398 SECTION IV Pediatric Critical Care Cardiovascular patients In addition, the left AV valve may be severely regurgi tant 162 Inotropic support for the failing heart, afterload reduction for mitral r[.]
398 S E C T I O N I V Pediatric Critical Care: Cardiovascular patients In addition, the left AV valve may be severely regurgitant.162 Inotropic support for the failing heart, afterload reduction for mitral regurgitation, and measures to decrease PVR may be required perioperatively Patients with trisomy 21 frequently have an associated complete AV canal Measures to decrease PVR and the use of prolonged ventilatory support are often necessary because of their tendency toward upper airway obstruction, sleep-disordered breathing, and abnormal pulmonary vascular reactivity The large tongue, hypotonia, upper airway obstruction, and difficult vascular access of these patients pose additional problems The most frequent postoperative problems in patients with trisomy 21 are residual VSDs, left AV valve insufficiency, and pulmonary hypertension.163 Truncus Arteriosus Communis Pathophysiology With truncus arteriosus communis, the embryonic truncus fails to septate normally into the two great arteries A single great artery leaves the heart and gives rise to the coronary, pulmonary, and systemic arteries The truncus straddles a large VSD and receives blood from both ventricles Complete mixing of systemic and pulmonary venous blood in the single great artery causes mild hypoxemia Both pulmonary arteries usually originate from the ascending truncus, but occasionally only a single PA originates from the common trunk; the pulmonary artery orifice is seldom restrictive The resulting shunt (simple) produces excessive pulmonary blood flow early in life as the PVR decreases This pulmonary steal may decrease the systemic blood flow; however, the presence of two functional ventricles often prevents as significant a clinical manifestation as in patients with true single ventricle Patients with truncus arteriosus may have anatomically anomalous coronary origins; the addition of a coronary runoff lesion may make them prone to early coronary ischemia and subsequent ventricular compromise Children with truncus arteriosus are at risk for developing early pulmonary vascular obstructive disease, especially if delayed in their repair.164 Regurgitation of blood through the truncal valve may place an additional volume load on the ventricles Critical Care Management Complete repair of this lesion should be performed early in the neonate, before the pulmonary vascular resistance drops further, resulting in clinical compromise.165 The VSD is closed with a synthetic patch, and the pulmonary arteries are detached from the truncus Continuity is established between the RV and the pulmonary arteries with a valved conduit.166 The truncal valve may require valvuloplasty if a significant amount of blood regurgitates through it The presence of a dysplastic and moderately regurgitant truncal valve poses additional challenges; most data suggest that these patients are best served long term by cardiac transplantation Pulmonary arterial banding or valve replacement may be considered as an interim bridging strategy to this destination Critical care management centers on control of pulmonary blood flow and ventricular support Pulmonary blood flow may increase further with anesthetic agents, hyperventilation, alkalosis, and oxygen administration, resulting in hypotension and acute ventricular failure If measures for increasing PVR not decrease pulmonary flow, temporary occlusion of one branch of the pulmonary artery with a tourniquet limits pulmonary flow and restores systemic perfusion pressure until CPB can be instituted Because these patients are often in high-output CHF, myocardial depressants should be used with caution Immediately after repair, the combination of persistent pulmonary arterial hypertension and RV failure can be fatal Hence, aggressive measures should be taken to support myocardial function and lower PVR adequately A residual VSD adds volume and pressure load on the ventricles and may have a devastating impact on the patient’s hemodynamics and oxygenation This should be suspected in patients who are not doing well postoperatively, and any residual VSD should be repaired, if feasible Truncal valve regurgitation or stenosis may induce LV failure early during the postoperative period Critical Care Management for Late Postoperative Care Obstruction of the pulmonary conduit and the accompanying RV hypertension may occur early or late during the postoperative course Usually, the conduit is unable to support