20 Interventional Cardiology
THE USE OF CATHETERIZATION in the care of children with congenital heart disease (CHD) was first described by Dexter and colleagues in 1947.1 It has evolved from a physiologic assessment tool to a technique to define anatomic relationships and has become a therapeutic modality. The first interventional procedure, balloon atrial septostomy, was described by Rashkind and Miller in 1966,2 and since then, the discipline of interventional cardiology has continued to evolve.
As echocardiography and magnetic resonance imaging (MRI) diagnostic capabilities have increased, the need for purely diagnostic cardiac catheterization has declined.3,4 However, technologic advances and more sophisticated equipment have increased the scope for interventional procedures, and the patient population has changed as more children with CHD are surviving longer. As the surgical management of CHD has evolved, it has introduced a new spectrum of surgical complications. Some surgical operations have been replaced altogether by interventional procedures, and some interventional procedures have facilitated more complex heart surgery.5 The shifts in practice and population have affected the anesthetic management of these children.6 Procedures are more diverse, and patients can vary from moribund neonates to healthy adolescents. There are no simple anesthesia recipes for all children and all heart conditions; the type of anesthesia must fit each child and each procedure.
Types of Procedures Performed
Diagnostic Catheterization
Diagnostic catheterization allows accurate documentation of pressure and oxygen content from all regions of the circulation. Interpretation of these hemodynamic data allows quantification of the degree of intracardiac shunting and calculation of the vascular bed resistances. This information is necessary to assess the suitability of a child to undergo palliative or reparative surgery for congenital heart lesions. Expected values for hemodynamic variables are listed in Table 20-1. There are no absolute values for these variables, and they vary according to the age of the child. The use of angiocardiography to define anatomy is waning because of the widespread use of noninvasive imaging modalities such as echocardiography, computed tomography, and MRI.
TABLE 20-1 Normal Values in Diagnostic Cardiac Catheterization
| Structure | Value (mm Hg) |
|---|---|
| Right atrium | 3-5 (mean) |
| Right ventricle | 20-25/3-5 (systolic/end-diastolic) |
| Pulmonary artery | 12-15 (mean) |
| Left atrium | 7-10 (mean) |
| Left ventricle | 65-110/3-5 (systolic/end-diastolic) |
| Aorta | 65-110/35-65 (systolic/diastolic) |
Interventional Catheterization
Atrial Septostomy
Atrial septostomy improves mixing of oxygenated and deoxygenated blood at the atrial level in neonates with d-transposition of the great vessels. Children with this disorder are born with ventriculoarterial discordance. The right ventricle pumps deoxygenated blood to the aorta, and the left ventricle pumps oxygenated blood to the main pulmonary artery. Enlargement of the foramen ovale by atrial septostomy improves mixing of oxygenated and deoxygenated blood, resulting in increased systemic oxygen saturation. This procedure can be performed in the catheterization laboratory with fluoroscopic guidance, or it can be easily and safely undertaken at the bedside in the intensive care unit using echocardiographic guidance.7 A femoral venous or umbilical venous approach can be used. The drawback with the umbilical venous route is the often-encountered difficulty in traversing the ductus venosus to secure access to the inferior vena cava. The major risks with this procedure are vessel injury, paradoxical embolism, arrhythmia, and cardiac perforation.
Atrial Septal Defect 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. The choice of closure device depends on the size and the margins of the defect. The two types of closure devices have either a centering or a noncentering design (Fig. 20-1). The choice of one design over another is based more on the clinician’s preference than scientific performance, although the Amplatzer Septal Occluder (AGA Medical Corporation, Golden Valley, Minn.) can close a wider range of defect sizes.8–10 Daily aspirin in a dose of 3 to 5 mg/kg is recommended for a minimum 6 months after implantation of either type of device. The main complications associated with ASD closure include vessel injury, cardiac arrhythmia, cardiac perforation, and device embolization.11 Atrial septal closure devices have also been used to close surgically created fenestrations between the atrium and venous conduits after a Fontan operation. This is undertaken only when the fenestration is no longer required.
Ventricular Septal Defect Closure
Ventricular septal defect (VSD) closure presents a technically greater challenge than ASD closure and is associated with a greater risk. The VSDs most suitable for device closure are those in the midmuscular septum or those closer to the apex.12 With further refinement of the implantation technique and equipment, this approach has been undertaken with perimembranous defects.13,14
During device closure of VSDs, 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 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. 20-2). Complications include dysrhythmias, blood loss, valve dysfunction, and device embolization.15,16 At our institution,17 device closure of perimembranous VSDs with the Amplatzer Membranous VSD Occluder had an unacceptable incidence of complete heart block and is therefore not currently performed. However, other medical units have continued to undertake this intervention, and alternative devices are being developed with the goal of implantation that does not cause complete heart block.
