Chapter 499. Interventional Cardiology

As the diagnostic role of cardiac catheterization has diminished over the years, its role as a mode of primary therapy has exponentially increased. In most large congenital cardiac centers today more than 70% of all children undergoing cardiac catheterization have an interventional therapy as part of the procedure. Interventional cardiac catheterization has become the standard of care for treating an increasing number of congenital heart lesions, while in others it remains investigational (Table 499-1). Common interventional procedures include balloon septostomy in neonates with d-transposition of the great arteries, balloon valvoplasty in valvar pulmonic or aortic stenosis, balloon angioplasty with or without stent repair of branch pulmonary artery stenosis or coarctation of the aorta, device closure of a patent ductus arteriosus, atrial septal defect, muscular ventricular septal defect, and embolization of abnormal venous or arterial vessels. Investigational interventional catheter based treatments include stented valve implant for pulmonary insufficiency, ductal stenting for first stage treatment of infants with hypoplastic left heart syndrome or pulmonary atresia, and fetal intervention for critical aortic or pulmonic stenosis to promote ventricular growth in utero.

Interventional procedures are directed at avoiding, postponing, or complementing surgery with its attendant risks, scars, and lengthy hospitalization and recovery times. Occasionally there is no suitable surgical procedure. Most patients treated with interventional catheterization go home the same day as the procedure and can return to full activity within 5 days. The therapeutic procedures performed in pediatric populations are dilatations, valve implants, or closures. Dilatations are performed using balloons alone or in combination with stents, valve implants use specially designed valved stents, whereas closures are done with embolization coils or specially designed devices or plugs.

An unrestrictive atrial septal defect may be necessary for patients with certain cardiac abnormalities. Adequate mixing through an atrial septal defect is essential for survival in neonates with d-transposition of the great arteries (dTGA) as well as in patients with a functional single ventricle who have a severe mitral stenosis or atresia, tricuspid atresia, or total anomalous pulmonary venous connection. Balloon atrial septostomy (Rashkind procedure) involves passing a balloon-tipped catheter through the foramen ovale into the left atrium (LA), inflating the balloon, and then pulling it back rapidly across the atrial septum. The resulting tear in the atrial septum usually improves mixing. In most centers, this procedure is performed under echocardiographic guidance and moderate sedation at the bedside (Fig. 499-1). Although balloon catheters successfully tear the thin valve of the foramen ovale of neonates with dTGA, the thicker septum in neonates with left-heart obstruction, or in older infants is not usually amenable to balloon septostomy. Techniques used to open the septum in these patients include static balloon dilatation with high pressure or cutting balloons, and atrial septal stenting (Fig. 499-2).

Balloon pulmonary valvoplasty is safe and highly successful in reducing the transvalvar gradient while producing little pulmonary insufficiency. With large balloons that exceed the size of the pulmonary valve annulus by 20% to 40%, pulmonary valve gradients are typically reduced to less than 15 mmHg. The residual obstruction and insufficiency are similar to that seen after surgery. It has become the standard procedure for valvar pulmonic stenosis because the mortality and morbidity are extremely low, it is an outpatient procedure, and there is no sternotomy, cardiopulmonary bypass, blood transfusions, general anesthetic, or scar (Fig. 499-3). Only very thick dysplastic valves, as occur in Noonan syndrome, and supravalvar stenosis may respond poorly to balloon dilatation and require surgery. Even neonates with pulmonary atresia and intact ventricular septum can undergo successful balloon valvoplasty after the atretic valve is perforated by a radio frequency or laser-tipped wire.

