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Continued Development of Devices for Transcatheter Closure<br />
of Atrial Septal Defects
The Amplatzer Septal Occluder (AGA Medical Corp., Golden Valley, Minnesota) was approved for general clinical use by the U.S. Food and Drug Administration (FDA) several years ago, and more recently, the Helex septal occluder (W. L. Gore & Associates, Flagstaff, Arizona) received FDA approval. A few other devices are allowed for limited clinical use. FDA approved (under Investigational Device Exemption) clinical trials with local IRB supervision are in progress with some other devices. Design, laboratory and clinical trials, redesign and retesting have been the case with many devices, and rightfully so, to optimize feasibility, safety and efficacy.
At present, the Amplatzer septal occluder is the most commonly used ASD closure device worldwide. The feasibility, safety and efficacy of device occlusion are based on the selfexpandable, retrievable and repositionable design of the device.13 Even very large defects can be closed successfully with the Amplatzer device using a variety of techniques.14,15 Reports on long-term results, though scanty, have suggested good outcomes.16 The Amplatzer device is constructed with wire made of nitinol (nickel-titanium compound), a shapememory alloy. Release of nickel into the circulation following Amplatzer device implantation is well documented.17,18 It would appear that nickel release ceases once the device is endothelialized.17,18 There does not seem to be any adverse effect in the short term, although long-term effects of higherthan- normal levels of nickel in the circulation are not known. However, if the patient is sensitive (allergic) to nickel, it would pose an immediate problem.19,20 Nickel is also a component of the wire structures used in the PFO-Star (Cardia Inc., Burnsville, Minnesota) and HELEX devices, and nickel allergy with these devices has also been reported.21–23
In this issue of the Journal, Lertsapcharoen and associates24 address the nickel release problem. They studied 29 patients, aged 4–59 years, who had undergone device closure with a nanoplatinum-coated nitinol device.25 Serum nickel levels were measured prior to and 1 day, 1 week, 1 month and 3 months following device implantation. Serum nickel levels prior to device closure were 0.65 ± 0.28 ng/ml; these levels were similar (p > 0.5) to those in 100 normal volunteers. The baseline levels did not increase (p > 0.11) during follow up; this is in contradistinction to increases in serum nickel levels from 0.47 to 1.5 ng/ml 1 month following Amplatzer septal occluder implantation in 67 patients reported by Reis et al.17 These data indicate that nanoplatinum coating prevents nickel release from Amplatzer devices. This is an excellent study helping to address device closure of ASDs in patients who may have nickel allergy. The limited number of patients studied, failure to measure the nickel levels in all 29 patients and no control subjects who had a regular Amplatzer device occlusion of an ASD are shortcomings of the study, but may not adversely effect the conclusions drawn.
Sensitivity to nickel has been reported in 1–10% individuals studied;26 this appears to be more frequent in women (8–10%) than in men (1–2%). Failure of cardiac valves,27 coronary stents,28 abdominal aortic stent grafts,29 orthopedic joint prostheses,30 dental implants31–33 and, more recently, septal closure devices19-23 related to nickel allergy, though rare, has been well documented. The risk for development of nickel allergy secondary to cardiac device implantation is extremely rare and the estimated prevalence is 1 in 17,000 patients.20 Treatment with steroids20 was found to be useful in some cases, but device explantation was necessary in others.
As alluded to above, nickel allergy is rare and our center has not encountered this problem in more than 300 consecutive device implantations to occlude ASDs and patent foramen ovale (PFOs) in adult34 and pediatric patients using the Amplatzer septal and Amplatzer PFO occluders, occlusion of patent ductus arteriosus with the Amplatzer duct occluder and abnormal vascular channels with the Amplatzer vascular plug; this is not inconsistent with the estimated prevalence of1 in 17,000.20 However, because of the potential for the development of nickel allergy, methods must be devised to prevent this problem. Patient history of nickel allergy has not been routinely sought and should be obtained, although it may not be accurate.19 Skin patch testing may detect nickel allergy,35,36 but has limitations in that the results are variable37,38 and may not necessarily reflect systemic response to nickel-containing devices implanted in the heart. In vitro testing of lymphocyte TH1 response to nickel38–40 has been attempted, but does not seem to be reliable in predicting nickel allergy in a given patient. Furthermore, such elaborate testing may not be practical. Alternate solutions are either to avoid nickel in the implants, or modify the device in such a manner that nickel will not be released into the circulation. Chemical processing of nitinol to induce titanium oxide or calcium phosphate coating may prevent nickel release,41 but has not been clinically tested. Nanoplatinum coating of nitinol wire such as that proposed by Lertsapcharoen and associates24,25 is another such method and seems attractive. Larger studies of this device to further explore its safety and efficacy should be conducted before its general use or before replacement of the Amplatzer and other nickel-containing devices is considered.
References
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