Hypoplastic Left Heart Syndrome and the Staged Norwood Procedure
Hypoplastic left heart syndrome (HLHS) refers to a constellation of congenital cardiac anomalies characterized by marked hypoplasia or absence of the left ventricle and severe hypoplasia of the ascending aorta.
The first successful palliation of HLHS was reported by Norwood et al in a series of infants who underwent surgery from 1979-1981. The procedure has been refined technically over the years, but the essential components remain (1) atrial septectomy, (2) anastomosis of the proximal pulmonary artery to the aorta with homograft augmentation of the aortic arch, and (3) aortopulmonary shunt. Staged orthoterminal correction of HLHS with a Fontan operation using the right ventricle as the systemic ventricle was first reported in 1983 by Norwood et al. More recent reviews describe continued improvement in short- and long-term survival rates.
An alternative approach to staged reconstructive surgery is orthotopic cardiac transplantation. This was first performed successfully by Bailey in November 1985 when he transplanted the heart and ascending aorta of an 8-day-old neonate into a 4-day-old 2.8-kg infant. This followed years of research, including experimentation with xenotransplantation. The advantage of cardiac transplantation is replacement of an abnormal circulation with a normal 4-chambered heart in a single operation. Chief disadvantages of this approach are the limited availability of donor hearts and the requirement for lifelong immunosuppression.
Dramatic improvements in both staged reconstructive approaches and transplantation techniques have been achieved in recent years. Currently, both staged reconstruction and transplantation have a role in the management of HLHS. Staged reconstruction entails 3 procedures with an overall 5-year survival rate of approximately 70%. Long-term durability of the tricuspid valve and right ventricle at systemic workloads remains to be determined.
Cardiac transplantation offers a single operation with, perhaps, a lower operative mortality rate, yet 25% of neonates listed for transplantation do not receive donor hearts. In addition, after transplantation, neonates face a lifetime of immunosuppression with the attendant risks of rejection and infection. Both staged reconstructive surgery and transplantation have shown remarkable improvements in results with ongoing evolution of surgical techniques and improvements in perioperative care.
Supportive care only, without intervention, is becoming a less acceptable alternative for neonates with HLHS. Recommendations by any given pediatric cardiac surgical unit must take into consideration that center's results and expertise with the 2 approaches. Surgical techniques and results of staged reconstruction are reviewed in this article (see Surgical therapy).
History of the Procedure
The term hypoplastic left heart syndrome was introduced by Noonan and Nadas in 1958 to describe the morphologic features of combined aortic and mitral atresia. This followed Lev's description in 1952 of congenital cardiac malformations associated with underdevelopment of the chambers on the left side and a small ascending aorta and arch.
HLHS is a relatively common form of congenital heart disease, occurring in 7-9% of neonates in whom heart disease is diagnosed in the first year of life. Without surgical intervention, HLHS is fatal, accounting for 25% of cardiac deaths in the first week of life.
While the etiology of HLHS is unknown, Lev has postulated that premature narrowing of the foramen ovale leads to a faulty transfer of blood from the inferior vena cava (IVC) to the left atrium during fetal life. Thus, altered intrauterine hemodynamics may be the physiologic cause of HLHS. Other authors have postulated that the embryologic cause is severe underdevelopment of the left ventricular outflow in the form of isolated aortic valve atresia. This aortic atresia results in abnormal development of the remaining cardiac structures resulting from the associated blood flow patterns.
Systemic circulation depends on the right ventricle via a patent ductus arteriosus, and obligatory mixing of pulmonary and systemic venous blood occurs in the right atrium.
HLHS is often diagnosed in patients during the newborn period because of tachypnea and cyanosis within 24-48 hours of birth. When the ductus arteriosus begins to close, diminished systemic perfusion rapidly occurs, with pallor, lethargy, and diminished pulses. Cardiac examination reveals a dominant right ventricular impulse, a single second heart sound, and a nonspecific soft systolic murmur at the left sternal border. Ductal closure results in diminished systemic perfusion with the development of metabolic acidosis and renal failure.
The presence of HLHS is an indication for therapy. Without intervention, HLHS is, essentially, universally fatal within the first month of life. As survival rates for both staged repair and transplantation have improved, the continued role of comfort-measures-only therapy can be questioned. Certainly, both pediatric and adult patients routinely undergo therapy for conditions with far worse prognosis than HLHS.
