Interventional Cardiology

Atrial Septostomy

Atrial septostomy involves passing a balloon-tipped catheter across the atrial septum, typically through the membranous foramen ovale. The balloon is inflated and pulled back through the septum creating a larger intraatrial communication that improves mixing of oxygenated and deoxygenated blood at the atrial level. The procedure is most commonly performed in neonates with d -transposition of the great vessels ( d -TGA) as an emergency procedure. Children with d -TGA have systemic and pulmonary circulations in parallel rather than in series; the right ventricle pumps deoxygenated blood to the aorta, and the left ventricle pumps oxygenated blood to the main pulmonary artery. Atrial septostomy allows critical mixing of oxygenated and deoxygenated blood, thereby increasing systemic oxygen saturation. The procedure can be performed in the catheterization laboratory under fluoroscopic guidance or undertaken at the bedside in the intensive care unit using echocardiographic guidance. Other indications for atrial septostomy include tricuspid atresia, mitral atresia, and pulmonary atresia with intact ventricular septum. The major risks associated with the procedure are vessel injury, paradoxical embolism, arrhythmia, and cardiac perforation. More recent concerns of an association with increased brain injury do not seem to have been evidence-founded.

Atrial Septal Defect Closure

With the development of specifically designed closure devices, atrial septal defect (ASD) closure has become one of the most commonly performed endovascular procedures. The technique is intended for closing secundum ASDs, which are defects located in the region of the fossa ovalis. Defects falling outside this area, such as sinus venosus and primum ASDs, are generally not suitable for percutaneous closure.

To warrant closure, children need to demonstrate clear evidence of volume loading of the right heart structures and a defect that is unlikely to close spontaneously in the short to medium term. Devices have evolved from the early bulky meshes and a wide variety of sizes and designs are now available. The choice of closure device depends on the size and margins of the defect, but brand selection depends more on the clinician's preference than objective performance ( Fig. 22.1 ). Daily aspirin in a dose of 3 to 5 mg/kg is recommended for a minimum of 6 months after the procedure. The main perioperative complications associated with ASD device closure include vessel injury, cardiac arrhythmia, cardiac perforation, and device embolization. In the long term, devices are well tolerated with atrial arrhythmias the most common problem, although life-threatening complications such as cardiac erosion have been reported. ASD closure devices can also be used to close surgically created fenestrations when they are no longer required, such as between the atrium and venous conduits after a Fontan operation.

Ventricular Septal Defect Closure

Ventricular septal defect (VSD) closure presents a technically greater challenge than ASD closure and is associated with a greater incidence of complications. Defects of the midmuscular septum or apex are most suitable for device closure, although perimembranous VSDs may also be closed percutaneously. A combined surgical and interventional approach may be appropriate for certain cases, such as the small infant with an anterior apical VSD that is difficult to reach surgically.

When using a device to close a VSD, a snare is placed in the right side of the heart to capture a guidewire that has been passed across the VSD from the left ventricle. The guidewire is brought outside the body via the venous access to form an arteriovenous rail. The delivery sheath for the VSD device is then advanced over the wire to approach the VSD from the right side of the heart. For anterior and high muscular defects, the wire is best snared and exteriorized through a femoral vein approach, whereas for defects in the middle to low muscular septum, the wire is best snared and exteriorized through a jugular venous approach ( Fig. 22.2 ). Complications include dysrhythmias, blood loss, valve dysfunction, low cardiac output state, and device embolization. Device closure of perimembranous VSDs in particular has been associated with an increased incidence of complete heart block and aortic valve disruption owing to the close proximity of conduction pathways and the aortic valve apparatus. This has led to some controversy in their use, with many centers considering the risk unacceptable, given the good outcomes following surgical VSD closure.

