Paediatric cardiac interventions started in
mid 60s with the use of balloon atrial septostomy by William Rashkind to palliate newborns and infants with transposition of great arteries. Following the footsteps of coronary interventions, paediatric cardiac interventions have made a remarkable progress in the last couple of decades. Transcatheter interventions in children and adolescents are mainly performed to dilate narrow valves or vessels, close abnormal communications, create or maintain patency of communications to improve oxygenation or to replace abnormally functioning valves. Most of these procedures are being performed in our country with great degree of safety and efficacy. Some of these interventions can palliate or cure the defect by themselves while the others are being used in conjunction with the surgical procedures for more effective and sometimes less morbid palliation).
Atrial Septostomy procedures: Balloon Atrial septostomy
Balloon atrial septostomy (BAS), introduced by Rashkind in 1966, is a lifesaving procedure and one of the few remaining indications for an emergency catheterization in newborns and infants. Because of septal thickening with age, BAS is effective only in infants younger than 1 month of age. It is indicated in almost all infants with transposition of the great arteries with intact interventricular septum especially younger than 1 month of age who are not immediately scheduled for surgical correction. It is life saving in infants of d-TGA presenting with severe hypoxaemia and acidosis. It is also indicated for palliating newborns in whom all systemic, pulmonary or mixed venous blood must traverse a restrictive interatrial communication to return to the active circulation. These include tricuspid and mitral atresia with hypoplastic right or left ventricles and some instances of total anomalous venous connection. The procedure is usually performed from the femoral vein, although occasionally it has been accomplished successfully via the umbilical vein. It is most often done under fluoroscopic guidance, although it can be carried out at the bedside using echocardiographic guidance. The balloon is inflated in the LA and then jerked across the septum, the entire procedure being repeated 3-4 times till there is no resistance to the movement of the balloon. The success of the procedure is decided by increase in the size of the interatrial communication on echo with disappearance of turbulence on colour flow mapping and spectral Doppler. Fracture of the septum primum with excessive movement is also an indicator of a good and lasting septostomy. In the catheterization laboratory, an equalization of the atrial pressures and improvement in oxygen saturation by 10% is suggestive of a successful outcome. Although during the early years, atrial arrhythmias, tricuspid valve injury and cardiac perforation were described as some of the complications, with increasing experience, echo guidance and improved hardware these have become very rare.
Balloon Valve Dilatations
Significant pulmonary and aortic valve stenoses account for almost 10% of all congenital heart disease (CHD).
Pulmonary valve dilatation
Critical stenosis of pulmonary valve (PS) presents in the newborn with cyanosis, cardiac failure or occasionally with sudden cardiovascular collapse following ductal closure. Patients with less than critical PS are diagnosed incidentally due to an audible murmur. If left unattended during infancy and early childhood, some of them with more severe stenosis may present in the second or third decade with shortness of breath, easy fatiguability, exertional syncope or right sided failure characterized by ascites, puffiness of face and oedema feet. Data obtained from a sequential follow-up study, suggest that patients with pulmonic stenosis with a gradient across the stenotic valve of more than 50 mm Hg had a better outcome at 20 years follow-up when treated with surgery as compared with no intervention. Balloon pulmonary valvuloplasty is currently the procedure of choice for symptomatic as well as asymptomatic but significant valvar PS. The procedure is performed under sedation or general anaesthesia. Patients are usually observed in hospital overnight and then discharged home the following day. Post procedural care is minimal, with exercise restriction for about 48-72 hours to allow healing of catheter entry sites.
In pulmonic stenosis, balloon dilation is effective in most patients. The main exception is the subset of patients with so-called dysplastic pulmonary valve (common in Noonan's syndrome), where the valve is thick and often has associated supravalvar narrowing. In those with adhesion of the cusps to the pulmonary artery wall, balloon dilatation is unlikely to give significant relief. Calculation of the annulus size on echocardiography and on angiography is extremely important to determine the balloon size needed for adequate dilatation. For a single-balloon dilatation, the balloon diameter chosen is equal to 1.2 times the diameter of the pulmonary annulus. For dysplastic valves it is 1.4 times the pulmonary annulus diameter. To avoid the marked drop in systemic blood pressure (common while using large balloons when annulus size is > 20 mms) and to reduce the trauma to the veins at the site of entry, a double balloon technique is occasionally used. When using this tehcnique, the combined diameters of the two balloons should equal 1.5-1.7 times the measured diameter of the valve annulus. With pure stenosis, the gradient across the valve should reduce to less than 20 mm Hg. In some cases, relief of valvar obstruction unmasks an infundibular obstruction resulting a persistent residual right ventricular outflow gradient. Experience has shown that this infundibular obstruction is ususally dynamic and regresses with time. Follow-up for pulmonary valve balloon dilatation now extends to nearly 25 years. Efficacy is long lasting in most cases, although about 8% of individuals require repeat dilatation for restenosis. Although dilation results in mild to moderate valvular regurgitation, the physiologic consequences of the insufficiency are rarely significant in childhood and adolescence since it is a low pressure regurgitation. Thus the main long-term issues are the need for observation for the relatively rare cases of restenosis, the continued need for endocarditis prophylaxis and the unknown long-term (e.g.30-60 years) effects of the pulmonary regurgitation.
