Congenital Heart Disease

Chapter 59 Congenital Heart Disease




This chapter is designed to provide medical students, general surgery residents, and practicing general surgeons with a working tool to aid in their understanding of the features of anatomy and physiology in patients presenting for general surgical procedures in the setting of repaired or unrepaired congenital cardiac lesions. The large scope and breadth of the evolving field of congenital heart surgery precludes an exhaustive treatise on all aspects of this specialty. Several excellent and thorough textbooks of congenital heart surgery will be referenced in this chapter, and the reader is encouraged to use them for additional in-depth understanding of the lesions to be reviewed. Today’s practicing general surgeon needs to be well versed in the basics of cardiac anatomy, physiology, and specific derangements associated with the various known congenital cardiac lesions. Furthermore, there are few patients with complex congenital cardiac lesions who may be considered cured of their cardiac problem, even after successful reconstructive surgery. Thus, it is imperative that the general surgeon who needs to perform a noncardiac operation on such a patient be familiar with the specific issues of ongoing concern in those with congenital cardiac disease.



History and Other Considerations


The era of surgical treatment for congenital cardiac anomalies was initiated in November 1944, when Dr. Alfred Blalock and associates Vivien Thomas and Dr. Helen Taussig combined their unique talents and vision to treat a young child dying of cyanotic congenital heart disease (CHD).1 This palliative operation involved the surgical creation of a systemic to pulmonary artery connection in the patient suffering from inadequate pulmonary blood flow. The procedure has since been recalled as miraculous and has carried the eponym of the Blalock-Taussig shunt (BT shunt) during the ensuing years, now more than 60 years later. The striking success of this simple concept and the reproducible nature of the operation in children suffering from otherwise fatal cardiac conditions has emboldened subsequent surgical innovators to venture inside the congenitally malformed heart. At first, a parent was asked to serve as a biologic oxygenator using the technique of controlled cross-circulation; soon thereafter, the mechanical, extracorporeal, heart-lung bypass pump was developed.2,3 With the aid of this ability to support the patient’s circulation during intracardiac exploration, surgeons have sequentially attacked almost every described congenital cardiac anomaly. The prospect of meaningful survival for patients born with otherwise devastating congenital cardiac lesions is now expected in most, if not all, cases.


As a result of this success story, there is now a large and growing population of adults with repaired or unrepaired CHD; estimates in the United States for 2005 placed the number of adult patients surviving with repaired or palliated congenital cardiac lesions at more than 1 million persons.4 This reality has been associated with new challenges in the ongoing medical maintenance of such patients, with particular focus on the care of patients with congenital cardiac lesions presenting for surgery for noncardiac illnesses. The evolving subspecialty of adult CHD points to the unique needs of this population of patients.



Pathways For Practicing Congenital Heart Surgery


Before embarking on a review of the field, it is worthwhile to describe the setting in which patients with CHD seek and receive care in today’s medical environment. With the development of sophisticated methods of fetal ultrasound, a large percentage of children requiring surgery for CHD are diagnosed during gestation (Fig. 59-1). Although not yet confirmed as affecting overall survival rates, a fetal diagnosis of complex CHD is of inordinate help to parents and the medical management team. This is particularly important in the setting of lesions dependent on persistent patency of the ductus arteriosus for postnatal survival. In these individuals, survival after delivery is predicated on the maintenance of ductal patency through the IV infusion of prostaglandin E1 (PGE1) initiated in the delivery suite, often through an umbilical vein catheter.



A growing number of congenital cardiac lesions is known to be associated with specific genetic mutations, many clearly inherited and some presumed to be sporadic. As such, a chromosomal analysis is frequently performed in those found to have major structural cardiac abnormalities; this analysis may be performed during gestation through an amniocentesis. The chromosomal evaluation is of benefit to the family when planning the risk of such an occurrence in future offspring. For the clinician, knowledge of chromosomal abnormalities in their patients, such as DiGeorge sequence, velocardiofacial syndrome, and Marfan syndrome, aids in the delivery of acute medical management.


In general terms, the timing of surgery for various congenital cardiac conditions depends on the presenting symptomatology and expectations for further associated complications. Children presenting with limited pulmonary blood flow or atretic pulmonary connections typically require surgery during the first few days of life and occasionally within hours of delivery. Lesions associated with excessive pulmonary blood flow result in early heart failure, which may manifest as poor feeding, tachypnea, or even respiratory failure. These patients are operated on during early infancy to ameliorate their symptoms and prevent the development of pulmonary vascular disease.


Preterm and low-birth-weight babies with CHD have been presenting for surgical consideration with more frequency. This treatment strategy requires thoughtful planning and coordination among the surgery, anesthesia, cardiology, intensive care, and neonatology teams. Recently, at our institution, the Texas Children’s Hospital, we successfully operated on an 800-g baby with transposition of the great arteries (TGA).


