Invited article (1.8MB)	Grech V*, Felice H**, Fenech A**, DeGiovanni JV***. Amplatzer ASO device closure of secundum atrial septal defects and patent foramen ovale. Images Paediatr Cardiol 2003;15:42-66
*	Editor-in-Chief, Images Paediatr Cardiol
**	Consultant Cardiologist, St. Luke’s Hospital, Malta
***	Consultant Paediatric Cardiologist, Birmingham Chilren’s Hospital, UK

Abstract
Transcatheter closure of atrial septal defects and patent foramen ovale is now a well established therapeutic option. In this paper, we illustrate, step by step, the technique of Amplatzer ASO closure of these defects.
 
Article
Introduction
Atrial septal defects
Atrial septal defects (ASDs) are congenital deficiencies in the interatrial septum, and are most commonly found in the fossa ovalis. These lesions comprise 10% of all congenital heart defects.

The haemodynamic effects of ASDs are related to the degree of left to right shunting and its duration. Large defects cause volume overload of the right side of the heart with pulmonary hypertension, that is initially reversible, and later irreversible, with shunt reversal (right to left). At this stage, usually in middle age, survival is limited, and such individuals become cyanosed with reduced exercise tolerance and are at risk of atrial arrhythmias that may precipitate frank heart failure.

Small ASDs often close spontaneously in the first few years of life. Larger defects seldom do. Significant ASDs (Qp/Qs of > 1.5) are therefore closed surgically or by interventional catheter techniques before school age or at the time of diagnosis later in life.

Patent foramen ovale
In utero, the foramen ovale serves as a physiologic conduit for right to left shunting. After birth, the left atrial pressure is higher than that in the right atrium, resulting in functional closure of the foramen ovale, and later in anatomical closure. A patent foramen ovale (PFO) is a persistent communication due to lack of anatomical closure.

A patent foramen ovale (PFO) is found in almost 50% of cryptogenic strokes and transient ischaemic attacks (TIA). In these individuals, the recurrence risk for stroke is 2-4% per annum, and for TIA the risk is 1-2% per annum. There is no consensus with regard to the ideal type or length of medical treatment for the prevention of such events. Indeed, it has been shown that there are no differences in risk reduction between different modes of anticoagulant or antiplatelet therapy with respect to recurrent stroke or TIA. On the other hand, a recent study with a mean of 15 months of followup showed that device closure of a PFO in individuals who have sustained a neurological event resulted in no strokes and a 1.7% per annum risk of TIA.¹

A wide variety of devices for transcatheter closure of ASDs and PFOs have been developed in the past few decades. We illustrate the technique of ASD/PFO closure using the Amplatzer ASO (atrial septal occluder) device (AGA Medical Corporation, 682 Mendelssohn Avenue, Golden Valley, MN 55427, USA).

This particular device consists of a collapsible meshwork of NITINOL (Nickel Titanium National Ordinance Ltd), an alloy that returns a device to its original shape after being collapsed into a sheath for delivery within the heart. The device shape is a self-expandable, double disk and the two disks are linked together by a connecting waist. Both discs and waist are filled with a polyester fabric in order to ensure complete closure of the defect.

Method
Transoesophageal echocardiography assessment of the defect is crucial

• It is important to have inferior and posterior rims.
• An anterior rim is not as important as the device will grasp the aorta.
• A superior rim is also not as important as the device will grasp the orifice of the superior vena cava.
• The defect should be well away from the pulmonary veins and mitral valve.
• A more detailed review of defect assessment by TOE with regard to device suitability will be the subject of another article.

The catheter is passed through the defect into the left atrium (LA) and is wedged in the left upper pulmonary vein (LUPV), pointing upward or downward. If it proves difficult to cross to the LA (e.g. very small PFO), use an exchange wire over the MPA catheter to probe the interatrial septum with the tip of the wire. Alternatively, a transeptal catheter may be used to cross to the LA with an exchange wire. An exchange wire is passed through the MPA catheter and wedged in a pulmonary vein for stability, preferably the left upper pulmonary vein.	Figure 1: Catheter through defect into left upper pulmonary vein
The catheter can be seen on TOE crossing over from RA into LA across the ASD.  The MPA catheter is now removed over the wire.	Figure 2: Catheter crossing a PFO from RA (below left) to LA (above right)
A suitably chosen Amplatzer sizing balloon is opened and flushed (24 / 34 mm diameter sizes – table 1). The balloon is held vertically pointing downward and is inflated with saline in order to remove all trapped air.	Figures 3 and 4: Removal of all trapped air from the balloon catheter

• Use a 24mm balloon for all adult PFOs and for children with transthoracic defect diameter <18mm.
• Use a 34mm balloon for all adult ASDs and for children with transthoracic defect diameter >18mm.

