Interventional cardiac catheterisation describes procedures where cardiac catheters are used to modify, palliate, or treat congenital or acquired cardiac disease. Evolution of interventional techniques has been a natural progression from 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 in order to achieve results comparable with surgical techniques. Although the aim is to do something to alter the course of disease the basics of interventional catheterisation are drawn from experience with diagnostic cardiac catheterisation. Not all interventional catheterisation techniques are therapeutic. Some do no more than modify the course of the disease, or help delay future interventional or surgical procedures. The design and organisation of the catheterisation laboratory, personnel, use of equipment, catheters and techniques are a progression of the exercise of gathering of information related to diagnostic catheterisation and angiography. In sick neonates, infants, and children, however, any catheterisation is 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 catheterisation outlined by Werner Forssman in 1929. The use of interventional catheterisation was first initiated by the use of balloon dilation in pulmonary and tricuspid valvoplasty, 1 and in dilation of atherosclerotic lesions. 2 It was Rashkind and his colleagues who widened the therapeutic implications of interventional catheterisation with the first intracardiac procedure in paediatrics and congenital cardiac disease when they introduced balloon atrial septostomy. 2,3 The use of occlusive devices was first reported by Porstmann and his colleagues in 1967, when a patent arterial duct was occluded with the aid of an Ivalon plug. 4 Attempts were then made to close left-to-right shunts with other devices, such as an atrial septal occluder for atrial septal defects, 5 and the double umbrella device for the persistently patent arterial duct and atrial septal defects. 6 The application of percutaneous transluminal balloon angioplasty by Gruntzig and Hoppf in 1974 7 was a landmark that expanded the field of interventional cardiology to the situation where it became recognised as a subspecialty in its own right. The principles of percutaneous transluminal balloon angioplasty were first applied by Lock and his colleagues 8–11 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, 12 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 stenosed pulmonary and aortic valves. The development of balloon-expandable stents has helped overcome problems of residual stenosis and restenosis in vessel walls. 13 The development of newer materials, such as Nitinol, a nickel-titanium alloy, has revolutionised technology, and expanded its use in closure of left-to-right shunts. 14–16 The use of this shape-memory alloy has simplified the delivery and retrieval of these devices by significantly reducing the size of the catheters 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 defects. Transcatheter insertion of valves is the most recent development in the field of interventional catheterisation. 17 Percutaneous implantation of biological 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. 18–22 Transcatheter techniques for repair of the mitral valve, based on surgical principles such as the creation of dual orifices and annuloplasty, are also being actively investigated in the clinical setting. 23,24 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. 25–28
PRINCIPLES OF CATHETERISATION
The field of interventional catheterisation 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. The basic tenets of interventional catheterisation, however, are likely to remain constant, and have already stood the test of time over the last few decades. The success of an interventional catheterisation 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.
Pre-procedural Planning
Consent should ideally be obtained either during outpatient consultation, or in a dedicated pre-admission clinic that provides parents the opportunity to discuss relevant issues. 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 senior 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. As it is difficult to approach parents during catheterisation 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. 29
The planning of an interventional catheterisation procedure cannot be over-emphasised. 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 decision made for the procedure. 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 anaesthetist and, if applicable, the cardiac surgeon, in order to maximise the information leading to the procedure. An approach based on consensus also adds to the safety and efficacy of the decision-making process, as individuals with different areas of expertise contribute in a complementary manner, maximising the benefit to every patient. Use of additional cross sectional imaging, such as three-dimensional echocardiography, magnetic resonance imaging, or computerised 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 catheterisation. Decisions regarding access, via the femoral, jugular, or bilateral jugular 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 step-wise manner with the fellow in training, scrub nurse, cardiac physiologist, anaesthetist, radiographer, and all 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 catheterisation is performed. Femoral, internal jugular, subclavian, axillary 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. Repeated catheterisation, prolonged periods in intensive care, and multiple operations for complex staged palliative procedures can make access difficult due to repeated use of the vessels. Ultrasonically guided access allows for visualisation of vessels, detects unusual arrangements, thrombosed veins and arteries, and also reduces the risk of inadvertent puncture. Stenosis or atresia with luminal continuity of systemic veins may have to be dealt with by crossing the site with a floppy-tipped guide-wire, and use of long sheaths, which go 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. 30,31 In neonates and small infants, the availability of small catheters and sheaths, of 3 and 4 French sizes, have facilitated procedures, and reduced the risk of vascular injury. 32
Catheters and Guide-Wires
In infants and children, angled and curved tipped catheters are most commonly used in situations where catheters need to be manoeuvred 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, Medi-tech, or Boston Scientific products, track well over guide-wires into difficult sites. Balloon-tipped catheters, such as the Berman angiographic catheter, or the Arrow balloon wedge catheter, are useful for wedge injections, or to cross atrioventricular valves without entrapment in the intercordal spaces. Catheters of short length help 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.