The specialty of congenital heart surgery is now recognized as a subspecialty of cardiothoracic surgery. Congenital heart surgeons were previously certified in cardiothoracic surgery by the American Board of Thoracic Surgery (ABTS) and received additional fellowship training in the United States or abroad in congenital heart surgery. As of 2009, the ABTS offers a formal certification process for subspecialty training in Congenital Heart Surgery. At this time, there are 10 congenital cardiac surgery residency programs approved by the Accreditation Council for Graduate Medical Education. Most pediatric cardiac surgery is performed in large, multispecialty children’s hospitals in association with formal programs focused on the care of these complex patients. The management team includes pediatric cardiac anesthesiologists, perfusionists, and nursing staff. Focused pediatric cardiac intensive care units have been developed to optimize the patients’ opportunity for recovery.


Historically, pediatric cardiologists have provided the medical management of patients born with CHD. Pediatric cardiology is also evolving. With advances in catheter-based technology, lesions previously treated with surgery are now being addressed by interventional pediatric cardiologists. Examples include device closure of atrial and ventricular septal defects (VSDs), occlusion of patent ductus arteriosus (PDA), and dilation and stenting of stenotic vessels in the systemic and pulmonary circulation. For a more in-depth recent review of this specialty, see the excellent technical text by Mullins.5


The situation of care for adults with CHD is not as well organized as for children. This issue is of particular relevance to the general surgeon faced with operating on an adult patient with significant CHD. One overriding message needs to be clear to the general surgeon in this setting: it must be assumed that in patients with previously repaired congenital cardiac lesions, even without overt cardiac symptomatology, the potential for significant perioperative cardiorespiratory derangement exists. More simply stated, the presence of a surgical scar on the chest of a patient with known CHD does not suggest that the lesion has been cured. With this firmly in mind, the general surgeon may find it challenging to determine the best source for a qualified consult for such a patient. At present, many adult cardiologists are not adequately trained in CHD to be expected to provide competent consultation on adult patients with CHD.


On the other hand, pediatric cardiologists are not educated in adult medicine and cardiology; many feel uncomfortable providing consultation on adult patients with CHD. As noted, the subspecialty of adult CHD is still in a state of development but, at present, there are few physicans who have been educated specifically to care for these patients. This underscores the necessity of the practicing general surgeon to become familiar with the specific issues of concern for patients with CHD to ascertain that the patient’s unique anatomic and physiologic issues have been evaluated properly. Adult patients with CHD who present for care in a center without a designated qualified specialist must be evaluated by a pediatric cardiologist in coordination with an adult cardiologist. Of equal importance, the anesthesiologists and intensivists caring for such a patient must have a working understanding of the complexities and nuances of the patient’s cardiac condition.6 The anesthetic management of patients with CHD undergoing general surgical procedures is complicated and can become disastrous if managed improperly.



Anatomy, Terminology, and Diagnosis



Anatomy and Terminology


One of the most intimidating aspects for the student of CHD is developing a level of comfort with the terminology used for describing specific lesions. To begin, a thorough and sound understanding of normal cardiac anatomy is mandatory. There are several excellent texts on this subject; in particular, the one edited by Wilcox and coworkers7 is especially concise and clear. One difficulty that challenges proper understanding of anatomy is the frequent use of abbreviations and eponyms for various congenital lesions—for example, congenitally corrected transposition of the great arteries (ccTGA), ventricular inversion, and L-transposition all describe the same heart, but none provides a complete anatomic description. Unless otherwise clear to all involved in the care of these complicated patients, the anatomic description needs to be segmental and complete to avoid mistakes and misinterpretations of structure.


In describing congenital cardiac lesions, a segmental approach is used to determine the relationship of the various structural elements. The situs describes the relationship of sidedness—situs solitus (normal), situs inversus (reversed), or situs ambiguous (indeterminate). The cardiac elements described include (in sequence) the atria, ventricles, and great vessels. The relationship of the connections must be understood; connections are concordant (e.g., right atrium connecting to right ventricle) or discordant (e.g., right ventricle connecting to the aorta). The chamber sidedness must be clarified (e.g., a morphologic right atrium may be on the left side of the patient). The relationship and connections of the cardiac valves must then be assessed; connections may be normal, stenotic, atretic, or straddling. Of note to the general surgeon, abnormal sidedness of the cardiac structures is frequently associated with abnormal relationships of the thoracic and abdominal organs. A thorough assessment of the patient’s anatomy is recommended before surgery.


