The practice of interventional cardiac catheterization consists of minimally invasive procedures where catheters are used to modify, palliate, or treat congenital or acquired cardiac disease. Evolution of interventional techniques has been a natural progression from open surgical procedures used to treat such lesions. The development of newer interventional techniques has largely been possible by pushing the boundaries of established interventional procedures to achieve results comparable with traditional surgical techniques. Although the aim of interventional catheterization is to provide one or more interventions to alter the course of disease, the basics are nevertheless drawn from experience with diagnostic cardiac catheterization. Not all interventional catheterization techniques are therapeutic. Some do no more than modify the course of the disease or help to delay future interventional or surgical procedures. The design and organization of the catheterization laboratory, personnel, use of equipment, catheters, and techniques are a progression of the exercise of gathering of information related to diagnostic catheterization and angiography. However, in sick neonates, infants, and children, any catheterization may be considered an intervention, involving higher risks than therapeutic elective procedures performed in stable patients.
Historical Background
The evolution of interventional techniques has followed the basic principles of cardiac catheterization outlined by Werner Forssman in 1929. The use of interventional catheterization was first initiated by the use of balloon dilation in pulmonary and tricuspid valvoplasty, and in dilation of atherosclerotic lesions. Rashkind and colleagues widened the therapeutic implications of interventional catheterization with the first intracardiac procedure in pediatrics and congenital cardiac disease when they introduced balloon atrial septostomy. The use of occlusive devices was first reported by Porstmann and colleagues in 1967, when a patent arterial duct was occluded with the aid of an Ivalon plug. Attempts were then made to close left-to-right shunts with other devices, such as an atrial septal occluder for atrial septal defects and the double umbrella device for the persistently patent arterial duct and atrial septal defects. The application of percutaneous transluminal balloon angioplasty by Gruntzig and Hoppf in 1974 expanded the field of interventional cardiology such that it became recognized as a subspecialty in its own right. The principles of percutaneous transluminal balloon angioplasty were first applied by Lock and colleagues in the field of congenital cardiology, when they addressed stenotic pulmonary arteries, the aorta, and systemic veins, both in animal experiments and in humans. Kan and colleagues, in 1982, then reported the first use of balloons introduced percutaneously for dilation of congenital valvar pulmonary stenosis. This approach has since became an accepted first intervention for treatment of stenotic pulmonary and aortic valves. The development of balloon-expandable stents has helped to overcome problems of residual stenosis and restenosis in vessel walls. The development of newer materials, such as nitinol, a nickel-titanium alloy, has revolutionized technology and expanded its use in closure of left-to-right shunts. The use of this shape-memory alloy has simplified the delivery and retrieval of these devices by significantly reducing the sheath or catheter profile used for delivery, thereby increasing their application in infants and smaller children. Various designs are now available, with different characteristics, allowing the operator to choose the most appropriate device for the morphology of the defect. Transcatheter insertion of valves is the most recent major innovation in the field of interventional catheterization. Percutaneous implantation of biologic or pericardial tissue valves mounted on balloon-expandable or self-expanding stents are now clinically approved for use in treatment of stenotic and regurgitant lesions in both the left and right ventricular outflow tracts (RVOTs). Transcatheter techniques for repair of the left- and right-sided atrioventricular valves, based on surgical principles such as the creation of dual orifices and annuloplasty, are also being actively deployed and investigated in the clinical setting. The final frontier in interventional techniques could well be the transcatheter treatment of complex congenitally malformed hearts, replacing surgical interventions such as the Norwood procedure or completion of Fontan circulation. Short of this, recent efforts have pushed early neonatal palliations to the catheterization laboratory, including the use of patent ductus arteriosus (PDA) and RVOT stent placement—as opposed to surgical arteriopulmonary shunt placement—in lesions with inadequate pulmonary blood flow.
Principles of Catheterization
The field of interventional catheterization is rapidly expanding as newer techniques and devices appear on the market. Any description of a standard procedure is therefore unlikely to stand the test of time and will soon be outdated. Moreover, given substantial differences in resources and regulatory environments across countries (and continents) and institutional and even individual practitioner biases, we cannot possibly cover all specific approaches to procedures within this chapter. Instead, we intend to describe a series of approaches to interventional procedures, admittedly with a North American bias, given the current working location of the authors. However, the basic tenets of interventional catheterization are likely to remain constant and have already stood the test of time over the past few decades. Subtle variations in available technology or strategies should not negate the value found in the advice housed within. Ultimately, the success of an interventional catheterization procedure is dependent not only on the performance of the procedure but also on good planning prior to the procedure, coupled with anticipation and preparation for unexpected events.
Preprocedural Nursing Considerations
A thorough chart review should be conducted within 30 days of the procedure. The patient’s current health condition should be assessed for infectious processes that could postpone an elective procedure. Consideration should be given to mitigating existing comorbidities prior to the procedure, to decrease risk. For example, patients with chronic renal insufficiency may receive prophylactic renal protection with hydration and N-acetylcysteine prior to contrast administration, in an effort to preserve kidney function. Patients with diabetes may need to adjust insulin dosing to avoid hypoglycemia, or hold oral hypoglycemic agents to prevent lactic acidosis. Discussion of specific care concerns with the patient’s existing specialists should take place well in advance of the procedure, to customize a periprocedural care plan. In addition, medication review is necessary to modify key therapeutics such as chronic anticoagulants or antiplatelet agents, which may need to be held or reduced in dose several days prior to procedure. Consideration of bridge anticoagulation therapy (e.g., low-molecular-weight heparin) may be necessary for patients with a high risk for thrombus, such as those with prosthetic heart valves. Use of an anticoagulant agent with a short half-life maintains anticoagulation for days prior to the procedure but decreases the risk of periprocedure bleeding with discontinuation hours prior to the procedure. Finally, inquire about any allergies that may require either treatment prior to the procedure (e.g., contrast allergy) or development of an alternate periprocedural medication plan (e.g., penicillin allergy).
Before the procedure, a provider must complete a history and physical. The exam could take place the day prior to, or day of, the scheduled procedure. Discuss changes or increases in symptoms since referral with the interventional cardiologist. Red flags such as decrease in feeding, desaturations, or increased work of breathing could warrant expediting the procedure or, occasionally, delaying the procedure.
Providers must be familiar with procedures to serve as a resource to patients and families. The provider sets expectations for care immediately after a procedure (e.g., supine positioning to prevent bleeding, monitoring equipment, and possibly a urinary catheter), which can facilitate a smooth postprocedure experience for patients and families. The developmental level of the patient is necessary to keep in mind during this counseling encounter. It is necessary to provide guidance in terms that both patients and families can understand. Use of a child life specialist should be considered when both appropriate and available.
Preprocedural Planning
Consent should ideally be obtained either during outpatient consultation or in a dedicated preprocedural clinic that provides parents the opportunity to discuss relevant issues, prior to the “stress” of the procedure.
