Interventional paediatric cardiologyBMJ 2003; 327 doi: http://dx.doi.org/10.1136/bmj.327.7411.385 (Published 14 August 2003) Cite this as: BMJ 2003;327:385
- Kevin P Walsh, consultant paediatric cardiologist
Interventional paediatric cardiology mainly involves dilatation of stenotic vessels or valves and occlusion of abnormal communications. Many transcatheter techniques—such as balloon dilatation, stent implantation, and coil occlusion—have been adapted from adult practice. Devices to occlude septal defects, developed primarily for children, have also found application in adults.
Interventional procedures follow a common method. General anaesthesia or sedation is required, and most procedures start with percutaneous femoral access. Haemodynamic measurements and angiograms may further delineate the anatomy or lesion severity. A catheter is passed across the stenosis or abnormal communication. A guidewire is then passed through the catheter to provide a track over which therapeutic devices are delivered. Balloon catheters are threaded directly, whereas stents and occlusion devices are protected or constrained within long plastic sheaths.
Balloon atrial septostomy, introduced by Rashkind 35 years ago, improves mixing of oxygenated and deoxygenated blood in patients with transposition physiology or in those requiring venting of an atrium with restricted outflow. Atrial septostomy outside the neonatal period, when the atrial septum is much tougher, is done by first cutting the atrial septum with a blade.
Pulmonary valve stenosis
Balloon valvuloplasty has become the treatment of choice for pulmonary valve stenosis in all age groups. It relieves the stenosis by tearing the valve, and the resultant pulmonary regurgitation is mild and well tolerated. Surgery is used only for dysplastic valves in patients with Noonan's syndrome, who have small valve rings and require a patch to enlarge the annulus.
Valvuloplasty is especially useful in neonates with critical pulmonary stenosis, where traditional surgery carried a high mortality. In neonates with the more extreme form of pulmonary atresia with an intact ventricular septum, valvuloplasty can still be done by first perforating the pulmonary valve with a hot wire. Pulmonary valvuloplasty can also alleviate cyanotic spells in patients with tetralogy of Fallot whose pulmonary arteries are not yet large enough to undergo primary repair safely.
Aortic valve stenosis
Unlike in adults, aortic valve stenosis in children (which is non-calcific) is usually treated by balloon dilatation. A balloon size close to the annulus diameter is chosen, as overdilatation (routinely done in pulmonary stenosis) can result in substantial aortic regurgitation. The balloon is usually introduced retrogradely via the femoral artery and passed across the aortic valve. Injection of adenosine, producing brief cardiac standstill during balloon inflation, avoids balloon ejection by powerful left ventricular contraction.
In neonates with critical aortic stenosis and poor left ventricular function the balloon can be introduced in an antegrade fashion, via the femoral vein and across the interatrial septum through the patent foramen ovale. This reduces the risk of femoral artery thrombosis and perforation of the soft neonatal aortic valve leaflets by guidewires. The long term result of aortic valve dilatation in neonates depends on both effective balloon dilatation of the valve and the degree of associated left heart hypoplasia.
Balloon dilatation for coarctation of the aorta is used for both native and postsurgical coarctation and is the treatment of choice for re-coarctation. Its efficacy in native coarctation depends on the patient's age and whether there is appreciable underdevelopment of the aortic arch. Neonates in whom the ductal tissue forms a sling around the arch have a good initial response to dilatation but a high restenosis rate, probably because of later contraction of ductal tissue. Older patients have a good response to balloon dilatation. However, overdilatation may result in formation of an aneurysm.
The problems of vessel recoil or dissection have been addressed by the introduction of endovascular stents. This development has been particularly important for patients with pulmonary artery stenoses, especially those who have undergone corrective surgery, for whom repeat surgery can be disappointing. Most stents are balloon expandable and can be further expanded after initial deployment with a larger balloon to keep up with a child's growth.
Results from stent implantation for pulmonary artery stenosis have been good, with sustained increases in vessel diameter, distal perfusion, and gradient reduction. Complications consist of stent misplacement and embolisation, in situ thrombosis, and vessel rupture.
Stents are increasingly used to treat native coarctation in patients over 8 years old. Graded dilatation of a severely stenotic segment over two operations may be required to avoid overdistension and possible formation of an aneurysm. In patients with pulmonary atresia without true central pulmonary arteries, stenotic collateral arteries can be enlarged by stent implantation (often preceded by cutting balloon dilation) to produce a useful increase in oxygen saturation.
An exciting new advance has been percutaneous valve replacement. A bovine jugular vein valve is sutured to the inner aspect of a large stent, which is crimped on to a balloon delivery system and then expanded into a valveless outflow conduit that has been surgically placed in the right ventricle. Several patients have been treated successfully with this system, although follow up is short.