Guide-wires are used to access vessels, stabilise 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 (Bloomington, IN), is usually required to obtain multiple haemodynamic measurements, provide stability across a lesion, for multiple crossings after interventions, to perform angiography, and to mount balloon catheters, stents, or large sheaths.
Anti-coagulation
Heparin is used as an anti-coagulant during cardiac catheterisation to prevent thromboembolism during and after the procedure. Some operators monitor heparin 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. 33
For short procedures, a single dose of 50 units per kilogram body weight is administered after vascular access is obtained. For long procedures, between 100 and 200 units per kilogram 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. Protamine may be used to reverse the effect of heparin should there be persistent bleeding from the site of access.
INTERVENTIONAL CATHETERISATION 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 co-axial balloons has reduced the time required for inflation and deflation, with only transient haemodynamic 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 non-contiguous normal anatomical structures. The use of an over-sized balloon increases the chance of a successful dilation of the lesion, but also increases the risk of trauma to contiguous anatomical 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 effective valvar orificial area. The principle of creating a controlled tear or split along the zone of apposition, thus improving excursion of the leaflets, provides a better effective orificial area, and relieves the stenosis. As 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 valvoplasty for different diseases. The technique, however, is not useful in treating valves that are hypoplastic because of narrowing at the ventriculo-arterial junction. Dilation of arterial 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 valvoplasty also forms the basis for angioplasty and implantation of stents. High-pressure balloons have been more recently used in dilating tight lesions, such as calcified conduits or pulmonary arterial stenosis. 34,35 Cutting balloons have been used in substrates which do not respond to standard balloon angioplasty, such as severe pulmonary arterial stenosis or recurrent pulmonary venous stenosis, with encouraging results. 36 Balloon-in-balloon catheters, known as BIB, and produced by NuMed (Hopkinton, NY), have been very useful in implanting stents in the aorta and pulmonary arteries. 37 The inner balloon is an additional tool to help confirm the position before deployment of the stent. The use of two balloons inserted over a single guide-wire for valvoplasty was first introduced for dilation of the mitral valve. 38 It provides a large effective diameter of the combined balloons, and has been used in pulmonary valvoplasty in adults who have a large diameter of the pulmonary outflow tracts. 39 Stability of the balloon during inflation depends on choice of a balloon of correct length and diameter, appropriate selection of a stiff guide-wire, obtaining a good position for the guide-wire, 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 for lesions in the systemic circulation. In balloon valvoplasty, the size of the balloon is chosen based on the size of the valve measured. In pulmonary valvoplasty, the balloon size is usually one-fifth to one-quarter larger than the measured diameter of the valve at the basal hinge points of the leaflets. In aortic valvoplasty, the size is usually nine-tenths of the diameter at the hinges of the leaflets. Size for dilating the coarcted aorta equals the diameter of the proximal transverse arch, or a size is chosen not greater than three times the size 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, and not too long to cause trauma to the proximal or distal structures. The size of the patient should be taken into consideration in choosing the correct balloon. Balloons are filled with contrast medium diluted 1 in 5 with saline, 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, haemodynamics and angiography should be repeated to evaluate results and assess complications. Further evaluation by echocardiography 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 and covered by a sheath. Self-expanding stents are used in patients who have already achieved their potential for growth. Balloon-expandable stents can be redilated within limits, and may be used in children. The design of the cells may be open, avoiding jailing or covering of neighbouring arterial branches, or closed. The properties of materials considered favourable for use in congenital cardiology are those with a low profile, good 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 the adult. In small infants, however, a coronary arterial stent may be used in extenuating circumstances of severe haemodynamic compromise, despite its limited final maximal diameter. Stents are implanted using balloons of appropriate size through long, large-bored, sheaths to reach the lesion. Stents may be pre-mounted 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 longer than the length of the stent. The diameter of the balloon determines the final diameter of the stent. Stability of the stent during deployment can be improved by using the balloon-in-balloon catheters, extra-stiff wires, long sheaths, and rapid right ventricular pacing to reduce stroke volume. 40 The luminal surface of the stent endothelialises in 8 to 10 weeks, and patients may need to take anti-platelet agents or, in some situations, anti-coagulants during this period to prevent in-stent restenosis.
