There are two kinds of invasive procedures that are used in the practice of pediatric cardiology. The first is cardiac catheterization and angiocardiography, which together are used for diagnosis (diagnostic catheterization). The second is to treat certain structural heart defects nonsurgically using specially designed catheters and implantable devices that are delivered through cardiac catheters (therapeutic cardiac catheterization).
Cardiac Catheterization and Angiocardiography
Cardiac catheterization and angiocardiography usually constitute the final definitive diagnostic tests for most cardiac patients. They are carried out under general sedation using various sedatives (discussed later). For newborns, cyanotic infants, and hemodynamically unstable children, general anesthesia with intubation may be used.
Under local anesthesia and with strict aseptic preparation of the skin, catheters are placed in peripheral (most commonly the femoral) vessels and advanced to the heart and central vessels under fluoroscopy with image intensification to reduce radiation exposure. At each position in the heart and blood vessels, values of pressure and oxygen saturation of blood are obtained. The oxygen saturation data provide information on the site and magnitude of the left-to-right or right-to-left shunt, if any. The pressure data provide information on the site and severity of obstruction. Cardiac output may be obtained from oxygen saturation data (e.g., the Fick principle) or by indicator dilution (e.g., indocyanine green dye) or thermodilution (e.g., cold saline injection) technique. Selective angiocardiography is usually performed as part of the catheterization procedure (described later).
Normal Hemodynamic Values
Normal oxygen saturation on the right side of the heart is usually 70% but it may vary between 65% and 80%, depending on cardiac output. Left-sided saturations are usually 95% to 98% in room air. In newborns and heavily sedated children, the oxygen saturation may be lower. Pressures are lower in the right side than in the left side of the heart, with systolic pressures in the right ventricle (RV) and pulmonary artery (PA) about 20% to 30% of those in the left side of the heart (Fig. 7-1).
Routine Hemodynamic Calculations
The following calculations are routinely obtained: flow and resistance for systemic and pulmonary circuits and left-to-right or right-to-left shunt.
Flows (Cardiac Output) and Shunts. Flow is calculated by use of the Fick formula:
where flows are in L/min, Vo2 is oxygen consumption (mL/min), C is oxygen content (mL/L) at various positions, PV is pulmonary vein, PA is pulmonary artery, AO is aorta, and MV is mixed systemic venous blood (superior vena cava or right atrium). Normal systemic flow or pulmonary flow in the absence of a shunt is 3.1 ± 0.4 L/min/m2 (i.e., cardiac index).
FIGURE 7-1 Average values of pressure and oxygen saturation in normal children. AO, aorta; LA, left atrium; LV, left ventricle; M, mean pressure; PA, pulmonary artery; PV, pulmonary vein; RA, right atrium; RV, right ventricle; VC, vena cava.
Oxygen consumption is either directly measured during the procedure or estimated from a table for children 3 years and older (see Appendix A, Table A-6). Assumed oxygen consumption of 150 to 160 mL/min/m2 is used in older infants and children. In infants under 2 to 3 weeks of age, 120-130 mL/min/m2 may be used. Oxygen capacity is the maximum quantity of oxygen that can be bound to each gram of hemoglobin (i.e., 1.36 mL × Hb level; each gram of hemoglobin [Hb] combines maximally with 1.36 mL of oxygen). Oxygen saturation is the amount of oxygen bound to hemoglobin compared with the oxygen capacity, and it is expressed as a percentage.
When there is a pure left-to-right or right-to-left shunt, the magnitude of the shunt is calculated as follows:
The flow data are subject to much error because of difficulties in measuring accurate oxygen consumption or because of the frequent use of assumed oxygen consumption in pediatric patients. Therefore, the ratio of pulmonary-to-systemic flow 
is frequently used because it does not require an oxygen consumption value. The ratio provides information on the magnitude of the shunt. A 
ratio of 1:1 would indicate no shunting in either direction or bidirectional shunting of equal magnitude. A ratio of 2:1 implies that there is a left-to-right shunt equal to systemic blood flow. A ratio of 0.8:1 signifies that the pulmonary blood flow is 20% less than the systemic blood flow (e.g., the flow ratio seen in a cyanotic patient). Patients with a flow ratio greater than 2:1 are usually surgical candidates.
