Surgical repair has been the cornerstone of treatment for congenital heart diseases (CHD). However, cardiac catheterization has evolved from being a diagnostic modality to a therapeutic one in the past four decades. Application of catheter-based therapy has become the standard of care for some congenital heart defects, thus obviating surgery. This review will discuss congenital heart defects that are amenable to percutaneous, non-surgical therapy under two broad headings, namely established procedures and evolving procedures. Within these headings, we also discuss instances of therapeutic cardiac catheterization complementing surgery and the evolving hybrid strategies that combine surgical and catheter techniques to achieve better results than either can achieve alone.
Balloon Valvuloplasty (Pulmonary and Aortic Valves)
In current medical practice, balloon valvuloplasty is considered first-line management for pulmonary and aortic valve stenosis. Balloon pulmonary valvuloplasty (BPV) is performed for patients with mean Doppler pressure gradients exceeding 30mmHg. In this procedure, a low-profile, low-pressure balloon is inflated across the valve and stenosis relieved. It is effective in over 90% and has favorable long-lasting results.1 Valves with thin leaflets and minimal dysplasia, characterized by doming appearance in echocardiograms, respond better than severely dysplastic valves. Pulmonary valvular regurgitation induced by this procedure is usually tolerated well for several years. In contrast, balloon aortic valvuloplasty (BAV) carries a higher procedural risk and relatively lower success rate.2 Aortic valve regurgitation induced by balloon valvuloplasty may be relatively poorly tolerated. For these reasons, BAV is considered more palliative than BPV and BAV is usually not performed until mean Doppler pressure gradient exceeds 50mmHg or signs of left ventricular (LV) pressure overload occur on ECG.
Coarctation of Aorta
Balloon angioplasty of native coarctation of aorta remains controversial among pediatric cardiologists.3 Some believe that surgical repair should be the first-line management for all native coarctation of aorta in infants and young children unless significant comorbidities preclude surgical repair. Recoarctation rate and aneurysm formation after the balloon dilatation are concerns. Balloon angioplasty and primary stenting of coarctation of aorta are successfully carried out in young adulthood and beyond.
Re-coarctation of aorta after initial surgical repair is less controversial in that balloon angioplasty is universally applied. Stent placement is performed for older children and adults.4
Atrial Septal Defects
Atrial septal defects (ASDs) are namely primum, secundum and sinus venosus defects (see Figure 1). Only secundum type ASDs are amenable to device closure. Criteria for further selection often requires transesophageal echocardiography (TEE) evaluation to ascertain the presence of at least 5mm of septal tissue all around the defect in order to anchor the device without encroaching upon surrounding cardiac structures.
Amplatzer septal occluder (AGA Medical, Minneapolis, MN) is the commonly used device for this purpose since US approval in 2001 (see Figure 2). Recently, the Helex device (WL Gore, Flagstaff, AZ) has been approved.The CardioSEAL device (NMT, Boston, MA) is used for this purpose in several institutions on an off-label basis or under research protocols. During the procedure, minimum flow-occlusion stretch diameter of the ASDs is determined using a sizing balloon. Patients above 12kg who fulfill anatomic and hemodynamic characteristics are eligible for the procedure. Exclusion criteria are ASDs that are not secundum-type, secundum ASDs without adequate rim of atrial septum around them, and stretch diameter of ASD within the capability of the type of device chosen (varies for each device).5 The Amplatzer device is used worldwide. It is estimated that over 60,000 devices have been implanted. Patients having complete closure by one year range from 93% to 96%. Recently, there have been reports of pericardial effusion from erosion of cardiac wall with associated morbidity and mortality. Modifications in patient and device selection have been proposed to overcome this risk.6
Patent Foramen Ovale and Stroke
Cryptogenic stroke accounts for a significant proportion of all strokes.7 There is a high incidence of patent foramen ovale (PFO) with or without atrial septal aneurysm in such patients. Based on these observations, it is postulated that a significant proportion of patients with cryptogenic stroke represented paradoxical embolism via PFO. In the past, surgical closure of PFO had been advocated for high-risk patients. With successful device closure of ASD, the same principle is now applied to PFO.
The Amplatzer septal occluder has been modified for PFOs. CardioSEAL and Helex devices are being used for this purpose as well. Safety and efficacy of PFO device closure is established.5 But, the indications for this procedure are still evolving. In the US, two randomized trials under way using the Amplatzer device (Randomized Evaluation of recurrent Stroke comparing PFO closure to Established Current standard of care TreatmentÔÇöRESPECT) and CardioSEAL (CLOSURE) to identify the candidates who are considered normal- or low-risk stroke patients. Since estimated prevalence of PFO in the general population is up to 25%, implications of the findings from these trials will be significant.
Patent Ductus Arteriosus
The ductus arteriosus is a fetal communication connecting the distal aortic arch to the bifurcation of pulmonary arteries. It closes spontaneously shortly after birth. Persistence of ductus arteriosus contributes to pulmonary over-circulation, possibly leading to heart failure and pulmonary hypertension. Incidence of patent ductus arteriosus (PDA) is high in preterm babies, although closure can be promoted by using indomethacin. Chances of spontaneous closure after neonatal period are minimal. In the US, options available to close them in the catheterization laboratory are Gianturco coils and the Amplatzer duct occluder.A third device, Nit-Occlud┬«, is undergoing clinical trial. The Gianturco coil is used for PDAs less than 2mm diameter while the Amplatzer duct occluder is used for PDAs larger than 2mm diameter. Results have been excellent, with minimal complications.8 Due to the low complication rate, even a small, hemodynamically insignificant PDA is closed using coils in order to discontinue endocarditis prophylaxis.
