(210Kb)	Boehm W, Emmel M, Sreeram N. The Amplatzer duct occluder for PDA closure: indications, technique of implantation and clinical outcome. Images Paediatr Cardiol 2007;31:16-26.
	Department of Paediatric Cardiology, University Hospital of Cologne, Germany.

Introduction
A number of devices are currently available for percutaneous closure of the patent ductus arteriosus (PDA). For the smaller ducts, the Gianturco coil and its modifications, including the detachable release coil, have proven to be efficacious, utilising delivery systems of 4F or 5F diameter, and allowing implantation from either the arterial or venous approach.¹ For ducts with minimum diameters exceeding 3mm however, coil implantation is associated with higher procedural complexity such as the use of multiple coils usually via a combined arterial and venous approach to allow simultaneous deployment with intertwining of coils, and a higher rate of embolization and residual shunting. The Amplatzer duct occluder (ADO) has proven to be an elegant device that allows moderate and larger sized ducts (upto 11 mm in minimum diameter) to be successfully occluded by the percutaneous approach. It combines ease of implantation with a high occlusion rate and a low rate of procedure – related complications.^2-6 The procedure can be safely carried out in infants >3.5 kg in weight with symptomatic PDA.

Device description
The Amplatzer Duct Occluder (AGA Medical Corporation, Golden Valley, MN) is a self-expanding and self-centering device, made from 0.0004 to 0.0005 inch Nitinol wire mesh. It is mushroom-shaped with a low profile and consists of a flat retention disk and a cylindrical main body, into which polyester fibers are sewn. Platinium marker bands are laserwelded to each end and a steel sleeve with a female thread is welded into the marker band (figure 1). The retention disk is 4 mm larger than the main body, which itself has a conical structure. The delivery system consists of a delivery cable, a Mullins-type sheath, loader and a pin vise. The device comes in different sizes, requiring sheath sizes from 5 to 7 F for delivery. These details are available from the accompanying graphic charts supplied by the manufacturer. The size of device chosen is generally such that the diameter of the pulmonary end of the device is at least 2 mm larger than the narrowest diameter of the duct. Device sizes are categorised according to the diameters of the aortic and pulmonary ends of the device. The standard device sizes are 6/4, 8/6, 10/8, 12/10, 14/12 and 16/14 mm respectively, where the first number refers to diameter of the the aortic end and the second number to the pulmonary end of the conical shaped device. The devices are all 7mm long. The device can be delivered through sheath sizes ranging from 5F (for devices upto 8/6) to 7F (for all larger devices).
 

Implantation technique
The procedure can be performed under conscious sedation in older patients, or using general anesthesia. A single dose of intravenous antibiotic is administered (usually a cephalosporin), as is standard practice for all interventional implantation procedures. The femoral vein and artery are canulated percutaneously. The size and configuration of the duct are determined by descending aortic angiography, using a 4F or 5F pigtail catheter (figure 2).
 

The arterial catheter is then withdrawn to the femoral artery to avoid interference with ADO deployment. The minimum diameter, the diameter of the aortic ampulla and the length of the duct are measured. An endhole catheter (usually 5F) is passed through the duct from the pulmonary side into the descending aorta, if necessary with the help of an 0.035"guidewire (figure 3).
 

The endhole catheter is then exchanged for a delivery sheath, over an 0.035" exchange length (260 cm long for older patients) guidewire (figure 4).
 

 
The appropriate ADO device is chosen, such that the diameter of the pulmonary end is at least 2 mm larger than the narrowest diameter of the duct, and immersed into saline solution. The delivery cable is passed through the loader and the device is screwed on clockwise to the tip (figure 5).

Thereafter, the whole system is immersed into saline again (figure 6). The device is now pulled into the loader and the loader is introduced into the delivery sheath.
 

The device is advanced through the delivery sheath into the descending aorta (figure 7).
 

Following successful detachment of the device the delivery system is removed. A repeat aortogram may be done 5 to 15 minutes after the release, to reconfirm device position (figure 10).
 

Discussion
Follow-up studies following ADO deployment have confirmed occlusion rates of >99% within 6 months of device deployment, with minimal complication rates.^2-6 The majority of occlusions can be confirmed within 24 hours, prior to discharge from hospital. Protrusion of the retention disc into the descending aorta, producing aortic obstruction is a rare complication, and may necessitate removal of the device.⁷ To avoid this potential complication, aortography is always recommended after device deployment, prior to release, and following release of the device. Even after the device has been released, it can be retrieved if necessary by transcatheter techniques, and the duct occluded using a new device. A modification of the ADO has been described to avoid this complication, in which the aortic retention disc is angulated at approximately 32^o to the body of the device and is concave towards the aorta, and may be indicated in special instances.⁸ Device protrusion into the left pulmonary artery is also infrequently seen when compared with the Rashkind device or following the use of multiple coils,^9,10 as the device has a low profile on the pulmonary side. Late device embolization into the pulmonary arteries, occurring at upto 24 hours following implant, was reported in the early series, and was probably due to the use of a smaller than optimal device.⁴ This may be avoided by confirming that no part of the retention disc has prolapsed into the body of the duct, prior to release.

There has to date been a single procedure-related death with use of the ADO.¹¹ In that patient the device, which was probably too small for the duct in question, embolized into the descending aorta and was not retrieved until 4 hours later, resulting in mesenteric vascular complications and sepsis. Device embolization into the aorta would constitute a medical emergency, necessitating immediate transcatheter or surgical retrieval of the embolized device.

In conclusion, the implantation and clinical follow-up data available to date confirm that moderate to large PDAs can be safely occluded using the ADO in patients from 3.5 kg in weight upwards, with excellent occlusion rates and minimal complications.
 
References

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