Resistance. Hydraulic resistance (R) is defined by analogy to Ohm’s law as the ratio of the mean pressure drop (ΔP) to flow (Q) between two points in a liquid flowing in a tube (R = ΔP/Q). Therefore, pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR) are calculated using the following formulas:
The normal SVR is about 20 units/m2 in children, but it varies markedly between 15 and 30 units/m2. In newborn infants, the SVR is lower (10–15 units/m2) and rises gradually to about 20 units/m2 by 12 to 18 months of age. The normal PVR is high at birth but approaches adult values by about 6 to 8 weeks after birth. Normal values in children and adults are 1 to 3 units/m2. Accordingly, the ratios of PVR to SVR range from 1:10 to 1:20. High PVR values increase the risk associated with corrective surgery for many congenital cardiac defects.
Selective Angiocardiography
Information derived from echocardiography and oxygen saturation and pressure data from catheterization help determine the number and sites of selective angiocardiograms required to delineate cardiovascular structures. A radiopaque dye is rapidly injected into a certain site, and angiograms are recorded, often on biplane views. Depending on the cardiovascular anomaly under study, special views are obtained by moving the fluoroscopic camera (or by positioning the patient at desired angles). Multiple injection sites are often necessary to obtain a complete anatomic diagnosis (Fig. 7-2, A).
Contrast agents used in angiocardiography are water-soluble, complex organic compounds, with three iodine atoms bound to a benzene ring. Old contrast agents (e.g., Renografin 76, Renovist, Hypaque M-75, Vascoray) are ionic agents with high osmolality (i.e., osmolality of 1690–2150 mOsm/kg; much [five to eight times] higher than serum osmolality of 275–300 mOsm). Nonionic contrast agents (e.g., Isovue, Omnipaque) are low-osmolality agents (i.e., osmolality of 200–300 mOsm/kg), and some are hypotonic to the serum. After the injection of a high-osmolality contrast medium, there is a rapid shift of fluid from the interstitial and intracellular spaces into the intravascular space. This causes volume expansion, a slight drop in hematocrit, and a change in electrolyte concentration. These changes adversely affect newborns and infants with congestive heart failure (CHF). Low-osmolality agents cause less volume shift and are safer. Other toxic effects of high-osmolality agents include decreased red cell pliability, increased viscosity, osmolar diuresis, proteinuria, hematuria, and renal failure (occasionally).
Risk
Cardiac catheterization and angiocardiography can lead to serious complications and occasionally death.
• Complications related to catheter insertion and manipulation include serious arrhythmias; heart block; cardiac perforation; cardiac valve injury; hypoxic spells; vascular injury, perforation, or tears; hemorrhage (that requires transfusion); and infection.
• Complications related to contrast injection include reactions to the contrast material, intramyocardial injection, and renal complications (e.g., hematuria, proteinuria, oliguria, anuria).
• Complications related to exposure, anesthesia, sedation, and medications include hypothermia, acidemia, hypoglycemia, convulsions, hypotension, respiratory depression, diffuse central nervous system injury, stroke, and even death. These complications are more likely to occur in newborns.
FIGURE 7-2 Angiocardiography and balloon valvuloplasty. A, Lateral view of a right ventriculogram showing a thick, dome-shaped pulmonary valve and a marked poststenotic dilatation of the pulmonary artery. B, A maximally inflated sausage-shaped valvuloplasty balloon is seen, which suggests that the stenotic pulmonary valve has been widened. The balloon catheter was introduced over a guidewire, which was positioned in the left pulmonary artery.
• Complications also include exposure to ionized radiation.
• The risk of cardiac catheterization and angiocardiography varies with the patient’s age and illness, the type of lesion, and the experience of the physician doing the procedure. The reported rate of fatal complications varies from lower than 1% to as high as 5% in the newborn period. In one study, the incidence of significant but nonfatal complications requiring treatment (e.g., arrhythmias and arterial complications) was 12% in infants younger than 4 months old. In comparison, the incidence of such complications was 1.5% in older infants. Major complications (e.g., ventricular arrhythmias, hypotension, arterial complications, perforation of the heart, breakage or knotting of catheters, allergic reactions, hypoxic spells) occurred 1.4% of the time, and minor complications occurred 6.8% of the time. With better preparation and monitoring, as well as the use of prostaglandin infusion in critically ill newborns, the mortality and morbidity rates can be minimized.
Indications
Details of anatomy, including situs, venous and arterial connections, septal integrity, severity of valvular stenosis or regurgitation, size of pulmonary arteries, coronary artery origins, and aortic arch anatomy, are easily established with echocardiography to the degree of certainty required for surgical intervention. When additional information is needed for intervention, it can be obtained by other noninvasive techniques, such as cardiac magnetic resonance imaging or cardiac computed tomography. In centers where these noninvasive imaging techniques are not available and when echocardiography does not provide sufficient detail, cardiac catheterization is indicated (Feltes et al, 2011). In most centers, two thirds of cardiac catheterizations are for interventional purposes, and only one third are for diagnostic purposes.
