Percutaneous Catheter Closure of Secundum Atrial Septal Defects: A Review
- Volume 14 - Issue 1 - January, 2002
- Posted on: 8/1/08
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Atrial septal defects (ASD) have been closed surgically for over 4 decades with very low morbidity and mortality. The position of ASDs has rendered itself to the ingenious attempts of a number of pediatric cardiac interventionalists for catheter closure. It was recognized early that the entry to the left atrium from the inferior vena cava through an ASD is an easy approach for placing occlusive devices. The challenge is to design an ideal device that can achieve results as good as surgical closure. The device should be safe, easy to deliver, position, reposition or retrieve if necessary, and should be delivered through a small sheath suitable for children with minimum discomfort. A number of devices have been manufactured attempting to achieve successful and safe closure of ASDs, aiming for a “perfect device”. Most of these were designed to enclose the atrial septum between 2 discs placed across the ASD and to be held in position across the atrial septum by varying mechanisms. They vary significantly in material, design, shape, delivery method, etc.
Historical background. In 1976, King and Mills1 first described the percutaneous closure of an ASD without opening the chest or placing the patient on cardiopulmonary bypass circuit. This new approach became known as catheter closure of ASDs. The device consisted of 2 independent umbrellas that had to be opened in the atria and then snapped together. It was used successfully in 5 out of 10 attempts in human subjects. The device used at that time required a large delivery sheath (23 French). Because of the sheath size and the complexity of the delivery procedure, the device did not gain wide acceptance. A decade later, Rashkind2,3 described preliminary trials for catheter closure of ASDs. The Rashkind ASD device consisted of a single umbrella with hooks on 3 of 6 arms. The umbrella would self-expand in the left atrium once pushed outside the delivery sheath; the system was brought against the atrial septum and anchored in place by the hooks. Once anchored, the device could not be removed or repositioned. Although it was successful in approximately two thirds of the patients in whom it was tested, the device was felt to be unsafe because of its inability to reposition once deployed (requiring emergency surgery to remove). Its use was abandoned.
Current status of ASD devices
The devices described hereafter represent those which are currently or have recently been in clinical trials. The devices are discussed in alphabetical order rather than chronologically because some devices underwent modifications and were reintroduced at later dates under new names. The most recent name is chosen for the purpose of alphabetical listing.
Amplatzer Septal Occluder (Figure 1). The Amplatzer Septal Occluder (AGA Medical Corporation, Golden Valley, Minnesota) is a self-expanding, double-disc device made from 0.004–0.0075 nitinol wire tightly woven into 2 discs with a 3–4 mm connecting waist.4 The diameter of the centering disc is from 4–40 mm in 1 or 2 mm increments. The left and right atrial discs are 12–16 mm and 8–10 mm larger than the centering disc, respectively. Depending on the size of the device, it is delivered through a 6–12 French sheath using a delivery cable attached to the center of the right atrial disc by a micro screw. The device is chosen so the central disc is 1–2 mm larger than the stretched diameter of the defect. It is advanced through a sheath previously positioned in the left atrium.
The sheath is pulled back, allowing the left atrial disc to assume its circular position. The centering disc is uncovered across the atrial septum. The sheath is then pulled back, maintaining the position of the device and allowing the right atrial disc to assume its circular configuration as well. The device is thus deployed straddling the atrial septum. The stability of the device is tested by gentle pushing and pulling. If the device is in an appropriate position, it is released by unscrewing the delivery cable. Prior to unscrewing the device, it can be easily retrieved by a gentle and steady pull on the device into the delivery sheath. Wilkinson et al.5 and my own personal experience have indicated that the device can also be retrieved after release with mild difficulty by recapturing the right atrial knob (usually by a snare). Preliminary human experience has been very encouraging.4–7 There was immediate closure in 80% of the patients, which increased to 98% at 3-month follow-up exam. The residual shunt after 3 months was estimated to be trivial, without requiring additional intervention.