Critical pulmonic stenosis in the newborn
In a neonate with critical PS, very little blood can flow across the valve; instead the majority of the venous return to the heart shunts from right to left across the foramen ovale. Left-to-right shunting at the level of the ductus arteriosus maintains pulmonary blood flow and is life saving. As the normal constriction of the ductus arteriosus occurs, the infant becomes progressively and severely hypoxaemic and acidotic. These neonates need to be stabilized in the ICU with IV fluids, prostaglandin E 1 (PGE 1) infusion to maintain ductal patency, correction of acidosis and electrolyte imbalance and positive inotropes to maintain perfusion. In this group of patients, the procedure is technically more demanding than in older children. In early series, technical failures and serious complications were common. Refinements in technique and technology (such as use of coronary angioplasty wires and very low profile balloons for those with very pin-hole critical stenosis) have resulted in progressively improved outcome. In current practice technical success (i.e successful dilation of the valve) is achieved in almost all cases. Clinical success, which is defined as relief of significant hypoxaemia with no more than mild residual valvular obstruction, occurs in 94% of patients. Overall, the prognosis of patients with isolated critical pulmonic stenosis with normally developed right ventricle (i.e. non hypoplastic) is excellent through childhood, however, long term sequelae need further follow up.
Aortic valve dilatation
Significant aortic stenosis presents with syncope, angina or cardiac failure. All known forms of therapy C balloon dilation, surgical valvotomy or replacement of the valve C are palliative in the sense that, in all cases, further surgery will probably be needed at some point because of valve failure. Balloon dilation of the aortic valve relieves obstruction either by separating fused leaflets or by creating small tears that increases the size of the valve orifice. In either case, it is common for the procedure to result in some degree of aortic insufficiency. Attempts to alleviate obstruction completely by using larger balloons (exceeding annular diameter) result in an unacceptable amount of regurgitation defeating the very purpose of non surgical dilatation. Hence, it has been our policy to accept reduction in the gradient by 60% to 70% or a residual gradient of less than 40 mm Hg. This can usually be accomplished without inducing significant aortic regurgitation. Despite using a conservative approach and a stepwise dilatation, significant residual obstruction or aortic insufficiency occurs in about 10% of patients. During the early years of BAV, a significant number of patients did not get effective dilatation due to ping-pong effect (i.e. inability of the balloon to stabilize itself across the aortic valve during inflation). This is more commonly seen in those with normal left ventricular contractility. With the advent of long balloons (5-6 cm in length) and with the use of rapid ventricular pacing during dilatation, this difficulty has been overcome in majority of the patients. Another important consideration is the damage to the femoral artery caused by the introduction of balloons, but this has been largely overcome with newer low- profile balloon designs and use of the double balloon technique. The benefit achieved after aortic valve dilation is of variable durability. Intervention-free survival is reported to be 50% to 60% at 10 years after dilation. The need for subsequent intervention may result from the development of recurrent obstruction, insufficiency or both. In the first case, repeat valve dilation is an option, however, when aortic insufficiency becomes severe surgery is the only modality of treatment. Thus follow-up care of patients after intervention for aortic valve disease is quite important. Depending on the severity of residual stenosis and insufficiency, patients may be limited from competitive and contact sports. It is mandatory to evaluate them at regular intervals for assessing their symptomatic status and haemodynamics by echocardiography and colour flow mapping. All of them need lifelong infective endocarditis prophylaxis.
Critical aortic stenosis in the newborn
Critical aortic stenosis in the newborn remains a challenging and high-risk lesion. This lesion encompasses a spectrum with hypoplastic mitral annulus and/or left ventricle and/or ascending aorta at one end while the other end comprises those patients with normal sized mitral valve, LV and the ascending aorta. Most of the patients with former anatomical subset have what is essentially a hypoplastic left heart syndrome (HLHS) and will need treatment on those lines. For those belonging to the latter subset, balloon aortic valvuloplasty is a preferred option although some centres practice surgical aortic valvuloplasty. In this group of patients, there is a variable affection of left ventricular contractility. Although, the LV function tends to recover in the majority after balloon dilation, in a few of them there is such severe myocyte injury that the ventricle is not recoverable even after successful relief of the narrowing.