There are two widely accepted and applied schools of cardiac morphologic description. The Van Praagh nomenclature uses abbreviations to describe the relationship of the atria, ventricular looping, and position of the aorta sequentially. The first letter describes the situs of the atrial chambers (and usually the abdominal organs): S for situs solitus (normal), I for situs inversus (reversed), or A for situs ambiguous (indeterminate). The second letter describes the relationship of the embryologic looping of the ventricles; D for dextro looping or right-handed topology (normal) or L (levo) for left-handed topology. The third and last letter describes the relationship of the aortic valve to the pulmonary valve, D for right-sided and L for left-sided (Fig. 59-2).



The Anderson nomenclature is more wordy and longer, but is perhaps simpler to understand. The descriptions are again of the sequential relationship of the structures. Starting with the atria, the connections and relationships are sequentially described. Thus, the atrial sidedness is described, followed by the sequence of connections to the ventricles and then great vessels. For example, atrial situs solitus (normal) with atrioventricular discordance (reversed) and ventriculoarterial discordance (reversed) describes the heart mentioned earlier as corrected transposition, or S,L,L by the Van Praagh classification (Fig. 59-3).




Diagnosis


As with all aspects of surgery, there is a wide variety of highly sophisticated diagnostic tools available to examine cardiac structure and function. Despite the widespread availability and application of these tools, none has replaced or eliminated the necessity of a thorough history and physical examination. Most patients who have a history of CHD become very well informed about the specifics of their cardiac conditions, as do their parents. A detailed review of the patient’s past medical history is absolutely mandatory. This includes, when possible, securing records from all previous diagnostic and procedural reports. It is disturbing how often an incorrect assumption is made about a patient’s previous surgical history and anatomy, frequently in a setting in which a patient’s old operative report or clinical summary could easily clarify the misunderstanding.


In adults with CHD, in particular, there are specific points of medical history that must be elucidated. A history of palpitations, syncope, and neurologic deficit must be further investigated. The incidence of significant dysrhythmias in certain categories of adults with CHD is high and, in many cases, warrants further investigation, including continuous monitoring (Holter), electrophysiologic study, and/or provocative testing.



Physical Examination


A complete physical examination in a patient with previously repaired CHD will often yield information critical to the proper planning of a general surgical procedure. Patients need to be completely undressed and thoroughly examined. In many cyanotic patients, color changes may be prominent, particularly in the nail beds, lips, and mucous membranes. In other patients, cyanosis may be subtler, giving the patient a gray or even pale appearance. Previous surgical incisions need to be noted and reconciled with the known medical history. Thoracotomy incisions on either side may indicate a previous BT shunt using the turned-down, divided subclavian artery or with a prosthetic interposition graft, the so-called modified BT shunt. In patients with a left aortic arch, a left thoracotomy incision will be present if a previous coarctation repair has been carried out. Median sternotomy incisions or anterior thoracotomy incisions may indicate previous intracardiac or extracardiac surgery.


A complete vascular examination is often overlooked in patients with CHD. It is important to assess pulses and obtain blood pressure measurements in all four extremities. Patients who have an existing or have previously had a BT shunt often have diminished or absent pulses in the upper extremity corresponding to the previous shunt. This may also be true in the left upper extremity in patients with previous coarctation repairs, especially if a subclavian flap angioplasty was performed (Waldhausen procedure). Furthermore, a history of previous coarctation repair does not guarantee that the lower extremity pulses and blood pressures will be normal. Also, patients who have undergone previous cardiac catheterization may have chronically stenosed or occluded femoral vessels. All these issues may be of significance for monitoring and vascular access in a patient undergoing a general surgical procedure.


Later in this chapter, the Fontan procedure for single-ventricle palliation will be reviewed. Briefly, this operation results in significant systemic venous hypertension, often in the range of 12 to 15 mm Hg. In patients with a Fontan circulation, physical examination may reveal hepatic congestion, ascites, pedal edema, venous varicosities, and jugular venous distention. In some individuals, macronodular hepatic cirrhosis may be suspected on the basis of a firm fibrotic liver edge.


Entire textbooks have been dedicated to the physical examination of patients with cardiac disease and a thorough discussion of this issue, particularly the specifics of cardiac auscultation, is beyond our scope here. In general, however, the cardiac examination includes an assessment of the patient’s rhythm, point of maximal impulse, and character of any auscultated murmurs. It must also be emphasized that the absence of a significant cardiac murmur does not rule out significant cardiac pathology.



Diagnostic Tests








Cardiac Catheterization


Cardiac catheterization has long been considered the gold standard for diagnostic imaging of congenitally malformed hearts. With the current sophistication of echocardiography, this is no longer the case for most patients. Nonetheless, there are still circumstances in which diagnostic cardiac catheterization is necessary to obtain accurate anatomic detail. This may true for patients who have poor echocardiographic windows, although even this issue may be overcome using transesophageal echocardiography. More often, there are specifics of anatomic detail that neither echocardiography nor MRI can delineate, such as branch pulmonary artery (or segmental) stenoses, origin and course of aortopulmonary collateral vessels, and fistulous connections and intracardiac communications (septal defects) not clarified by other imaging modalities.