flow in the growing child after several postoperative years Late development of truncal (aortic) valve regurgitation is possible For patients who underwent initial repair beyond late infancy, residual persistent pulmonary hypertension will most likely be a problem Total Anomalous Pulmonary Venous Connection Pathophysiology Patients with TAPVC are cyanotic because their pulmonary veins connect to a systemic vein (complete mixing), and they have varying degrees of pulmonary venous obstruction The venous connection may be supracardiac (e.g., to the SVC, innominate, or azygos vein), cardiac (e.g., to the coronary sinus), or infracardiac (e.g., to the hepatic veins, portal vein, or ductus venosus) Patients with this anomaly must have a patent foramen ovale or an ASD that allows blood flow to the left side of the heart This anatomic arrangement provides complete mixing of all systemic and pulmonary venous blood in the right atrium Unless there is significant stenosis of the pulmonary venous connection, most of this RA blood passes through the RV into the pulmonary artery, which increases pulmonary blood flow If pulmonary venous return is significantly diminished due to obstruction, there is increased pulmonary venous congestion and decreased pulmonary blood flow Critical Care Management Patients with significant obstruction, typically those with PV that drain into subdiaphragmatic vessels, may be very ill with hypoxemia, severe pulmonary edema, and pulmonary artery hypertension Resuscitation, including mechanical ventilation, PEEP, and inotropic support of the myocardium, is followed by early surgical intervention to relieve the pulmonary venous obstruction Although patients are hypoxemic, their primary pathology is caused by obstructed venous return from the lungs Therapy that increases pulmonary blood flow (e.g., PGE1 or iNO) must be avoided Surgical repair of TAPVC requires attachment or redirection of the pulmonary venous confluence to the left atrium Intraoperative and postoperative problems often are related to residual or recurrent stenosis of the pulmonary veins In patients who have severe and prolonged (often fetal) preoperative pulmonary venous obstruction, the pulmonary vascular bed is poorly reactive, reflected by highly pulmonary vascular resistance indices (PVRi) This elevation in PVRi results in high pulmonary artery pressures and poor RV function after bypass and during the early postoperative period Critical care management of these patients after completion of the repair should emphasize inotropic support of the RV, CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease avoidance of myocardial depressant drugs, and minimization of PVR Prolonged mechanical ventilation with gentle hyperventilation and other postoperative therapy to decrease PVR are required Inhaled NO has been particularly useful in this population, provided that there is no residual pulmonary vein obstruction.49 Critical Care Management for Late Postoperative Care Other than the potential for late development of recurrent pulmonary venous obstruction, these patients generally well and have good cardiovascular reserve once recovery from the surgery is complete.167 The size of the pulmonary veins at birth may be a predictor of late complications with recurrent pulmonary vein stenosis.168 Transposition of the Great Arteries Pathophysiology With transposition of the great arteries (d-TGA), the right ventricle gives rise to the aorta Almost 50% of patients with this anomaly have a VSD, and some have a variable degree of subpulmonic stenosis Oxygenated pulmonary venous blood returns to the left atrium and is recirculated to the pulmonary artery without reaching the systemic circulation Similarly, systemic venous blood returns to the RA and ventricle and is ejected into the aorta again Obviously, this arrangement is compatible with life only for a few circulation cycles unless there is some mixing of pulmonary and systemic venous blood via a PDA or an opening in the atrial or ventricular septum at birth The physiologic disturbance in these patients is one of inadequate mixing of pulmonary and systemic blood rather than one of inadequate pulmonary blood flow Mixing of blood at the atrial level can be improved by balloon atrial septostomy If dangerous levels of hypoxemia persist after the septostomy and metabolic acidosis ensues, an infusion of PGE1 can maintain the patency of ductus arteriosus, increase pulmonary blood flow (by increasing left-to-right shunting across the PDA), and thereby increase the volume of oxygenated blood entering the left atrium The volume-overloaded LA is likely to shunt part