Catheter Therapy Complementing Surgical Therapy
Treatment of certain complex CHDs entails multiple, staged palliative or reparative surgical procedures e.g. hypoplastic left heart syndrome (HLHS) and pulmonary atresia with ventricular septal defect (PA-VSD). Therapeutic catheterization procedures complement these staged surgeries, so that subsequent surgery can be delayed with advantage or optimized to allow for better patient outcome. Balloon angioplasty of aortic coarctation in HLHS patients after stage 1 Norwood procedure and rehabilitation of pulmonary arteries in PA-VSD using a combination of balloon and stent angioplasty enables the surgeon to obtain improved results during subsequent repair in respective lesions.
A further example of this strategy is the application of balloon valvuloplasty with stent placement in surgically placed right ventricle-pulmonary artery (RV-PA) conduits that may prolong the longevity of that conduit by a few years.9 Such strategy potentially reduces the number of open heart surgeries in the patientÔÇÖs lifetime by one or even two.
This section discusses percutaneous procedures that are not yet approved by the US Food and Drug Administration (FDA) for routine clinical use; devices that are still in the early stages of development are also mentioned.
Ventricular Septal Defects
Ventricular septal defects (VSDs) account for 40% of all congenital cardiac defects. The majority are small and close spontaneously by four years of age.When the VSD is medium or large, it may lead to heart failure and pulmonary hypertension. Anatomically, the VSDs are largely classified as membranous and muscular (see Figure 4). Muscular VSDs in turn are named according to their location in the muscular part of the ventricular septum as represented in Figure 3.
When muscular VSDs are bordered by septal muscle and when they are clear of any significant intracardiac structures, they can be closed using the Amplatzer muscular VSD device. The clinical trial has concluded in the US and the data are under consideration by the FDA.10
The membranous defect is located anterior to the tricuspid valve and somewhat below the aortic valve (see Figure 3). Proximity to the aortic valve is an issue in closing these defects by the transcatheter technique. A modified Amplatzer membranous VSD device is undergoing clinical trial in North America at this time. CardioSEAL has been available in US for the past few years to close muscular VSDs in high-risk patients.11
Pulmonary Valve Implantation
A subgroup of patients with tetralogy of Fallot with or without pulmonary atresia is left with significant pulmonary regurgitation after surgical repair with conduits placed between right ventricle and pulmonary artery. This chronic pulmonary regurgitation is tolerated for several years. Traditionally, these patients need surgical pulmonary valve implantation to preserve right ventricular function.
Recently, pulmonary valve has been successfully implanted in patients using a transcatheter technique. The principle of the technique is relatively straightforward. A bovine jugular valve is suspended from a stent and the stent is deployed in position using a balloon catheter. This has been performed successfully in several patients with minimal complications.12 This procedure is approved in Europe; a clinical trial is about to start in the US. Current limitations include inability to insert such valves in patients without a conduit inserted during their first heart surgery. With improved design and further studies, this limitation may be overcome in the future.
Aortic Valve Implantation
Insertion of valve in aortic position adds yet another layer of complexity due to the proximity of mitral valve leaflets and coronary orifices. Current attempts have been largely limited to insertion of aortic valve within a calcified native aortic valve. This allows for continued patency of coronary orifices. Several designs have been proposed and are under study to overcome these problems. Small numbers of terminal patients have received this valve as humanitarian therapy.13
Atrioventricular Valve Implantations
Insertion of valves in tricuspid and mitral valve positions is being studied in animals. Currently, these are inserted after surgically opening the chest.
Transcatheter Mitral Valve Repair
In adult patients with mitral valve disease, several strategies and devices are being investigated for mitral valve repair by applying a suture similar to Alfieri sutures using a transcatheter technique. Mitral annuloplasty is being attempted using a prosthesis placed inside the coronary sinus via a percutaneous technique.
Hybrid Catheterization and Surgical Procedures
There are clinical situations where both surgery and catheterization have significant risk. Such situations have forced the evolution of hybrid procedures where cardiac catheterization is performed after a sternotomy. For example, pulmonary arteries and PDA in newborn are difficult to access for catheter interventions. Therefore, access is obtained by direct puncture of the right ventricular outflow tract and the catheter intervention is accomplished. This hybrid approach avoids the need for cardiopulmonary bypass as well as the risks associated with percutaneous catheterization in such small patients. Examples include:
- newborn with HLHS undergoing pulmonary artery banding and stenting of PDA in lieu of much more risky surgical stage I Norwood procedure;14 and
- perventricular closure of muscular VSD in infants and small children.15
The hybrid strategy requires dedicated procedure suites designed to perform surgery and fluoroscopy on the same table. Such hybrid suites will evolve in the course of next few years.
Future Directions and Conclusion
Some existing transcatheter devices will probably undergo design change. Newer cardiac defects will be targeted for transcatheter therapy. Transcatheter valve implantation will move forward complementing surgical therapy and probably decrease the number of heart surgeries a patient needs in his or her lifetime for CHD. The future will also see the evolution of newer strategies in the transcatheter realm such as completion of the Fontan procedure in the catheterization laboratory.