Transcatheter occlusion of intracardiac and extracardiac communications has been revolutionised by the development of the Amplatzer devices. These are made from a cylindrical Nitinol wire mesh and formed by heat treatment into different shapes. A sleeve with a female thread on the proximal end of the device allows attachment of a delivery cable with a male screw. The attached device can then be pulled and pushed into the loader and delivery sheath respectively. A family of devices has been produced to occlude ostium secundum atrial septal defects, patent foramen ovale, patent ductus arteriosus, and ventricular septal defects.
Atrial septal defects
The Amplatzer atrial septal defect occluder has the shape of two saucers connected by a central stent-like cylinder that varies in diameter from 4 mm to 40 mm to allow closure of both small and large atrial septal defects. Very large secundum atrial septal defects with incomplete margins (other than at the aortic end of the defect) may require a surgically placed patch.
An atrial septal defect is sized with catheter balloons of progressively increasing diameter. An occluder of the correct size is then introduced into the left atrium via a long transvenous sheath. The left atrial disk of the occluder is extruded and pulled against the defect. The sheath is then pulled back to deploy the rest of the device (central waist and right atrial disk) and released after its placement is assessed by transoesophageal echocardiography. The defect is closed by the induction of thrombosis on three polyester patches sewn into the device and is covered by neocardia within two months. Aspirin is usually for given for six months and clopidrogrel for 6-12 weeks.
Worldwide, several thousand patients have had their atrial septal defects closed with Amplatzer devices, with high occlusion rates. Complications are unusual and consist of device migration (< 1%), transient arrhythmias (1-2%), and, rarely, thrombus formation with cerebral thromboembolism or aortic erosion with tamponade. Transcatheter occlusion is now the treatment of choice for patients with suitable atrial septal defects. Other devices are available, but none has the same applicability or ease of use.
Patent foramen ovale
The Amplatzer atrial septal defect occluder can also be used to treat adults with paradoxical thromboembolism via a patent foramen ovale. The Amplatzer patent foramen ovale occluder has no central stent and is designed to close the flap-valve of the patent foramen ovale. Randomised trials are under way to compare device closure with medical treatment for preventing recurrent thromboembolism.
Patent ductus arteriosus
Although premature babies and small infants with a large patent ductus arteriosus are still treated surgically, most patients with a patent ductus arteriosus are treated by transcatheter coil occlusion. This technique has been highly successful at closing small defects, but when the minimum diameter is > 3 mm multiple and larger diameter coils are required, which prolongs the procedure and increases the risk of left pulmonary artery encroachment. The Amplatzer patent ductus arteriosus plug, which has a mushroom shaped Nitinol frame stuffed with polyester, is used for occluding larger defects. The occlusion rates are close to 100%, higher than published results for surgical ligation.
Ventricular septal defects
Occlusion devices are especially useful for multiple congenital muscular ventricular septal defects, which can be difficult to correct surgically. The Amplatzer occluder device has a drum-like shape and is deployed through long sheaths with relatively small diameter.
Such devices have also been used to occlude perimembranous defects, although in this location they can interfere with aortic valve function. A device with eccentric disks, which should avoid interference with adjacent valves, has recently been introduced. The Amplatzer membranous device has two discs connected by a short cylindrical waist. The device is eccentric, with the left ventricular disc having no margin superiorly, where it could come near the aortic valve, and a longer margin inferiorly to hold it on the left ventricular side of the defect. The end screw of the device has a flat portion, which allows it to be aligned with a precurved pusher catheter. This pusher catheter then extrudes the eccentric left ventricular disk from the specially curved sheath with its longer margin orientated inferiorly in the left ventricle. Initial results are promising, particularly for larger infants with haemodynamically important ventricular septal defects.
Transcatheter occlusion has also been used to treat ventricular septal defects in adults who have had a myocardial infarction, and a specific occluder has been introduced. It differs from the infant device in having a 10 mm long central stent to accommodate the thicker adult interventricular septum. Its role in treatment is uncertain, but it offers an alternative for patients who have significant contraindications to surgical closure.
Coil occlusion of unwanted blood vessels
Coil occlusion of unwanted blood vessels (aortopulmonary collateral arteries, coronary artery fistulae, arteriovenous malformations, venous collaterals) is increasingly effective because of improvements in catheter and coil design.
Percutaneous intervention versus surgery
The growth of interventional cardiology has meant that the simpler defects are now dealt with in catheterisation laboratories, and cardiac surgeons are increasingly operating on more complex lesions such as hypoplastic left heart syndrome. More importantly, interventional cardiology can complement the management of these complex patients, resulting in a better outcome for children with congenital heart disease.
Complications such as device embolisation, vessel or chamber perforation, thrombosis, and radiation exposure can be reduced by careful selection of patients and devices, meticulous technique, low dose pulsed fluoroscopy, and, most importantly, operator experience. Further developments in catheter and device design will improve and widen treatment applications.
The ABC of interventional cardiology is edited by Ever D Grech and will be published as a book in autumn 2003. Ever D Grech is consultant cardiologist at the Health Sciences Centre and St Boniface Hospital, Winnipeg, Manitoba, Canada, and assistant professor at the University of Manitoba, Winnipeg.
Competing interests None declared.