• Most congenital heart defects, such as ventricular septal defect (VSD), atrial septal defect (ASD), atrioventricular (AV) canal, tetralogy of Fallot (TOF), double outlet right ventricle (DORV), coarctation of the aorta (COA), HLHS, and other complex congenital heart disease (CHD) do not need diagnostic catheterization. Most of them can be adequately diagnosed by noninvasive methods. It is indicated when complete diagnosis cannot be made by noninvasive testing or when such testing yields incomplete information.
• The following lists some circumstances that suggest the need for diagnostic catheterization.
a. To determine accurate pressure gradients in combined aortic stenosis and aortic regurgitation (AR) or pulmonary stenosis (PS) and pulmonary regurgitation or multiple levels of obstruction. Doppler assessment of pressure gradient is different from true peak-to-peak gradient measurement
b. Assessment of pulmonary hypertension and its responsiveness to vasodilator therapy
c. To calculate PVR in the setting of low-flow lesions, such as seen in patients after cavopulmonary anastomosis or after complete Fontan operation
d. Patients with pulmonary atresia with intact ventricular septum or pulmonary atresia with complex ventricular anatomy (to determine details of pulmonary vascular supply, the aortopulmonary collateral supply, and the coronary artery anatomy)
e. To find answers to postoperative problems: Some of these situation may require interventional procedures at the time of catheterization.
1) Excessive desaturation after a systemic-to-pulmonary shunt (to rule out shunt stenosis or occlusion and branch PA stenosis)
2) Excessive desaturation after cavopulmonary anastomosis (to rule out venovenous, venoatrial, or pulmonary AV malformation)
3) When excessive aortopulmonary collateral is suspected
4) Suspected RV outlet tract (RVOT) obstruction after TOF surgery
f. Cardiac transplantation (for both CHD and cardiomyopathy), to assess preoperatively and for surveillance of vasculopathy, and to obtain endomyocardial biopsy for rejection identification
g. Assessment of cardiomyopathy or myocarditis
h. To assess coronary circulation in some cases of Kawasaki’s disease
Sedation
A number of sedatives have been used by different institutions with equal success rates. Smaller doses of sedatives are usually used in cyanotic infants. When an interventional procedure is planned, general anesthesia is usually employed.
1. No sedation is used in newborns.
2. For small infants weighing less than 10 kg, a combination of chloral hydrate (75 mg/kg; maximum of 2 g) and diphenhydramine (2 mg/kg; maximum of 100 mg) by mouth has been used with good results.
3. For older children, demerol compound (i.e., a solution containing 25 mg/mL of meperidine [Demerol], 12.5 mg/mL of promethazine [Phenergan], and 12.5 mg/ mL of chlorpromazine [Thorazine]) is a popular sedative mixture. The dosage of the demerol compound is 0.11 mL/kg intramuscularly (IM). Some centers exclude chlorpromazine from the sedative mixture. In cyanotic children, the dosage of the demerol compound is reduced by one third. For children in severe CHF, the dose is reduced by half.
4. Some cardiologists use a combination of meperidine (1 mg/kg) and hydroxyzine (Vistaril) (1 m/kg) intramuscularly. Others use a combination of fentanyl (1.25 µg/kg, maximum of 50 µg) and droperidol (62.5 µg/kg, maximum of 2500 µg) with equal success.
5. Ketamine (3 mg/kg IM or 1 to 2 mg/kg intravenously [IV]) may be used, but it can change the hemodynamic data because it increases the SVR and blood pressure.
6. Morphine (0.1–0.2 mg/kg) administered subcutaneously can be used to prevent or treat hypoxic spells.
7. If more sedation is required during the study, IV diazepam (Valium) (0.1 mg/kg) or morphine (0.1 mg/kg) is used.
Preparation and Monitoring
Adequate preparation of the patient before the procedure and careful monitoring during the procedure can minimize complications and fatality from the invasive studies.