Patent Ductus Arteriosus Closure

Transcatheter closure of patent ductus arteriosus (PDA) was the second specific intervention developed for children with CHD, and the procedure continues to be performed using techniques similar to the original methods pioneered by Rashkind and associates. The procedure has a high occlusion rate with the smallest incidence of adverse events of all interventional procedures and is indicated in any child with evidence of left ventricular overload. PDA morphology varies from short and broad to narrow and tortuous, so the customary approach is to perform an aortogram to define the size and geometry. For closure of small and moderate PDAs, stainless steel coils (e.g., Gianturco, Cook Medical, Bloomington, IN) are most commonly used, whereas for larger PDAs, occluder devices (e.g., Amplatzer, St. Jude Medical, St. Paul, MN) are more appropriate. Devices can be deployed with a retrograde or anterograde approach. Embolization of the device at the point of deployment is a risk but there are several techniques that can help control device release. Embolization may also be delayed, so proper follow-up is required; the other major risk associated with this procedure is vessel injury. Despite impressive technical evolution over the years, PDA device closure in premature or low body weight infants remains prohibitively challenging and further catheter design is required in this area. These techniques can also be used to close other unwarranted vascular connections such as major aortopulmonary collateral arteries (MAPCAs) and Blalock-Taussig (BT) shunts that are no longer required ( Figs. 22.3 and 22.4 ).

Balloon Dilation and Stent Implantation

Balloon angioplasty techniques are used to dilate stenotic valves, most commonly pulmonary and aortic, as well as stenotic segments of the aorta or pulmonary arteries and surgically placed shunts or pulmonary artery bands. Neonatal membranous pulmonary atresia can be treated using this technique, crossing the pulmonary valve membrane with the stiff end of a guidewire or with radiofrequency catheters before subsequent dilatation of the valve annulus. Balloon valvuloplasty of isolated pulmonary stenosis in older infants and children is often a curative procedure, whereas neonates with critical pulmonary stenosis or atresia often require further interventions to supplement pulmonary blood flow such as ductal stenting or a BT shunt. Inflation of the balloon temporarily arrests right ventricular output and is often accompanied by transient hypotension but is generally well tolerated. Paradoxically, those with tighter stenosis and little antegrade flow may maintain hemodynamic stability better, particularly if the duct is still open, as cardiac output is less disrupted.

The role of balloon valvuloplasty for critical aortic stenosis remains controversial; in some centers, it remains the treatment of choice, whereas others prefer a primary surgical approach. Concerns relate to longer-term outcomes and the rate of surgical intervention required in those treated initially with valvuloplasty. When performed, balloon dilation of aortic stenosis in the neonate is a particularly high-risk procedure. These infants often present in a low–cardiac output state requiring ventilation, inotropic support, and prostaglandin E ₁ (PGE ₁ ) infusion to maintain ductal patency. Catheterization can be complicated by arrhythmias (including asystole), the development of significant aortic regurgitation (which may require surgical intervention), and sudden death resulting from acute coronary ischemia. The complication rate in older children is less than in younger children, yet transient hypotension, bradycardia, and left bundle branch block are commonly reported.

Stents are sometimes implanted across focal areas of persistent stenosis in the systemic and pulmonary circulations or within surgically placed shunts. The technique of implantation requires great precision for correct positioning of the stent, and the cardiac interventionalist needs to take into account the inevitable shortening that occurs with stent implantation when selecting a device for a particular lesion. There is also a risk of stent malposition with the potential for dislodgment. Although rare, late aneurysm formation has been reported after stenting the aorta for coarctation.

Nonsurgical Pulmonary Valve Replacement

Bonhoeffer and colleagues first described the technique of replacing a dysfunctional valve in a right ventricle to pulmonary artery (RV-PA) conduit with a catheter-implanted valve in 2000. The Melody valve (Medtronic Inc., Minneapolis, MN) is one such device that has been approved for use in surgically placed RV-PA conduits meeting specific requirements. Studies have confirmed a high procedural success rate and satisfactory short-term and medium-term valve function after implantation of the Melody valve. The need for careful patient selection and for adequate relief of right ventricular outflow tract (RVOT) obstruction at the time of valve implantation are paramount in achieving results comparable to those of surgical replacement of dysfunctional conduits. Off-label use has additionally demonstrated promising results with implantation of Melody valves in children with native RVOTs. Unfortunately, most children who are managed with transannular patch repair of tetralogy of Fallot are currently unsuitable for transcatheter valve replacement because of an aneurysmal RVOT. New hybrid procedures are, however, emerging to circumvent this, allowing more options for patients with tetralogy of Fallot, many of whom are likely to require recurrent interventions over their lifetime. Alternative devices are also being developed to reduce the size of the delivery systems to enable use of these technologies in younger and smaller children. As with surgical valve replacements, thrombus formation and infective endocarditis are concerns after transcatheter valve implantation.