For similar reasons balloon aortic valvoplasty is the treatment of choice in patients with valvar aortic stenosis and can be performed with low mortality, good relief of aortic obstruction, and variable but usually mild aortic insufficiency. Patients with calcific aortic stenosis, moderate to severe aortic insufficiency, or annular hypoplasia are not good candidates for valvoplasty. Early and medium-length follow-up studies show results comparable to primary surgery; usually there is less aortic regurgitation but occasionally severe aortic regurgitation necessitates valve replacement. Longer-term studies suggest the durability or repair with balloon dilatation may be less than that with surgery. The risks of valvoplasty include arrhythmias, emboli, neurologic events, and injury to access vessels. In contrast, surgical risks include mortality, risks of anesthesia, cardiopulmonary bypass, blood products, the disadvantages of a long hospitalization, an undesirable scar, and greater cost. Both balloon aortic valvoplasty and surgical valvotomy are palliative. Longer-term follow-up suggests that repeat treatment for either recurrent stenosis or worsening insufficiency occurs in 50% of patients within 8 years of valvoplasty. In some patients who develop restenosis after surgical or balloon procedures, balloon valvoplasty has been used as a means of deferring valve replacement; such delays are particularly important in small children who would otherwise require multiple valve replacements.

Balloon mitral valvoplasty has been performed via a transseptal approach in a few children in the United States, and a larger number in Asia and the Middle East. Preliminary results indicate very good relief of obstruction with minimal resulting mitral insufficiency in children with rheumatic mitral stenosis. Results for congenital mitral stenosis are variable, with a greater propensity for developing mitral insufficiency. Balloon dilatation in this situation is used sparingly, usually reserved for children in whom surgical repair carries an unusually high risk.

Angioplasty of obstructed vessels in children has been performed since 1982. Relief of obstruction is achieved by tearing the intimal and medial layers. The most commonly involved vessels are arteries, specifically the pulmonary arteries and aorta, though some postoperative venous obstructions are amenable to dilatation as well. Recent advances in balloon catheter technology, allowing for smaller balloon catheters that can be inflated to extremely high pressures (25 atm), have made these procedures safe and more effective. Balloons with tiny surgical blades attached, called cutting balloons, are now available. They allow dilatation of even the most resistant vessel stenosis. For some lesions, such as distal pulmonary artery stenosis, direct surgical relief is extremely difficult, making angioplasty clearly the treatment of choice.

Stenosis of the branch pulmonary arteries may be congenital, acquired, or postsurgical (ie, at shunt insertion sites, bands, or conduits). Examples of congenital pulmonary artery branch stenosis (PABS) include tetralogy of Fallot with pulmonary atresia, Williams syndrome, Alagille syndrome, and congenital rubella. Stenosis caused by scarring from previous Blalock-Taussig or other aortopulmonary shunts is usually amenable to balloon palliation. Native stenoses or hypoplastic pulmonary arteries can be less responsive, although with the current improved balloon technology success rates are greater than 90% (Fig. 499-4). In some patients there may be modest initial improvement in the size of the pulmonary arteries, which then show significant growth thereafter. A combined surgical-transcatheter approach to patients with complex pulmonary artery stenosis has now become commonplace. Surgery to proximal stenoses and any intracardiac defects is used in conjunction with transcatheter therapy of distal pulmonary stenosis and recurrent obstruction improves short- and long-term outcomes.

Balloon dilatation of native aortic coarctation in neonates and children is successful in 80% of patients but has been associated with significant complications, including aortic rupture and death (< 1%) as well as late aneurysm formation at the site of the previously torn vessel (7%). Recurrence of coarctation following dilatation in neonates occurs in up to 75% of patients, and for this reason most cardiac centers recommend surgical treatment of neonatal coarctation. The role of this procedure for native coarctation in older children is unsettled, with equivalent immediate efficacy and complications, shorter hospitalization, but what appears to be a higher late recoarctation rate. Most centers offer dilatation as an alternative treatment to surgery in toddlers and preteens. For teenagers endovascular stent repair has become the treatment of choice (see below). On the other hand, recoarctation angioplasty has achieved wide acceptance because the surrounding scar from the previous surgery makes repeat surgical repair more difficult. The late results of recoarctation balloon angioplasty appear to be at least as good as reoperation.