Complete closure was seen in the patients who completed 1-year follow-up. No significant complications were encountered. In the initial studies, patients with ASD diameters > 21 mm were excluded. Subsequently, the size of the device has been increased to allow closure of ASDs up to 40 mm (stretched diameter). The reported combined United States and worldwide experience with the Amplatzer in all ASDs has exceeded 3,000 patients8 (> 9,000 at the time of manuscript preparation according to personal communication with AGA Medical Corporation). The size of the stretched ASD diameter ranged from 4–44 mm (unstretched diameter, 1–38 mm). There were no major complications. Success (defined as residual shunt < 2 mm) was achieved in 97% immediately after the procedure and increased to 99% at 1 year, with complete closure seen in 95% at 1 year. The results have been similar for the large ASDs (stretched diameter > 25 mm).9
Atrial Septal Defect Occlusion System (ASDOS) (Figure 2). In 1999, Babic et al.10 described the ASDOS (Dr. Ing Osypka Corporation, Gmbh, Germany), which consisted of 2 separate umbrellas made of nitinol wire covered with a polyurethane patch. Each umbrella is delivered on either side of the septum. The delivery method involves making a femoral/venous loop to cross the atrial septal defect. The material used in the loop is a 0.014´´ nitinol wire with a 0.035´´ conus in the middle and maintained in the left atrium.11 Once the loop is formed, an 11 French sheath is advanced from the venous side into the left atrium. The left atrial umbrella is advanced using a 22 gauge pusher cannula and is prevented from advancing by the conus on the guidewire. This allows the operator to pull it against the atrial septum. Subsequently, the right atrial umbrella is advanced using a screwdriver catheter. For definitive implantation, the 2 umbrellas are brought together across the atrial septum using the wire conus on the left atrial umbrella and the screwdriver catheter on the right atrial umbrella. When the position’s accuracy is confirmed by echocardiogram, the umbrellas are screwed together by the screwdriver catheter and the guidewire is pulled from the arterial side. If position is inappropriate, the umbrellas can be unscrewed and repositioned multiple times. The published experience with this device is limited. There was a small incidence of fractures and cardiac perforation after implantation; this, in addition to the complexity of the delivery mechanism, has made the device less attractive.12
Buttoned Device. In 1990, Sideris et al.13 introduced the Buttoned Device (Custom Medical Devices, Amarillo, Texas), which was used to close ASDs in an animal model. The use of the device was subsequently extended to clinical trials. The device consists of an occluder, counter-occluder and loading wire. The occluder is a square-shaped polyurethane foam supported by 2 diagonally-situated, Teflon-coated 0.018´´ wires.13,14 The skeleton wires are floppy at the ends (2 mm) and stiffer in the center. They have an x-shaped appearance when unfolded and are almost parallel when folded to the introducing position. The occluder resumes its shape when extruded from the delivery sheath in the left atrium. A button was also attached to the occluder. The occluder remains attached by nylon thread, looped through a hollow loading or delivery wire. This maintains continuous hold of the occluder after it is unfolded in the left atrium and allows the operator to pull it back against the left atrial side of the ASD. The counter occluder is also made of foam, and is in a rhomboid shape with a Teflon-coated wire skeleton. A rubber piece is sutured in the center of the counter-occluder. The occluder is loaded into the delivery sheath and advanced by a pusher catheter, introduced over the wire until the occluder is extruded in the left atrium. The occluder is then pulled against the left atrial side of the ASD. The pusher catheter is removed; the occluder is maintained in position by the wire and nylon thread. The loading wire is then threaded through the rubber piece in the center of the counter-occluder. The counter-occluder is loaded into the sheath and advanced by the pusher catheter and delivered into the right atrium.
The counter-occluder is pushed with the tip of the sheath until the occluder loop is “buttoned” in the rubber center of the counter-occluder by a process of buttoning the counter-occluder onto the occluder against the atrial septum. Position and stability are then confirmed, and if appropriately placed, the device is released by cutting the delivery wire and nylon thread outside the body and withdrawing one end of the thread. This will free the device from the delivery system. Phase 1 Food and Drug Administration clinical trials began in 1991. Successful device implantation was achieved in 80% of the initial trial, with the incidence of residual shunts decreasing to 19% over a 12-month period.15 Because of unbuttoning and migration of the support wire’s corewire and residual shunts requiring surgical removal of the device, it has undergone several modifications. In the most recent modification (fourth-generation device), the single button loop was replaced with 2 spring radio-opaque buttons mounted 4 mm apart. The intent is to reduce the unbuttoning seen with the earlier generations.16 The incidence of major complications decreased from 7.8% (with the first 3 generations) to 1.4% using the fourth-generation device. Effective occlusion was achieved in 90% of patients using the fourth-generation device. An inverted buttoned device was used in a few patients with right to left atrial septal defects.17 A newer modification of the fourth-generation version included a centering on demand device (Figure 3).18 In this rounded, fourth-generation device, the centering wire ring is sutured to the center of the occluder. The centering ring could be used for centering purposes or buttoned with the occluder (ring augmentation, non-centering) (Rao et al.18 and personal communication with Dr. Sideris). In addition to the centering ability, this allows the option of using smaller-size devices for the same size ASD. Although the experience with the centering-on-demand device is still limited, there have been no incidences of unbuttoning or major complications.