of its contents into the RA and thereby improve the oxygen saturation of aortic blood Unlike other lesions, increased left-to-right shunting of blood during anesthesia improves arterial oxygen saturation before correction of the transposition Depending on the particular anatomy and the presence of a VSD or pulmonary stenosis, one of three corrective procedures is used The intraoperative and postoperative problems encountered differ with each type of procedure Atrial Switch Procedure (Mustard and Senning) An atrial-level partition is created with baffling to redirect pulmonary venous blood across the TV to the RV and thus to the aorta.169 Systemic venous (SVC and IVC) return is directed across the atrial septum to the mitral valve, into the LV, and out the pulmonary artery Although the pulmonary and systemic circuits are then connected serially instead of in parallel, this arrangement leaves the patient with a morphologic RV and TV in continuity with the aorta Therefore, this ventricle must work against systemic arterial pressure and resistance One problem with atrial baffles is that they can obstruct systemic and pulmonary venous return.170 When this occurs, the patient manifests signs and symptoms of systemic venous obstruction, as evidenced by signs of systemic venous hypertension When the pulmonary venous pathway is obstructed, pulmonary venous hypertension may be manifested by respiratory failure, poor gas exchange, and pulmonary edema Severe pulmonary 399 venous obstruction is manifested in the operating room by the presence of copious amounts of bloody fluid in the endotracheal tube, low cardiac output, and frequently poor oxygenation Residual interatrial shunts also may cause intraoperative or postoperative hypoxemia Long-term rhythm disturbances and the limitations of ventricular and AV valve function have made this operation nearly obsolete for standard transposition anatomy Arterial Switch Operation (Jatene Procedure) ecause of the complications associated with atrial baffle proceB dures, Jatene and others explored whether anatomic correction of this lesion by dividing both great arteries and reattaching them to the opposite anatomically correct ventricle would improve survival.171,172 This procedure requires excision and reimplantation of the coronary arteries to the neoaorta (formerly the proximal main pulmonary artery) LV mass decreases progressively after birth; thus, the ASO is done in the early (day to 10 of life) neonatal period when the PVR (LV afterload) and LV pressure are high The success of the ASO depends on adequate conditioning of the LV and technical proficiency with the coronary transfer If the LV’s ability to tolerate the work required is misjudged, the child may develop severe LV failure postoperatively, necessitating significant vasoactive or mechanical support to maintain cardiac output In the instance of a late postnatal diagnosis of TGA with intact ventricular septum, the LV may require “reconditioning” by banding the pulmonary artery to encourage LV hypertrophy and hyperplasia, as well as a modified Blalock-Taussig shunt (BT shunt) to augment pulmonary blood flow.173 Although the ASO can often be accomplished week later, during this interval, these patients are often cyanotic and require considerable pharmacologic support.174 In contrast, if the neonate has a nonrestrictive VSD, the LV is accustomed to high systemic resistances and will tolerate the increased workload at any age Myocardial ischemia or infarction may occur after mobilization and reimplantation of the coronary arteries, especially if they are stretched or twisted Inotropic support, maintenance of coronary perfusion pressures, control of heart rate, and treatment with vasodilators may be particularly useful, as in adult patients with myocardial ischemia Postoperative bleeding and tamponade occur more commonly with this operation because of the presence of multiple arterial anastomoses At experienced centers, mortality after neonatal repair of transposition of the great arteries now is less than 3% and may be less than 2% for most anatomic arrangements of coronary arteries if the aortic arch is normal.175 Midterm and longer-term outcomes for the ASO are excellent, demonstrating a 25-year survival and freedom from reoperation rates of 96.7% and 75%, respectively.176 Alternative operations are reserved almost exclusively for patients with particularly difficult coronary anatomy177,178 or pulmonic (neoaortic) stenosis Ventricular Switch (Rastelli Procedure) This procedure can be used in TGA with VSD or double-outlet RV when there is an unrestrictive outlet VSD and when coexisting