography. However, the atrial appendage is entirely a soft tissue structure, and unfortunately, the angiographic projections that minimize foreshortening of the appendage length may not match the coplanar angle for the ostium of the appendage.11 In a procedure where minimizing the number of device exchanges may help prevent complications, simplifying the procedure to one catheter, one device, and one deployment should enhance safety. Furthermore, narrowing the number of angiographic projections can minimize contrast and radiation exposure, another quality marker and safety measure in the catheterization lab.
Additional uses of CT data include the creation of physical models that can be used for ex vivo bench testing of device fit and catheter suitability (Table 1). The 3D data from a CT can be exported to computer-aided design software, but the data must be manually manipulated and then sent to a 3D printer for creation of an actual physical model. Using this heart replica, catheters and devices can be fit tested and tried prior to starting a procedure. Therefore, many assumptions about coaxial catheter and accurate device selection can be investigated without manipulation in the body, instead of a dogmatic progression from the same standard guiding catheter and changing catheters after failed attempts.
Although there are many advantages to using CT data, its use may not be broadly applicable. For instance, a CTA requires an additional dose of radiation and contrast, which may be harmful or undesirable in some patients. Furthermore, processing the data is laborious, and not all centers may have the resources or infrastructure to manually analyze additional CT data. To go forward an additional step to create 3D models, there is an additional cost and infrastructure challenge that may not be easily met in today’s health care environment. Nevertheless, improving how we use advanced imaging data is yet another iterative step in advancing the field of interventional cardiology.
TEE will remain the cornerstone of performing complex structural heart procedures, but the role of CT in treating aortic valve disease, mitral valve disease, and now left atrial appendage occlusion is becoming indispensible.11,13,14 The breadth and complexity of structural heart disease interventions continues to expand, and achieving our goal to continue improving the safety, quality, and success of percutaneous interventions will heavily depend on advanced imaging. A mentor once taught me, “Know what you are seeing, and see what you are doing,” which remains a fundamental axiom for performing procedures in the catheterization lab.
1. Reddy VY, Holmes D, Doshi SK, et al. Safety of percutaneous left atrial appendage closure: results from the Watchman Left Atrial Appendage System for Embolic Protection in Patients with AF (PROTECT AF) clinical trial and the continued access registry. Circulation. 2011;123:417-424.
2. Holmes DR Jr, Kar S, Price MJ, et al. Prospective randomized evaluation of the Watchman left atrial appendage closure device in patients with atrial fibrillation versus long-term warfarin therapy: the PREVAIL trial. J Am Coll Cardiol. 2014;64:1-12.
3. Holmes DR Jr, Lakkireddy DR, Whitlock RP, et al. Left atrial appendage occlusion: opportunities and challenges. J Am Coll Cardiol. 2014;63:291-298.
4. Boston Scientific Corporation. 2015. Package insert: Watchman left atrial appendage closure device and delivery system.
5. Price MJ, Valderrabano M. Left atrial appendage closure to prevent stroke in patients with atrial fibrillation. Circulation. 2014;130:202-212.
6. Spencer RJ, DeJong P, Fahmy P, et al. Changes in left atrial appendage dimensions following volume loading during percutaneous left atrial appendage closure. JACC Cardiovasc Interv. 2015;8:1935-1941.
7. Patel AR, Fatemi O, Norton PT, et al. Cardiac cycle-dependent left atrial dynamics: implications for catheter ablation of atrial fibrillation. Heart Rhythm. 2008;5:787-793.
8. Saw J, Fahmy P, Spencer R, et al. Comparing measurements of CT angiography, TEE, and fluoroscopy of the left atrial appendage for percutaneous closure. J Cardiovasc Electrophysiol. 2016;27:414-422.
9. Budge LP, Shaffer KM, Moorman JR, et al. Analysis of in vivo left atrial appendage morphology in patients with atrial fibrillation: a direct comparison of transesophageal echocardiography, planar cardiac CT, and segmented three-dimensional cardiac CT. J Interv Card Electrophysiol. 2008;23:87-93.
10. Jaguszewski M, Manes C, Puippe G, et al. Cardiac CT and echocardiographic evaluation of peri-device flow after percutaneous left atrial appendage closure using the Amplatzer cardiac plug device. Catheter Cardiovasc Interv. 2015;85:306-312.
11. Wang DD, Eng M, Kupsky D, et al. Application of 3-dimensional computed tomographic image guidance to Watchman implantation and impact on early operator learning curve: single-center experience. JACC Cardiovasc Interv. 2016;9:2329-2340.
12. Binder RK, Leipsic J, Wood D, et al. Prediction of optimal deployment projection for transcatheter aortic valve replacement: angiographic 3-dimensional reconstruction of the aortic root versus multidetector computed tomography. Circ Cardiovasc Interv. 2012;5:247-252.
13. Binder RK, Webb JG, Willson AB, et al. The impact of integration of a multidetector computed tomography annulus area sizing algorithm on outcomes of transcatheter aortic valve replacement: a prospective, multicenter, controlled trial. J Am Coll Cardiol. 2013;62:431-438.
14. Wang DD, Eng M, Greenbaum A, et al. Predicting LVOT obstruction after TMVR. JACC Cardiovasc Imaging. 2016;9:1349-1352.
Dee Dee Wang, MD
Center for Structural Heart Disease
Division of Cardiology
Henry Ford Health System
Disclosures: Co-inventor on a patent application assigned to employer Henry Ford Health System for LAA planning software.
Marvin H. Eng, MD
Center for Structural Heart Disease
Division of Cardiology
Henry Ford Health System
(313) 916-1878; firstname.lastname@example.org