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a Clamshell, CardioSEAL, and STARflex devices represent progres-sive modifications of a design.

a Clamshell, CardioSEAL, and STARflex devices represent progres-sive modifications of a design.

Table 2

Frequent Complications in Phase II FDA Trial of Amplatzer Septal Occluder

Major complications

Minor complications

Pericardial effusion with tamponade Repeat surgery Cardiac arrhythmias requiring permanent pacemaker placement or long-term antiarrhythmic medication Device embolizations requiring immediate surgical removal

Device embolization with percutaneous retrieval Cardiac arrhythmia with treatment

Pericardial effusion requiring medical management Surgical wound complications center; (3) ability to pass easily through a small delivery system; (4) recapturability and redeployability; (5) high resiliency without fracturing; and (6) high effectiveness in avoiding significant residual shunts. Furthermore, the materials it is constructed from should be biocompatible and nontoxic. Nevertheless, durability is important when the majority of patients are children, and there is a long "lifetime" after implantation.

All Amplatzer® atrial septal defect devices have been designed to fulfill the aforementioned requirements. For example, the Amplatzer Septal Occluder is a woven mesh of 72 Nitinol (see Section 3) wires 0.003- to 0.008-in diameter with shape memory. There are two retention disks with a central waist that sits within the defect (Fig. 1); the left atrial disk is 12-14 mm larger than the waist. The stenting action of the waist and the clasping of the atrial septum by the retention disks hold it in place. Fabric baffles, sewn inside the disks and waist, promote thrombosis and occlusion of the defect. The delivery system is relatively small (6- to 12-French delivery sheaths). Further, the device is recapturable and redeployable with a microscrew/ cable attachment. To date, available waist diameters range from 4 to 40 mm, allowing closure of even large defects (11).

As with all implantable devices, animal trials have been performed and have demonstrated the effectiveness of the Amplatzer Septal Occluder approach. In one trial, dilating the foramen ovale in dogs created an atrial septal defect, and a 10-

mm device was placed; there was complete occlusion with no residual shunt. Furthermore, the devices were completely covered by a neoendothelium at sacrifice 3 mo after implantation, and no thrombus formed on the device (12). Subsequent patient trials confirmed that no retroaortic rim was required for stable device position and complete closure. Importantly, and even amazingly, patients could be discharged the morning after device placement and remained on low-dose aspirin and endocarditis prophylaxis for 6 mo after closure.

1.3. Food and Drug Administration Testing

A Food and Drug Administration (FDA) clinical trial to determine the effectiveness of the Amplatzer Septal Occluder technology was begun based on the success of animal studies and European trials in humans. Nevertheless, the optimal study design was difficult to determine. Many patients and their families wanted to avoid any such surgery despite the long history of safe surgical closure; in addition, they were concerned about the lack of long-term follow-up of this new device. Thus, randomization was extremely difficult and unsuccessful because many patients and families originally chosen for the surgical group simply opted out of the trial, preferring to wait for final FDA approval. Subsequently, the study design was changed to allow device closure at some institutions with patients recruited to designated surgical centers. Hence, we are left with a trial without true randomization; this illustrates how difficult it is to employ such a study design in the real world.

Importantly, the results of phase II of this FDA trial have shown that an Amplatzer Septal Occluder is more effective and safe compared with the surgical group. At the end of 12 mo, there was complete closure, or a <2-mm residual shunt, in 98.5% of device patients compared to 100% of surgically closed patients. Major and minor complications most frequently observed in either group are listed in Table 2; there was no difference between groups in the incidence of major complications. Minor complications were more common in surgical patients (27/442, 6.1% in the Amplatzer group vs 29/ 154, 18.8% in the surgery group).

However, recall that these patients were not randomized; there were differences between groups, with the surgical patients younger (18.1 ± 19.3 yr in the Amplatzer group vs 5.9 ± 6.2 yr in the surgery group, p < 0.001) and smaller (42.3 ± 27.3 kg in the Amplatzer group vs 20.6 ± 15.2 kg in the surgery group, p < 0.001) (11). Nevertheless, based on this positive outcome, the FDA granted premarket approval of the Amplatzer Septal Occluders in December 2001, and to date it remains the only atrial septal defect closure device with FDA approval.

2. THE AMPLATZER® FAMILY OF DEVICES

Amplatzer devices are designed for occlusion of abnormal congenital cardiovascular communications. The devices are based on the model of a self-expanding stent with the ends of the wires bound together forming a closed frame. The shape of the wire frame is tailored to fit the abnormal vascular or intra-cardiac communication. Retention disks fix the device against vascular or cardiac walls. A central waist further holds the device in place with radial force against the margins of the communication. This provides stable fixation of the device.

Amplatzer Septal Occluder

Fig. 1. Amplatzer Septal Occluder device. (A) Right atrial angiogram performed after deployment of the device in a secundum atrial septal defect, but before release. The right atrial disk is obscured by contrast with the waist within the atrial septal defect. (B) Levophase of the right atrial angiogram opacifying the left atrium. Contrast outlines the left atrial disk completely within the left atrium.

Fig. 1. Amplatzer Septal Occluder device. (A) Right atrial angiogram performed after deployment of the device in a secundum atrial septal defect, but before release. The right atrial disk is obscured by contrast with the waist within the atrial septal defect. (B) Levophase of the right atrial angiogram opacifying the left atrium. Contrast outlines the left atrial disk completely within the left atrium.

Initially, occlusion occurs through thrombosis within the polyester baffles or the stuffing sutured inside the wire frame. Furthermore, over 3 mo, the device is covered with a protein and cellular layer, reducing the potential for forming a surface thrombus and eliminating the risk of bacterial endocarditis (12).

The development of Amplatzer devices began when thin-wire technology reached a developmental point that allowed the construction of a frame of nontoxic Nitinol wires. Like all stents, the collapsed device is long and narrow to fit through the delivery sheath. It is important to note that Nitinol metal has shape memory. Thus, as it exits the sheath, the device expands and assumes its original shape at body temperature. Each current device also has a microscrew fixed to the proximal end that allows attachment to a delivery cable. This then enables the device to reconnect with the cable after deployment to allow it to be either removed or repositioned. The device is detached by unscrewing once secure, and the effective position is confirmed (e.g., by fluoroscopy).

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