The efficacy of balloon valvotomy in newborn critical aortic stenosis is comparable to that of surgical valvotomy and thus has largely replaced the surgical procedure. Patients are intubated and mechanically ventilated for the procedure. Most of them are commonly on inotropic support and PGE1. After balloon aortic valvotomy, some infants need several days of continued intensive care with inotropic support to allow recovery of left ventricular performance. In an attempt to avoid femoral arterial trauma, several other approaches to aortic valve dilatation have been introduced. However, in our experience, with the availability of low profile balloons and smaller arterial sheaths clinically significant femoral arterial injury has become extremely rare. The prograde approach from the femoral vein across the interatrial septum into the left atrium and then crossing the aortic valve antegradely is becoming more popular. This procedure however, has a higher incidence of failure in delivering the balloons and a significant incidence of damage to the mitral valve apparatus. Also, this approach is more prone to ventricular arrhythmias which are ill tolerated by some with poor LV contractility. Another option is a trans-carotid approach which gives a direct access to the aortic valve requiring less catheter manipulation and less overall time and is associated with a very minimal complication rate.
Reported early survival of newborns after balloon dilation of critical aortic stenosis is close to 90% in patients without significant left ventricular hypoplasia. Most deaths are procedure related. Subsequent mortality was negligible when followed for up to 8 years. Nowadays, with more experience, the procedural mortality is lower than in past reports (4%), but subsequent intervention remains quite prevalent. The actuarial freedom from reintervention is only 45% at 3 years. If reintervention is necessary in childhood, it is likely to be necessary in the first year of life. Recurrent aortic stenosis, severe aortic insufficiency or both necessitate reintervention. Patients with isolated restenosis may benefit from repeat balloon dilation, but many of these patients with predominantly regurgitant lesion will undergo autograft root replacement (Ross procedure).
To summarize, aortic valve disease is a lifelong disease, and patients who require dilation of aortic stenosis as newborns are likely to have significant residual disease and on-going cardiovascular concerns. Although all patients with aortic stenosis require cardiac follow-up, newborns with critical aortic stenosis require frequent evaluation during growth and are virtually certain to need subsequent aortic valve interventions during infancy, childhood and possibly throughout adulthood. With appropriate follow-up management, however, the majority of these children remain asymptomatic.
Coarctation of the aorta
Coarctation of the aorta occurs in 0.04% of individuals and accounts for 5% of congenital heart defects. Like aortic stenosis, critical coarctation presents in the newborn period with severe heart failure or shock when the ductus arteriosus closes. Older patients are most often asymptomatic but sometimes present with hypertension or complication of hypertension pertaining to cerebrovascular or cardiovascular system. They can come to attention due to a murmur produced by an associated bicommissural valve or by presence of intercostal collaterals. All patients with significant coarctation require treatment. Balloon dilation has been used as a treatment for coarctation since the 1980s. It was first used to successfully dilate post-surgical recurrent coarctation of the aorta. The dense scar tissue surrounding the recurrent coarctation makes repeat surgery difficult and provides support against aortic rupture during balloon dilatation, hence, this mode of treatment has become the preferred approach for tackling recoarctation. As regards native coarctation, however, there is still substantial variation in practice. Surgery is the benchmark against which interventional catheter treatment must be judged. Most agree on the choice of therapeutic approach at the extremes of age. In newborns, the preferred treatment is surgical because there is a high rate of recurrent obstruction after balloon dilation, although in some centres the first procedure may be a balloon dilatation and surgery reserved only for those who develop neonatal recoarctation. In infants and older children with coarctation, balloon angioplasty is widely used as the primary form of therapy, but surgery continues to remain a common option. The controversy surrounding these options is due to varying reported rates of recurrence and of aneurysm formation at the site of balloon dilatation. For example, the incidence aneurysm formation (the most worrisome complication of this procedure) has been variously reported as ranging from less than 2% to 40% of cases. Therefore, clinicians should go by the age of the patient and experience and results of the local institutions.
In patients who present after adolescence and into adulthood, stenting of the coractation at catheterization is gaining wide acceptance as first line treatment or at least as an acceptable alternative to surgery. Stents result in effective and predictable relief of the obstruction in the majority of cases. The complications with this procedure are infrequent. At follow-up recurrent coarctation and aneurysm formation is uncommon.