Risks associated with stent angioplasty include dislodgement and embolisation, trauma to the vessel walls, fracture of the stent, and restenosis. Covered stents made by suturing expanded polytetrafluoroethylene 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. The use of these covered stents in younger patients is limited by their size, and the calibre of the delivery systems currently available. Newer bioabsorbable stents are currently being investigated to reduce restenosis in coronary arterial lesions. If approved, these stents could prove useful in treating stenosis of small vessels in infants, albeit temporarily, thus allowing for normal growth. 41
Closure of Septal Defects and Vascular Occlusion
The advent of shape-memory alloy has revolutionised transcatheter interventions for intra- 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, produced by Amplatz at AGA Medical, has a central occluding part, with left- and right-sided discs. A Dacron polyester patch sewn into the device is responsible for thrombogenicity and complete occlusion. Sizing of a septal defect is performed by trans-oesophageal or intracardiac echocardiography, or by inflating a balloon during the procedure. Reported complications of such devices eroding through the atrial or aortic walls, and devices designed to occlude ventricular septal defects causing complete heart block, emphasise the importance of choosing a device of appropriate size. Various practices from over-sizing, to reduce the risk of embolisation, 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 stenosis was made by Kan and her colleagues in 1982. 12 Since then, the technique has been accepted as a first-line treatment for congenital valvar pulmonary stenosis. 42–45 Balloon dilation is usually indicated when the gradient across the stenosed valve is 50 mm Hg or more, or when there is an increase in right ventricular systolic pressure by more than half of the systemic pressure. The indications for the procedure are, however, different in neonates with a duct-dependent pulmonary circulation, when gradients are unreliable. A high right ventricular systolic pressure, and the presence of a dysplastic valve, is an accepted indication for treatment.
The right ventricular pressure is measured, following which right ventricular angiography is performed in the lateral projection in order to measure the diameter of the ventriculo-arterial junction at the basal attachment of the valvar leaflets. The stenotic pulmonary valve is crossed using an end-hole catheter, such as a multi-purpose catheter, a cobra-shaped catheter, or a Judkins right coronary arterial catheter. A guide-wire, from 0.014 to 0.035 inch in diameter, is passed through the catheter across the valve, and placed in a branch of the pulmonary artery supplying the lower lobe of either lung. In neonates, the guide-wire may be placed across the patent arterial duct into the descending aorta. A balloon that is about one-fifth to one-quarter larger than the diameter of the measured valve is passed through the sheath in the femoral vein over the wire, and placed across the pulmonary valve. The balloon is rapidly inflated and deflated with dilute contrast across the stenosis. The balloon is then withdrawn, with the guide-wire still in place, and a catheter is passed into the pulmonary arteries to measure the persisting gradient. The Multitrack catheter designed by Bonhoeffer is very useful, as 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 guide-wire. In patients with a very dysplastic pulmonary valve, balloons that are up to three-fifths larger than the diameter of the supporting subpulmonary infundibulum can be used, with acceptable relief of the stenosis. The technique of balloon dilation is more demanding in neonates. Although balloon dilation of pulmonary valvar stenosis carries low risks when performed in infants and children over the age of 1 year, there is a significant morbidity and mortality in the early neonatal period. 46–48 In neonates, it is the size and function of the right ventricle that determine outcome. High right ventricular pressure, an irritable myocardium with a risk of arrhythmia, and splinting of the tricuspid valve, can all lead to haemodynamic instability. This necessitates very short periods of inflation, which may be helped by using balloons with low profile.
