Over the last three decades numerous transcatheter therapies for the treatment of congenital heart disease (CHD) have been developed.
Interatrial Septal Defect
Balloon atrial septostomy has been performed in patients with transposition physiology and in patients where egress of blood is needed from the left or the right atrium and in adults with pulmonary vascular disease where the creation of an atrial septal defect (ASD) would improve the cardiac output. In patients older than six weeks of age balloon atrial septostomy is not effective because of the thick atrial septum and a blade atrial septectomy or stent enlargement of the interatrial septum would be indicated. Blade atrial septectomy is cumbersome to perform and the ASD created by balloon/ blade atrial septostomy is unpredictable. An alternative to balloon/blade atrial septostomy may be stent enlargement of the interatrial septum.
Valvuloplasty and Angioplasty
The basic principle of balloon angioplasty is the dilation of a stenotic vessel with a non-compliant balloon to produce neointimal tears that enlarge the vessel lumen. For vessels that are resistant to balloon dilation, stents are implanted to keep the vessel wall from recoiling. For patent vessels, occlusion can be performed using the coil, the Amplatzer plug or the Gianturco-Grifka bag. Occluder devices are available for closure of patent ductus arterious (PDA), ASD and ventricular septal defects (VSD).
Pulmonary valve stenosis occurs in 7.5-9% of patients with CHD. Valvar pulmonic stenosis can be secondary to commissural fusion or secondary to a hypoplastic pulmonary valve annulus or a dysplastic pulmonary valve. The presentation can vary from a neonate with cyanosis to an adult with an increasing gradient across the pulmonary valve. The indications for balloon valvuloplasty are critical pulmonary valve stenosis with a peak to peak gradient >40 mmHg. Balloon valvuloplasty is not effective in patients with a dysplastic pulmonary valve or a hypoplastic pulmonary valve annulus. The type of access obtained depends upon the diameter of the balloon required and can be accomplished through the femoral vein or the umbilical vein in a neonate or through the transhepatic technique in patients with absent femoral venous access. Complications are infrequent but include rupture of the tricuspid valve apparatus, perforation of the pulmonary artery or the right ventricular outflow tract and balloon rupture or embolisation.
Reports suggest that in select patients with a tripartite right ventricle and normal sized inflow it may be prudent to perforate the pulmonary valve plate. That in select patients with a normal-sized right ventricle perforation of the pulmonary valve would be effective.
Congenital aortic valve stenosis is present in 5-6% of patients with CHD. The aetiology of aortic valve stenosis is a bicuspid aortic valve, commissural fusion of the aortic valve and rarely a unicuspid aortic valve may be present. The majority of patients with aortic valve stenosis present with a heart murmur and are asymptomatic. When symptomatic these patients can present with dyspnoea, easy fatigability or chest pain and in cases of severe aortic stenosis syncope can be the presenting feature. Neonates with critical aortic stenosis present with congestive heart failure and are ductal dependent. The treatment of aortic valve stenosis is balloon valvuloplasty with the only contraindication being the presence of more than mild aortic regurgitation. Indications for balloon aortic valvuloplasty are neonates with critical aortic stenosis. Outside the neonatal age group the indications for balloon aortic valvuloplasty are a peak to peak gradient >50mmHg, patient who is symptomatic or with ST-T wave changes and a peak to peak gradient >40mmHg. Access for this procedure is via the umbilical vein or artery (neonate), femoral artery or vein (trans-septal) or the carotid artery. The advantage of the carotid artery cut down route is the direct, straight course for the catheter into the left ventricle. The sheath required is dependent on the diameter of the balloon catheter required for the procedure. Following the procedure, haemodynamics are reassessed and a repeat aortogram is carried out to assess for aortic regurgitation. Complications reported of this procedure are aortic regurgitation, vessel trauma, balloon rupture and embolisation.