Patent Ductus Arteriosus Closure
Closure of patent ductus arteriosus (PDA) was the second specific intervention developed for children with CHD, and it continues to be a common procedure performed using techniques that are similar to the original methods pioneered by Rashkind and associates.18 The customary approach is to perform an aortogram to define the size and geometry of the PDA. Based on this information, a choice is made between using a stainless steel coil or an occluder device.19 Most interventional cardiologists implant a stainless steel coil to close a small PDA (no greater than 3 mm) using a retrograde or antegrade approach.20 To lessen the chance of coil embolization during implantation, several techniques can control release of the coils.21–23 For the larger PDA, most interventional cardiologists implant an occluder device because it lessens the risk of a significant residual shunt. The major risks associated with this procedure are vessel injury and device or coil embolization. Coils are also used to close major aortopulmonary collateral vessels (Figs. 20-3 and 20-4).
Balloon Dilation and Stent Implantation
Balloon angioplasty techniques are used to dilate stenotic aortic, mitral, tricuspid, and pulmonary valves and stenotic segments of the aorta or of the pulmonary arteries. In neonates, membranous atresia of the pulmonary valve may be crossed with the stiff end of a guidewire24 or with radiofrequency catheters.25 After both techniques, the valve is dilated with a balloon that is approximately 120% the size of the annulus. Balloon angioplasty of stenotic pulmonary valves in children beyond infancy is often a curative procedure, whereas balloon valvuloplasty of critical pulmonary stenosis in the neonate often requires intervention again in later infancy. The potential hemodynamic behavior of the child depends on the nature of the lesion. A neonate with duct-dependent critical stenosis and little antegrade flow can tolerate balloon dilation well because there is little disruption of the cardiac output, whereas neonates and infants with less critical stenosis can suffer significant reductions in cardiac output when the balloon is inflated, especially if the ductus arteriosus is not patent. Older children tend to tolerate balloon valvuloplasty surprisingly well,26 and life-threatening hypotension is uncommon.27
In contrast to pulmonary balloon valvuloplasty, aortic balloon valvuloplasty is usually only a palliative procedure, with most children eventually requiring surgery. Balloon dilation of aortic stenosis in the neonate is a high-risk procedure. These infants often present in a low cardiac output state requiring ventilation, inotropic support, and prostaglandin E1 (PGE1) 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 due to acute coronary ischemia.26 The complication rate in older children is less than in younger children, and transient hypotension, bradycardia, and left bundle branch block are commonly reported.
Nonsurgical Pulmonary Valve Replacement
It is more than a decade since Bonhoeffer and colleagues28 first described the technique of replacing a dysfunctional valve in a right ventricle to pulmonary artery conduit with a catheter-implanted valve. The technology used has matured, and the Melody Valve (Medtronic Inc, Minneapolis, Minn.) is available for use in Europe and is undergoing clinical trials in the United States. The Edwards Sapien Transcatheter Heart Valve (Edwards Lifesciences LLC, Irvine, Calif.) has also been used but is currently not licensed for this indication. Other results29 have confirmed a high procedural success rate and satisfactory short-term valve function with implantation of the Melody Valve. The need for careful patient selection and for adequate relief of right ventricular outflow tract obstruction at the time of valve implantation are paramount in achieving results comparable to those of surgical replacement of dysfunctional conduits. Unfortunately, most children after tetralogy of Fallot repair with a transannular patch are currently unsuitable for implantation of a stented valve because of an aneurysmal right ventricular outflow tract.
Alternative devices are being sought to overcome these problems and to reduce the size of the delivery systems to enable use of these technologies in younger and smaller children. A novel use of Melody devices in an animal model that replicates the clinical situation of an aneurysmal right ventricular outflow tract has been reported.30 Implantation of Melody Valves in branch pulmonary arteries appears to favorably reduce the regurgitant fraction in this animal model.
Electrophysiologic Catheterization
Endocardial catheters that record an electrocardiogram first became available in the early 1960s. Endovascular techniques were developed as an alternative to surgery for certain forms of tachycardia. These therapies initially used direct current energy and subsequently have made use of radiofrequency energy and localized freezing techniques. Tachycardia may be treated by this technique in children with structurally normal hearts and those who have dysrhythmias after surgery for CHD.26 Ablative procedures account for about 20% of all cardiac catheterization procedures.
