Background
The Amplatzer Cardiac Plug (ACP) device, used for percutaneous left atrial appendage closure, frequently presents as an unexplained figure-of-eight on echocardiography. The aim of this study was to clarify the figure-of-eight display of the ACP device during echocardiography and to relate this finding to device position and function.
Methods
A mathematical model was developed to resemble device geometry and predict the echocardiographic appearance of the ACP device. In addition, an in vitro setup was used to validate the model. Finally, echocardiographic images of consecutive patients referred for percutaneous left atrial appendage closure ( n = 24) were analyzed for the presence of a figure-of-eight display.
Results
Because the ACP device resembles an epitrochoid curve, those points with tangent vector perpendicular to the ultrasound waves are emphasized, resulting in a figure-of-eight display, which can be replicated in vitro in the coronal imaging position. We found the figure-of-eight display in 100% (11 of 11) of three-dimensional periprocedural transesophageal images and in 87% (34 of 39) of postprocedural transthoracic echocardiographic images.
Conclusions
The figure-of-eight display of the ACP device during echocardiography is the result of the specific epitrochoid geometry of the device mesh and its interaction with ultrasound waves. It is important to recognize the figure-of-eight as being a normal imaging artifact of a correctly deployed device in the coronal imaging position on both transesophageal and transthoracic echocardiography. In the future, this could be used during follow-up to aid clinical practitioners in assessing device position and function.
In recent years, percutaneous closure of the left atrial appendage (LAA) has emerged as a promising technique for the prevention of stroke in a selected group of patients with atrial fibrillation and a contraindication to anticoagulation therapy. Two different devices are currently available in clinical practice: the WATCHMAN device (Atritech, Plymouth, MN) and the Amplatzer Cardiac Plug (ACP; AGA, St Jude Medical, Minneapolis, MN). The latter is a disk occluder device, developed on the basis of the Amplatzer double-disk septal occluders used for closure of atrial septal defects and patent foramen ovale, and is constructed of self-expandable nitinol wires woven into two disks. When expanded, the disks function as an occluder of the LAA and in addition stabilize the device relative to the surrounding structures. Echocardiography is increasingly important in the preprocedural anatomic assessment of the LAA, the real-time guidance of device deployment, and the long-term follow-up of device position and function. The ACP device frequently presents on echocardiography as a figure-of-eight superimposed on the occluder device ( Figure 1 ).
The aims of this study were (1) to clarify the figure-of-eight display while imaging an LAA closure device using mathematical modeling and in vitro data and (2) to assess the prevalence and clinical relevance of the figure-of-eight display during and after deployment of the ACP device in 24 consecutive patients from two referral centers.
Methods
Mathematical Model
We hypothesized that the planar mesh structure of an expanded ACP device closely resembles an epitrochoid curve ( Supplemental Figure 1 ; available at www.onlinejase.com ). Ultrasound waves falling onto the device are deflected in many directions because of the heterogeneity of mesh fiber orientations. Only those waves reflected toward the probe constitute the ultrasound image. Therefore, mesh points at which the tangent vector of the mesh (i.e., the derivative in that point) is perpendicular to the direction of the ultrasound beam are expected to be very reflective and highlighted on the resulting image ( Figure 2 ). This hypothesis was implemented in a custom-written MATLAB routine (The MathWorks, Natick, MA) used for plotting of the epitrochoid curve and calculation of the mesh points that are expected to be most reflective.
In Vitro Validation Setup
An ACP device (16 mm in diameter) was mounted into a custom-made in vitro setup consisting of a small water-filled tank and an LAA phantom used to insert the ACP device. Transducer position was externally controlled using a fixation arm. Two-dimensional (2D) and three-dimensional (3D) echocardiography was performed with a commercially available system (iE33; Philips Medical Systems, Andover, MA) using the X5-1 probe and the CX7-2t probe. Images were obtained from a “frontal” (sagittal or transversal) probe position and a “coronal” probe position, with the ultrasound plane being parallel with the surface of the disk. All images were stored in digital format for subsequent offline analysis, using the commercially available CardioView software (TomTec Imaging Systems, Unterschleissheim, Germany).
Patient Cohort
Between October 2009 and February 2013, a total of 24 patients underwent percutaneous LAA closure procedures using the ACP device at Ziekenhuis Oost-Limburg (Genk, Belgium) ( n = 5) and University Hospital Gasthuisberg (Leuven, Belgium) ( n = 19). Periprocedural transesophageal echocardiographic guidance was performed at both centers. After deployment of the ACP device, device position and function was assessed on transesophageal echocardiography (TEE) using Doppler of the LAA area. Before discharge, 2D and Doppler transthoracic echocardiography (TTE) was performed in all patients to exclude pericardial effusion, assess mitral valve function and left ventricular function, and confirm device positioning and function. Standard clinical follow-up with TTE and/or TEE at the discretion of the treating cardiologist was performed at 2 to 6 months at the referring center ( n = 5) or the center of implantation ( n = 19).
Images from periprocedural TEE, postprocedural TTE, and follow-up TTE and/or TEE were retrospectively analyzed in all 24 patients. In case of a figure-of-eight display, the respective imaging plane was noted.
Results
Mathematical Model
The MATLAB output assumed for an ACP device of 16 mm in diameter is shown in Figure 3 , with close resemblance to the nitinol mesh configuration of the real device. When emphasizing only those curve points with a tangent vector perpendicular to a vertical ultrasound beam, a symmetric figure-of-eight configuration is established, similar to the echocardiographic image.
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