The consent should be obtained by a person suitably qualified, with sufficient knowledge to explain the procedural details and its risks or, ideally, by the interventional cardiologist. It is unreasonable to expect to receive a blanket consent, covering all procedures, although detailed consent for specific anticipated events might be obtained. The patient and the family should have sufficient time and information to make a fully informed decision. Because it is difficult to approach parents during catheterization for consent to additional procedures, treatment of life-threatening complications or events that may lead to significant deterioration in the health of the patient must be performed as deemed necessary.
The planning of an interventional catheterization procedure cannot be overemphasized. Procedural planning aids in giving sufficient time to order necessary laboratory equipment and devices not stocked on a regular basis. Admission of the patient should include a meeting with the patient and family, explaining details and risks associated with the procedure, so that any doubts and fears specifically pertaining to the procedure are reclarified. All investigations should be reviewed on the day of the procedure. A repeated clinical examination of the patient helps determine the need for any additional investigations. Imaging should be reviewed to reconfirm the diagnosis and the indication for the procedure and to reverify planned approaches to the intervention. Ideally, the symptoms, findings on clinical examination, and investigations should be reviewed by a team of doctors, including the primary cardiologist, the interventional cardiologist, the imaging cardiologist, the anesthetist, and, if applicable, the cardiac surgeon, to maximize the information leading to the procedure. An approach based on consensus also adds to the safety and efficacy of the decision-making process because individuals with different areas of expertise contribute in a complementary manner, maximizing the benefit to every patient of this team-based philosophy. Use of additional cross-sectional imaging, such as three-dimensional echocardiography, magnetic resonance imaging, or computerized tomography, can add significantly to the clinical information by providing details of complex cardiac anatomy that could suggest the need for a modified approach or even contraindicate catheterization. Decisions regarding access, via the femoral, jugular, or hepatic approach, for example, choice of sheaths, catheters, wires, dosage of contrast agents, and projections to be used, can be made with reasonable certainty before starting the procedure. It is always helpful to discuss the whole strategy in a stepwise manner with cardiology fellows in training, catheterization laboratory staff (including nurses and technologists), anesthetist, and any other staff involved with the procedure. Steps that can be performed quickly and safely should be identified and delegated to assistants in the interest of time, particularly for long procedures.
Vascular Access
The conventional approach, namely to have both an arterial and a venous access, works in almost all situations where interventional catheterization is performed. Femoral, internal jugular, subclavian, axillary, carotid, and hepatic vascular approaches have all been used for various interventions. The possible need for reintervention should be borne in mind, thus avoiding unnecessary access, especially in smaller patients. Repeated catheterization, prolonged periods in intensive care, and multiple operations for complex staged palliative procedures can make access difficult due to repeated use of the vessels. Ultrasound-guided access allows for visualization of vessels, detects unusual arrangements and thrombosed veins and arteries, and also reduces the risk of inadvertent vascular puncture. Stenosis or atresia with luminal continuity of systemic veins may have to be dealt with by crossing the site with a floppy-tipped guidewire and use of long sheaths, which track across the stenosis and provide access to the central circulation. On the arterial side, in small neonates or infants, vascular cut-down has been used to access the carotid or axillary arteries for interventions on the aortic valve or arch. More recently, percutaneous access to the carotid and axillary arteries have been used to facilitate PDA stent implantation in neonates. In neonates and small infants, the availability of small catheters and sheaths, of 3-Fr and 4-Fr sizes, has facilitated procedures and reduced the risk of vascular injury, although this remains the highest risk group for arterial thrombosis.
Catheters and Guidewires
In infants and children, angled and curved-tipped catheters are most commonly used in situations where catheters need to be maneuvered through tight bends and small chambers and vessels. The operator needs to have sufficient knowledge of the differences in the types of catheter when performing cardiac and peripheral interventions in order to modify the approach to access difficult sites. Hydrophilic catheters, such as the Glide catheter (Terumo), Medi-tech, or Boston Scientific products, track well over guidewires into difficult sites. Balloon-tipped catheters, such as the Berman angiographic catheter or the balloon wedge catheter, are useful for wedge injections or to cross atrioventricular valves without entrapment in the intercordal spaces. Catheters of short length help to make manipulation easy in small babies. Long catheters in older patients help to form loops in dilated proximal chambers, such as the right atrium, to provide stability, and allow tracking into distal vessels such as the pulmonary trunk. Increasingly, complex lesions require use of a coaxial system, which may involve passage of a microcatheter through a directional catheter, which itself may be passed through a long sheath.
Guidewires are used to access vessels, stabilize catheters, and provide easy access for multiple crossings of stenotic lesions. A soft hydrophilic wire, such as the Terumo, with an angled tip, can be used to enter small tortuous vessels. A stiff exchange length wire, such as the 0.035-inch, 260-cm product from Cook Medical, is usually required to obtain multiple hemodynamic measurements, to provide stability across a lesion, for multiple crossings after interventions, to perform angiography, and to mount balloon catheters, stents, or large sheaths. Ultrastiff wires, such as the Lunderquist wire (Cook Medical), have increasingly important roles with delivery of large-profile stiff interventional equipment, such as transcatheter valves, but these require both knowledge and caution because they may be associated with considerable risk of distal vascular injury (guidewire perforation).
Anticoagulation
Heparin is most commonly used as an anticoagulant during cardiac catheterization to prevent thrombosis during and after the procedure. Some operators monitor heparin’s effect by measuring the activated clotting time or the partial thromboplastin time, albeit that most use a standard dose based on the weight of the patient.
For short procedures, a single dose of 50 to 100 units per kilogram body weight of heparin is typically administered after vascular access is obtained. For long procedures, between 100 and 200 u/kg body weight is administered and may be repeated either after 2 to 3 hours or by monitoring either the activated clotting or the partial thromboplastin times. The direct thrombin inhibitor bivalirudin is an alternative to heparin, which has some pediatric dosing data to support its use. Protamine may be used to reverse the effect of heparin should there be persistent bleeding from the site of access.