pulmonary valve stenosis precludes a standard arterial switch operation The pulmonary valve is oversewn and the RV is connected to the pulmonary artery with a conduit.179 Complications of the Rastelli procedure include obstruction of LV outflow as a result of the narrowing of the subaortic region by the VSD patch The conduit also may obstruct during or after the immediate postoperative period A small but significant incidence of heart block in these patients can be a difficult postoperative problem 400 S E C T I O N I V Pediatric Critical Care: Cardiovascular Critical Care Management Management of patients following an atrial switch procedure rests on optimizing systemic oxygen delivery, monitoring for signs of baffle obstruction, and control of atrial arrhythmias Most patients post-ASO without a VSD have an unremarkable postoperative course Persistent ventricular dysfunction heralded by LA hypertension, hemodynamic instability, ventricular arrhythmia, or evidence of ischemic changes should prompt an intensive evaluation of the adequacy of the coronary anastomosis Any of these perioperative issues or the unanticipated need for extracorporeal support necessitates immediate coronary evaluation and revision Special attention should be paid to postoperative bleeding, given the extensive arterial suture lines Patients with delayed intervention (either due to late presentation or comorbidities) usually will need to have a careful assessment for possible LV insufficiency For these, an aggressive strategy of systemic afterload reduction, deep sedation, and muscle relaxation while expecting a more protracted ICU course is often the norm Occasionally, these patients will benefit from the use of ECLS or temporary LVAD support for retraining of the LV in the postoperative course Late Complications Following atrial baffle, patients can be regarded as having a physiologic or functional two-ventricle repair (i.e., the morphologic LV is the pulmonary ventricle and the morphologic RV remains the systemic ventricle) Actuarial survival rates at 15 years have been quoted to be up to 85%; however, significant long-term functional deterioration is likely with increasing risk for right heart failure, sudden death, and dysrhythmias.180,181 This situation is evidenced by systemic (right) ventricular dysfunction and TV regurgitation long after the repair.182 These patients also are prone to develop significant atrial dysrhythmias, including supraventricular tachyarrhythmias and sick sinus syndrome later in life.183 Virtually all coronary artery patterns are amenable to ASO No particular pattern has been associated with late death A report of coronary artery angiography in 366 patients following ASO (median age at follow-up, 7.9 years) revealed coronary artery stenosis or occlusion in 3% of patients.184 Despite the angiographic findings, evaluation with serial ECG, exercise testing, and wallmotion abnormalities on echocardiography rarely demonstrate evidence of ischemia.185 After repair, the native pulmonary valve becomes the neoaortic valve A 30% incidence of trivial to mild aortic regurgitation has been reported on intermediate-term follow-up, without significant hemodynamic changes.186 Severe regurgitation is unusual There appears to be a very low incidence of significant rhythm disturbances after ASO.187 Supravalvar pulmonary AS was an early complication but now is less common with surgical techniques that extensively mobilize, augment, and reconstruct the pulmonary arteries Supravalvar AS may develop but is rare Assessment of myocardial performance using echocardiography, cardiac catheterization, and exercise testing following ASO has demonstrated function identical to that in age-matched controls Based on the currently available clinical, functional, and hemodynamic data, a patient who has undergone ASO with no evidence of subsequent problems should be treated like any patient with a structurally normal heart when presenting for noncardiac surgery Late complications of the Rastelli procedure include progressive conduit obstruction and RV hypertension, residual VSDs, and occasional subaortic obstruction from diversion of LV outflow across the VSD to the aorta Tetralogy of Fallot Pathophysiology The four anatomic features of TOF are VSD, RV outflow tract obstruction, overriding of the aorta, and RV hypertrophy There may be additional muscular VSDs, and obstruction of the pulmonary valve and main and branch pulmonary arteries Resistance to RV outflow forces systemic venous return from right to left across the VSD and into the aorta, producing arterial desaturation The amount of blood that shunts