Balloon-expandable stents (metallic mesh tubes) are now used to treat many lesions that are not amenable to balloon dilatation alone. Lesions with significant elastic recoil that resist tearing can often be treated with endovascular stents.

The largest experience in pediatrics is with stenting for branch pulmonary artery stenosis. Results have shown an increase in vessel diameter, a fall in peak systolic gradient across the obstruction, an increase in flow to the stented lung, and a decrease in right ventricular pressure. Restenosis is rare, occurring in only 3% of patients, and redilatation has been effective. Similar success has been reported with stents in postoperative right ventricular to pulmonary artery conduit stenosis, and stent placement has become the treatment of choice for systemic venous obstruction. Stent placement as primary treatment of coarctation of the aorta, both native and recurrent, has become a preferred therapy for adolescent patients in most centers (Fig. 499-5). Procedural success is excellent in over 95% of patients with no significant restenosis at mid-term follow-up. Serious complications are seen in 1% of patients including death, stroke, and aneurysm formation requiring surgical repair.

Aortopulmonary collaterals, arteriovenous malformations, Blalock-Taussig shunts, venous collaterals, coronary artery fistulas, and small patent ductus arteriosus (PDA) have all been successfully occluded by coil or vascular plug embolization (Fig. 499-6). The embolization coils consist of a straight metal wire, either stainless steel, platinum, or Inconel (nickel–chromium alloy) with or without Dacron strands, available in multiple sizes, lengths, and shapes, that coil into a helix when extruded from the catheter. Vascular plugs are Nitinol (nickel–titanium alloy) wire mesh that when extruded from the catheter expand into the shape of a plug. Although PDA or coronary artery fistula embolization may obviate the need for surgery, most embolizations serve either to reduce the cardiac workload by decreasing the amount of shunting or to simplify a planned surgical procedure.

The technique for coil or vascular plug closure of collaterals or other communications is straightforward. A catheter is placed in the vessel to be occluded, and a selective angiogram is done to delineate the anatomy and diameter of the vessel to be closed. Coils or plugs are chosen that are slightly larger than the diameter of the vessel, as the vessel will distend when the coil or plug is deployed. With a long wire the coil or plug is pushed through the catheter and deployed in the vessel (Fig. 499-7). Repeat angiography is performed to confirm complete closure. If residual flow remains, additional coils or plugs are placed. Coils can be placed through smaller catheters so they are particularly good if the lesion is difficult to get to with a tortuous catheter course. Larger vessels or lesions are best closed with plugs.

Patent ductus arteriosus (PDA) coil, vascular plug, or device occlusion have become standard therapy for closure of PDA in infants, children, and adults. Equipment is still too large for use in premature infants although technical development is underway to meet this challenge. Recent reports have demonstrated closure rates of nearly 100% with PDAs measuring up to 6 mm diameter. The coil is deployed with one loop of coil in the pulmonary artery and the rest in the ductal ampulla. Because the ductus is often funnel shaped, this arrangement anchors the coil in the ductus and prevents embolization to the pulmonary bed or lower body. If a single coil does not completely close the PDA, multiple coils can be placed until no residual shunting exists. The coils can be placed either anterograde from the femoral vein or retrograde from the femoral artery (Fig. 499-8). The latter is technically less challenging and therefore more common. Larger PDAs are typically closed with vascular plugs especially designed for the PDA. These are delivered anterograde from the femoral vein and close PDAs up to 14 mm in diameter (Fig. 499-9). Complications are exceedingly rare and most often consist of coil embolization to the pulmonary artery; the coil can be retrieved and removed from the patient in the catheterization laboratory with minimal effort and risk. Larger plugs or devices pose the risk of left pulmonary artery stenosis or coarctation of the aorta due to extension into these areas. This is quite rare, and seen only with closure of a very large ductus in a very small child. Pulse loss is a risk for small infants but can be minimized by a venous approach. Rarely recanalization of the PDA after coil closure, documented by color flow Doppler, has been reported.