Every child undergoing cardiac catheterization should have the following studies:
1. A 12-lead electrocardiogram, chest radiographs (both posteroanterior and lateral), two-dimensional echocardiography, urinalysis, and a complete blood count within days or weeks in advance of the study
2. Baseline coagulation studies and a platelet count for deeply cyanotic children
3. Blood type and cross-match for infants less than 5 kg of body weight
The following preparation and monitoring are particularly important for the safety of patients:
1. Increasing the temperature in the cardiac catheterization laboratory when an infant is being studied.
2. Using a warming blanket and a rectal thermistor to monitor rectal temperature to avoid hypothermia.
3. Checking arterial blood gases and pH and correcting acidemia and hypoxemia.
4. Correcting hypoglycemia or hypocalcemia before and during the procedure.
5. Monitoring oxygen saturation and administering oxygen (if indicated) during the procedure.
6. All patients undergoing catheterization should have a reliable IV line (for sedation, resuscitation, or volume replacement).
7. Children with high hemoglobin levels should be given overnight IV fluid to reduce the risk of dehydration, thrombosis, and hypotension.
8. Digitalis should be held beginning the night before catheterization to reduce the risks of catheterization-induced arrhythmias.
9. Having emergency medications (e.g., atropine, epinephrine, bicarbonate) drawn up and ready.
10. Initiating prostaglandin infusion in cyanotic infants who seem to be ductus dependent.
11. Intubating or readiness for intubating infants with respiratory difficulties.
12. Whenever possible, having another physician (preferably an anesthesiologist) available to monitor the noncardiac aspects of the patient so that the operator can concentrate on the procedure.
Catheter Intervention Procedures
Recent advances have allowed for the development of a variety of therapeutic procedures using specially modified catheters and catheter-delivered devices. The lives of critically ill neonates may be saved by these procedures. They may also eliminate or delay the need for elective surgical procedures in children with certain CHDs. These procedures can open things that are closed, widen things that are too small, or close things that are open. More specifically, blood vessels and heart valves that are too small can be enlarged using balloon catheters and /or implantable devices known as stents. Too small an opening in the atrial septum can be enlarged by using balloon or blade catheter. An opening can be created in an intact atrial septum for left-to-right or right-to-left shunt to occur. Abnormal connections within the heart (ASDs and VSDs) can be closed using innovative devices. Abnormal blood vessels (patent ductus arteriosus [PDA] or collaterals) can also be closed using coils or plugging devices. In recent years, percutaneous valve replacement in the aortic or pulmonary position is gaining more experience.
Balloon and Blade Atrial Septostomy
In balloon atrial septostomy (Rashkind’s procedure), a special balloon-tipped catheter is placed in the left atrium (LA) from the right atrium (RA) through a patent foramen ovale or an existing ASD. The balloon is inflated with diluted contrast material, and the catheter is rapidly pulled back to the RA through the interatrial communication, thereby creating a large opening in the atrial septum. This procedure is indicated in patients with an intact or nearly intact atrial septum in whom a better mixing of systemic and pulmonary venous blood would benefit their oxygenation, cardiac output, or both. Infants who have transposition of the great arteries (TGA), with or without associated ASD, are candidates for the procedure unless an arterial switch operation is to be performed immediately. It is also indicated in infants with total anomalous pulmonary venous return with restrictive ASD if surgery is delayed for some reason. The procedure may be appropriate in selected patients with pulmonary atresia, mitral atresia, and tricuspid atresia.
In infants older than 6 to 8 weeks of age, the atrial septum may be too thick to allow an effective balloon septostomy. In such cases, the atrial septum can be opened with a blade catheter (i.e., Park blade). The blade catheter uses a small blade that unfolds from the tip of the catheter to actually incise the atrial septum as the catheter tip is withdrawn from the LA to the RA. The opening can be torn further with a balloon catheter. Conditions for which the procedure is necessary are the same as those listed for balloon atrial septostomy.
Balloon Valvuloplasty
The balloons used in these interventional procedures are made of special plastic polymers and retain their predetermined diameters. A long guidewire is advanced far beyond the valve of interest, and the balloon catheter is placed over the wire. The middle of the elongated, sausage-shaped balloon is placed in the valve position. The balloon is then inflated with diluted contrast material to relieve obstruction at the valve.
Pulmonary Valve Stenosis. This technique is the treatment of choice for valvular PS in children and, to a large extent, has replaced the surgical pulmonary valvotomy (see Fig. 7-2, B). Balloon valvuloplasty may be indicated in patients with Doppler peak gradient of 40 mm Hg or greater. The results of this technique are excellent, and it does not have significant complications. This technique can be used in neonates with critical PS, although the complication rate is higher. The effectiveness of balloon valvuloplasty for a severe dysplastic pulmonary valve is questionable, but it may be attempted. The procedure is not useful for the treatment of infundibular PS that is not associated with valvular PS.