right to left through the VSD varies with the magnitude of the RV outflow tract obstruction and with SVR Distal PVR is low and has minimal influence on shunting Systemic vasodilation, in conjunction with increasing dynamic infundibular stenosis, intensifies rightto-left shunting and can lead to hypercyanotic spells Such spells can occur at any time before surgical correction of the anomalies and can be life-threatening Because the morbidity associated with recurrent hypercyanotic spells is significant, many physicians consider recurrent episodes of hypercyanosis an indication for corrective surgery at any age Critical care management of TOF patients with hypercyanotic episodes should focus on minimizing oxygen consumption, acidosis, tachycardia, and acute elevations in PVR while augmenting preload and SVR Hypercyanotic spells in nonanesthetized children should initially be managed with 100% oxygen by facemask, a knee-chest position or squat position (to increase SVR), and sedation Classically, intravenous morphine is used However, intranasal medications, such as fentanyl, have been used effectively when IV access has not yet been established Dexmedetomidine has been reported in the management of hypercyanotic spells, as it provides not only sedation but also the additional benefit of lowering the heart rate.188 Regardless of the specific drug used, this regimen can usually stabilize the dynamic infundibular stenosis while keeping SVR elevated Deeply cyanotic and lethargic patients are given rapid IV crystalloid infusions to augment circulating blood volume Continued severe hypoxemia should be treated with a vasopressor bolus (e.g., phenylephrine 1–2 mg/kg, titrated up to mg/kg) to further augment SVR, and judicious use of IV propranolol or esmolol to slow the heart rate may be considered as necessary The latter allows more filling time and relaxes the infundibulum If a hypercyanotic spell persists despite treatment, either stabilization on VA ECMO or immediate surgical intervention (palliative aortopulmonary shunt or complete repair) is indicated Induction of anesthesia must proceed cautiously after minimal fasting times and administration of a premedication, if possible The child can be anesthetized with IV narcotics and/or inhalational agents, but care must be taken to minimize reduction in SVR The pattern of mechanical ventilation is critical, as excessive intrathoracic pressure can further reduce antegrade flow across the RV outflow Critical Care Management for the Early Postoperative Course The surgical approach to the patient with TOF who presents with recurrent early hypercyanotic spells is variable Traditionally, complete repair is completed at to months of age Delayed repair also is often necessary when a coronary artery crosses the RV outflow tract, precluding transannular patch repair There are currently two palliative interventions to facilitate a delayed repair CHAPTER 36 Critical Care After Surgery for Congenital Cardiac Disease strategy The first is the use of a systemic-to-pulmonary artery shunt Excellent outcomes have been achieved with this approach, and the need for a transpulmonary valve annulus outflow patch at the time of definitive surgery is reduced.189 However, the risks of cyanosis and complications related to a systemic-to-pulmonary artery shunt argue for early complete repair of TOF The alternative approach, developed more recently, is stenting the RV outflow tract in the cardiac catheterization laboratory.190 This procedure has the additional benefit of improving pulmonary artery growth prior to the definitive repair.191 Another approach for patients with TOF is to proceed with an early complete repair For that method, a ventriculotomy is performed in the RV outflow tract and frequently is extended distally through the pulmonary valve annulus and beyond any associated pulmonary artery stenosis The outflow tract is enlarged with pericardium or synthetic material, and obstructing muscle bundles are resected to relieve the outflow tract obstruction.192 Because they are smaller and younger, these patients may be at increased risk for complications associated with CPB Pulmonary regurgitation results after a transannular incision that may compromise ventricular function in the postoperative period In approximately 8% of patients, abnormalities in the origin and distribution of the coronary arteries preclude placement of the RV outflow patch, making it necessary to bypass the stenosis by placing an external conduit from the body of the right ventricle to the pulmonary artery.193,194 An analysis of 3059 TOF repairs between 2002 and 2007 demonstrated