Interventional Catheterization Procedures
Balloon Dilation
Balloon dilation is performed to relieve stenosis of valves, vessel walls, surgically created pathways, or intracardiac structures such as a fenestration in the atrial septum. There have been significant advances in the size, profile, design, and materials used in balloon catheters, facilitating their use in various applications. Design of coaxial balloons has reduced the time required for inflation and deflation, with only transient hemodynamic compromise. The size of the balloon used for a particular procedure not only depends on the diameter of the lesion to be dilated, but also on the diameter of the contiguous and noncontiguous normal anatomic structures. The use of an oversized balloon increases the chance of a successful dilation of the lesion but also increases the risk of trauma to the target lesion and to contiguous anatomic structures. Balloons have been used to treat valvar stenosis when fusion of the leaflets along their zones of apposition is responsible for reduction in the area of the effective valvar orifice. The principle of creating a controlled tear or split in the commissure, but not in the leaflet, thus improving excursion of the leaflets, provides a larger area of effective orifice and thus relieves the stenosis. Because the valve is abnormal, competence may be affected to various degrees after balloon dilation. Pulmonary, aortic, mitral, and tricuspid valves have all been treated by balloon valvuloplasty for different diseases. However, the technique is not useful in treating valves associated with significant hypoplasia at the basal hinge point of the leaflets. Dilation of semilunar valves is performed commonly for congenital lesions, and dilation of atrioventricular valves is performed almost exclusively for acquired lesions. The technique used in performing balloon valvuloplasty also forms the basis for angioplasty and implantation of stents. High-pressure balloons have been more recently used in dilating highly resistant lesions, such as calcified conduits, postoperative anastomotic stenosis, or native pulmonary arterial stenosis. Cutting balloons have been used in substrates that do not respond to standard balloon angioplasty, such as severe pulmonary arterial stenosis or recurrent pulmonary venous stenosis, with encouraging results. Balloon-in-balloon catheters, known as BIB catheters (NuMed), have been very useful in implanting stents in the aorta, pulmonary arteries, and conduits. The inner balloon is an additional tool to help confirm the position before deployment of the stent, and the serial dilation helps to reduce stent malposition and foreshortening. The use of two balloons simultaneously for valvuloplasty was first introduced for dilation of the mitral valve. It provides a large effective diameter of the combined balloons and has been used in pulmonary valvuloplasty in adults who have a large diameter of the pulmonary outflow tracts. Stability of the balloon during inflation depends on choice of a balloon of correct length and diameter, appropriate selection of a stiff guidewire, obtaining appropriately distal position for the guidewire, and achieving a rapid sequence of inflation and deflation. Stability could be further aided by using techniques to reduce stroke volume, such as rapid ventricular pacing, mainly but not exclusively for lesions in the systemic circulation. In balloon valvuloplasty, the size of the balloon is chosen based on the size of the target valve annulus measured. In pulmonary valvoplasty, the balloon size is usually 120% to 140% of the measured diameter of the valve at the basal hinge points of the leaflets. In aortic valvoplasty, the size is usually 80% to 100% of the diameter at the hinges of the leaflets. A serial approach to aortic valvuloplasty with interval reassessment of residual gradient and degree of valvar incompetence can prevent the development of an adverse outcome. Size for dilating coarctation of the aorta equals the diameter of the distal transverse arch, prior to the development of hypoplasia or stenosis, or a size is chosen not greater than four times the diameter of the lesion but less than the diameter of the descending aorta at its position close to the diaphragm. The length of the balloon should not be so short as to produce instability during inflation or make capture of the lesion difficult and not too long to cause trauma to the proximal or distal structures (including the adjacent tricuspid valve, as is the case with pulmonic valvuloplasty). The size of the patient should be taken into consideration in choosing the correct balloon. Balloons are filled with dilutions of contrast medium 1:3 and 1:5 with saline, chosen based on balloon size and location, as well as patient thickness, and should be de-aired thoroughly to reduce the risk of air embolism, should the balloon rupture. If the margins of the balloon, at its ends, are parallel, it suggests that inflation is at nominal pressure, and any further inflation can increase the risk of rupture. After successful dilation, hemodynamics and angiography should be repeated to evaluate results and assess complications. Further evaluation by echocardiography, cross-sectional imaging, or lung perfusion scan is imperative to decide long-term management.
Stent Angioplasty
Stents are capable of maintaining patency of vessels and prevent elastic recoil after balloon dilation. There have been major advances in stent technology, and their impact can be easily observed in congenital cardiology. Typically, stents are cut from stainless steel tubes with a laser or made from platinum alloy wires welded together. Stents can be expanded on balloons or be self-expanding when made of shape-memory alloy (nitinol) and delivered from a constraining sheath. Self-expanding stents are used in patients who, or structures which, have already achieved their potential for growth and typically offer benefit in regions of dynamic stress (e.g., femoral artery). Balloon-expandable stents can be redilated within limits, each distinct to the specific model of stent chosen, and may be used in children and adults. The design of the cells may be open, such as the ev3 LD series (Medtronic, Inc.), avoiding jailing or covering of neighboring arterial branches, closed, such as the Palmaz Genesis or XL series (Cordis), or a hybrid of these two designs, such as the Formula series (Cook Medical). The properties of materials considered favorable for use in congenital cardiology are those with a low profile, good radial strength and flexibility, and ability to withstand cyclic compressive stresses of the cardiovascular system. The diameter of the stent should also have the potential to reach maximal dimensions of the vessel wall, as seen in a typical adult. However, in small infants, a premounted biliary stent or coronary arterial stent may be used in circumstances of severe hemodynamic compromise, despite their limited final maximal diameter. This is especially true in patients in whom subsequent surgical revision (e.g., conduit replacement) is inevitable; moreover, intentional transcatheter stent fracture is an increasingly viable potential. Stents are implanted using balloons of appropriate size through long, large-bored, sheaths to reach the lesion. Stents may be premounted on the balloons or may need to be crimped on to the balloon manually or by using a crimping device. The length of the balloon should always be equal to or longer than the length of the stent but ideally not by much, to avoid “dog boning,” which can shorten a desired stent’s length. The diameter of the balloon determines the final diameter of the stent. Stability of the stent during deployment can be improved by using the BIB catheters, extra-stiff wires, long sheaths, and rapid right ventricular pacing to reduce stroke volume. The luminal surface of the stent endothelializes in 8 to 10 weeks, and patients may need to take antiplatelet agents or, in some situations, anticoagulants during this period to prevent in-stent thrombosis and restenosis.
Risks associated with stent angioplasty include dislodgement and embolization, trauma to the vessel walls, fracture of the stent, and restenosis. Covered stents made by fashioning expanded polytetrafluorethylene to balloon-expandable or self-expanding stents have been used in situations where the risk of vascular injury and aneurysm is considered to be high or to exclude existing vascular pathology, such as a pseudoaneurysm or dissection. The use of covered stents in younger patients is limited by their size and the caliber of the delivery systems currently available. Covered stents approved by regulatory agencies throughout the world are now readily available. Newer bioabsorbable stent platforms are currently being investigated to reduce restenosis and improve vasomotion in coronary arterial lesions. Such stents could prove useful in treating stenoses of small vessels in infants and children, albeit temporarily, thus allowing for normal growth without the need for later surgical stent transection or intentional stent fracture to facilitate further interventional therapy.
Closure of Septal Defects and Vascular Occlusion
The advent of shape-memory alloy has revolutionized transcatheter interventions for intracardiac and extracardiac shunts. Nitinol is the most common alloy used. Several devices for closing septal defects and vascular occlusion are currently available. The most commonly used occluder, the Amplatzer Septal Occluder (now manufactured by Abbott Medical), has a central occluding component, with left- and right-sided discs. A Dacron polyester patch sewn into the device is responsible for thrombogenicity and acute occlusion. A large number of devices are available around the world that largely mimic the design of the ASO device, including the Occlutech ASD occluder, which is very popular in Europe. The second most commonly used occluder in the United States is the Cardioform Septal Occluder (W.L. Gore & Associates), which consists of a nitinol coil frame with Gore-Tex covering on the left- and right-sided discs. This device covers the defect but does not contain a central occluding component and thus is not self-centering like the Amplatz device. The Gore Cardioform ASD Occluder, currently in clinical trial, offers a hybrid approach to ASD closure with a nitinol coil frame and Gore-Tex covering but also containing an anatomically adaptable central component that fills the defect itself. Sizing of a septal defect is performed by transesophageal or intracardiac echocardiography, with or without inflating a balloon across the defect during the procedure. Reported complications of such closure devices eroding through the atrial or aortic walls, and devices designed to occlude ventricular septal defects (VSDs) causing complete heart block, emphasize the importance of choosing a device of appropriate size and the ongoing need for further device development. Various practice strategies, from oversizing to reduce the risk of device embolization, to appropriate sizing to reduce the risk of trauma to contiguous structures, have been used.