The balloon is then completely deflated.	Figure 5: Balloon completely deflated
The standard short sheath is removed over the exchange wire and the sizing balloon is inserted over the wire.	Figure 6: Catheter in over wire without sheath
The hole in the groin must be generous as the balloon catheter is 9F, and is inserted through the skin without a sheath.	Figure 7: Catheter in through generous groin incision
The defect is situated approximately at the right border of the vertebral column in straight AP view.	Figure 8: Sizing balloon catheter being deployed
The balloon is inflated across the defect with a 25% contrast solution. A good waist should be obtained without under/overdoing it.    Figure 9: Schematic diagram showing inflated sizing balloon	Figure 10: Sizing balloon inflated
The waist should be acquired and measured in the posteroanterior view and in the left anterior oblique view at an angle of about 15°. A suitable image is frozen on the slave monitor.	Figure 11: Sizing balloon at 15° of LAO
For calibration purposes, the sizing rings on the balloon shaft are spaced 10mm, 5mm and 2mm apart.	Figure 12: Schematic showing sizing rings on balloon shaft
TOE is used to check that the defect is completely closed with the balloon, that no other defects in the interatrial septum (IAS) have been exposed, and the balloon diameter is measured. The best angle to view and measure the inflated balloon is at about 45 to 55°.	Figure 13: TOE showing inflated balloon
The volume of fluid injected in the balloon is noted and the balloon is now deflated. The balloon catheter is removed leaving the wire wedged in the LUPV. The balloon is now reinflated using the same volume as was used when the balloon was inflated across the defect.  The balloon is now passed through the template sizing holes and the waist obtained is compared with that of the image on the slave monitor.  Visually check that waist obtained is about the same as that seen on the slave monitor.	Figure 14: Balloon though template - 1
In this way, the diameter of the defect (the waist of the inflated balloon) has been estimated by three methods: by radiology, by TOE, and externally.	Figure 15: Balloon though template - 2
The appropriate sheath (table 2) and introducer pack are opened (sizes 45 by 60/80 cm), and both sheath and introducer are flushed while still mounted on the cardboard.	Figure 16: Sheath and introducer flushed

The loader is also flushed and the introducer is passed into the sheath. The sheath and introducer are now passed into the femoral vein, incidentally stopping bleeding from around the wire.	Figure 18: Loader being flushed
The two piece loader is connected.	Figure 19: Loader being connected
The loader is now flushed through the side port.	Figure 20: Loader flushed through side port
The delivery wire is inserted through the loader.	Figure 21: Delivery wire inserted into loader
The end of the delivery wire is pushed out of the other end of the loader.	Figure 22: Delivery wire passed right through loader
The Amplatzer device (table 3) is opened and the size advertised on the package labeling is checked with the template. The device is now screwed clockwise onto the delivery wire. It is then untightened slightly until a click is felt.	Figure 23: Device being screwed onto the delivery wire

The device is loaded under water and can be helped manually in order to avoid splay of the end of the loader.	Figure 24: Device loaded underwater
If splay occurs, press around the end of the loader in order to decrease the degree of splay.	Figure 25: Pressing around the loader end to diminish splay
The side port of the loader is flushed with tip of loader under water to ensure removal of all air.	Figure 26: Flush loader underwater
The introducer is removed from the sheath, while ensuring that the sheath is pushed well into the LA.	Figure 27: Introducer removed leaving sheath well in LA
The loader is brought to the sheath.	Figure 28: Loader brought to sheath