that 83% (2534) had a complete repair as their initial index procedure (with 6%, 19%, 38%, and 24% undergoing operation at the ages of to 1, to 3, to 6, and to 12 months, respectively).195 There were 217 (7%) patients who underwent complete repair following initial palliation Rates of ventriculotomy, transannular patch, and RV-PA conduit use were significantly higher in those requiring initial palliation Discharge mortality was higher in palliative patients versus initial complete repair (7.5% vs 1.3%) There was less disparity in discharge mortality between the two approaches among neonates (6.2% vs 7.8%).195 When weaning patients from CPB following TOF repair, the aim of therapy is to support RV function and minimize afterload on the right ventricle This is particularly important following repair in neonates or small infants Although systolic dysfunction of the RV may occur following neonatal ventriculotomy, the clinical picture is more commonly one of a restrictive physiology reflecting reduced RV compliance or diastolic dysfunction.36,37 Factors contributing to diastolic dysfunction include ventriculotomy, lung and myocardial edema following CPB, inadequate myocardial protection of the hypertrophied ventricle during aortic cross-clamp, coronary artery injury, residual outflow tract obstruction, volume load on the ventricle from a residual VSD or pulmonary regurgitation and arrhythmias Patients usually separate from CPB with satisfactory blood pressure and atrial filling pressures less than 10 mm Hg on modest inotropic support However, in neonates during the first to 12 hours after surgery, a low–cardiac output state with increased right-sided filling pressures from diastolic dysfunction is common following a right ventriculotomy Continued sedation and paralysis usually are necessary for the first 24 to 48 hours to minimize the stress response and associated myocardial work Preload must be maintained despite elevation of RA pressure In addition to high right-sided filling pressures, pleural effusions or ascites may develop Inotropic support is often required and, if the blood pressure can tolerate it, introduction of a 401 phosphodiesterase inhibitor, such as milrinone, is beneficial because of its lusitropic properties Because of the restrictive physiology, even a relatively small volume load from a residual VSD or pulmonary regurgitation is often poorly tolerated in the early postoperative period; to days may be required before RV compliance improves and cardiac output increases Although the patent foramen ovale or any ASD is usually closed in older patients at the time of surgery, it is beneficial to leave a small atrial communication following neonatal repair In the face of diastolic dysfunction and increased RV end-diastolic pressure, a right-toleft atrial-level shunt maintains preload to the LV and, therefore, cardiac output Patients may be desaturated initially following surgery because of this shunting As RV compliance and function improve, the amount of shunt decreases and both antegrade pulmonary blood flow and systemic arterial oxygen saturation increase Arrhythmias following repair include heart block, ventricular ectopy, and junctional ectopic tachycardia (JET) Maintaining sinus rhythm is important to optimize end-diastolic filling and minimize end-diastolic pressure AV pacing may be necessary for heart block Complete right bundle branch block is typical on the postoperative ECG Although JET is typically transient, it can result in significant deleterious effects on the child’s hemodynamics Treatment of JET may include sedation, cooling, paralysis, antiarrhythmic medications, temporary pacing, and, in rare circumstances, mechanical support to maintain hemodynamics Most patients recover systolic ventricular function postoperatively However, in a small group of patients, especially those repaired at older ages, significant ventricular dysfunction remains.196,197 These patients can have left ventricular subendocardial ischemia that impairs LV myocardial mechanics.198 Pulmonary valve insufficiency may contribute to residual ventricular systolic dysfunction.199 The most common cause of systolic dysfunction immediately after repair of TOF is a residual or previously unrecognized VSD, which causes a volume load on the LV and pressure load on an already stressed RV, leading to RV failure and poor cardiac output.25 A residual VSD combined with residual RV outflow obstruction is particularly deleterious In some patients, the distal pulmonary arteries may be so hypoplastic and stenotic that they cannot be satisfactorily corrected Suprasystemic pressure develops in the