Aortic Valve Stenosis. This procedure is more difficult and carries a higher complication rate than does pulmonary valve balloon dilatation, especially for infants. The gradient reduction is less effective than for the pulmonary valve. Indications for balloon valvotomy include peak systolic pressure gradients greater than 50 to 60 mm Hg without significant AR in children and adolescents. Newborns or small infants with critical valve obstruction are also candidates for the procedure, regardless of the measured pressure gradient value. Complications include production or worsening of AR, iliofemoral artery injury and occlusion, ventricular fibrillation, and even death in small infants. Although the effectiveness of the procedure has been questioned, it may be tried in discrete membranous subaortic stenosis but not in fibromuscular subaortic (or “tunnel”) stenosis.
Mitral Stenosis. Balloon dilatation valvuloplasty has been effective for rheumatic mitral stenosis (MS) but less effective for congenital MS. Passage of the balloon catheter across the atrial septum is necessary. Complications include perforation of the left ventricle, transient complete AV block, tearing of the anterior leaflet of the mitral valve, and severe mitral regurgitation.
Stenosis of Prosthetic Conduits and Valves within Conduits. The balloon dilatation procedure may reduce the transconduit gradient across stenotic areas of prosthetic conduits and across valves contained within conduits.
Balloon Angioplasty
Balloon catheters similar to those used in balloon valvuloplasties are used for the relief of stenosis of blood vessels. Appropriate guidewires are placed beyond the point of narrowing, and the balloon catheter is placed over the guidewires. The midportion of the balloon is positioned at the point of narrowing, and the balloon is inflated with diluted contrast material to relieve the narrowing of vascular structures. This procedure has been used for COA, PA branch stenosis, and stenosis of the systemic veins. After the balloon procedure, some blood vessels recoil and do not maintain the dilated caliber of the vessel.
Endovascular stents are sometimes used to maintain vessel patency after balloon angioplasty of any vascular structure. The stent prevents recoil of the vessel, providing better acute results and considerably reduced rate of restenosis than with balloon angioplasty alone. The stent is positioned over an angioplasty balloon, and the balloon is inflated after positioning it at an appropriate site. After stent placement, the vascular endothelium grows over the struts over several months, functionally incorporating the stent into the vessel wall. Occasionally, however, the endothelialization may go awry, resulting in a thick neointimal layer causing a functional stenosis. There is also active work in the development of biodegradable stents, which would eliminate some concerns of repeated dilatation in a growing child.
Recoarctation of the Aorta. Balloon angioplasty is an extremely useful tool in the management of postoperative residual obstruction of COA. It has become the procedure of choice for patients with this condition, because reoperation carries a significant risk of morbidity and mortality. The procedure’s success rate is close to 80%, and late development of an aortic aneurysm rarely occurs. Some centers use a stent to prevent restenosis (see Chapter 12 for further discussion).
Native (or Unoperated) Coarctation of the Aorta. Balloon angioplasty for native unoperated coarctation is controversial. The rate of recoarctation after the balloon procedure appears higher than that after surgery in infants. The complication rate is 17%, with aortic aneurysm formation (both acute and late) occurring in 6% of patients. The long-term effects of the procedure on aneurysm formation are unknown. Therefore, surgery may be a better choice than the balloon procedure for native coarctation. Some centers use a cutting balloon or low-profile stent in very sick infants, which may reduce aneurysm formation.
Branch Pulmonary Artery Stenosis. The most frequent use of stents in pediatric patients is to treat peripheral PA stenosis. Peripheral PA stenosis may be seen as an isolated lesion but more commonly as a component of complex cyanotic heart defects. Hypoplastic and stenotic branch PAs are seen with postoperative TOF, pulmonary atresia, and hypoplastic left heart syndrome. Because operative treatment of peripheral PA stenosis is often not possible, attempting the balloon procedure with stent for this condition is well accepted.
The immediate success rate of the balloon procedure is about 60%, but restenosis occurs in a significant number of patients, and aneurysm formation occurs in approximately 3% of patients. High-pressure balloons appears to improve the effectiveness. Vessels resistant to high-pressure balloons respond to either cutting balloon angioplasty alone or that followed by high-pressure ballooning. Cutting balloons have three or four microsurgical blades with a cutting depth of 0.15 mm, which are activated when the balloons are inflated. Use of an intravascular stent has also improved immediate results and may improve the long-term success rate.