Mitral Valve Dilatation
Rheumatic mitral valve stenosis is still a common lesion in children in India. The pliable leaflets, fusion of commisures, mild subvalvar affection and absence of calcification make these valves most suitable for a dilation procedure, which has been demonstrated to be effective in children. Most of the patients with juvenile MS, have small left atria and severe PHT. Hence they are unable to tolerate acute MR if it were to occur following BMV. Hence, it is better to accept a mild residual MS rather than producing acute MR in an effort to achieve complete relief of the stenotic element. The anatomy of congenital mitral stenosis is quite variable and is generally less favourable for balloon dilation, although the procedure has occasionally been effective for this lesion. The procedure can be performed by using standard valvuloplasty balloon catheters. In older children, the specially designed Inoue balloon is found to be safe, simple and effective.
The initial success of transcatheter balloon dilation of congenital mitral valve stenosis appears equal to that of surgical commissurotomy; however, the total experience is limited. The duration of the relief from the obstruction is unknown. The morbidity and mortality of the catheter technique may be less than that of the surgical techniques. The decision to proceed with balloon valvuloplasty for congenital mitral stenosis should be based on a complete echocardiographic assessment of mitral valve anatomy. The procedure is less likely to be effective when there is a single papillary muscle or severe shortening or virtual absence of the chordal apparatus (the arcade-type mitral valve). In view of suboptimum results either with surgery or with balloon dilatation for congenital MS, our threshold for any form of intervention in congenital MS is quite high unless the patient is symptomatic despite medical treatment or has progressive worsening of PHT.
Dilation of Branch Pulmonary Artery Stenosis
The dilation of all varieties of branch pulmonary artery stenosis is a widely accepted standard procedure, in large part because most of these lesions (especially those beyond the hilum) are not amenable to surgical repair. The success is usually partial i.e. some percentage reduction of the gradient or percentage improvement in the measured stenosis rather than actually abolishing the gradient or producing a vessel of normal diameter. The technique for dilation of these stenosis is similar to that for pulmonary valve dilation. The balloon size must be at least 1.5 times the diameter of the normal vessel on each side of the stenosis or three to four times the diameter of the actual narrowing. There is a suggestion that the use of high pressure balloon in these lesions will improve the results: however the data from VACA registry for dilation of branch pulmonary arteries does not show significant difference with high pressure balloons.
Short term results are quite gratifying but there is a high incidence of restenosis either immediately or a short time later mainly due to recoil. Less than 20% of these dilated vessels are maintained at near normal diameter with insignificant gradient during the follow up. Moreover, there is a definite morbidity and even mortality related to the procedure. Since there are no predictors of success, balloon dilation is performed as a therapeutic trial. More recently, cutting balloons have been used with more encouraging results.
Due to suboptimum results with balloon dilatation, stents are being increasingly used to dilate these obstructions. The experience with stents in these lesions has significantly changed the approach to branch pulmonary stenosis. The results are excellent and they virtually eliminate any gradient and open the vessel to achieve a normal end diameter. The initial results have been sustained over years. In addition, it has been demonstrated that if the appropriate stents are implanted initially, these stents can be dilated further up to the adult diameter of the vessel. Since their introduction, intravascular stents have become the primary mode of therapy for branch pulmonary artery stenosis in children beyond 5 years of age. Balloon dilation alone of branch pulmonary stenosis presently is recommended only for patients who urgently require some therapy for their lesion but who are too small for the implant of intravascular stents that can be dilated to adult size at a later date. Recently, there have been isolated reports of biodegradable stents being successfully used in neonates with significant branch PA stenosis.
Dilation of Systemic Vein Stenosis
Dilation of stenosed systemic veins, particularly post surgical, often is acutely successful and carries little risk. The surgical alternative for these lesions is poor. These are usually seen in the venous baffles following Senning's or Mustard's operation. The other common post operative venous stenosis is seen in the SVC following repair of sinus venosus ASD or at the site of SVC cannulation for various open heart procedures. Like pulmonary branch stenosis, the results are not uniform or predictable. As with balloon dilation of other vessels, there is immediate haemodynamic, anatomic, and symptomatic improvement, however, recurrence of the stenosis is almost a rule. The balloon diameter chosen is about 6-8 times the narrowest portion. High pressure dilatation is rarely required within the veins.