Early and long-term follow-up of balloon aortic valvuloplasty reported safe and effective relief of the gradient in patients with congenital aortic stenosis. Published results indicate that in neonates, children and young adults there is an acute reduction in gradient ranging from 49% to 70% and this reduction in gradient persists at least in the intermediate follow-up period. In neonates the morbidity and mortality are higher, but similar to the surgical group. The only major complication is the development of aortic regurgitation, which appears to be well tolerated outside the neonatal age group.
Coarctation of the Aorta
The incidence of coarctation of the aorta is 5.1-8.1% of patients with CHD. The indications for balloon angioplasty for coarctation of the aorta are: recurrent arch obstruction with a gradient greater than 20 mmHg; and patients with coarctation where there is left ventricular hypertrophy or systemic hypertension proximal to the site of coarctation. Balloon angioplasty is controversial in native coarctation; however, most centres advocate balloon dilation in patients over one year of age with a discrete coarctation and a well developed isthmus.
Complications of aortic angioplasty are vessel trauma leading to loss of the distal arterial pulse. Aortic aneurysm formation secondary to the weakening of the aortic wall at the site of balloon angioplasty occurs in <5% of cases.
Published reports for balloon angioplasty demonstrate that at long-term follow-up the restenosis rate ranges from 25% to 36%. In adolescents and adults with an adult-sized aorta, stent may be placed primarily to minimise the risk of recurrence.
Pulmonary artery stenosis is present in 2-3% of patients with CHD and can be congenital or post surgical. Congenital pulmonary artery stenosis is seen in patients with Alagille's and William's syndrome. It can also be part of CHD such as in patients with pulmonary atresia or aorto-pulmonary collaterals following unifocalisation of the pulmonary arteries, or at the site of arterial shunt placement. In these patients the pulmonary artery stenosis is fairly refractory to balloon angioplasty and cutting balloon angioplasty or stent placement might be indicated. The prognosis with congenital or acquired pulmonary artery stenosis is poor and surgical correction is difficult.
Indications for balloon angioplasty of pulmonary artery stenosis are in patients with a right ventricular pressure equal to or greater than 70% of systemic. In cases of isolated right or left pulmonary artery stenosis the decision to intervene is based on the relative distribution of blood flow via nuclear perfusion scan as well as the presence of any associated cardiac defects. Normal lung perfusion is 55-60% flow to the right lung and 40-45% to the left lung.
Intervention is considered if the flow to the left lung is less than 30% and that to the right lung is less than 40%. Rothman et al. outlined the criteria for successful balloon angioplasty as:
- an increase in pulmonary artery size by more than 50%;
- greater than 50% reduction in distal pulmonary artery to main pulmonary artery systolic pressure gradient;
- 20% reduction in peak systolic right ventricular pressure or the ratio of the right to left ventricular pressure; and
- a 25% increase in total pulmonary blood flow.
Patients refractory to balloon angioplasty are those with stenosis at previous shut site, arterial switch operation, William's syndrome or Alagille's syndrome. In these patients a cutting balloon maybe effective.
Pulmonary arteries resistant to balloon angioplasty may benefit from stent placement. The complications of stent placement are lack of stent growth, neointimal proliferation and jailing of small branching arteries and, therefore, stent placement of the pulmonary arteries should be reserved for pulmonary arteries that are not responsive to other interventions.
Patent Ductus Arteriosus
The two most commonly used approved devices for closure are the Gianturco coil (Cook, Bloomington, IN) for a small PDA and the Amplatzer Duct occluder (AGA Medical, Golden Valley, MN) for a larger PDA. Indication for closure of the PDA is the presence of a clinically apparent PDA because of the risk of enarteritis and haemodynamic compromise. Closure of the silent PDA is controversial.
Complications of coil occlusion of the PDA include coil embolisation. Detachable or Flipper coils (Cook Cardiology, Bloomington, IN) are available and minimise this risk. In addition, other techniques such as the use of snares or bioptomes have been used to position the coil and prevent the risk of embolisation. Immediate closure rate with the coil ranged from 60% to 95% with an increased risk of residual shunts in PDAs larger than 2.5mm in diameter.