Relevant anatomy and contraindications
Relevant Anatomy: HLHS refers to a constellation of congenital cardiac anomalies characterized by marked hypoplasia or absence of the left ventricle and severe hypoplasia of the ascending aorta.
Pathologic findings by Bharati et al in a series of 230 patients with HLHS included 105 with aortic atresia and mitral stenosis (45%), 95 with aortic and mitral atresia (41%), and 30 with severe aortic and mitral stenosis (13%). The dilated and hypertrophied right ventricle is the dominant ventricle and forms the apex of the heart. The tricuspid valve annulus is invariably dilated, and significant anomalies in morphology have been described in 5-7% of patients. Clinically significant tricuspid regurgitation has been reported by both Barber and Chang in 8-10% of patients studied, and it has been identified as a significant risk factor in short- and long-term survival.
In 95% of these infants, the ventricular septum is intact and the left ventricular cavity is only a small slit with thick endocardial fibroelastosis. The ascending aorta is usually very small, ranging in size from 1-8 mm as measured using 2-dimensional echocardiography; mean diameter is 3.8 mm, and in 55% of patients, the ascending aorta is smaller than 3 mm. The portion of ascending aorta between the atretic valve and the innominate artery serves only as a conduit for the retrograde flow of blood into the coronary arteries. The main pulmonary artery is very large and is the origin of a large ductus arteriosus carrying blood from the right ventricle into the aorta. A localized coarctation of the aorta is present in 80% of patients.
Contraindications: Other than the presence of a lethal chromosomal anomaly, other anomalies, or an extremely poor clinical condition, no absolute contraindications exist to surgical repair. However, several factors have been noted to convey higher surgical risk. Patients older than 1 month undergoing the Norwood procedure, patients with severe obstruction to pulmonary venous return, and patients with significant noncardiac congenital conditions (e.g., prematurity, low birth weight, chromosomal anomalies) are at high risk. Details of the outcomes for standard-risk and high-risk patients are outlined in Outcome and Prognosis.
Routine laboratory studies, such as CBC, platelets, electrolytes, BUN, creatinine, liver function tests, and coagulation studies, are indicated. In addition to ensuring that laboratory test values return to reference ranges, maintain the hematocrit at 45% or more if the patient is cyanotic.
Routine serial monitoring of arterial blood gases is important in balancing the relative pulmonary and systemic blood flows in patients with single ventricle physiology (see Medical therapy, Surgical therapy).
Chest radiographs reveal cardiomegaly and increased pulmonary vascular markings.
In 2% of patients, a reticular pattern of obstructed pulmonary venous return is seen because of a restrictive atrial septal defect.
Diagnosis is made using 2-dimensional and color Doppler echocardiography for determination of cardiac morphology and evaluation of the arch hypoplasia.
Color-flow Doppler images demonstrate that the blood flow in the ascending aorta is typically retrograde.
Electrocardiogram results demonstrate right atrial enlargement and right ventricular hypertrophy.
Cardiac catheterization is rarely necessary. An exception would be to gain additional information in patients with borderline left ventricle size to assist in the decision-making process regarding the optimal treatment method.
Initial medical support in infants with HLHS requires a specific medical regimen. The goals of preoperative management are to maintain ductal patency and to provide the appropriate balance between the systemic and pulmonary vascular resistances. Intravenous prostaglandin E is infused at 0.05 mcg/kg/min to maintain patency of the ductus arteriosus. This dose may be titrated to keep the ductus arteriosus open, while minimizing the risk of apnea.
Oxygen saturation is monitored by pulse oximetry. Acidosis is rapidly reversed using sodium bicarbonate. The fraction of inspired oxygen (FIO2) is adjusted to maintain a relative hypoxemia (oxygen saturation 75-80%), which aids in preventing the pulmonary vasodilatation associated with high oxygen concentrations. Even in the neonate who is being resuscitated because of circulatory collapse, ventilation with a high concentration of oxygen is avoided, since it may only further decrease pulmonary vascular resistance and systemic blood flow.