The technique requires specialized equipment, specially trained staff, and use of multiple catheters to measure the electrical signals within the heart at any given time. These procedures are often more time consuming than other catheterization procedures. The success of the therapy depends on the mechanism of the tachycardia, the location of the aberrant pathway, and the technique for interrupting the aberrant pathway. Ablation of ectopic foci has a good success rate and small complication rate.31,32 The main risks with this procedure are heart block, cardiac perforation, vessel injury, and stroke.
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 vein is 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 can decrease the risk of compromising the superior vena cava. However, internal jugular vein access sometimes is required, such as during VSD closures, investigation of cavopulmonary connections in children, and when the cardiac interventionalist is unable to obtain access through the femoral veins. In neonates, the umbilical vein may be used, although it can sometimes be difficult to cross the ductus venosus. Patency of the ductus venosus can be assessed by ultrasound before the procedure to avoid unnecessary manipulation of the umbilical vein. An alternative is transhepatic puncture. This route has been used for temporary access during catheterization and for long-term vascular access.33
Complications and Limitations of Procedures
Interventional cardiology can be associated with significant morbidity and mortality. Complications attributable to the procedure or the physiology of the child occur far more frequently than purely anesthesia-related problems. An important prerequisite for providing quality anesthesia care is understanding the diagnosis and management of anticipated complications. Complications such as tamponade, dysrhythmia, embolism, and rupture may occur suddenly and without warning. The anesthesiologist must be vigilant and maintain communication and rapport with the cardiologist throughout the procedure. The availability of backup from surgeons, cardiologists, and anesthesiologists is preferable, and standard procedures for emergencies should be in place. Some clinicians advocate the availability of cardiopulmonary bypass or extracorporeal membrane oxygenation (ECMO) for children with unanticipated difficulties.16 Although this type of therapy is available in major referral hospitals, it may not be an option in some centers. Institutions must develop policies regarding the procedures that can be undertaken locally (based on experience and infrastructure) and those that require referral of children to centers that are better equipped to address more complex procedures.
Overall Mortality
Despite the increased complexity of interventional procedures, the mortality rate is steadily decreasing. A report from the early 1960s found an overall mortality rate (neonates through to adulthood) of 0.44%,34 but more recent data show overall mortality rates of 0.08%,35 0.14%,36,35 and 0.39%.27 All reviews describe a relatively high mortality rate among infants and neonates in particular.27,36,37 Explanations include a reduced physiologic reserve, presence of uncorrected or partially palliated congenital heart defects, increased risk of obstruction to great vessels and cardiac chambers, and greater susceptibility to catheter-induced damage in infancy.27 However, neonatal mortality rates are diminishing; one institution reported a decrease from 6.7% to 0.9% during a span of 20 years.36 The explanations cited for this decrease were noninvasive imaging that reduced the number of neonates who required cardiac catheterization, improved management of the critically ill child, correction of metabolic abnormalities, use of PGE1, and use of improved catheters and better support equipment such as temperature control.36
Overall Morbidity
Complications are frequently categorized as major, minor, and incidental.27,37 Major complications are potentially life-threatening events that require surgical intervention or are significant permanent lesions resulting from the procedure (e.g., cerebral infarct). Minor complications are transient and resolve with specific treatment (e.g., transient arterial thrombosis, temporary loss of a pulse or decreased perfusion after arterial puncture). An incidental complication has no effect on the patient’s condition and requires minimal or no treatment (e.g., transient hypotension responding to volume infusion, catheter-induced arrhythmia). The incidence of major complications is between 1.4%37 and 2.6%,38 and the incidence of minor complications is between 6.8%37 and 7.5%.38 The overall complication rate has remained stable for the past 20 years.38
Three groups of children are at substantial risk for complications: those who are young, those with low weight, and those undergoing interventional rather than diagnostic procedures; balloon interventions are associated with the greatest risk.36–38 The incidence of vascular access complications after interventional procedures is three times greater than the rate for diagnostic procedures36; this may reflect the use of larger-diameter catheters during interventional procedures than during purely diagnostic procedures. Closure of a PDA and balloon atrial septostomy carries a small overall risk.27,36
Vascular Complications
Vascular complications are the most common and broadest category of complications.36 They may be acute, leading to unexpected hemodynamic instability, or delayed, leading to longer-term morbidity. Many factors contribute to unexpected hemodynamic instability, including the child’s condition, blood loss, dysfunction of a valve, arrhythmias, tamponade, vessel rupture, balloon dilation, catheter-induced interruptions in blood flow or coronary perfusion, and device malposition.