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. 49 Occasionally, however, there may be very little immediate reduction in gradient across the pulmonary valve. This is because of associated 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. Serious complications of balloon dilation include a tear of the pulmonary trunk, or perforation of the heart. 50,51 In general, the complication rate, at 0.4%, is low, and reported mortality is no more than 0.2%. 52 The consequences of chronic pulmonary regurgitation, nonetheless, can be underestimated, and more conservative dilation is now recommended.
Balloon dilation of the pulmonary valve can also be carried out as a palliative procedure in patients with tetralogy of Fallot and other complex congenital cardiac malformations. It can also be performed in patients with a functionally univentricular circulation to 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 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, and to reduce the risk of pulmonary regurgitation. Reports have also emerged for dilation for infundibular stenosis using balloons, as palliative procedures, although without consistently desired results.
Valvar Pulmonary Atresia with Intact Ventricular Septum
The transcatheter interventions available to alter the course of this lesion (see also Chapter 30 ) include relief of right ventricular outflow obstruction with perforation of the atretic valve and balloon dilation, stenting of the arterial duct to provide additional flow of blood to the lungs, enlargement of the atrial communication by balloon atrial septostomy to reduce right atrial hypertension, and occasionally, stenting of the subvalvar muscular right ventricular outflow tract in the setting of residual obstruction.
The success of interventional catheterisation, as determined by achieving a biventricular circulation, depends upon specific morphological characteristics. Patients should have a right ventricle with a tripartite cavity, a tricuspid valve with a diameter greater than 10 mm, or z score more than −1.5, a pulmonary valvar and infundibular diameter more than 7 mm, and absence of right ventricular-dependent coronary arterial circulation. 53
The principles of catheterisation involve appropriate selection of patients, maintaining haemodynamic stability with ventilation, maintaining patency of the arterial duct with infusion of prostaglandins, careful catheterisation to avoid cardiac trauma or excessive bleeding through the catheter lumen, selection of the appropriate technique to perforate the atretic pulmonary valve, continuous monitoring of systemic arterial pressure, and anticipation and prompt management of pericardial tamponade by pericardiocentesis.
Antero-posterior and lateral projections of right and left ventricular angiography help confirm the absence of right ventricle-dependent coronary arterial circulation, delineate the right ventricular outflow and the pulmonary arterial end of the atretic valve, assess the left ventricle, and determine the morphology of the aorta and the arterial duct. Appropriate frames from the angiograms are fixed as reference images after identifying landmarks for perforation. An end-hole catheter with a curved tip, typically either cobra shaped or a Judkins right 3.5-cm curve, is used to achieve stable and precise position of the tip of the catheter in the right ventricular infundibulum, just beneath the atretic pulmonary valve. Clockwise rotation of the catheter hooks it around the ventriculo-infundibular fold, and directs the tip towards the right ventricular outflow tract. After pushing the catheter tip into the infundibulum, a counter-clockwise rotation engages it in most cases against the atretic pulmonary valve. Multiple angiograms should be performed to confirm the position of the tip of the catheter, which will determine the site of perforation ( Fig. 17-1 A). By attaching a Tuohy-Borst Y connector to the hub of the catheter, biplane angiography can be performed with or without simultaneous aortography, thus delineating the right ventricular and pulmonary arterial surfaces of the atretic pulmonary valve ( Fig. 17-1 B). Once the position of the tip of the catheter against the atretic valve is satisfactory and stable, a radio-frequency wire connected to a generator is inserted into the guiding catheter. A commercially available radio-frequency perforation generator with a perforation catheter and co-axial injectable catheter, produced by the Bayliss Medical Company, is now available, and is most commonly used. This system is designed for tissue perforation and uses high voltage at 150 to 280 volts, with low power at 5 to 10 watts, to reach very high impedance, up to 7000 ohms, for short durations of application, from 1 to 5 seconds. An earthing plate is required, and should be placed under the buttocks before draping the patient. Care should be taken to avoid pooling of the antiseptic over this plate