Usually, however, diagnostic cardiac catheterization is performed to obtain precise hemodynamic information needed to make an informed assessment of the consequences of the patient’s cardiac lesions. Using oximetric measurements, pressure data, and thermodilution cardiac output determination, accurate assessment of the patient’s hemodynamic profile is obtained. Measured or derived data include central venous pressure, atrial pressure, ventricular pressures (including end-diastolic pressure), shunt fraction (in the case of atrial or VSDs), pulmonary artery pressures, pulmonary capillary wedge pressure, systemic arterial pressure, and segmental oximetry of cardiac structures, including systemic and pulmonary venous return (Fig. 59-5). Thus, critical information is obtained about the presence and degree of shunting, systemic and pulmonary vascular resistance, and cardiopulmonary function. In certain clinical settings, these data are mandatory to a successful clinical management strategy. This may be particularly true for the adult patient with congenital cardiac disease requiring noncardiac surgery.



A thorough understanding of normal cardiorespiratory physiology is critical in interpreting data obtained by cardiac catheterization in the patient with CHD. Specifically, the normal pressure range, pulse waveforms, and oxygen saturations for the various cardiac chambers must be compared against data obtained in a deranged circulation. The various cardiac chambers have normal pulse waveforms. In the atria, there are characteristic waveforms—a wave corresponding to atrial contraction, c wave corresponding to atrioventricular valve closure, and v wave corresponding to atrial filling from venous return against the closed atrioventricular valve. Typical normal right atrial mean pressures range from 1 to 5 mm Hg and left atrial pressures range from 2 to 10 mm Hg. Right ventricular pressure tracings in normal hearts demonstrate a more gradual upstroke when compared with the left ventricle. Filling or end-diastolic pressures range between 2 and 10 mm Hg in normal hearts. The normal right ventricular systolic pressure ranges from 15 to 30 mm Hg (and thus pulmonary artery systolic pressure) and the left ventricular systolic pressure ranges from 90 to 110 mm Hg.


In normal hearts, there is a small, physiologically insignificant right-to-left shunt, which results from ventilation-perfusion mismatch in the lungs and coronary venous return directly to the left ventricle (thebesian venous return). This physiologic shunt represents less than 5% of the cardiac output and, in normal circumstances, does not produce detectable systemic arterial desaturation. Thus, significant systemic arterial desaturation represents a pathologic finding, consistent with pulmonary disease, intracardiac shunting, or both. As noted, the origin and degree of intracardiac shunting may be assessed by echo study. In certain circumstances, however, cardiac catheterization is necessary to measure cardiac oximetry, calculate shunt fraction, and derive systemic and pulmonary vascular resistance. Using a derivation of the Fick principle, the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs) flow can be determined as follows:



where SaO2 sat is systemic arterial oxygen saturation, image sat is mixed venous oxygen saturation, image sat is pulmonary venous oxygen saturation, and PaO2 sat is pulmonary arterial oxygen saturation.


Thus, in a patient with image sat of 60%, image sat of 100%, Sao2 sat of 100%, and PaO2 sat of 80%,



image



Calculating vascular resistances may also be extremely important in determining operability in the patient with CHD. In many settings, a precise measure of vascular resistance is unnecessary based on the clinical evidence. For example, in the small child with a large VSD seen on the echocardiogram, the clinical findings of tachypnea, cardiomegaly, and failure to thrive confirm a large left-to-right shunt and thereby infer acceptable pulmonary vascular resistance. In less clear circumstances, however, a precise calculation may be important in clinical decision making. The pulmonary vascular resistance may be calculated from cardiac catheterization data as follows:



image



In general, patients with an elevated Rp are further evaluated with pulmonary vasodilation—hyperventilation, hyperoxygenation, and inhaled nitric oxide—to determine whether the resistance is responsive. This information may be critical for patients who are otherwise marginal candidates.


Finally, it must be mentioned that cardiac catheterization has been evolving as the primary therapeutic method for a number of important structural cardiac defects. In many children’s hospitals, including Texas Children’s Hospital, most catheterizations now performed are for interventional procedures rather than diagnostic. This may be particularly pertinent to the general surgeon faced with treating a patient with a previous catheter-based correction of a cardiac defect. For example, the patient may have had an atrial or VSD closed with an occluder device in the past. This information may have important ramifications for infectious exposure and vascular access.