Due to high rates of restenosis, primary therapy for these venous lesions has become the implantation of intravascular stents. The large iliac stents are appropriate for the large central veins, even in adult sized patients. The venous stent delivery procedure is similar to any other intravascular stents. For stent delivery, a single balloon of a diameter not less than that of the adjacent nearest normal vein is used. The results of implantation of stents within systemic veins have been excellent. No adverse reactions or long-term complications of the stents have been reported. Some instent restenosis in the venous location has occurred when the stents were dilated to a diameter significantly larger than the adjacent vessel at the time of implant. In these instances the lumen within the stent remodels with neointima to the size of the normal adjacent vessel.
Pulmonary Vein Dilation
Pulmonary vein dilation has been performed in humans but now is considered only as a last resort, providing transient relief. The procedure is acutely successful in most cases; however, restenosis has been observed in all attempted cases. Attempted dilation of these lesions may be recommended in an infant or child who is severely symptomatic. High pressure balloons and cutting balloons too have been used in an attempt to improve immediate and long-term results. The experience with intravascular stents in pulmonary vein stenosis to date has had no better results than dilation alone and has been associated with a high percentage of complications, including systemic embolization of the stents. Stents have been placed in pulmonary veins surgically under direct vision with limited short-term success.
Transcatheter Closure of Intracardiac Shunts
Atrial septal defects
Atrial septal defects (ASD) are among the more common defects and account for about 10% of all CHD. Most of the children are asymptomatic and are usually diagnosed after referral to a cardiologist for the evaluation of an ejection murmur. Some may present with repeated respiratory tract infections and failure to thrive usually beyond infancy. A very small minority (< 5%) will present with cardiac failure during infancy. All ASDs of consequence (either symptomatic or producing RVVO on echo) need to be closed. Since the impact of ASD is evident only after first few decades of life, the timing of closure is elective unless the child is significantly symptomatic. In our practice, most children are advised to undergo closure between 2 and 3 years of age (pre-school going) or at the time of diagnosis if this occurs later. The first device for ASD closure was used almost 30 years ago. Device technology matured in the 1980s and 1990s. Now most secundum ASDs are closed by placement of a transcatheter device. Patients with ASD are screened by echocardiography to determine whether they are candidates for the catheter approach. Closure using a device is possible only for secundum defects, not sinus venosus or atrioventricular canal-type (so-called primum) ASDs. The defect must have adequate rims (mitral rim of > 7mm, other rims > 5 mm) and be of a size that permits placement of the device. Although devices to close very large defects (up to 40 mm in diameter) are available, the larger devices fit only in the heart of an adult. There are three devices currently in use for closure of ASD: the Amplatzer Septal Occluder (AGA Medical Corporation, Golden Valley, California), which is used in the vast majority of implants, the Cardioseal Occluder (NMT Medical, Boston, Massachusetts) and the Helex Occluder (W.L.Gore and Associates, Inc. Flagstaff, Arizona). Only the Amplatzer device is approved for this use. The Cardioseal device is approved for other purposes and the Helex device is still considered investigational. The Amplatzer ASD device is a double mushroom of fine Nitinol wire mesh filled with polyester fibres. The two mushrooms are fixed on the opposite side of the ASD by a central hub of the same material C the diameter of the hub corresponding to the size of the ASD. The device is delivered through a 7 to 12 French sheath and is removable without damaging the device or the patient even after full deployment of both sides until it is released
Patients usually undergo ASD closures as in-patients requiring hospitalization for a single day only. Device placement is performed under a combination of fluoroscopic and transoesophageal or intracardiac echocardiographic guidance. In children of school age and younger, a general anaesthetic is administered to permit transoesophageal echocardiography. In older patients intracardiac echo can be performed using a specialized catheter and the procedure may then be performed with sedation and local anaesthesia. Patients typically remain supine for several hours after the procedure but may ambulate normally by the time they leave hospital. Subsequently care is straightforward, with abstention from contact sports for about 3 months. Thereafter they are allowed resumption of all normal activities without restriction. Patients receive low-dose aspirin and adhere to bacterial endocarditis prophylaxis precautions for 6 months. At that time a follow-up echocardiography examination is performed to document effective and complete ASD occlusion, after which prophylaxis is no longer needed. The follow up echo also includes evaluation of surrounding structures such as the systemic and pulmonary veins, the ventricular inflows, the AV valves, right ventricular size and shape, biventricular function, presence of a thrombus on the device and any evidence of pericardial effusion.