when the groin or umbilicus is prepared for access. A wire of 0.024-inch diameter, and 260-cm length, can be connected to a customised radio-frequency generator, which cuts off if the impedance exceeds the specified range. The wire has an exposed metal tip of 2 mm that is responsible for generating the thermal energy needed for the perforation. Rest of the wire is covered with Teflon. Repeated angiography should always be performed to confirm that the position of the catheter has not changed during loading of the perforating wire. The stiff-end of a coronary arterial wire, or a fibre-optic wire such as a 0.018- or 0.021-inch trimedyne wire connected to a Nd Yag or Excimer laser generator, may be used in place of the radio-frequency wire. After confirming the final position, perforation of the atretic pulmonary valve is carried out, taking extreme caution to prevent injury to the pulmonary trunk. 53–58 The position of the radio-frequency wire beyond the perforated valve should again be confirmed before proceeding further. The position of the tip of the wire within the cardiac silhouette on both antero-posterior and lateral projections should raise suspicion of cardiac perforation suggesting that wire is in the pericardial space. In these circumstances, the wire should be promptly withdrawn and systemic arterial pressure should be monitored. If necessary, an echocardiogram should be performed to rule out cardiac tamponade. The hole made by the radio-frequency wire is usually very small, and unlikely to cause significant bleeding into the pericardial space. Once the atretic valve is successfully crossed, a fine catheter that can go over the wire is used, creating a co-axial system allowing for graded dilation of the pulmonary valve ( Fig. 17-2 ). Various balloons are available to dilate the pulmonary valve. Pre-dilation with a small coronary arterial balloon of 2.5- to 4-mm diameter allows a larger balloon, of 7- to 10-mm diameter and 2-cm length, to be used effectively ( Fig. 17-2 C). An echocardiogram should be performed soon after the procedure to confirm adequate relief of right ventricular outflow obstruction. Pericardial effusion, if present, should be monitored closely after the procedure with invasive systemic arterial pressure monitoring and frequent echocardiography.
If adequate relief of obstruction has been achieved, the infusion of prostaglandin could be stopped to prevent the complications of systemic arterial steal from a large patent arterial duct. It is not, however, unusual to need prostaglandin for a few days to maintain adequate flow of blood to the lungs until right ventricular diastolic function improves, and there is effective antegrade flow across the right ventricular outflow tract. If weaning from prostaglandin fails to maintain systemic arterial saturations within an acceptable range, ductal stenting can be undertaken to provide additional pulmonary blood flow. 59 Ductal stents have a high risk of restenosis with intimal proliferation, and need close monitoring and anti-platelet therapy. Presence of infundibular muscle may contribute to dynamic obstruction after adequate relief of valvar stenosis. If severe, implantation of a stent into the outflow tract may also produce successful relief of obstruction. 60 In less severe situations, chronic treatment with oral β-blockade has been effective in providing adequate relief until regression of the muscular hypertrophy improves forward flow into the pulmonary arteries. During late follow-up, if despite an effective biventricular circulation, systemic arterial desaturation is observed due to right-to-left shunting, devices can be inserted to occlude the interatrial communication. 61
Implantation of Pulmonary Valves
Bonhoeffer and his colleagues 62 described the first implantation of a valve in the pulmonary position, placing the device through a catheter in a dysfunctional prosthetic conduit to relieve stenosis and regurgitation. The Medtronic Melody valve was made of a bovine jugular vein sutured inside a balloon-expandable platinum-iridium stent, and was deployed using a custom-made system, now known as Ensemble, and produced by Medtronic Inc. The system contains a balloon-in-balloon catheter inside a long sheath with a dilator at the tip. Current systems have outer balloons of 18-, 20-, and 22-mm diameter. These balloons determine the final diameter of the implanted valved-stent, which should equal the diameter of the homograft conduit initially inserted surgically in the right ventricular outflow tract. The valve is suitable for insertion in right ventricular outflow tracts with diameters varying between 16 to 22 mm in patients with circumferential-valved conduits implanted surgically during their definitive repair. 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 fractions, and quantify the pulmonary regurgitant fraction. Echocardiography is used for surveillance and haemodynamic monitoring.