Perioperative Care


Perioperative management of the patient with unrepaired or palliated congenital cardiac disease can be an extremely challenging proposition. Standard hemodynamic, respiratory, and pharmacologic manipulations appropriate for structurally normal hearts may be entirely inappropriate in settings of complex CHD. This is especially true in the operating room and intensive care settings. General rules include a thorough knowledge of the patient’s intracardiac anatomy and expected physiology. It is certainly possible to make significant management errors based on incorrect physiologic expectations in the setting of incomplete understanding of the patient’s anatomy. For example, in a patient with unrepaired tetralogy of Fallot (TOF) and associated significant right ventricular outflow tract obstruction (RVOTO), it is expected that the patient will exhibit some degree of systemic arterial desaturation. However, the patient with repaired tetralogy, with no residual intracardiac shunts, needs to be fully saturated. This is not an infrequent clinical scenario; a patient with a specific cardiac diagnosis, despite having undergone a successful correction, continues to be incorrectly presumed to have ongoing physiologic perturbation.



Anesthesia Pitfalls


Providing physiologic anesthetic management can be challenging in patients with congenital cardiac disease, especially in situations such as chronic single-ventricle palliation, unrepaired CHD, chronic cyanosis, and residual intracardiac pathology. It is important to note that standard anesthetic management paradigms may be completely inappropriate and potentially disastrous in the setting of complex CHD. A thorough understanding of the patient’s anatomy is mandatory, along with knowledge of the potential for unexpected response to anesthetic agents and ventilator settings. The field of pediatric and congenital cardiac anesthesia has evolved relative to this specific clinical need; the recent text by Andropoulos and colleagues is an excellent resource.8


Several points concerning anesthesia management merit discussion. The first is vascular access for intraoperative and postoperative management. In patients with complex CHD, especially those who have undergone previous complex surgical and catheterization procedures, obtaining appropriate vascular access may be challenging. Typically, a large-bore, multilumen central venous line is necessary for appropriate resuscitation and monitoring of right-sided filling pressures. In some patients, the placement of a thermodilution pulmonary artery catheter (oximetric) must be considered because one cannot presume that right-sided filling pressures correlate well with left heart volume or functional status (e.g., after a Fontan operation). Options for central access include percutaneous internal jugular or subclavian routes, with a secondary option of common femoral access to the inferior vena cava (IVC). Access may be difficult in the setting of previous catheterization or venous reconstruction; this situation may be addressed with the aid of ultrasound-guided catheter placement, which has become a standard in many cardiac operating theaters. Arterial access for continuous blood pressure monitoring and sampling is important for many patients. Percutaneous radial arterial cannulation can be readily achieved in most patients; however, upper extremity blood pressure values may be factitiously altered by previous systemic-to-pulmonary artery shunts, previous aortic arch surgery (especially coarctation), and abnormalities of vascular origin (e.g., aberrant subclavian origin from the descending aorta).


Ventilator management in the perioperative setting of CHD requires special understanding. In settings of large potential left-to-right shunts (e.g., unrepaired VSDs), hyperventilation and hyperoxygenation will promote excessive pulmonary blood flow and potentially diminish systemic cardiac output. Positive pressure ventilation, particularly positive end-expiratory pressure (PEEP), will negatively influence hemodynamics in many patients, especially in palliated single ventricle patients after the Fontan procedure. Early extubation in this population can be done to limit the deleterious effects of PEEP on the Fontan circulation. Early data have shown that this improves outcomes for these patients and reduces overall hospital costs.9 Finally, pharmacologic manipulation of systemic and pulmonary vascular resistance and cardiac performance is an important adjunct in the perioperative management of patients with CHD. In general, a low-dose infusion of epinephrine (0.05 µg/kg/min) with the addition of a phosphodiesterase inhibitor is an effective pharmacologic cocktail to promote cardiac inotropic state, lower systemic and pulmonary vascular resistance, and limit tachycardia. Other agents frequently used include dopamine, vasopressin, sodium nitroprusside, and nitroglycerin. Appropriate perioperative analgesia and sedation are also important aspects of the patient’s management.10




Lesion Overview



Defects Associated With Increased Pulmonary Blood Flow



Persistent Arterial Duct (Patent Ductus Arteriosus)


A persistent arterial duct or PDA is a frequently encountered congenital cardiac condition. The arterial duct is necessary during gestation to shunt right ventricular blood away from the unventilated pulmonary vasculature; ductal flow is from the pulmonary artery to the aorta during gestation. At delivery, after the first breath of the neonate, ductal flow reverses and becomes left to right in most individuals. Over the first several hours or days of postnatal life, the PDA closes spontaneously and is completely closed in most infants by 2 to 3 weeks of life.