Systemic Venous Stenosis. For obstructed venous baffles after the Mustard or Senning operation for TGA, the balloon procedure is an attractive alternative. The procedure is inappropriate for stenosis of the pulmonary vein because stenosis recurs in each case.
Closure Techniques
Various devices have been used for nonsurgical closure of ASD, PDA, and muscular VSD in cardiac catheterization laboratories. All closure devices are delivered through a catheter that goes through long, large sheaths. The sheaths are inserted into the femoral vein, the femoral artery, or both. These nonsurgical devices have the advantages of a short hospital stay, rapid recovery, and no residual thoracic scar. In many centers, these devices and techniques are considered the procedures of choice for ASD, PDA, and collateral arteries.
Atrial Septal Defect. In the past, a double-umbrella device was used to close secundum ASD, but because of fractures of its arms, it has been taken off the market in the United States. Several devices are available, some are approved by the U.S. Food and Drug Administration, and others are in clinical trial stages. In the United States, currently only the Amplatzer septal occluder (AGA Medical) and Helex septal occluder (W. L. Gore and Associates) are approved for closure of secundum ASD.
The use of the closure device may be indicated to close a secundum ASD, measuring 5 mm or more in diameter (but less than 32 mm for the Amplatzer device and less than 18 mm for the Helex device), and there must be at least a 4-mm rim of atrial septal tissue around the defect. The appropriate size of the device allows the connecting stalk to fill the ASD, self-centering the device for a better result. The procedure is performed under general anesthesia under the guide of transesophageal echocardiography. The patient is observed overnight and discharged the next morning. Patients take a baby aspirin daily for 6 months until endothelialization of the device is complete. Follow-up consists of echocardiography and a chest radiograph at 6 months and 1 year. Rare possible complications include infection, arrhythmia, stroke, cardiac perforation, device embolization, and incomplete closure.
Ventricular Septal Defect. Nonsurgical device closure of selected muscular VSDs is possible by using the double-umbrella clamshell (or other devices) when the defect is not too close to cardiac valves. Device closure is not popular for the perimembranous VSD because of the unacceptable rate of postprocedure heart block.
Patent Ductus Arteriosus. A double-umbrella plug has been used outside the United States to close PDA in infants and young children, with a closure rate better than 85%. Recently, less costly coils have become popular in the United States. Most transcatheter PDA closures are now performed using Gianturco vascular occlusion coils. They are small, coiled wires coated with thrombogenic Dacron strands that open like a small “pigtail” when placed in the vessel. When delivered to the aortic ampula, a blood clot is formed around the coil, obstructing blood flow with ultimate endothelialization. Good candidates for the coil occlusion are children weighing 6 kg and larger with the ductus 4 mm and smaller. The incidence of minor complications is low (less than 5%); complications include coil embolization, incomplete closure, mild left pulmonary artery ( LPA) stenosis, and very rarely hemolysis.
For larger PDAs but smaller than 12 mm in diameter, specialized devices, such as the Amplatzer duct occluder, are available for catheter-based closure. The devices are implanted antegrade from the femoral vein. There is a 98% or greater closure rate at 6 months with minimal complications and no mortality. Very large ducti in small infants are still probably best treated surgically.
Occlusion of Collaterals and Other Vessels. This technique is used for closing aortopulmonary collaterals (often seen with TOF), systemic arteriovenous fistulas, pulmonary arteriovenous fistulas, and surgically placed shunts that are no longer needed. The Gianturco coil and the White balloon are examples. When delivered, the coil occludes the vessel by creating a thrombus around the coil. Alternatively, a balloon is placed in a selected spot with an elaborate harpoon-like hydraulic delivery system on a thin catheter. Both devices need a discrete area of stenosis within a tubular vessel for fixation. The vessel should not be larger than 6 to 7 mm in diameter. Peripheral embolization of the coil or balloon into the PAs or the aorta is a major risk.
Percutaneous Valve Replacement
Since Bonhoeffer and his colleagues first replaced a pulmonary valve percutaneouly in 2000 (Bonhoeffer et al, 2000), this technique is gaining increasing experience. Candidates for this technique are typically patients who received surgery for TOF and late development of severe pulmonary regurgitation. This technique is expected to reduce the need for repeated cardiac surgeries by replacing surgically placed conduits. Most of the reported cases used the Melody transcatheter pulmonary valve (Medtronic, Minneapolis). The Edwards SAPIEN valve (Edwards Lifescience, Irvine, CA) is a new valve with which experience is very limited. This technique has sparked the development of other valve replacement procedures such as transcatheter aortic valve replacement in selected adult patients.