The procedure is performed under general anaesthesia. A balloon-tipped or curved-tip catheter is inserted through the femoral or jugular vein to access the distal left or right pulmonary artery with the aid of a floppy tipped Terumo wire. An Ultrastiff guide-wire, of 0.035-inch diameter and 260-cm length, with a pre-formed curve, is then positioned in one of the pulmonary arteries. A Multitrack catheter is passed over this stiff wire to measure right ventricular pressure, the gradient across the right ventricular outflow tract, and to perform angiography ( Fig. 17-3 A). Different projections are employed to define the morphology of the outflow tract, the bifurcation of the pulmonary arteries, and to assess the pulmonary regurgitation. Aortography performed through a pigtail catheter inserted into the femoral artery helps define the coronary arterial anatomy. If an anomalous course of a coronary artery is suspected, a selective injection into the artery, with simultaneous inflation of a balloon in the right ventricular outflow tract, is performed to rule out arterial compression. Once the outflow tract is deemed suitable for implantation, the valved-stent is washed in three different saline baths for 5 minutes each to wash off the glutaraldehyde preservative. The venepuncture is dilated in a graded fashion with 14 and 22 French dilators. The delivery system is thoroughly flushed, de-aired, and the inner and outer balloons prepared with syringes filled with diluted contrast, 10 mL for the inner balloon, and 20 ml for the outer balloon. The valved-stent is crimped on a 2.5-mL syringe by a gentle rolling action, and loaded on the balloon catheter. The outer sheath of the delivery system is brought gently over the crimped valved-stent, ensuring complete covering of the proximal struts. The sheath is then slid over the entire length of the valved-stent, which is fully covered and ready to be inserted. The tip of the delivery system has a dilator, which provides a tapered tip to facilitate entry into the vein through the skin. The flexible delivery system can be looped in the right atrium to facilitate delivery of the valved-stent into an appropriate position. Standard principles of manipulation ensure delivery of the device in the right ventricular outflow tract without losing position of the wire. In patients with severe calcification and stenosis, pre-dilation with a high-pressure balloon, or pre-stenting with a bare metal stent, such as the Max LD, Intrastent, or Cheatham-Platinum stent, may be required. Once within the conduit, the valved-stent is uncovered by pulling back on the outer sheath. Angiography confirms satisfactory position of the valved-stent ( Fig. 17-3 B). Calcification of the conduit, or the bare stent itself, usually provides good landmarks for optimal positioning. The valve is deployed by sequentially inflating the inner and outer balloons. Haemodynamic assessment and angiography is then performed using the Multitrack catheter after implantation. In patients with a significant residual gradient, post-dilation with a high-pressure balloon may be required, using pressures of 10 to 12 atmospheres.
Implantation has now been carried out for dysfunction of the right ventricular outflow tract in patients with repaired tetralogy of Fallot and variants, transposed arterial trunks with ventricular septal defect and pulmonary stenosis, the Ross operation for left ventricular outflow disease, and repaired common arterial trunk. 19 The majority of the patients had a homograft in the right ventricular outflow tract. 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. 19 The incidence of complications decreased with subsequent implantations as a result of improvements in selection of patients and design of the device. Restenosis due to a hammock effect created by the venous wall hanging within the stent was not observed after these alterations in design. 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. 63
Adults who have undergone repair of the right ventricular outflow tract without use of a conduit, but have suffered aneurysmal dilation, are not suitable for implantation of the current device. Future research to design a device that can be implanted in larger right ventricular outflow tracts, more than 22 mm in diameter, is ongoing. Self-expanding stents designed to reduce the size of the dilated aneurysmal right ventricular outflow tract can hold the valved-stent within it to provide a secure anchoring mechanism. 64 These devices are likely to be most suited to treat isolated pulmonary regurgitation in dilated outflow tracts.