Intracardiac Interventions
Valvar Heart Disease
Pulmonary Valve
Pulmonary Valvar Stenosis.
As already discussed, the initial description of balloon dilation of pulmonary valve stenosis was made by Kan and colleagues in 1982. Since then, the technique has been accepted as a first-line treatment for congenital valvar pulmonary stenosis. Balloon dilation is usually indicated in the presence of related cardiac symptoms (such as poor feeding in an infant or exertional intolerance in an older child), when the gradient across the stenotic valve is 40 mm Hg or more, or when there is an increase in right ventricular systolic pressure by more than half of the systemic pressure. However, the indications for the procedure are different in neonates with a ductal-dependent pulmonary circulation, when gradients are unreliable. The presence of a dysplastic valve with ductal-dependent pulmonary blood flow (critical pulmonary stenosis) is an accepted indication for treatment.
The right ventricular pressure is measured, after which right ventricular angiography is performed in the lateral projection to measure the diameter of the ventriculoarterial junction at the basal attachment of the valvar leaflets. The stenotic pulmonary valve is crossed using an end-hole catheter, such as a balloon-tipped catheter or a directional catheter (e.g., Judkins right coronary). A guidewire, from 0.014 to 0.035 inch in diameter, is passed through the catheter into a branch of the pulmonary artery (PA) supplying the lower lobe of either lung. In neonates, the guidewire may be placed across the patent arterial duct into the descending aorta, for maximal wire “purchase.” A balloon that is between 110% and 140% of the diameter of the measured valve is passed through the sheath in the femoral vein over the wire and advanced across the pulmonary valve. The balloon is rapidly inflated and deflated with dilute contrast across the stenotic valve. A significant waist is typically visualized on the balloon, which resolves with further dilation, until only a mild persistent annular waist remains, consistent with the use of a balloon that is slightly larger than the valve. The balloon is then withdrawn, with the guidewire still in place, and a catheter is passed into the pulmonary arteries to reassess the hemodynamics with a pressure pullback. The Multitrack catheter can be useful in this scenario because it allows measurement of both right ventricular pressure and the gradient across the pulmonary valve, coupled with the ability to perform angiography before and after dilation of the balloon without loss of position of the guidewire. That stated, most operators do not feel that routine right ventriculography is strictly necessary following routine and uncomplicated balloon pulmonary valvuloplasty. In patients with a very dysplastic pulmonary valve, and a poor response to routine pulmonary valvuloplasty, high pressure angioplasty balloons can be used, with acceptable relief of the stenosis. The technique of balloon valvuloplasty is more demanding in neonates, especially in those without critical pulmonary stenosis, whereby transductal wire position cannot be established and there is no secondary source of pulmonary blood flow to be relied upon periprocedurally. Although balloon dilation of pulmonary valvar stenosis carries low risks when performed in infants and children older than 1 year, there is significant morbidity and mortality in the early neonatal period. In neonates, it is the size and function of the right ventricle that determines outcome. High right ventricular pressure, an irritable myocardium with a risk of arrhythmia, and equipment-related splinting of the tricuspid valve can all lead to hemodynamic instability. This necessitates rapidity of the procedure, use of a relatively soft guidewire, and very short periods of balloon inflation, which may be helped by using balloons with low profile. The presence of an atrial level shunt generates cyanosis but not severe hypotension during balloon inflation.
Adequate relief of the stenosis, with a reduction in the transvalvar gradient and in right ventricular systolic pressure, is achieved in the majority of patients. However, occasionally, there may be very little immediate reduction in gradient across the pulmonary valve. This is because of associated dynamic infundibular muscular stenosis, which disappears over a period in a similar fashion to that observed after surgical pulmonary valvotomy. Repeat balloon valvoplasty, after a few months, in those patients where the initial result was suboptimal, can produce a further reduction in gradient. Occasionally, the severely dysplastic pulmonary valve may not respond adequately to one or more attempts at balloon dilation, and surgical volvotomy, valvectomy, or transannular patch are considered. Serious complications of balloon dilation include a tear of the pulmonary trunk or perforation of the heart. In general, the complication rate, at 0.4%, is low, and reported mortality is no more than 0.2%. The consequences of chronic pulmonary regurgitation, nonetheless, has historically been underestimated, and more conservative dilation is now recommended in an effort to reduce the degree of chronic pulmonic regurgitation.
Balloon dilation of the pulmonary valve can also be carried out as a palliative procedure in patients with tetralogy of Fallot and other complex two-ventricle congenital cardiac malformations, typically in a subset with isolated valvar pulmonary stenosis. It can also be performed in patients with a functionally univentricular circulation to augment pulmonary blood flow and improve the size of the pulmonary arteries prior to staged palliations or repair. The basic principles of the procedure in these situations are the same as for isolated congenital valvar pulmonary stenosis, although crossing the stenotic subpulmonary outflow tract can be challenging. Problems with atrioventricular conduction (e.g., heart block) can occur if the position of the atrioventricular bundle is abnormal. A more conservative approach is followed to avoid excessive flow of blood to the lungs or excessive pressure in the pulmonary arteries and to reduce the risk of pulmonary regurgitation.
Valvar Pulmonary Atresia With Intact Ventricular Septum.
The transcatheter interventions available to alter the course of this lesion (see also Chapter 43 ) include relief of right ventricular outflow obstruction with perforation of the atretic pulmonary valve followed by balloon pulmonary valvuloplasty ( Fig. 18.1A–B and Fig. 18.2A, C ). In some cases, stenting of the arterial duct may be necessary to augment pulmonary blood flow, especially in the setting of right ventricular diastolic dysfunction and/or borderline hypoplasia. Furthermore, enlargement of the atrial communication by balloon atrial septostomy may be necessary in a select subgroup to reduce right atrial hypertension and improve systemic cardiac output. Occasionally, stenting of the subvalvar muscular RVOT is necessary in the setting of residual subvalvar obstruction. A more detailed consideration of patient selection, procedural approach, and outcomes is discussed in Chapter 30 .
Implantation of Pulmonary Valves.
