Gurumurthy Hiremath, MD; John L. Bass, MD
Introduction
A twelve-month-old infant is followed with a continuous murmur, and echocardiographic confirmation of a Patent Ductus Arterosus (PDA). There is left atrial and left ventricular enlargement, normal right-sided pressures, runoff from the abdominal aorta, and transcatheter closure is recommended as spontaneous closure is unlikely beyond this age. The patient weighs 8.5kg. Access to the femoral artery is made with a 4F sheath, and to the femoral vein with a 5F sheath. Cardiac catheterization confirms normal pulmonary artery pressure with a large left-to-right shunt. Aortography shows a conical ductus (Figure 1) narrowed at the pulmonary end. A decision is made to implant a Nit-Occlud® PDA device to close the ductus. Measurements show a 1.8mm minimum diameter at the pulmonary artery, and 8.5mm at the aorta (Figure 1). A 9x6 Nit-Occlud® device is chosen, a 0.025in. guidewire is advanced from the pulmonary artery into the descending aorta, and the 5F delivery catheter advanced through the ductus. The 9x6 Nit-Occlud® device is flushed, is advanced through the delivery catheter, the aortic end exposed and pulled into the aortic PDA ampulla, and the pulmonary end exposed. Aortography confirms good position, the coil is detached, and the aortogram is repeated,confirming repositioning of the device after release and a moderate residual shunt (Figure 2). Catheters are removed with a good pulse distal to the arterial sheath site. Before discharge 4-hours later, the residual PDA shunt is gone.
This relatively straightforward procedure raises a number of questions:
Why choose a Nit-Occlud® PDA device?
What is different about this device and its implantation?
How can you leave this residual shunt behind in the cardiac catheterization laboratory?
Are there any disadvantages to using this device?
FIGURE 1 Lateral view of aortogram in a patient with a Type A Patent Ductus Arteriosus (A). The narrowest portion at the pulmonary end measures 1.8mm, and the ampulla at the descending aorta just under 9mm, nearly the same diameter as the descending aorta at the level of the ductus.
Why Choose a Nit-Occlud®?
Transcatheter closure of the PDA was reported over 40 years ago.[1] Yet today, there are only three transcatheter PDA closure devices with FDA approval, most recently the Nit-Occlud® device. The first two are the Amplatzer PDA Occluders (Types 1 and 2; ADO1 and ADO2). There are minor disadvantages with these two devices. The ADO1 device aortic disc can protrude into the aorta, particularly in small infants, and it requires a relatively large delivery sheath (6F or more).
The ADO2 device was designed to overcome this with discs that rotate to lie flat against the aorta and pulmonary artery, passing through a smaller delivery system, and horizontally symmetrical so that it can be implanted from either the pulmonary artery or aortic side. The animal model for the ADO2 was a tubular PDA that was filled by the connecting waist, yet 65% of PDAs in humans are conical PDAs. The aortic disc of the ADO2 can lie horizontally in the PDA ampulla with residual shunting, or with a shorter PDA, the waist and aortic disc may remain floating in the aorta despite successful occlusion. For decades the primary method of transcatheter occlusion of the PDA was the Gianturco stainless steel coil,[2] and this worked well for smaller PDAs. But this is off-label use; the coil is not designed to occlude a PDA. Tubular PDAs can also be closed with implantation of the Amplatzer Vascular Plug 2, usually quite effectively, but still an off-label use of the device. It is into this milieu of off-label use for transcatheter PDA occlusion, occasional obstruction of the aorta, and some hemodynamic instability with a large delivery sheath, that the Nit-Occlud® PDA device was introduced and reached FDA approval in August 2013. The advantages of this device are the smaller delivery catheter (4-5F), less chance of protrusion into the aorta or pulmonary artery especially in conical PDAs, FDA approval (on-label use of a device designed specifically to close the PDA), and a high degree of effectiveness. The cost of the Nit-Occlud® PDA device is competitive with, or cheaper than, the alternative FDA-approved PDA closure devices. PDAs with minimum diameters up to 4mm can be effectively closed with this device.
What Is Different about the Nit-Occlud®?
Unlike other coils placed in the PDA, the Nit-Occlud® device has no fibers attached. The Nitinol surface of the coil leads to rapid thrombosis and occlusion. It is designed to be deployed from the venous side, and the delivery catheter must be placed from the femoral or internal jugular vein. The attachment mechanism uses friction between coils of the proximal end of the device and a mandrel (Figure 3) to maintain the connection, allowing easy retrieval once deployed. The Amplatzer device family and the Flipper coils use a screw attachment. In the unlikely event of embolization of the Nit-Occlud® PDA device, it is easily snared and retrieved through a 6F sheath (through the PDA if embolized to the aorta).
Sizing the device may be a little uncertain for beginning users. Device sizes are given as two numbers, e.g. 6x5. The second number is the diameter of the proximal-pulmonary end of the conformed coil, and the first the diameter of the distal-aortic end of the conformed coil (Figure 4). A sizing table is supplied by the manufacturing company (PFM) (Figure 4) with the distal/aortic end designed to be at least 3-4mm larger than the narrow pulmonary end of the PDA, and no more than 2mm larger than the aortic ampulla. This guide is a starting point. In general we have chosen a proximal/pulmonary diameter 2-4mm larger than the minimum PDA diameter to maximize the occlusion rate, and a distal/aortic diameter that will fit into the PDA ampulla keeping it out of the aortic lumen. In the case presented here, with a nearly 9mm distal aortic diameter and a 1.8mm pulmonary diameter, an 11x6 device could have been chosen. But an 11mm distal coil would have protruded into the aorta, even if it configured when exposed with a descending aortic diameter of 9mm. A 7x6 device would have worked as well, and perhaps even a 6x5. So why not choose a minimum distal coil diameter? A smaller distal diameter may leave the coil “rattling around” in the PDA ampulla, and changing position could influence occlusion.
To read the full article, please go to the January 2016 Issue of CCT.