Aortic Valve
Aortic Stenosis
Balloon dilation of the aortic valve was first reported by Lababidi. 65 Currently accepted indications for intervention include the presence of a peak gradient greater than 70 mm Hg on Doppler with a left ventricular strain pattern on the electrocardiogram and symptoms such as syncope, effort intolerance, or angina. Neonatal indications for intervention are based on the presence of a duct-dependent systemic circulation, a low cardiac output state with severe left ventricular dysfunction, and a dysplastic stenotic aortic valve. Asymptomatic infants with congenital valvar aortic stenosis are treated for gradients greater than 50 mm Hg in the absence of a duct-dependent systemic circulation due to the risk of progression of the stenosis and development of left ventricular dysfunction. Since the original documentation, good results of balloon dilation of the aortic valve have been reported in both the short and medium term. 66–68 There was some concern regarding femoral arterial occlusion, but this complication is less frequently seen now with the availability of low-profile balloons.
Parameters given consideration prior to the procedure, particularly in sick neonates with a low cardiac output, include achieving access, maintaining haemodynamic stability, ensuring hydration, adequate control of glycaemia and acid-base balance, ventilation, infusion of prostaglandin to maintain ductal patency, and appropriate cardiovascular drugs to maintain cardiac output. In infants and children, the procedure is performed under general anaesthesia. Heparin is used for anti-coagulation 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 haemodynamic compromise. The procedure can be performed through femoral arterial, femoral venous, umbilical arterial, axillary or carotid arterial access. 31,67,69–71 The advent of rapid right ventricular pacing has reduced the need for an anterograde approach with trans-septal puncture with atrial septostomy. Femoral arterial puncture is used for monitoring of systemic arterial pressure when dilation is carried out anterograde through the femoral vein.
In haemodynamically stable patients, an angiogram is performed in the ascending aorta via a pigtail catheter profiled in antero-posterior and lateral projections. The aortic valvar leaflets are delineated, and the diameter of the ventriculo-arterial junction is measured and compared with those obtained on echocardiography, to avoid the risk of using an oversized balloon. Severe angulation of the left ventricular outflow tract can complicate accurate measurement of the valvar diameter. In haemodynamically unstable patients, angiography poses a risk of severe ventricular arrhythmia in the presence of left ventricular dysfunction. Hence, the diameter of the aortic valve as measured by echocardiography alone is used to determine the appropriate diameter of the balloon. Small sheaths, and catheters of 3 French diameter, are employed when using umbilical access in neonates, and 4 or 5 French catheters with angled-tip guide-wires are used in older children. A ratio of the diameter of the balloon to the outflow tract of 0.9 indicates an appropriately selected balloon, and is unlikely to cause significant regurgitation. An angiogram 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 catheter, such as a Judkins right coronary catheter, a cobra-shaped catheter, or a cut-pigtail to provide a curved tip, and a floppy steerable guide-wire. Multiple rapid gentle stabs are made with the guide-wire to cross the valve. This step reduces the risk of perforating the valvar leaflets and traumatising the orifices of the coronary arteries.