Bonhoeffer and colleagues described the first transcatheter implantation of a valve in the pulmonary position, placing the device in a dysfunctional prosthetic right ventricular to PA conduit to relieve stenosis and regurgitation. In fact, this initial transcatheter pulmonary valve (TPV) implant preceded the first transcatheter aortic valve implant by 18 months! The Medtronic Melody TPV is made of a modified bovine jugular vein segment sutured inside a balloon-expandable platinum-iridium stent and is deployed using a custom-made long-sheathed delivery catheter, known as Ensemble (Medtronic). The Melody TPV was the first commercially available TPV. The system contains a BIB catheter inside a long sheath with a “carrot” dilator at the tip, facilitating direct entry into the skin without the need for an independent sheath. Current systems have outer balloons of 18-, 20-, and 22-mm diameter. The outer balloon determines the final diameter of the implanted valve, which should approximately equal the nominal diameter of the conduit (up to 110% of the nominal diameter) when inserted surgically in the RVOT. More recent experience suggests important conduit dilation beyond the 110% of the nominal diameter may be accomplished, although the risk of conduit injury is increased. The valve is suitable for insertion in RVOT conduits (including surgically implant bioprosthetic pulmonary valves) in patients with circumferential-valved conduits implanted surgically during their definitive repair or at subsequent surgical revision. Clinical experience does suggest good valve function is maintained outside of this working range (both in smaller and slightly larger diameter substrates). Magnetic resonance imaging helps to define the morphology of the outflow tract and the bifurcation of the pulmonary trunk, determine right ventricular volume and ejection fraction, and quantify the pulmonary regurgitant fraction. Echocardiography is used for postprocedural surveillance and hemodynamic monitoring.
The Edwards Sapien XT Transcatheter Heart Valve (Edwards Lifesciences), developed as a balloon-expandable transcatheter aortic valve, has more recently been approved in the United States for use in the pulmonic position. The Sapien XT valve is made of bovine pericardial tissue leaflets sewn into a cobalt chromium stent frame and is deployed using the NovaFlex+ delivery catheter. To reduce the required sheath profile (as the system was designed for aortic valve delivery), the valve is mounted onto the shaft of the catheter and then balloon-mounted within the inferior vena cava after introduction through the femoral sheath. The XT valve is marketed in 23-, 26-, and 29-mm diameters and is thus capable of treating larger-diameter RVOT conduits than is Melody TPV. Robust clinical data are lacking. The third-generation Sapien valve—S3 or Sapien 3—is currently in trial for pulmonic implantation and is expected to offer several benefits over the XT system, including an outer skirt (to minimize the risk of paravalvar leak) and a more flexible delivery system (to facilitate delivery to the RVOT).
TPV replacement is typically performed under general anesthesia. Although multiple approaches may be used, the following description is typical and well regarded. A balloon-tipped or curved-tip catheter is inserted through the femoral (routinely) or jugular vein (less commonly) to access the distal lower lobe of the left or right PA, often with the aid of a floppy-tipped or angled Glidewire. A super-stiff or ultra-stiff guidewire, of 0.035-inch diameter and exchange length, with a preformed curve, is then positioned in the distal PA. A Multitrack catheter is passed over this stiff wire to assess hemodynamics and to perform RVOT and PA angiography ( Fig. 18.3A ). Some operators do choose to perform angiography prior to establishing distal PA interventional wire position. Different projections are used to define the morphology of the outflow tract, the bifurcation of the pulmonary arteries, and to assess the pulmonary regurgitation, with extreme cranial angulation on the “A” plane and straight lateral on the “B” plane typical. In cases of conduit stenosis, serial conduit angioplasty with high-pressure and Kevlar-wrapped ultrahigh-pressure angioplasty balloons (Bard Vascular) is the next step. The initial angioplasty balloon is chosen to be approximately 2 to 4 mm larger than the minimal conduit diameter, based on preprocedural imaging and baseline angiographic assessment. Subsequent angioplasty balloons are chosen in increasing 2-mm increments. It is extremely important that the operator perform repeat conduit angiography after each dilation, to be sure conduit injury is identified when it is still mild. This process is complete when the conduit has been serially dilated to the intended TPV implant diameter. Nonselective aortography performed through a pigtail catheter inserted into the aortic root, during conduit balloon angioplasty at the intended TPV implant diameter, is performed to define the coronary arterial anatomy and rule out the presence of extrinsic coronary artery compression. This step is key to reduce the incidence of coronary artery compression, which can be catastrophic. Coronary compression occurs in 5% to 6% of planned TPV cases and is more likely in the setting of an anomalous coronary artery course. Selective coronary angiography may be performed with or without conduit angioplasty if coronary compression is suspected. Once the outflow tract is deemed suitable for implantation, consideration is given to the placement of covered or bare-metal stents, prior to actual valve implantation. A covered stent may be used in the setting of existing or acquire conduit injury. One or more bare-metal stents may be used to bear the compressive forces typically present in the setting of a retrosternal RVOT conduit, to avoid transferring these forces to the valve-stent itself. In the case of Melody TPV, the platinum-iridium stent is rather soft and pliable, and stent fracture has been well established as a mode of early valve failure (recurrent pulmonic stenosis). The use of prestent placement has effectively reduced, if not eliminated, the incidence of Melody stent fracture. It has become common practice to use prestents in the RVOT conduit until the conduit gradient is eliminated (or reduced substantially) and minimal stent recoil is present following deflation of the angioplasty balloon.
Following complete preparation of the RVOT, the valve-stent is prepared according to the manufacturers’ directions, which typically begins with serial washings to dilute the glutaraldehyde preservative. In the case of Melody, the valve is then hand-crimped, first onto a 3-mL syringe, and then onto the prepared BIB catheters of the Ensemble delivery system, with care taken to elongate the stent frame, while it is crimped onto the balloon. The integrated long sheath is then advanced carefully to fully cover the Melody valve during delivery. In the case of Sapien, the valve is mounted onto the shaft of the delivery balloon, using an included crimper device. This valve will be delivered to the RVOT through a short venous sheath in an uncovered fashion. The femoral venipuncture is dilated in a graded fashion, if necessary, and the delivery system is advanced either through the skin directly (Melody) or through the included eSheath (Sapien). At this point, the Melody TPV may be advanced directly to the RVOT landing zone. The Sapien THV must first be “mounted” onto the balloon portion of the delivery catheter, which is accomplished in straightforward fashion using the integrated delivery system in the inferior vena cava, prior to advancement through the right heart. Each delivery system can be looped in the right atrium to facilitate delivery of the valve-stent into an appropriate position, although the Ensemble system is typically a bit more forgiving in this regard. The NovaFlex+ system includes dual articulation adjustment capability (flexion), thereby facilitating delivery (although this system was designed to facilitate retroaortic delivery to the aortic valve). Standard principles of manipulation ensure delivery of the device in the RVOT without losing position of the wire. Once within the conduit, the Melody TPV is uncovered by pulling back on the outer sheath; the pusher catheter is withdrawn in the case of Sapien XT delivery. Calcification of the conduit, or the bare-metal stent(s) itself, usually provides good landmarks for optimal positioning. The valve is deployed by inflating the delivery balloon(s). Hemodynamic assessment and angiography are then performed after implantation (see Fig. 18.3B ). In patients with a significant residual gradient, post dilation with a high-pressure balloon may be considered.