Choice of Vessel Access

The most common approach for cardiac catheterization is the femoral route. Femoral venous catheterization avoids the risk of pneumothorax and the vessel is often easier to access than the internal jugular vein in the unanesthetized child. In children who are likely to have a cavopulmonary shunt placed surgically for palliation, avoiding routine cannulation of the internal jugular vein may decrease the risk of compromising the superior vena cava. Internal jugular vein access, however, is sometimes required, such as during some VSD closures, investigation of cavopulmonary connections in children, and when the cardiac interventionalist is unable to obtain femoral access. In neonates, the umbilical vein may be used, although difficulty can be encountered attempting to cross the ductus venosus to access the inferior vena cava. Patency of the ductus venosus can be assessed by ultrasound before the procedure to avoid unnecessary manipulation of the umbilical vein. An alternative route is transhepatic puncture. This route has been used for temporary access during catheterization and for long-term vascular access.

Arterial Thrombosis and Occlusion

Arterial thrombosis is common after pediatric cardiac catheterization, with a reported incidence in two large studies of 4.3% and 11.4%. However, diagnosis based on clinical assessment of pulses is likely to lead to underestimation; when measured by Doppler ultrasound, 32% of infants had compromised arterial blood flow to the leg. Young age, small size, larger sheath size, and repeated arterial catheter exchanges are independent risk factors for thrombosis; polycythemia and dehydration may increase risk further.

Prophylactic heparin reduces but does not remove the risk of arterial thrombosis ; and despite widespread use, there is no consensus on the appropriate dose. Common schedules prescribe 50 to 100 IU/kg; larger doses do not appear to add additional benefit. Most cases of reduced or absent pulse will resolve either spontaneously or with additional heparin anticoagulation. Thrombolysis is a viable next step, but surgical intervention will be needed for thrombosis resistant to medical therapy, arterial tears or avulsion, and pseudoaneurysms. Percutaneous thrombectomy may be suitable in older children. Occasionally, a pulse may be persistently reduced in a clinically well-perfused limb despite intervention. The long-term concern is delayed limb growth; cases have been reported but one small study failed to demonstrate limb-length discrepancy after median follow up of 3½ years. Currently there is no means to identify those at risk.

Venous Thrombosis and Occlusion

Isolated cases of femoral or iliofemoral venous occlusions with limb edema have been published as part of large series, but two small prospective observational studies found an incidence of 0% and 1.6%, respectively. All affected children responded to heparin therapy without the need for further intervention. Using the smallest catheter necessary and heparin prophylaxis should assist in limiting the incidence.

Vessel Rupture, Perforation, and Dissection

Vessel rupture can occur at the site of vessel entry or at the site of intervention. It is a rare but potentially catastrophic event. One death caused by intraabdominal hemorrhage after rupture of a femoral vein in a neonate was reported in a series of 4454 catheterizations. Arterial or venous perforations were responsible for four major complications and six minor complications in a series of 4952 procedures, and significant groin hematoma occurred in 25 cases.

Vessel rupture appears most common during balloon dilation of branch pulmonary arteries and during RVOT valve implantation procedures, but it has also been reported along the ascending aorta and arch after dilation on the aortic valve. Occasionally, arterial dissection, aneurysm, and pseudoaneurysm formation may occur. Rupture may cause hemopericardium or hemothorax, or both; pulmonary artery disruption after balloon dilation may manifest as hemoptysis. If rupture and hemorrhage occur, hypertension should be avoided, the trachea should be intubated (if the airway is not already secured), and any circulating heparin should be reversed. In extremis, blood from pericardial or pleural drains may be returned directly to the patient via femoral cannulae until surgical intervention can be achieved.