The wire is used to push the device out of the loader and into the sheath.	Figure 29: Wire used to push in device
The screw-on handle at the distal end of the wire is removed.	Figure 30: Handle removed
The loader is slid off the wire.	Figure 31: Loader removed
The handle is reattached.	Figure 32: Handle reattached to wire

The device is pushed to the end of the sheath.	Figure 33: Device pushed to sheath tip
	Figure 34: In vitro demonstration of device opening
The LA disk and the stalk are pushed out of the sheath into the LA.	Figure 35: Distal (LA) disk being deployed
	Figure 36: LA disk being pulled back against the interatrial septum
The device is pulled back gently against the septum, and this is confirmed by feeling resistance on the wire and by TOE.	Figure 37: Device being pulled back against IAS
The right atrial (RA) disk is now deployed in the RA. If the deployed device appears perfect on fluoroscopy and on TOE, then it is very likely that both disks have been deployed in one atrium.	Figure 38: RA disk also deployed
The device is given a ‘Minnesota wiggle’ in order to ensure that it is firmly deployed within the atrial septum. This is done by gently jerking the delivery wire in the sheath.	Figure 39: The 'Minnesota wiggle'
The device is now unscrewed off the wire.	Figure 40: Device released
Make sure to pull back the delivery wire back into the sheath immediately as the end of the wire is rigid and sharp and may produce trauma. The deployed device is acquired on cine in the posteroanterior view and with an angulation of 30° cranial with 30° LAO.	Figure 41: Device reviewed from different angles

Figure 42: Profiling the IAS - 1

Figure 43: Profiling the IAS - 2

Points to ponder
The device size refers to the central stalk. Roughly, the actual rim is 5mm for device sizes up to 19mm i.e. the actual device diameter is the device size plus 10mm. For 20mm devices and larger, the rim is 7mm. It is therefore important to ensure that the IAS can accommodate the required device size. If necessary, the size of the entire IAS can be measured on TOE. However, TOE foreshortens the length of the IAS, and such measurements are better done during transthoracic echocardiography.
 

The LA disk (and occasionally also the RA disk) may be deployed in a distorted manner (cobra formation). This may be due to a faulty device or the device may actually be catching on an intracardiac structure. If the latter, the device should be retrieved back in the sheath and deployed fully at a different angulation in the LA. Very occasionally, the device persists in deploying in this abnormal fashion and may have to be replaced.

Figure 44: Cobra formation

If the device embolises and the patient is stable, the device can be removed surgically or pulled back into a large sheath by means of a goose necked snare. If the device cannot be retrived or if the device is still attached to the delivery cable but cannot be brought back into the sheath then an AGA Bale Out kit may be empolyed. This kit consists of  a cable that screws on to the back of the delivery cable converting it into an exchange length. The Bale Out sheath is wide enough
to go over the cable. If a Bale Out Kit is not available, then remove the original sheath, open a larger sheath and use its cable to screw to the back of the cable inside the patient. Then cut the tip of the dilator to allow the cable to pass through as the cable is larger that 0.035".

If there are two atrial septal defects, balloon size both and assess not only the size and location of the defects, but also the distance between them. This will allow a decision as to whether to close the defects by using one oversized device or use two separate devices. If two devices are used, it is logical to first close the smaller defect so that when closing the larger defect, the larger device will overlap the smaller device.

If there is a large ASD in association with significant pulmonary stenosis, it is best to first close the ASD, leaving it attached to the delivery wire, and then balloon the pulmonary valve, releasing the device afterward. There is a significant risk of acute pulmonary oedema if pulmonary valvar stenosis is dilated before closure of the defect.

This animation summarises the procedure (figure 45).
 

Further reading
http://www.amplatzer.com/medical_professionals/index.html

References

 
1. Braun MU, Fassbender D, Schoen SP, Haass M, Schraeder R, Scholtz W, Strasser RH. Transcatheter closure of patent foramen ovale in patients with cerebral ischemia. J Am Coll Cardiol 2002;39:2019-2025

 

Contact information

Dr. Victor Grech  Consultant Paediatric Cardiologist & Editor-in-Chief, Images Paediatr Cardiol Paediatric Department  St. Luke's Hospital  Guardamangia MSD09 - Malta  victor.e.grech@gov.mt