TPV replacement has now been carried out for dysfunction of the RVOT in patients with repaired tetralogy of Fallot and variants, transposed arterial trunks with VSD and pulmonary stenosis, the Ross operation for left ventricular outflow disease, and repaired common arterial trunk, and others. The majority of the patients had a homograft in the RVOT but valve-in-valve implantation within an existing surgical bioprosthetic pulmonary valve is also common. There was a significant reduction in right ventricular systolic pressure, the gradient across the outflow tract, and improvement in pulmonary competence after valvar implantation, with no procedural mortality. Survival was 95.9% at 72 months. The incidence of complications decreased with subsequent implantations as a result of improvements in selection of patients and design of the device. Fractures remain an important cause of restenosis, being seen after one-fifth of insertions, and can be managed with a second implantation within the initial one. Early detection and anticipatory management of the fractured stent can be aided by chest radiography and echocardiography at regular intervals. Five-year freedom from reintervention and valve explantation was 76% and 92%, respectively. Endocarditis of a TPV is an important clinical problem to recognize because the diagnosis is associated with a substantial risk of morbidity and even mortality. Although data on the risk following Sapien implantation remain sparse, Melody TPV–related infective endocarditis carries an annual hazard of approximately 2.3% to 2.5%, which is similar to the Medtronic Contegra bovine jugular vein conduit risk.
Adolescents and adults who have undergone repair of the RVOT without use of a conduit (typically in tetralogy of Fallot), but have suffered aneurysmal dilation, will generally require pulmonary valve replacement to preserve right ventricular function and avoid right heart failure. The Melody TPV has been used in this setting, typically when residual pulmonary valve stenosis persists, but the maximal implantation inner diameter of 22 to 24 mm limits greater use in this dilated RVOT substrate. The Sapien XT and S3 valves have been increasingly used in this setting, whereby their larger maximal implantation diameter (outer diameter approaches 30 to 31 mm for the S3 valve) facilitates stability in the relatively dilated RVOT (see Fig. 18.3C–D ). Despite reasonable success in this “native” or patched RVOT substrate using balloon-expandable technology, the large diameter and compliant nature of the RVOT in this population begs for a purpose-built nitinol-frame self-expanding device. Although no such device has yet been approved as of the writing of this chapter, both Medtronic and Edwards have self-expanding native RVOT pulmonary valve replacement technology in clinical trial. The Medtronic Harmony TPV (Medtronic) is a porcine pericardial tissue valve mounted on a self-expanding nitinol frame with polyester covering. The valve is delivered via a custom-made delivery system with retractable sheath. A series of lengths and sizes are in development; the first design performed well in early feasibility testing. The Edwards Alterra Adaptive Prestent (Edwards Lifesciences) is a self-expanding nitinol frame covered stent with a central rigid landing zone intended to accommodate a commercial 29-mm Sapien 3 valve. The Adaptive Prestent is preloaded in a custom-designed delivery system with tapered tip. Following Prestent implantation, either at the same procedure or staged to a second procedure, a 29-mm Sapien 3 valve would be delivered to the rigid landing zone within the Prestent, completing the transcatheter PVR procedure. The Venous P-valve (MedTech) is another self-expanding TPV replacement option—with encouraging early results—that is currently used throughout Asia. These self-expanding devices are likely to be most suited to treat isolated pulmonary regurgitation in dilated native or patch-augmented RV outflow tracts.
Aortic Valve
Aortic Stenosis.
Balloon dilation of the aortic valve was first reported by Lababidi. Currently accepted indications for intervention include the presence of isolated critical valvar aortic stenosis in the newborn with ductal dependence or in children with isolated valvar aortic stenosis with left ventricular dysfunction. Additional indications include isolated valvar AS with a resting peak systolic ejection gradient 50 mm Hg or greater or 40 mm Hg or greater in the setting of syncope, ST-T changes (at rest or with exertion), or angina. Finally, valvuloplasty may be considered in the setting of a peak systolic ejection gradient of 40 mm Hg or greater without symptoms if the patient desires to become pregnant or participate in competitive sports, or in the setting of a mean gradient greater than 50 mm Hg acquired by nonsedated Doppler echo. Since the original documentation, good results of balloon dilation of the aortic valve have been reported in both the short and medium term. There was some concern regarding femoral arterial occlusion, related to sheath profile, but this complication is less frequently seen now with the availability of low-profile balloons. Furthermore, postcatheterization arterial pulse loss is readily treatable. The long-term outcomes following palliation of aortic valve stenosis with balloon valvuloplasty hinge on the combination of the degree of residual stenosis and resultant insufficiency. The longest freedom from aortic valve replacement appears to result from a postvalvuloplasty residual peak gradient less than 35 mm Hg with no or trivial aortic insufficiency.
Parameters given consideration prior to the procedure, particularly in sick neonates with critical AS and low cardiac output, include achieving access, maintaining hemodynamic stability, ensuring hydration, adequate control of glycemia and acid-base balance, ventilation, infusion of prostaglandin to maintain ductal patency, and appropriate cardiovascular drugs to maintain cardiac output. In infants and children, but also commonly in adolescents and young adults, the procedure is performed under general anesthesia. Heparin is used for anticoagulation to prevent vascular thrombosis of the femoral artery or vein and systemic thromboembolism. Avoidance of cooling and loss of blood during the procedure is very important to prevent hemodynamic compromise. The procedure can be performed through femoral arterial, femoral venous, umbilical arterial, axillary, or carotid arterial access. The advent of rapid right ventricular pacing has reduced the need for an anterograde approach with transseptal puncture and may contribute to reduced postvalvuloplasty aortic insufficiency by stabilizing the balloon during dilation, when used in children and adults.
In hemodynamically stable patients, an angiogram is performed in the ascending aorta via a pigtail catheter profiled in left anterior oblique and lateral projections. The aortic valvar leaflets are delineated, and the diameter of the ventriculoarterial junction is measured in both planes, typically averaged, and compared with those obtained on echocardiography, to avoid the risk of using an oversized balloon. Severe angulation of the left ventricular outflow tract and nonsymmetric aortic valve annulus can complicate accurate measurement of the valvar diameter. In hemodynamically unstable patients, angiography poses a risk of severe ventricular arrhythmia in the presence of left ventricular dysfunction, probably due to acute coronary ischemia. Hence the diameter of the aortic valve as measured by echocardiography alone may be used in certain very high-risk cases to determine the appropriate diameter of the balloon. Small sheaths, and catheters of 3-Fr diameter, are employed when using umbilical or femoral arterial access in small neonates. The ratio of the diameter of the initial balloon to the aortic valve annulus should be 0.8 to 0.9 to minimize the risk of creating significant aortic valve insufficiency. An aortogram illustrating a jet of negative contrast through the stenotic valve serves as a reference to locate the effective orifice, which most commonly lies posteriorly and to the left in the aortic root. The valve is crossed in retrograde fashion using a curved-tip directable catheter, such as a Judkins right (or even left) coronary catheter, a cobra-shaped catheter, or a cut-pigtail to provide a curved tip, and a guidewire that may either be floppy-tipped but steerable or an angled Glidewire. Multiple rapid gentle stabs are made with the guidewire to cross the valve. This step reduces the risk of perforating the valvar leaflets and traumatizing the orifices of the coronary arteries. In neonates, the guidewire used to cross the aortic valve may be a floppy-tipped coronary wire, which may be used to carry out the balloon valvuloplasty. However, in older patients the directable catheter must be advanced retrograde into the left ventricle, and a stiff exchange length wire with preformed loop to be placed at the apex should be parked in the left ventricle.