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 manoeuvered 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 trans-septal 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 towards 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 adenosine, and more commonly, rapid right ventricular apical pacing in older patients at fast rates of 180 to 220 beats per minute ( Fig. 17-4 ). 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 haemodynamic compromise and cardiac trauma ( Fig. 17-5 ). It is prudent to use a long balloon of 3.5 to 5 cm in older patients, as the left ventricle has a tendency to eject the balloon subsequent to inflation. Rapid inflation and deflation of the balloon are performed to minimise 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. 72 Independent predictors of unfavourable outcome have been a small aortic root, a valve with two leaflets, poor function of the left ventricle or mitral valve, and limited experience of the operator. 73 Procedure related mortality is reported at 4.8%. 73 Although the risk of vascular injury is high, the majority of the complications are transient, and respond to thrombolysis and anti-coagulation. In critical aortic stenosis, the morphology of the aortic root, the mitral valve and presence of left ventricular endocardial fibro-elastosis 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 favourable for effective biventricular circulations (see also Chapter 44 ).
Implantation of the Aortic Valve
Percutaneous interventions on the aortic valve in adults with calcific aortic valvar stenosis and other co-morbidities rendering the valve inoperable are encouraging. The first report of insertion of bovine pericardial trifoliate valve came from Cribier and his colleagues. 74 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 embolisation. 20 Self-expanding stent-mounted valves have also been used in similar clinical settings. 75 The current devices available, however, are not yet suitable for use in children and young adults.
Mitral Valve
Mitral Stenosis
Congenital mitral valvar stenosis is a complex disease, with involvement of supravalvar, valvar and subvalvar components (see Chapter 35 ). 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. Percutaneous valvoplasty, however, has successfully replaced closed and open mitral commisurotomy for rheumatic mitral stenosis. Selection of patients based on echocardiography is fundamental in predicting outcomes, and requires a detailed assessment of the mitral valve. 76
The approach is anterograde after trans-septal 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 guide-wire was introduced by Bonhoeffer and colleagues, 38 permitting successful dilation of the fused leaflets of the mitral valve.
Mitral Regurgitation
Percutaneous transcatheter interventions on the mitral valve to treat mitral regurgitation are being investigated 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. 23,24
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 catheterisation 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 haemodynamic compromise or trauma, are the general contraindications. Any associated lesions, such as anomalous pulmonary venous drainage, should be ruled out.
There are many devices available to close the defects, and they vary in their ease of loading and deployment, their suitability for the morphology of the defect, along with safety, efficacy and long-term behaviour. The most commonly used Amplatzer atrial septal occluder consists of two discs of Nitinol wire mesh connected by a waist of 4 mm thickness, which forms the central occluding disc ( Fig. 17-6 ). 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. A new Cribriform device is now available for closure of multi-fenestrated 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. 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 anaesthesia with sedation. Availability of trans-thoracic, trans-oesophageal, 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 guide-wire. Initially, complications of embolisation led operators to use large devices. The defect is sized using pulmonary arterial angiography, echocardiography, or with a contrast-filled balloon stretched across the defect ( Fig. 17-7 A). Care must be taken to avoid stretching the defect. 77 Colour 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. 17-7 B). Successful anchorage is checked by wiggling the device whilst 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, embolisation, thrombosis, endocarditis, and arrhythmias. Recently, concerns have been raised about late cardiac perforations after use of the Amplatz occluders. 78,79 The risk of erosion, however, has been low, as confirmed by the registry for adverse events in clinical trials in the United States of America and in other countries. 77 Patients with a deficient aortic rim, and/or a deficient superior rim, of the oval fossa may have a higher risk of erosion. Those patients who present with a pericardial effusion within 24 hours should be monitored closely, and may require removal of the device surgically should there be an increase in the effusion.
Other devices available to close atrial septal defects include the CardioSEAL and STARflex devices, based on the double umbrella design, and with struts made from a cobalt alloy. 80 The Helex device is a new concept with a helical arrangement of a long Nitinol wire to which is attached a long curtain of expanded polytetrafluoroethylene. 81 When deployed, two circular discs form at each end of a flat helix, the curtain covering the septal defect. By pulling on the suture connecting the right atrial disc to the inner catheter of the delivery system, the whole device uncoils from its circular shape, and can be retrieved even after deployment into the delivery system ( Fig. 17-8 ). A button device, and more recently, a frameless occlusion device, have also been described for use in defects without adequate rims. 82