RV, which can be ameliorated in some cases by partially opening the VSD to allow an intracardiac right-to-left ventricular shunt This shunt unloads the compromised RV at the expense of decreased arterial oxygen saturation Critical Care Management for Late Postoperative Care Reconstruction of the RV outflow tract may lead to significant problems that affect RV function and risk for arrhythmias over time Although most of the long-term outcome data pertain to patients following TOF repair, similar complications and risks are likely for those who have undergone an extensive RV outflow reconstruction, such as placement of a conduit from the RV to the pulmonary artery for correction of pulmonary atresia, truncus arteriosus, and the Rastelli procedure for transposition of the great arteries with pulmonary stenosis Complete surgical repair of TOF has been successfully performed for more than 40 years, with studies reporting a 30- to 35-year actuarial survival of approximately 85%.200 Many patients report leading relatively normal lives, but RV dysfunction may progress after repair and may be evident only on exercise stress testing or echocardiography A spectrum of problems may develop, ranging from a dilated RV with systolic dysfunction to 402 S E C T I O N I V Pediatric Critical Care: Cardiovascular diastolic dysfunction from a poorly compliant RV Continued evaluation is necessary because of the increased risk for ventricular arrhythmias and late sudden death Factors that may adversely affect long-term survival include older age at initial repair, initial palliative procedures, and residual chronic pressure or volume load as occurs from pulmonary insufficiency or stenosis Systolic dysfunction secondary to a residual volume load from pulmonary regurgitation after tetralogy repair is a predictor of late morbidity It is reflected as cardiomegaly on chest radiograph, an increase in RV end-diastolic volume and regurgitant volume by echocardiography and cardiac MRI,12 and a reduction in anaerobic threshold, maximal exercise performance, and endurance on exercise testing.201 Patients who have significant pulmonary regurgitation, RV dilation, and reduced RV function are at potential risk for a fall in cardiac output during anesthesia, particularly as positive-pressure ventilation may increase the amount of regurgitation These patients currently benefit from early surgical pulmonary valve replacement to reduce these symptoms and risks An important group to distinguish consists of those who have continued restrictive physiology or diastolic dysfunction secondary to reduced ventricular compliance They usually not have cardiomegaly, they demonstrate better exercise tolerance, and the risk for ventricular dysrhythmias is possibly decreased Although the RV is hypertrophied, function is generally well preserved on echocardiography, with minimal pulmonary regurgitation The incidence of significant RV outflow obstruction developing over time is low Residual obstruction contributes to early mortality within the first year after surgery but is well tolerated in the long term A wide variation in the incidence of ventricular ectopy has been reported in numerous follow-up studies, including up to 15% of patients on routine ECG and up to 75% of patients on Holter monitor Multiple risk factors—including older age at repair, the extent of ventriculotomy, residual hemodynamic abnormalities, and duration of follow-up—have all been considered important In common with these factors are probable myocardial injury and fibrosis from chronic pressure and volume overload, combined with cyanosis Although ventricular ectopy is common in asymptomatic patients during ambulatory ECG, Holter monitoring, and exercise stress testing, it often is low grade and does not identify those patients at risk for sudden death Electrophysiologic induction of sustained ventricular tachycardia (VT), especially when monomorphic, is suggestive of the presence of a reentrant arrhythmic pathway Although dependent on the stimulation protocol used to induce VT, the presence of monomorphic VT in a symptomatic patient with syncope and palpitations is significant and indicates treatment with radiofrequency ablation, surgical cryoablation, antiarrhythmic drugs, or placement of an implantable cardioverter-defibrillator.202 The risk for ventricular dysrhythmias during anesthesia and ICU care for subsequent hospitalizations is unknown Although preoperative prophylaxis with antiarrhythmic drugs is not recommended, a means for external defibrillation and pacing must be readily available Pulmonary Atresia Pathophysiology Atresia of the pulmonary valve