In the absence of other congenital cardiac lesions—although a PDA may be present in association with other structural cardiac conditions and may sometimes be necessary for systemic or pulmonary blood flow—a PDA becomes pathologic related to its presence and degree of left-to-right shunting. The amount of shunting produced relates to the size and geometry of the duct and the pulmonary vascular resistance. A PDA may be responsible for a large Qp/Qs and result in pulmonary overcirculation, left heart volume overload, and congestive heart failure (CHF). A large unrestricted PDA will be associated with pulmonary hypertension; if left untreated, this will proceed to irreversible pulmonary vascular disease (Eisenmenger’s syndrome), ultimately proceeding to pulmonary and right heart failure, only treatable by pulmonary transplantation. Even with a small, pressure-restrictive PDA, there is an ongoing risk for pulmonary congestion and left heart volume overloading; endocarditis is always of concern for even small PDAs. As such, closure is recommended for all PDAs.


The gold standard of therapy for closure of PDA is surgery, usually accomplished through a left thoracotomy using ductal division, ligation, or clipping (Fig. 59-6). This needs to be a low-risk procedure associated with minimal potential for persistence. Nonetheless, the invasive nature of this proven method has led to the development of alternative strategies for ductal occlusion. From a surgical perspective, many PDAs are amenable to thoracoscopic clipping through very small port incisions; robot-assisted PDA occlusion has been performed in many patients, with good results.12 At present, however, most PDAs are occluded in the cardiac catheterization laboratory using occlusive devices. Even the repair of large defects in small babies has been successfully addressed. The long-term effects of the devices remaining in the vascular tree are as of yet not fully understood; however, successful device closure appears to be an extremely effective and durable therapy.13



A PDA in an adult patient can be challenging. As noted, a long-standing large PDA may be associated with pulmonary vascular disease. Clearly, a right-to-left shunt in a PDA is cause for significant concern and warrants further investigation. In adults with PDAs, the arterial wall may calcify, making an attempt at ligation or division hazardous. In these patients, ductal occlusion may require resection of the adjacent descending aorta with patch grafting or short-segment graft replacement (Dacron).



Aortopulmonary Septal Defect (Aortopulmonary Window)


An aortopulmonary septal defect is a communication between the ascending aorta and, usually, the main pulmonary artery. This is a rare defect; it relates to the common embryologic origin of the arterial trunk and failure of complete separation into the aorta and pulmonary artery. Defects are classified by their location: type I is proximal, just above the aortic sinuses; type II is more distal on the ascending aorta and often involves the origin of the right pulmonary artery; and type III is more distal and associated with a separate origin of the right pulmonary artery from the aorta (Fig. 59-7). An aortopulmonary septal defect may occur in isolation or in association with other conditions, including interrupted aortic arch (IAA) and anomalous origin of a coronary artery. Defects are typically large and responsible for a large left-to-right shunt with systemic pulmonary artery pressures. Children with this problem typically present with CHF, failure to thrive, and frequent respiratory infections. Diagnosis may be made by echocardiography, MRI, or catheterization.



All aortopulmonary septal defects are surgically closed; this lesion is not amenable to catheter-based closure and such an attempt is hazardous. A small defect may be ligated through a thoracotomy or median sternotomy approach, but this method is not recommended because of significant risk for rupture or incomplete closure. Surgical closure is accomplished with cardiopulmonary bypass support. Options for closure include complete division and separate patch repairs of the great vessel defects or a sandwich type of closure, using a patch to construct a common intervening wall; both methods are effective (Fig. 59-8).




Atrial Septal Defect


An isolated atrial septal defect (ASD) is one of the most common congenital cardiac lesions. The most frequently encountered ASD relates to a defect in the interatrial wall, as defined by the fossa ovalis. The defect develops as the result of incomplete closure of the embryologic patent foramen ovale; thus, the defect is a result of incomplete closure of the septum primum. Although the terminology can be confusing, these defects are typically termed secundum atrial septal defects. They present in a wide variety of configurations, ranging from single small defects to multiple fenestrations to complete absence of the septum primum. The confines of the defect may extend from the IVC orifice up to the superior atrial wall adjacent to the aortic root (Fig. 59-9).



The primary pathophysiologic derangement in ASDs relates to a significant left-to-right shunt in the setting of normal pulmonary vascular resistance. It must be emphasized, however, that even in the setting of a normal Rp, patients with ASDs are capable of transient right-to-left shunting, particularly during times of increased intrathoracic pressure. The effects of chronic, large left-to-right shunting (in some patients producing a Qp/Qs >3 : 1) include right heart volume overloading and enlargement. Most children are not overtly symptomatic but may exhibit some degree of exercise intolerance or frequent respiratory tract infection. Symptoms typically become more prevalent in adulthood and include dyspnea on exertion, palpitations and, ultimately, evidence of right heart failure. Pulmonary vascular disease is not a typical finding in secundum ASDs, but one may demonstrate an ASD in a patient with primary pulmonary hypertension. A rare form of presentation relates to the potential of right-to-left shunting at the atrial level; the ever-present risk for paradoxical embolus and cerebrovascular accident must be considered when recommending ASD closure.