When approaching in anterograde fashion, a Judkins right or a cobra-shaped balloon angiographic or wedge catheter is placed across the patent oval foramen and maneuvered to enter the left ventricle through the mitral valve. Coronary wires are used in neonates and infants, and stiff exchange length wires are used in older patients requiring transseptal puncture for anterograde access to the aortic valve. Similar stiff wires can be also used in the retrograde approach. The balloon-tipped catheters reduce the risk of passing through the intercordal spaces of the mitral valvar tension apparatus. A large curve is formed in the cavity of left ventricle to direct the tip of the catheter toward left ventricular outflow tract. A floppy steerable wire is then used to cross the aortic valve and achieve a good position in the descending aorta. The catheter is then threaded over the wire so that a stiff wire could be positioned for subsequent steps. Some authors believe that the anterograde approach offers a reduced risk of aortic regurgitation as a result of valvar perforation.
In patients with a low cardiac output, balloons remain stable during inflation across the stenotic aortic valve. In the absence of a state of low cardiac output, balloons can be mobile during ventricular systole and can cause trauma to the valvar leaflets. Stability is achieved using rapid right ventricular apical pacing in older patients at fast rates of 180 to 220 beats/min ( Fig. 18.4 ). The anterograde approach leads to greater stability of the balloon, albeit that the risk of creating a tight loop across the atrial septum and the mitral valve increases the risk of severe hemodynamic compromise and cardiac trauma ( Fig. 18.5 ). It is prudent to use a long balloon of 4 to 6 cm in older patients because the left ventricle has a tendency to eject the balloon subsequent to inflation. Rapid inflation and deflation of the balloon are performed to minimize the duration of complete obstruction of flow through the valve.
Recent reports of long-term outcome after aortic balloon valvoplasty indicate that there is an excellent early relief of the valvar gradient but an increase in aortic regurgitation. Independent predictors of unfavorable outcome have been a small aortic root, poor function of the left ventricle or mitral valve, and limited experience of the operator. Valvar morphology has recently been demonstrated to relate to valvar function following valvuloplasty, with functionally unicuspid valves and other subtypes with greater leaflet fusion demonstrating better response to balloon dilation. Procedure-related mortality is reported at 4.8% and is highest in critical AS. Although the risk of vascular injury is high, the majority of the complications are transient and respond to thrombolysis and anticoagulation. In critical aortic stenosis, the morphology of the aortic root, the mitral valve and presence of left ventricular endocardial fibroelastosis have a major impact on outcome and need for reintervention. Neonatal critical aortic stenosis remains challenging despite continuing development of catheter technology for small babies. Despite effective relief of stenosis, patients may require functionally univentricular palliation if the morphology is not favorable for effective biventricular circulations or if the ventricular myocardium remains dysfunctional (see also Chapter 44 ).
Implantation of the Aortic Valve.
Percutaneous interventions on the aortic valve in adults with calcific aortic valvar stenosis and other comorbidities rendering the valve inoperable are encouraging. The first report of insertion of bovine pericardial trifoliate valve came from Cribier and colleagues. Procedural complications in early implantations were related to the anterograde approach and the large size of the system required for delivery. The technique has been refined, with development of a retrograde approach, and implantation of the valve with rapid right ventricular pacing to reduce the risk of embolization. Self-expanding stent-mounted valves have also been used in similar clinical settings. However, the current devices available are not yet suitable for routine use in children and young adults, although occasional implants have occurred.
Mitral Valve
Mitral Stenosis.
Congenital mitral valvar stenosis is a complex disease, with involvement of supravalvar, valvar, and subvalvar components (see Chapter 34 ). Balloon dilation is rarely used as first intervention, due to the high risk of restenosis or risk of injury to the valvar tension apparatus and leaflets, leading to severe regurgitation. However, percutaneous valvoplasty has successfully replaced closed and open mitral commissurotomy for rheumatic mitral stenosis. Selection of patients based on echocardiography is fundamental in predicting outcomes and requires a detailed assessment of the mitral valve.
The approach is anterograde after transseptal puncture. The Inoue balloon is most widely used, which consists of a coaxial balloon with a double lumen. Inflation leads to sequential dilation of the distal part, facilitating entry into the left ventricle, of the proximal part fixing the balloon across the mitral valve, and of the central part, which dilates the valvar annulus. A Multitrack technique with a monorail system with two balloons over a single guidewire was introduced by Bonhoeffer and colleagues, permitting successful dilation of the fused leaflets of the mitral valve.
Mitral Regurgitation.
Percutaneous transcatheter interventions on the mitral valve to treat mitral regurgitation have become increasingly commonplace in adults, permitting clipping or suture of the leaflets to produce dual orifices, or by inserting devices within the coronary sinus to improve coaptation of the leaflets. These therapies are not yet routinely used in patients with congenital heart disease (CHD).
Tricuspid Valve
Congenital tricuspid valvar stenosis rarely occurs as an isolated lesion and is most commonly associated with hypoplasia of the components of the right heart. Acquired stenosis in children is almost always due to rheumatic disease and virtually never occurs as an isolated lesion.
Balloon dilation of the stenotic tricuspid valve has been reported in parts of the world with high prevalence of rheumatic fever. The basic principles of the techniques used are similar to those applied for mitral stenosis. The Inoue balloon is most commonly used, albeit that double balloons can be used. In congenital lesions, the associated hypoplasia of the right heart usually takes precedence in making management decisions.
Shunts
Atrial Septal Defects
Interventional catheterization is the first modality of treatment to close defects in the atrial septum when increased pulmonary blood flow has caused dilation of the right heart. The morphology of the defect determines the suitability of the technique, those most suitable being the ones within the oval fossa with adequate margins at the rims. Superior and inferior sinus venosus communications, those defects in the oval fossa with deficient or floppy margins, or large defects encroaching on surrounding structures or resulting in hemodynamic compromise or trauma are the general contraindications and may be better managed by surgical patch closure. Any associated lesions, such as anomalous pulmonary venous drainage, should be ruled out prior to transcatheter closure.
There are many devices available to close the defects, and they vary in their ease of loading and deployment and their suitability for the morphology of the defect, along with safety, efficacy, and long-term behavior. The most commonly used Amplatzer atrial septal occluder (Abbott Medical) consists of two discs of nitinol wire mesh connected by a waist of 4-mm thickness, which forms the central occluding disc ( Fig. 18.6 ). The device is available in different sizes depending upon the diameter of the central disc. The left atrial disc is larger than the central occluding disc by 12 to 16 mm. An Amplatzer Cribriform device (Abbott Medical) is also available for closure of multifenestrated defects. This device has a much narrower waist to position it through one of the central defects, with the left and right atrial discs covering the surrounding holes. This device has been commonly used for closure of the oval fossa, although a new purpose-built device currently exists (Amplatzer PFO Occluder). A Dacron polyester patch is sewn into the device to increase thrombogenicity. The delivery system consists of a loading sheath to help collapse the device and load it into a long delivery sheath attached to a delivery cable. The long sheath is angled at 45 degrees and has varying diameters and lengths. The device is attached to the delivery cable with a screw-on mechanism allowing release of the device after satisfactory deployment. Rates of closure are excellent when patients are selected in appropriate fashion.
