Andersons pediatric cardiology 1126

“suicide right ventricle.” Careful attention to anesthesia, the preoperative state of hydration, and use of β-blockade will usually be sufficient to manage the acute right ventricular outflow tract reactivity.95 Residual right ventricular subvalvar narrowing will usually settle over time If the procedure is successful in terms of right ventricular pressure and transvalvar gradient, then a right ventricular angiogram is usually obtained The investigations prior to discharge are completed with echocardiography to assess the degree of pulmonary incompetence and the integrity of the tricuspid valve Outside of the neonatal period, it is usually possible to perform these procedures as day cases Patients with dysplastic pulmonary valves, in particular those with Noonan syndrome, are more likely to retain a significant residual gradient after balloon pulmonary valvuloplasty Whereas in the past these patients were often referred for surgical therapy, the availability of transcatheter pulmonary valve implantation has provided an additional treatment alternative that should be considered in selected patients.68 Severe or Critical Neonatal Pulmonary Stenosis The presentation and management of critical pulmonary stenosis in the neonatal period deserves special discussion (see Fig 42.33) Infants may present in a critically ill state, with cyanosis as a result of right-to-left shunting across the atrial septum and being dependent on patency of the arterial duct for survival The efficacy of balloon dilation of the pulmonary valve depends not just on the result of the valvotomy but also on the size and compliance of the right ventricle, tricuspid valve, and the ventriculoarterial junction.96 Thus the size of the structures in the right heart must be evaluated as part of the management In this context, critical pulmonary valve stenosis is somewhat similar to pulmonary atresia with intact ventricular septum, even though the chances of requiring reintervention are higher in patients with pulmonary atresia and intact ventricular septum than in those with critical pulmonary valve stenosis.97–99 Relative hypoplasia of the right heart structures itself is not a contraindication for balloon dilation of the pulmonary valve; indeed, follow-up studies have shown that the rate of growth of the right heart can exceed the rate of somatic growth after successful balloon dilation.96,100,101 Immediately following balloon dilation, despite adequate opening of the pulmonary valve, it may still be difficult to separate infants from infusions of prostaglandin This is most likely a result of hypertrophy and diastolic dysfunction of the right ventricle, favoring a cyanotic shunt across the atrial septum Persistent hypoxemia may settle over a few days as the right ventricle recovers Should hypoxemia persist, it may be necessary to establish an alternative source of supply of blood to the lungs, such as a systemic-to-pulmonary arterial shunt or stenting of the arterial duct A detailed analysis of the morphology of the right heart structures may help predict whether an alternative source of such flow is going to be required, even though firm predictions are difficult in most patients A diameter of the tricuspid valvar orifice of greater than 11 mm, right ventricular volumes of greater than 30 mL/m2, and dimension of the pulmonary valve of greater than 7 mm appear to stratify patients who are less likely to require an intervention to increase pulmonary flow.102 Further details are discussed in Chapter 43 (pulmonary atresia with intact ventricular septum) From a technical standpoint, keeping the wire positioned across the pulmonary valve until it is decided whether upsizing of the balloon is required is important in these patients The right ventricular outflow tract in neonates is very sensitive and often catheter manipulation can lead to a further increase in subpulmonary narrowing that is often temporarily present in these patients If wire position is lost, attempts at recrossing the right ventricular outflow tract can be difficult and associated with arrhythmias and hemodynamic instability For the same reason, in patients with marked infundibular narrowing after balloon pulmonic valvuloplasty (see Fig 42.33), commencing the patient on propranolol for a short period of time may be beneficial Fetal Balloon Pulmonary Valvuloplasty Fetal pulmonary balloon valvuloplasty has been performed in selected patients with pulmonary atresia and intact ventricular septum in the hope to aid right ventricular growth and development, thus allowing patients to progress postnatally through a biventricular pathway.36,103,104 At this stage, however, interventions are not yet performed for severely stenotic valves (rather than pulmonary atresia) In this context some studies have attempted to identify fetal parameters that may predict a nonbiventricular versus a biventricular outcome, which include a tricuspid/mitral valve ratio below 0.7, right/left ventricular length ratio less than 0.6, tricuspid valve inflow duration below 31.5% of cardiac cycle length, and the presence of sinusoids in the right ventricle.105 A study by Kawazu and colleagues used a tricuspid valve diameter to total cardiac dimension ratio of greater than 0.21 as a cutoff for ultimate biventricular repair.106 All these parameters may be helpful in selecting the appropriate patients for fetal intervention However, overall results of fetal interventions do not yet support widespread adoption of the technique, and at this stage the technique should be employed only by a limited number of centers in selected patients as part of a research protocol.103 Multiple Balloon Techniques Using the recommended sizing of balloons of 120% to 125% of the dimension of the pulmonary valve, it is clear that large balloons will be required for adolescents and adults Such balloons may be difficult to source, and the frequency of use might make it impracticable to keep these items in stock in the pediatric catheterization laboratory Furthermore, in the past, the maximum inflation pressure of larger balloons was limited, and an advantage of using two smaller balloons was the ability to obtain higher inflation pressures when needed Techniques using an additional balloon angioplasty catheter through an additional venous puncture and over an additional guidewire have been reported (Fig 42.34; Videos 42.6 and 42.7).71,107–109 The effective dimension of the double-balloon technique is calculated thus110: ... Such balloons may be difficult to source, and the frequency of use might make it impracticable to keep these items in stock in the pediatric catheterization laboratory Furthermore, in the past, the maximum inflation pressure of larger balloons was limited, and an advantage of using two