Most centers recommend ASD closure before school age. The standard therapy for ASDs since the late 1950s has been surgical closure using cardiopulmonary bypass support. The defect is closed using direct suture closure, autologous pericardium, or prosthetic patch material (Fig. 59-10). This is an effective method, with a low associated perioperative risk, including the virtual absence of residual or recurrent defects, as noted in one study.14 Minimally invasive techniques for ASD closure have also gained popularity.



The potential for closing defects using nonsurgical methods has led to the development of catheter-based therapies, which are now being widely applied to large numbers of patients worldwide for the treatment of ASD. The most commonly used device is the Amplatzer septal occluder (St. Jude Medical, St. Paul, Minn) device, of nitinol metal mesh, which is placed percutaneously and delivered with echocardiographic and fluoroscopic guidance. Early reports have indicated an acceptable procedure-related complication rate and successful closure rate.15 It is clear, however, that the long-term effects of having such a device in mobile cardiac structures are not fully understood. Several recent reports have documented an alarming incidence of device erosion through the atrial wall and into the adjacent ascending aorta, as well as disruption of the conduction system.16,17 A recent case of late severe endocarditis involving a previously placed Amplatzer ASD device has highlighted the need for ongoing observation of the long-term consequences of placing large prosthetic devices into the circulation.18


Sinus venosus atrial septal defects occur as the result of embryologic malalignment between the superior vena cava (SVC) or IVC. These defects are not associated with the ovale fossa and are frequently associated with partial anomalous pulmonary venous return. A superior sinus venosus ASD occurs high in the atrium, near the orifice of the SVC. This lesion is frequently associated with anomalous drainage of a portion of the right lung to the SVC. An inferior sinus venosus ASD is located low in the atrium, often extending into the IVC orifice. This lesion is typically associated with anomalous pulmonary venous drainage of the entire right lung to the IVC (potentially intrahepatic); pulmonary sequestration and an abnormal systemic artery perfusing the right lower lobe, with origin from the abdominal aorta, may also be present. In patients with total anomalous pulmonary venous return (TAPVR) to the IVC, the anomalous pulmonary vein may be readily obvious on a plain chest radiograph and has been described as appearing like a saber (scimitar syndrome), first described by Sabiston and Neill.19


Surgery for sinus venosus ASDs is recommended for the same pathophysiologic reasons as secundum ASDs. The repair is not amenable to catheter techniques, and surgery is more complicated than for an isolated secundum ASD. Superior sinus venosus defects with partial anomalous pulmonary venous return to the SVC may be treated with an intracardiac patch baffle; however, in the setting of high drainage of the anomalous pulmonary veins, an SVC translocation operation (Warden procedure) may be necessary.20 Surgery for an inferior sinus venosus ASD with a scimitar vein can be more complicated, potentially involving the need for a patch baffle within the intrahepatic IVC, which may require periods of hypothermic circulatory arrest.



Ventricular Septal Defect


A VSD is a pathologic communication involving a defect in the interventricular septum. Defects are classified in terms of their location and surrounding structures. Patients may be entirely asymptomatic, depending on the size and location of the VSD, along with associated lesions and pulmonary vascular resistance. In the setting of otherwise normal cardiac morphology and appropriate pulmonary vascular resistance, the net shunt in patients with VSD is left to right; the Qp/Qs is dependent on the size of the defect and pulmonary resistance. Large defects result in large shunts, high right ventricular and pulmonary artery pressures, and significant pulmonary overcirculation, CHF, and left heart volume overload. In these settings, unrestrictive pulmonary blood flow exposes the patient to the risk for pulmonary vascular disease and Eisenmenger’s syndrome.


The ventricular septum can be best thought of in terms of the pathway of blood and associated cardiac anatomy. Thus, the right ventricular (RV) aspect of the septum has an inlet portion, midmuscular portion, apical, posterior, anterior, and outlet portions, and subaortic component. This knowledge aids in the classification of VSDs. Furthermore, defects are understood relative to their embryologic origins and have varying propensities for spontaneous decreases in size or closure.





Subarterial (Supracristal or Outlet) Ventricular Septal Defect


Subarterial VSDs occur in association with the annulus of the aortic valve, pulmonary valve, or both. The defects are almost always associated with significant prolapse of the adjacent aortic valve cusp, usually the right coronary cusp, which may lead to significant cusp distortion, aortic valve insufficiency, and even cusp perforation. The only mechanism for spontaneous closure of these defects relates to the cusp prolapse and valve distortion and is generally not complete or a favorable arrangement. All these defects are surgically closed because of the ongoing risk for aortic valve injury (Fig. 59-11).