Several studies have documented the efficacy and safety of ASD closure using a device in comparison to surgery. In general these studies show no or little difference in efficacy rates between the two strategies (95%-98%), with longer hospital stay and
higher rate of complications after surgical closure. The number of complications and the length of stay vary substantially, the former as a result of variability in ascertainment and the latter as a result of regional differences in practice. Several other issues are important in evaluating published results. The first is patient selection whereas all ASDs are closeable by surgery, the same is not true for device closure procedures: thus with better patient selection, the efficacy of device closure improves. Also newer techniques such as the balloon assisted technique described by Dalvi et al, markedly improve success rates of closing large ASDs and size of defect is rarely a contraindication to ASD closure. The risk of major complications is low after both surgical or device closure therefore statistical comparisons of major complications are not very meaningful. The main difference in complication rate is attributable to the morbidity of surgery such as bleeding, infection, pain and pericardial effusion (post pericardiotomy syndrome), which are rare after closure using a device. Device integrity has not been an issue with the newer generations of devices, and other problems, such as formation of subacute thrombus on the device, have been rare.
Ventricular Septal defect
Ventricular septal defect (VSD) is the single most common heart defect, accounting for almost 40% of all defects. Patients with large VSDs present with overt congestive heart failure in infancy. Moderate defects may have more subtle manifestations of heart failure, such as failure to thrive, and patients with smaller defects are typically asymptomatic. VSD closure is indicated in infants with heart failure, pulmonary hypertension, or failure to thrive. In the absence of these manifestations, indications for closure are less clear, but most concur that closure is appropriate when the shunt through the defect exceeds 2:1 that is when the pulmonary blood flow is at least twice as much as the systemic cardiac output.
In contrast to ASDs, surgical closure remains the mainstay of treatment for VSD. However, device closure is being performed with increasing frequency with improvement in technique and technology and. Like ASD, device closure of VSD is performed under both fluoroscopic and ultrasound guidance. The procedure is much more complex than that for ASD. The need to manipulate relatively large and stiff catheters through the heart increases the risk of this procedure, especially in very small infants. Another option for small infants with muscular VSDs is a combined surgical-catheter (hybrid) approach. In this method, a midline sternotomy is performed, the heart is exposed and (without the need for cardiopulmonary bypass) the device-delivery catheter is advanced under echocardiographic guidance. The major advantage of this technique is the ability to close VSDs that are in portions of the heart that are difficult to reach by standard open surgical technique (e.g. apical VSDs). Also, in the absence of use of CPB, the pulmonary, cerebral and renal complications are much less commonly seen thereby reducing the hospital stay significantly
The main selection criterion for device closure of VSD is the type and location of the VSD and the size of the patient. Muscular defects especially those situated in the mid portion of the septum are ideally suited for this procedure and the first-generation devices for VSD closure were developed to close these defects. Patients who are of sufficient size (> 8 kg) to permit placement of the delivery catheter and in whom location of the VSD allows device placement without valve impingement are candidates for the procedure. Currently one device is approved for VSD closure (Cardioseal, NMT Medical), and one is invesigational (Amplatzer, AGA medical Corporation). Although the devices are originally designed for muscular VSDs, the most common, haemodynamically significant VSDs are perimembranous VSDs. Until recently, the proximity of these VSDs to the aortic valve precluded device closure. The Amplatzer Membranous VSD Occluder (AGA Medical Corporation), however, has recently been designed specifically for these defects. Early studies with this device have been encouraging although post deployment conduction disturbances including complete heart block, remain a concern and longer-term follow-up is necessary.
Published data are much more limited for VSD closure than for ASD closure. Several reports have demonstrated that the procedure is efficacious, reporting success rate form 86% to 100%. These reports include patients with VSDs in whom surgical closure was unsuccessful or who were considered poor surgical candidates. Follow-up care of children after device occlusion of VSD is essentially the same as after ASD closure. In summary, VSD closure by device is currently performed for muscular defects and for membranous defects. It is likely that the procedure will become more widespread as experience with these devices grow, and they are approved for general use.
Patent Ductus Arteriosus
Patent ductus arteriosus (PDA) accounts of 10% of CHD. Larger PDAs may lead to congestive heart failure or pulmonary vascular disease; however, this condition is uncommon other than in the premature neonate. Those with moderate sized shunts may present with failure to thrive. Most often children with a PDA have a small left-to-right shunt, are asymptomatic, and present with a continuous murmur. Thus, the most common indications for closure of the PDA is the prevention of bacterial endocarditis.