Arterial Thrombosis and Occlusion
Femoral artery occlusion due to thrombosis is a common complication after femoral cannulation.36 The true incidence of arterial compromise is unknown,39 although 32% of infants had compromised blood flow to the leg as measured by Doppler after femoral arterial cannulation in one study.40 The clinical incidence of arterial compromise is 2.4% to 3.7%.36,37 Infants undergoing dilational interventional procedures are at a greater risk.41 The incidence of these complications can be reduced by minimizing the size of the sheath, use of systemic heparinization, and avoidance of arterial entry by using alternative techniques to enter the left side of the heart.36 Despite the widespread use of intravenous heparin for prophylaxis against arterial occlusion, there is no agreement on the appropriate dosage. Commonly, 50 to 100 IU/kg heparin is used, but schedules vary.26 Larger doses than these do not reduce the incidence of arterial compromise.39
In most cases where the pulse is reduced or absent after catheterization, the occlusion either spontaneously resolves or is managed with anticoagulation or thrombolytic therapy.36,37,41 Guidelines are available for the management and prevention of femoral artery thrombosis, but advice should be sought from a pediatric hematologist.42 Although surgical intervention is rarely required, it is most commonly indicated for an arterial tear or avulsion, arterial thrombosis (including iliac arteries), and arterial pseudoaneurysm.41 Occasionally, despite medical therapy and a well-perfused lower limb, a pulse may be persistently reduced. There is little evidence to predict how and when a reduced pulse may cause delay in limb growth,36 although cases have been reported.41 Although femoral cannulation for balloon intervention is associated with vascular compromise of the superficial femoral artery, one small study (43 children between 1 day and 15 years of age) failed to demonstrate significant limb growth discrepancy after a median follow-up of 3.5 years.43
Venous Thrombosis and Occlusion
Although venous thrombosis is a well-known complication of central venous access, the incidence after cardiac catheterization is unclear. Isolated cases of femoral or iliofemoral venous occlusions with limb edema have been published as part of large series,36,37 in which the incidence of symptomatic venous occlusion was less than 0.3%. All of these children responded to heparin therapy without the need for further intervention.37 As in arterial thrombosis, the use of smaller catheters and heparin prophylaxis during catheterization procedures may reduce the incidence of venous thrombosis.
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 due to intraabdominal hemorrhage after rupture of a femoral vein in a neonate was reported in a series of 4454 catheterizations.27 Arterial or venous perforation was responsible for four major complications and six minor complications in a series of 4952 procedures, and significant groin hematoma occurred in 25 cases.36 Femoral artery injuries may require surgical consultation and exploration.
Vessel perforation has occurred at the site of intervention, particularly during balloon interventions. Ruptures have been reported most often after balloon dilation of branch pulmonary arteries,4,26 but they also have occurred along the ascending aorta and arch after balloon dilation of the aortic valve. Depending on the site of the tear, rupture may cause hemopericardium or hemothorax, or both.41 Intrapulmonary hemorrhage is usually self-limited. If rupture or hemorrhage occurs, hypertension should be avoided, the trachea should be intubated (if the airway is not already secured), and any circulating heparin should be reversed. Pulmonary artery disruption after balloon dilation may manifest as hemoptysis. Increased blood flow after balloon dilation of pulmonary vessels may lead to unilateral pulmonary edema, which may also present as hemoptysis. Occasionally, arterial dissection,41 aneurysm, and pseudoaneurysm formation may occur.
Cardiac Tamponade and Perforation
Cardiac tamponade is an uncommon complication of cardiac catheterization, but when it occurs, it can be responsible for significant morbidity and mortality. The incidence of cardiac tamponade in three large series was 0.1%,36 0.04%,27 and 0%.37 In one series of 4952 patients, tamponade was responsible for two deaths: one neonate after a balloon atrial septostomy and one 4-year-old child after a recent Fontan procedure for stent insertion in a branch pulmonary artery.
Although tamponade is uncommon, perforation is not. The atrial appendage and right ventricular outflow tract are the sites most commonly perforated,41 whereas the left ventricle has been punctured less commonly.42 Perforation of the heart is described during many procedures, including balloon and blade atrial septostomy, balloon dilation of the mitral valve,4 and attempted radiofrequency perforation of membranous pulmonary atresia.5