The Amplatzer duct occluder is US Food and Drug Administration (FDA) approved and is effective for the closure of a moderate to large PDA. The device design allows for closure of PDA irrespective of size and shape. A device 1-2 mm larger than the minimal PDA diameter is selected. The closure rate reported ranges from 44% to 86% immediately post occlusion increasing to 99-100% by one year. The risk of device embolisation continues to be less than 1% and in the large majority of patients the device can be retrieved by the percutaneous technique. In patients less than 5kg there is a small risk of coarctation from the protrusion of the retention disc into the aortic lumen. Other risks are left pulmonary artery stenosis and haemolysis if a residual shunt remains. After closure subacute bacterial endocarditis (SBE) prophylaxis is necessary for six months.
Atrial Septal Defect and Patent Foramen Ovale
Since then multiple occluder devices have been and still are being tested for closure of the secundum ASD. The only FDA-approved device in the US is the Amplatzer septal occluder (AGA Medical, Golden Valley, MN). The Helex device is still investigational. Indications for closure of the secudum ASD are volume overload of the right ventricle or the presence of a right to left shunt. Results of ASD closure with the Amplatzer septal occluder have demonstrated an immediate closure rate of 37-85% with the closure rate increasing to 80-88% at 24 hours after implantation and 93-95% complete closure rate at one year post procedure. The risks associated with the Amplatzer septal occluder are device displacement and arrythmias. Also reported infrequently is erosion of the device, which most likely is secondary to oversizing of the device.
There are numerous devices available for closure of the PFO but all are undergoing clinical trials at this time. The indications for PFO closure are: embolic stroke, transient ischaemic attack or peripheral embolism with evidence of right or left shunting across a PFO; orthodoxia/platypnoea syndrome; and the presence of PFO in a deepwater scuba diver to prevent decompression sickness.
Ventricular Septal Defect
VSD is present in 20% of all patients with CHD. Surgical closure of the paramembranous VSD is relatively uncomplicated with low morbidity and mortality. However, a Swiss cheese muscular septum continues to be problematic for surgeons because of the trabecular network of the right ventricle.
The anatomic location of the defect is important to define when assessing the feasibility of device closure. Currently the only device approved for muscular VSD closure is the Cardioseal device (NMT, Boston, MA). The Amplatzer muscular occluder (AGA Medical, Golden Valley, MN) is currently in clinical trials. Device closure of the VSD is more complex than closure of the ASD or PDA. Access required is the internal jugular vein, femoral vein and artery. The Amplatzer muscular occluder is currently awaiting FDA approval. The immediate and mid-term results for the US registry for the Amplatzer septal occluder included 75 patients, in whom 83 procedures were undertaken, with six of the 75 patients undergoing perventricular closure. Multiple devices were implanted in 21% of the patients and there were two procedure-related deaths. The complete closure rate at six months was 92.3%.
In select patients with pulmonary valve stenosis and/or regurgitation, placement of a percutaneous valve53-56 is now a viable option. There are numerous valve assemblies currently undergoing clinical trials. Khambadkone et al.55 described their results in 58 patients who underwent placement of the percutaneous pulmonary valve. In all patients the gradient, right ventricular pressure and pulmonary regurgitation were reduced. A magnetic resonance imaging (MRI) scan carried out following valve placement demonstrated a decrease in pulmonary regurgitation, reduced right ventricular end-diastolic volume and improved right ventricular stroke volume.
The hybrid approach is the collaboration of the interventional cardiologist with the cardiac surgeon to treat CHD in the hybrid operating room or the catheterisation suite. In recent years it has taken the form of the perventricular approach57 of closure of the VSD in the very small infant. In this approach a small incision is made in the chest and the right ventricular free wall is punctured under trans-oesophageal echocardiography guidance. The wire and the sheath are then placed across the VSD and a VSD occluder device is positioned.
Transcatheter therapy of CHD has evolved rapidly in the past three decades. The transcatheter treatment of CHD is associated with less pain, minimal scaring and decreased hospital stay and continues to have minimal morbidity and mortality.