The procedure is performed under general or local anesthesia with sedation. Availability of transthoracic, transesophageal, and intracardiac echocardiography has been crucial to the safety and success of the procedure. A catheter passed through the femoral vein is used to position the sheath across the defect. The pulmonary vein is used as the site for anchorage of a stiff guidewire. The defect is sized using echocardiography (to obtain a static measurement of the defect) and frequently also with a contrast-filled balloon inflated carefully across the defect ( Fig. 18.7A ). Care must be taken to avoid stretching the defect. Color flow mapping and occlusion of flow by inflating a balloon, the stop-flow technique, are also used as techniques for sizing. A device of size equal to or just larger than the size of the defect is commonly used. It is delivered through the sheath across the defect under fluoroscopic and echocardiographic guidance, ensuring appropriate deployment, absence of obstruction to contiguous structures, and lack of residual shunting ( Fig. 18.7B ). Successful anchorage is checked by wiggling the device while it is still attached to the delivery system, thus ensuring a secure position. The device can be retrieved and redeployed to the satisfaction of the operator prior to release. Various techniques used to deploy devices in larger defects include the use of specially designed sheaths with a double curve, a sheath positioned in the right upper pulmonary vein, a dilator, or balloon-assisted techniques that prevent prolapse of the left atrial disc across the defect.
Complications of the procedure include trauma leading to tamponade, embolization, thrombosis, endocarditis, and arrhythmias. Important concerns have been raised about cardiac perforations after use of the Amplatzer ASD occluders. However, the risk of erosion has been low, as confirmed by the registry for adverse events in clinical trials in the United States and in other countries. Patients with a deficient aortic rim, and/or a deficient superior rim, of the oval fossa may have a higher risk of erosion. A larger device to static defect diameter ratio may also increase this risk. Those patients who present with a pericardial effusion after Amplatzer device closure should be monitored closely and may require removal of the device with surgical repair of the cardiac erosion along with ASD closure.
The Cardioform septal occluder (W.L. Gore & Associates) is a newer device concept that is now frequently used for percutaneous closure of atrial septal defects. The Cardioform septal occluder is a second-generation device that consists of a platinum-filled nitinol wire frame covered by expanded polytetrafluoroethylene. When deployed, a double-disc configuration is assumed, thereby covering the septal defect. The device, much like the Amplatzer Cribriform device, does not fill or “stent” the atrial septal defect but merely connects the two discs across the defect ( Fig. 18.8A–B ). The Cardioform septal occluder is associated with excellent closure rates and has not been associated with cardiac erosion. This device is delivered via a custom delivery catheter with integrated handle and may cross the defect over a prepositioned stiff exchange length wire over a monorail, or the catheter may be advanced through the defect primarily. A long sheath is seldom used. A next-generation Cardioform ASD occluder is in clinical trial and modifies the existing Cardioform septal occluder design by filling the atrial septal defect with a central expandable polytetrafluoroethylene covered nitinol frame component. This device will theoretically be able to occlude large secundum ASDs, whereas the Cardioform septal occluder is only capable of closing small- and medium-size defects.
Ventricular Septal Defects
The transcatheter approach to closure of VSDs was first described in 1988 where operators used the Rashkind double-umbrella devices. Since that time, a few nitinol-based devices have been developed to close muscular and even perimembranous VSDs. The most commonly used device for transcatheter and hybrid VSD closure is the Amplatzer muscular VSD occluder (Abbott Medical), although various other devices have been used over the years.
Interestingly, although there had been enthusiasm for a self-expanding perimembranous VSD closure device in the early 2000s, implantation of the Amplatzer perimembranous VSD device ( Fig. 18.9 ) in particular was found to be associated with a risk of heart block ranging from 6% to 20%, depending on the series. Since that time the Amplatzer perimembranous device has fallen out of favor, but other approaches to the perimembranous VSD have been reported. Some operators have used an occlusion device designed for the PDA to close those perimembranous VSDs with aneurysmal tissue. In these cases the operators cross the VSD retrograde from the arterial side, advancing a floppy-tipped wire through the VSD and up into the main PA. From the venous side, a snare catheter is then advanced into the main PA and the floppy wire is snared, allowing a catheter and sheath to be advanced across VSD anterograde. Often, transesophageal echocardiography (TEE) guidance can be helpful, especially during deployment of the device. Thereafter the VSD is closed by placing the disc of the PDA occlusion device completely within the aneurysm of the tricuspid septal leaflet. Although this approach is reserved only for those patients who have tricuspid septal leaflet tissue partially covering the defect, the benefit is that the device does not sit astride the anatomic septal defect but rather sits within tricuspid valve tissue on the right ventricular aspect of the defect, hence theoretically removing risk of complete heart block. It should be stated that at the current time, existing devices have failed to prove superior to surgical perimembranous VSD closure.
The principles for closure of muscular defects are similar to those for perimembranous defects. Single muscular defects may be crossed from the right ventricular aspect without the need for an arteriovenous loop, although usually it is easier to cross the defect from the left ventricle as the LV septal surface is less heavily trabeculated and crossing the VSD then is more straightforward. The arteriovenous loop can then be attained as described previously. Again, TEE is usually used to assist with both crossing the VSD, particularly in the setting of multiple muscular VSDs. The Amplatzer muscular VSD device is symmetric, having two discs separated by a waist of 7 mm in length, and the device size ranges from 4 to 18 mm in diameter. Apical defects may be crossed easily from a jugular approach, and mid-muscular and anterior muscular defects may be best closed using a femoral approach. A hybrid periventricular approach to muscular VSD device closure has been used in infants, facilitating off-pump defect closure without the risks associated with percutaneous device delivery. Angiography and echocardiography aid in appropriate positioning of the device ( Fig. 18.10 ).
Hemodynamic assessment is performed to quantitate the shunt and demonstrate a restrictive defect. Angiography in the long axial oblique view usually defines the location and the size of a perimembranous defect. Transesophageal echocardiography, with views between 0 and 30 degrees and longitudinal views between 90 and 120 degrees, are best suited to define the morphology of these defects. The defect is crossed from the left ventricular side with a curved tip catheter and a Glidewire, which is positioned preferably in the main PA. The Glidewire can then be exchanged for a special floppy wire, the so-called noodle wire, which is snared using a goose-neck snare from the femoral vein, and exteriorized to form the arteriovenous loop. The delivery sheath is loaded over this wire and positioned across the defect. When the defect is perimembranous, the sheath may have to be positioned in the left ventricular apex by careful manipulation in tandem with the guidewire and the catheter. The device is deployed under fluoroscopic and echocardiographic guidance. Before and following release, left ventricular angiography and echocardiography help to confirm a good position and secure anchorage ( Fig. 18.11 ). Continuous monitoring of atrioventricular conduction is vital during occlusion of both muscular and perimembranous defects that are adjacent to the conduction system. Persistent complete heart block is an indication either for redeployment or device removal and abandonment of the procedure.
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