The indications for surgery to close VSDs relate to the size of the VSD, degree of shunting, and associated lesions. Thus, small babies presenting with large VSDs, refractory heart failure, and large shunts undergo surgical closure of the defects in the newborn period, irrespective of age or size. Other defects are addressed based on the ongoing concerns of left-to-right shunting, aortic valve cusp distortion, and risk for endocarditis. Asymptomatic patients with evidence of significant shunts and cardiomegaly are proposed for surgical therapy. Prophylactic closure of small defects in asymptomatic patients with normal cardiac size and function is advocated by some surgeons because of the lifelong risk for endocarditis and comparatively low risk for surgery.


Although catheter-based therapies for some VSDs have been developed, particularly muscular defects, this mode of therapy is still not widely applicable to most VSDs.21 The complex relationship of many defects, including close association with the aortic valve and cardiac conduction tissue, makes the existing technology less than ideal. At present, surgery remains the primary mode of therapy for VSD closure. Defects are approached with the aid of cardiopulmonary bypass support and may be closed with various materials, including autologous pericardium (our preference), Dacron, polytetrafluoroethylene (PTFE), and homograft material. Surgical closure of VSDs is a low-risk procedure with a high expectation of complete closure.22 Challenging anatomic situations such as Swiss cheese septum or multiple apical muscular VSDs may be initially palliated by limiting pulmonary blood flow with a pulmonary artery band and deferring corrective surgery to later in life.



Atrioventricular Septal Defect (Atrioventricular Canal Defect)


Atrioventricular septal defects (AVSDs) are a complex constellation of cardiac lesions involving deficiency of the atrial septum, ventricular septum, and atrioventricular valves. This lesion results from an embryologic maldevelopment involving the endocardial cushions; thus, the term endocardial cushion defect is often applied. AVSDs may be partial, involving no ventricular level component, intermediate or transitional, involving a small restrictive VSD, or complete, involving a large nonrestrictive VSD. The atrioventricular valve tissue is always abnormal in AVSD, although there is great individual variability in terms of the severity of the valvular malformation and thereby valve function. Complete AVSDs are frequently seen in patients with trisomy 21, but do occur in patients with normal chromosomes. The morphology of the septal defects in this condition is different than that previously discussed. The ASD in this defect is termed a primum ASD and is distinctly separate from the ovale fossa. There is displacement of the atrioventricular node and bundle of His to the inferior aspect of the primum defect and atrioventricular junction, a feature of critical importance during surgical repair. Patients with AVSD have an inlet VSD, which may extend into the subaortic region and have a component of septal malalignment. The chordal support of the atrioventricular valves has a variable relationship to the interventricular septum. The relationship of the chordal support and superior bridging component of the left atrioventricular (AV) valve have been used to classify complete AVSD, as described by Rastelli and associates23: type A with superior leaflet and chordal support committed to the left side of the ventricular septum; type B with straddling, shared chordal support; and type C with a floating left superior leaflet component and chordal support on the right side of the ventricular septum (Fig. 59-12).



Patients with complete AVSD typically present in infancy with large left-to-right shunts, cardiomegaly, and CHF. Without surgical treatment, patients exhibit severe failure to thrive, a susceptibility to severe respiratory infections, and potential for early development of pulmonary vascular disease. Surgical repair is recommended in infancy (usually before 6 months of life) but may be necessary in the newborn period for neonates with refractory heart failure, especially in association with aortic arch anomalies. Patients with partial or intermediate defects may have the surgery deferred until later in childhood, depending on the degree of atrial level shunting and presence of atrioventricular valve regurgitation. AVSD may also present in unbalanced forms, with dominance of right- or left-sided components. In severely affected individuals, biventricular repair is not feasible, and patients are managed along a single-ventricle pathway. AVSD may also be found in association with TOF; this combination is associated with cyanosis and repair is more challenging than for either condition considered in isolation.


Surgery is the primary mode of therapy for patients with AVSD. Operative goals include complete closure of ASDs and VSDs and effective use of available AV valve tissue to achieve valve competence. As noted, the inferiorly displaced conduction tissue must be protected to avoid the complication of surgically induced AV block (Fig. 59-13). Patients are approached with the aid of cardiopulmonary bypass support. The atrial and ventricular septal components are closed with a common patch (single-patch method) or separate patches (two-patch technique). We believe the two-patch method to be superior in preserving AV valve tissue (Fig. 59-14).24 The critical component of the repair lies in the valve repair; typically, after suspending the valve tissue to the reconstructed septum, the line of coaptation between the superior and inferior leaflet components (cleft) is closed. However, care must be exercised to avoid valvular stenosis.




Perioperative care is predicated on an accurate and hemodynamically favorable repair. Patients with long-standing pulmonary overcirculation may have a potential for early perioperative pulmonary hypertensive crisis. This may require therapy, including continuous sedation, hyperventilation and, possibly, inhaled nitric oxide.



Aug 1, 2016 | Posted by in CARDIAC SURGERY | Comments Off on Congenital Heart Disease
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