or main pulmonary artery forms a spectrum of cardiac defects Management depends on the extent of atresia, size of the RV and TV, presence of a VSD and collateral vessels, surface area of the pulmonary vascular bed, and coronary artery anatomy The timing of developmental abnormality defines the associated lesions Pulmonary atresia with intact ventricular septum (PAIVS) is primarily an abnormality of TV development that subsequently affects the pulmonary valve through its effects on fetal RV growth Because the impact on the pulmonary valve is late, the fetal truncus arteriosus has already divided and the mesenchymal distal pulmonary vasculature can connect to a main pulmonary artery pressure head appropriately As a result, this lesion predictably has well-developed central pulmonary arteries and pulmonary artery arborization At one end of the spectrum of PAIVS, platelike pulmonary atresia overlaps with critical pulmonary stenosis where there is a mild or negligible degree of hypoplasia of the RV and TV In these lesions, a fixed obligatory right-to-left atrial-level shunt of all systemic venous return exists Some blood may flow into the RV, but because there is no outlet, blood regurgitates back across the TV and eventually reaches the LA and LV Pulmonary blood flow is derived exclusively or predominantly from a PDA As a rule, these patients not have extensive aortopulmonary collateral blood flow; consequently, they often become cyanotic when the PDA closes after birth Critical pulmonary valve stenosis can be effectively treated by balloon valvuloplasty in the catheterization laboratory Antegrade flow across the RV outflow may not improve immediately but may gradually increase over days as RV compliance improves In platelike pulmonary atresia, radiofrequency perforation precedes balloon valvuloplasty Most patients with PAIVS have an underdeveloped TV and RV Depending on the degree of RV hypoplasia (which is directly related to the TV annulus z-score), the patient may be unsuitable for a biventricular repair in the long term In this situation, initial palliation with an aortopulmonary shunt is necessary However, if the RV is deemed to be of suitable size, then reconstruction of RV outflow with a pericardial patch or interventional catheter techniques may be considered (similar to the approach described earlier for platelike PA with mild RV hypoplasia) A large conal branch or aberrant left coronary artery across the RV outflow tract may restrict the size of a ventriculotomy and placement of a patch or conduit At the other end of the spectrum, severe pulmonary atresia may be associated with an extremely hypoplastic RV that is not suitable for biventricular repair A palliative procedure with a modified BT or central shunt usually is necessary at first to improve pulmonary blood flow, followed by staged single-ventricle repair (see the Fontan Procedure section) Patients with PAIVS and severe RV hypoplasia may have numerous fistulous connections (sinusoids) between the small hypertensive RV cavity and coronary circulation.203 This is distinct from RV-dependent coronary circulation (RVDCC), in which these sinusoidal connections are accompanied by proximal stenoses in the true coronary arteries If RV decompression or even staged palliation is being considered in such a patient, then a coronary angiogram is highly desirable to exclude this phenomenon In PAIVS with documented RVDCC, cardiac transplantation is often the treatment of choice In contrast to PAIVS, PA/VSD and TOF with PA represent an early failure of proper conotruncal development As a result, the mesenchymal segmental pulmonary arteries not see the main pulmonary artery pressure head and instead form connections with the nearest alternative (aorta) This is the nature of the development of the aortopulmonary collaterals (APCs) associated with the lesion If the collaterals are substantial, defining a large pulmonary arterial segment, they are referred to as major aortopulmonary collateral arteries (MAPCAs) As a rule, these patients ... connected serially instead of in parallel, this arrangement leaves the patient with a morphologic RV and TV in continuity with the aorta Therefore, this ventricle must work against systemic arterial... whether anatomic correction of this lesion by dividing both great arteries and reattaching them to the opposite anatomically correct ventricle would improve survival.171,172 This procedure requires... systemic venous blood returns to the RA and ventricle and is ejected into the aorta again Obviously, this arrangement is compatible with life only for a few circulation cycles unless there is some