Surgical closure of atrial and ventricular septal defects requires cardiopulmonary bypass with its attendant risks. Transcatheter closure of secundum atrial septal defects is safe and effective in greater than 96% of patients, with no mortality and complications in less than 3% of patients, and has become the treatment of choice at most centers worldwide. Patients with associated anomalies requiring surgical treatment, such as partial anomalous pulmonary venous return, or patients with extremely large or asymmetric defects, those extending too close to the atrioventricular (AV) valves or pulmonary veins, still undergo surgical closure. Over the past 5 years at the University of California, San Fransisco, over 97% of children with isolated secundum atrial septal defects have been successfully closed nonsurgically with device placement.

The procedure is performed under moderate sedation and takes approximately 3 hours. Placement of the device is guided by both fluoroscopy and echocardiography.(eFig. 499-1A,B). In smaller children surface echocardiography is used, in school-age children most centers use intravascular ultrasound, a catheter is placed from the femoral vein to the right atrium with a small echo transducer on the tip (eFig. 499.2). Patients usually go home the same day or morning after and resume full activities within 5 days. Complications are extremely rare with no reports of death, stroke, need for blood transfusion, thrombus, or significant arrhythmia in children.

There are currently two devices in common use in the United States and several others in development around the world (eFig. 499.3). All are similar in that they have two patches consisting of a flexible metal frame with a fabric or mucosal covering connected centrally. The device is compressed into a catheter or sheath and advanced to the left atrium where the distal patch is pushed out of the catheter and expanded. The system is brought back to the atrial septum and held in place. The sheath is then withdrawn over the proximal patch allowing it to expand in the right atrium. The two patches hold themselves in place by clamping onto the atrial septal tissue surrounding the hole. The device is then released and over the next 4 to 6 months the endocardium of the atrium grows over the device (several cells thick) to finalize closure (eFig. 499.4).

Ventricular septal defects (VSDs) can also be closed with device placement but the procedure is much more complex and at present limited primarily to muscular defects (Fig. 499-10). This procedure usually requires general anesthesia and transesophageal guidance of the device placement. The children stay a single night in the hospital and can resume full activity within 5 days. Success rates are high, greater than 97% with low complication rates, although higher than with ASD closure. Late complications are rare. Perimembranous ventricular septal defects, the most common type of VSD, are very close to the aortic valve and the conducting system, the AV node, posing additional challenges for device closure. Specially designed devices have been used successfully but with a significant incidence of complete heart block that presents unpredictably late requiring at times urgent pacemaker placement. Because of these issues, new devices are in development for closure of perimembranous VSD. Currently only patients with either extremely high surgical risk or an associated ventricular septal aneurysm that eliminates the risk for either aortic valve injury or atrioventricular (AV) nodal injury are closed by device (Fig. 499-11).

Pulmonary insufficiency with right ventricular dilatation is common in adolescents after repair of tetralogy of Fallot or truncus arteriosus. Although initially thought to be well tolerated, it has become clear that severe chronic pulmonary insufficiency in children leads to right ventriclar failure, exercise intolerance, and shortened life span in adults. In an attempt to minimize the need for repeat surgeries, and their inherent complications, a catheter deliverable stented valve has been developed. It is currently available for general use in Europe and is in phase 2 clinical trials in the United States. Due to the large size of the introducing system (22 Fr) it is limited to use in adolescent and adult patients.The procedure can be performed under moderate sedation taking only 3 hours with both fluoroscopic and intravascular ultrasound guidance for placement. A Bovine jugular venous valve is sewn inside a platinum metal balloon expandable stent. The stent valve is then compressed onto a dilatation balloon and the system threaded anterograde from the femoral vein to the pulmonary valve area. The stented valve is expanded and the delivery system removed (Fig. 499-12).