Transcatheter closure of PDA has been extensively studied. Smaller PDAs can be safely and completely closed with coils. A European registry series reported an overall efficacy of 95% in more than 1200 procedures performed between 1994 and 2001. In this series, successful occlusion was less likely in larger PDAs. Since that large European report, the Amplatzer PDA device has proven efficacious, with a closure rate of nearly 100% and is particularly useful in the closure of larger PDAs. Some investigators in an attempt to decrease cost (especially in developing countries) have used ingenious techniques to deliver multiple coils in an attempt to close large PDAs. These coils are either delivered using a bioptome or a balloon occlusion technique. However, residual shunting, intravascular haemolysis and coil embolisation remain real concerns and device closure remains a safe, effective, faster, easier and more complete way to close large PDAs. In current practice the procedure should have an efficacy of greater than 97% (defined by successful device placement with complete occlusion of flow on follow-up Echo study) with a low complication rate.
Cardiac Interventions in Complex Congenital Heart Disease
Pulmonary Atresia with Intact IVS
Newborns with pulmonary valve atresia present in a fashion identical to those with critical pulmonary stenosis, and the initial medical management is identical. The subsequent management of these patients varies enormously because the disorder is very heterogeneous. Some patients are born with an otherwise normal right heart with the exception of the atretic pulmonic valve, whereas others are born with severe right heart hypoplasia but patent tricuspid valve and may also have communications between the cavity of the right ventricle and the coronary arteries (coronary cameral fistulae). These fistulae are often associated with coronary artery stenosis so the coronary artery flow depends on maintaining a high pressure in the right ventricle. A variety of treatment approaches are used to deal with the heterogeneity of this disorder. When the right heart is well developed, the treatment may be much like the treatment for pulmonary stenosis, but surgical management is required when there is significant underdevelopment of any of the right heart structures. Surgery may be directed at achieving a biventricular repair or toward single ventricle palliation, depending on the severity of anatomic abnormalities.
Cardiac catheterization is performed in almost all patients with pulmonary atresia. The first goal of the procedure is to complete the diagnostic assessment: angiography is the only way to determine the extent of coronary artery involvement. Patients with a well-developed right heart are candidates for transcatheter treatment. Innovative strategies have been developed that allow the interventionologist to perforate the atretic valve plate safely using radiofrequency energy. Thereafter sequential balloon dilation of the valve can be performed. In developing countries where cost considerations play a major role in decision making, perforation of the pulmonary valve with the widely available hard end of the coronary guide wire is an effective and cheaper alternative. Patient selection is the most important factor determining success for both the techniques. Pericardial tamponade arising from inadvertent perforation of the right ventricular outflow tract remains a major concern with both techniques. Despite adequate relief of outflow obstruction it is not uncommon for patients to require surgical shunt / PDA stent for having a predictable and augmented pulmonary blood flow.
Follow up concerns in infants with pulmonary atresia vary depending on initial anatomy and the type of intervention performed. After transcatheter perforation and dilation, oxygen saturation is assessed for evidence of atrial right-to left shunting and degree of pulmonary blood flow. Echocardiography is performed to quantify residual obstruction, direction of the atrial shunt , as well as the residual RV hypertrophy and involution following relief of obstruction. In patients without significant residual hypoxaemia SaO2 > 90 % on room air), the prognosis through childhood tends to be quite good, although some will require repeat intervention for restenosis. As is true for almost all therapies for CHD, the truly long-term (decades) outcomes require on-going study.
Intravascular Stents in Congenital Heart Disease
As discussed under the individual lesions, the major problems with vascular dilation procedures relate to the need for overdilation of the vessel and to restenosis of the lesions, either acutely with vessel recoil or over the long-term. The use of intravascular stents has provided a definitive solution to this problem. There has been extensive favourable experience and more than 10 years follow-up in patients with pulmonary artery branch stenosis and systemic vein stenosis. In the single-centre series of Mullins et al at Texas Children's Hospital, more than 655 stents were implanted in 340 patients with pulmonary artery and systemic veins stenosis. Further dilation of these stents has been successful for as long as 4 years after implant. To be used in the growing patients, the stent that is used initially must be capable ultimately of dilation to a full adult-vessel diameter.
The largest group of patients in this series had lesion involving the central pulmonary arteries in postoperative patients and postoperative central systemic vein or systemic venous baffle stenosis. Many of these stenotic veins had a totally occluded initial lumen; some of the venous channels were purposely perforated with a wire or long needle. The mean vessel diameter increased from 5 to 12 mm. The success was lasting, with fewer than 0.5% showing restenosis during the period of follow-up. The number of complications from the procedure or the stents themselves was minimal. Intravascular stents in the branch pulmonary arteries and systemic veins have been demonstrated to provide definitive therapy for these lesions and offer an entirely new outlook for these previously inoperable patients.