The procedure is successful in 95% of implants with significant reduction in RV systolic pressures and of the pressure gradient across the right ventricular outflow tract (RVOT). Pulmonary insufficiency, severe in all before implant, is absent in over 60% and trivial or mild in 38% of patients in 18-month follow-up. Procedural complications included acute surgery for RVOT or existing homograft dissection in 5% with no associated mortality. Late complications included endocarditis, and reobstruction due to sternal compression or stent fracture. Repeat stent dilatation or stent implantation inside the existing stent is needed in up to 12% of patients due to late stenosis or fracture. Freedom from reoperation is 84% at 5 years. Percutaneous valve implant results in resolution of RV dilatation and improved exercise tolerance at 1 year. The hope is that this procedure may be extended to younger children with improvements in stent valve technology.

Investigational Procedures

Fetal Intervention

There is currently much interest and activity in fetal cardiac intervention in fetuses developing left heart or right heart hypoplasia. These babies are born with only a single ventricle and have significant morbidity and mortality. Because cardiac structures develop along lines of flow in utero it is thought that severe aortic or pulmonic stenosis/atresia in early gestation may be a major factor in the development of hypoplastic left or right heart syndromes. The hypothesis is that early interventional opening of the stenotic or atretic aortic or pulmonic valve will allow improved flow into the ventricles, preventing hypoplasia and allowing a normal two-ventricle circulation postpartum. This is an area of intense controversy but successful fetal cardiac aortic balloon valvuloplasty has been performed with resultant improvement in left ventricular development.

Single Ventricle Palliation

Currently patients with aortic atresia and hypoplastic left heart syndrome (HLHS) or pulmonary atresia with right ventricular hypoplasia are palliated with neonatal surgery to establish a stable source of systemic (for HLHS) or pulmonic (for pulmonary atresia) blood flow. Due to the associated morbidity, mortality, and prolonged hospitalization associated with neonatal cardiac surgery an interest in catheter palliation has developed. Stent placement in the ductus arteriosus to maintain patency allows for a stable source of systemic flow in HLHS and of pulmonary flow in pulmonary atresia with RV hypoplasia. Advances in coronary and peripheral stent technology have led to effective tools for stenting the ductus arteriosus even in neonates (eFig. 499.5A,B). The acute complications and long-term results are yet to be determined; however, this catheter-based palliative approach may play an increasing role in the management of infants with ductal dependent blood flow in the future.

Single Ventricle Total Cavopulmonary Connection

The final surgical stage in the treatment of patients with single ventricle physiology is connection of the inferior vena cava (IVC) to the pulmonary arteries, most commonly done with an extra-cardiac Gore-Tex tube, to assure that all desaturated venous blood flows passively to the lungs. In an attempt to eliminate the need for this final surgery investigators have been attempting interventional creation of this connection by implanting a covered stent from the IVC to the pulmonary arteries. This requires some surgical preparation at the time of the second-stage Glenn surgery to prepare the area to exclude the covered stent. Although still in its infancy this technique may allow nonsurgical completion of the total cavopulmonary connection in the future.

Hybrid Procedures

The term hybrid refers to procedures in which the surgeon and interventional cardiologist work together, combining techniques from both arenas to optimize results. These procedures are performed in a modified operating room or catheterization laboratory with angiographic equipment, operating lighting and equipment, and cardiopulmonary bypass. This is a rapidly evolving field. Current examples include (1) stage 1 palliation of hypoplastic left heart syndrome with simultaneous ductal stenting (interventional) and bilateral pulmonary artery banding (surgical); (2) valved stent implant (direct surgical access of the catheter through the right ventricle) in small high risk children with obstructed insufficient RV-to-pulmonary artery conduits (eFig. 499.6); (3) transventricular muscular VSD device closure in infants with direct surgical exposure of the RV; (4) intraoperative stent placement for treatment of branch pulmonary artery stenosis with surgical central pulmonary artery reconstruction; and (5) carotid surgical cutdown exposure for critical aortic stenosis dilatation or ductal stent placement in premature infants. It is unclear at this time which of these hybrid procedures will have significant advantage and truly evolve into new therapeutic strategies for these children with complex congenital heart disease.1-14