The intravascular stents are now used in many other areas such as the aorta and other intravascular stenosis. Larger stents are already available in Europe for the large adult patient. There are new developments in the area of split, open ring stents and biodegradable stents that would make these forms of therapy available for the infants and small children. Covered stents have been used in the adult catheterization laboratories for the treatment of ruptured vessels, including aortic aneurysms and coarctation of the aorta. In addition, this type of covered stent may be able to be used for catheterization completion of a lateral tunnel Fontan procedure.
Closure of Abnormal Vascular Communications : Embolization Therapy
Embolization of abnormal or persistent arterial or AV structures has been available for more than 30 years. The embolization techniques were developed and perfected primarily by the vascular radiologists working in the abdominal viscera, gastrointestinal areas, and central nervous system, particularly in end artery vessels. Many materials and devices, including the patients' own clotted blood, Gelfoam, colloidal plugs, glues, detached balloons, and coil occlusion devices, have been used for these peripheral occlusion.
The Gianturco (Cook, Inc.) coils are the most commonly used of all these occlusion devices for patients with congenital cardiac defects. These coils are made of spring wire with polyester fibres enmeshed in the coils, which are available in several sizes and multiple diameters and lengths. The coil is introduced into the delivery catheter through a straight metal loader as a straight wire. When it is delivered by extrusion out of the distal end of the catheter, it coils like a small pigtail. Once delivery with this particular coil has been started, there is no way of withdrawing the coil back into the wire. The Gianturco coil occludes the vessel by the creation of a mass of fabric and wire in which a thrombus is formed. The coil occlusion device usually is delivered into a vessel with a discrete distal narrowing, where it will fix in place and not migrate further through the vessel. Often, several coils are placed in a single vessel to achieve complete occlusion. In the absence of a distal narrowing, some other type of device for fixation such as the Amplatzer vascular plug is used. The coils are only usable in tubular structures with a distended diameter up to 7 to 8 mm. For larger vessels or vessels without an area of discrete stenosis, coils can be used in conjunction with other intravascular occlusion devices to complete the occlusion of the vessel. Recently, Amplatzer vascular plug is being used to occlude these abnormal communications. It has a smaller and manoeuvreable delivery system. In addition, the control over the plug, like all other members of Amplatzer family of devices, is far superior than the coils.
Many abnormal collateral vessels or persistent surgically created systemic to pulmonary artery shunts are associated with the more complex lesions. These vessels need occlusion when systemic flow competes with normal pulmonary flow, particularly when the major defect is corrected e.g. TOF with pulmonary atresia. These communications traditionally required surgical division during the corrective procedure or as a separate procedure. Other lesions in which these devices may be useful are AV fistulae, including systemic, coronary-cameral, and peripheral as well as pulmonary AV fistulae. In these lesions, it is critical to identify the stenotic or end vessel into which the device can be fixed in order to reduce the dangers of migration to vital structure.
Stenting of the PDA in duct dependent circulations
Recently, ductal stenting is emerging as an alternative to systemico-pulmonary shunt for palliating duct dependent circulations. Pulmonary atresia with intact ventricular septum, TOF with pulmonary atresia, tricuspid atresia with pulmonary atresia and HLHS are some of the indications for duct stenting. The procedure is usually performed under general anaesthesia with IPPR. Intravenous prostaglandin is stopped half to one hour prior to the stent delivery so as to let the duct constrict a little. This prevents migration of the stent during and immediately after the delivery. Most of the children remain on small dose aspirin till such time the patience of the ductus is required. The stenting can be performed from the arterial or the venous side; each having its merits and demerits. Local vascular injury, pulmonary artery obstruction, ductal spasm, stent migration, acute or subacute stent thrombosis and in-stent restenosis are some of the complications reported with this procedure.
Transcatheter replacement of pulmonary valve
Over last 5 years, a great deal of experience has been gathered in percutaneous transcatheter replacement of pulmonary valves. Currently, two valves (Medtronic and Edward) are being used for this purpose. Both are stent mounted valves delivered through the femoral vein using long sheaths. Currently, the procedure is being performed primarily for those patients with RV-PA conduits who have a free PR or PS with PR due to valve degeneration. In those with a significant PS, the narrowing is relieved by balloon dilation prior to implantation of the valve. This procedure is usually performed in adolescents and adults who have almost completed their growth. Recently, Bonhoeffer et al published their data of the first 100 implants with no mortality and a very low morbidity such as migration of the stent and vascular injury. There are efforts being made to modify the design so as to suit those with surgically corrected TOF with free PR in whom RV-PA conduit was not used. If this becomes possible, the number of patients benefiting from this procedure will increase exponentially.