Blood transfusion should be performed to maintain the hematocrit between 45-50%. Mechanical ventilation is avoided when possible, but infants on ventilation may require sedation with intravenous fentanyl to prevent tachypnea. In patients with significant pulmonary over circulation, hypoventilation to maintain a mild respiratory acidosis (partial pressure of carbon dioxide [PCO2] 45-55 mm Hg) and elevation of pulmonary vascular resistance may be used. Occasionally, inhaled nitrogen can be added to reduce the FIO2 to between 16-18% to increase pulmonary vascular resistance. Inotropic support is advantageous in patients with depressed right ventricular function.
Nourishment usually is provided via intravenous hyperalimentation, which avoids the added risk of necrotizing enterocolitis prior to surgery. Diuretics are added, as necessary, when pulmonary congestion becomes apparent. This regimen simulates the fetal balance of pulmonary and systemic vascular resistance, stabilizing the infant while deciding on therapeutic options.
Parents of children with HLHS are presented with the following 3 options: (1) supportive therapy only (leading usually to rapid demise), (2) staged reconstruction, and (3) orthotopic cardiac transplantation. Each institution must assess its results with the various modes of therapy and counsel the parents accordingly. As outcomes of palliative procedures and heart transplantation in patients with HLHS have improved, even surpassing therapies for other complex forms of congenital heart disease in some patients, the first option of supportive therapy only has been challenged. The techniques and results of staged reconstruction are discussed below.
The goal of staged reconstruction is a Fontan procedure, creating separate pulmonary and systemic circulations supported by a single (right) ventricle. The initial stage must provide unobstructed systemic blood flow from the right ventricle to the aorta and coronary arteries, relieve any obstruction to pulmonary venous return, and limit pulmonary blood flow by virtue of an appropriately sized systemic–to–pulmonary artery shunt.
As a result of the relatively high pulmonary vascular resistance present in the newborn period, an arterial shunt is necessary, and the right ventricle performs the increased volume of work of both the pulmonary and systemic circulations. Preservation of right ventricular function has been aided by using smaller initial aortopulmonary shunts to limit right ventricular volume overload and by using an interim procedure between the Norwood and Fontan operations. This staging procedure, either a bidirectional Glenn anastomosis or a hemi-Fontan procedure, usually is performed at age 6 months.
These procedures provide adequate pulmonary blood flow while decreasing volume overload to the right ventricle and improving effective pulmonary blood flow until the patient can undergo a completion Fontan procedure. As described in detail in Second-stage palliation: Hemi-Fontan or bidirectional Glenn anastomosis, the hemi-Fontan procedure is a modification of the bidirectional Glenn procedure. The hemi-Fontan procedure involves (1) a side-to-side connection between the superior vena cava (SVC)/right atrial junction and the pulmonary arteries, (2) routine augmentation of the branch pulmonary arteries, and (3) temporary patch closure between the pulmonary arteries and the right atrium.
First-stage palliation - Norwood procedure
Through a midline sternotomy, cardiopulmonary bypass (CPB) is established. A minimum of 20 minutes of cooling to a core temperature of 18°C is begun for deep hypothermic circulatory arrest. Alternatively, some groups have reported the use of regional low-flow cerebral perfusion in lieu of deep hypothermic circulatory arrest (see Future and Controversies).
Regardless of the technique used, the septum primum is excised completely (atrial septectomy). The ductus is ligated and divided. The main pulmonary trunk is divided proximally to the bifurcation of the pulmonary arteries. The resultant opening in the pulmonary artery is closed with a patch of pericardium, polytetrafluoroethylene, or homograft. The remaining ductal tissue (on the undersurface of the aortic arch) is excised completely, and the incision is extended at least 10 mm further down the descending aorta into a normal-appearing and normal-caliber aorta (see Figure 1).
This incision is extended proximally under the transverse arch and down the diminutive ascending aorta until the level of the previously divided main pulmonary trunk is reached (see Image 2).
A cryopreserved pulmonary allograft is trimmed to fashion a patch that will serve to enlarge the aorta and allow anastomosis to the proximal main pulmonary trunk (see inset in Image 2). The remainder of the aorta is attached to the pulmonary allograft, incorporating the main pulmonary trunk proximally. The cannulas are replaced to begin bypass and commence systemic rewarming to 37°C. A polytetrafluoroethylene shunt is placed from the innominate artery to the central pulmonary artery during rewarming (see Image 3). A 4-mm shunt is used in patients weighing more than 3.5-4 kg; smaller patients receive a 3.5-mm shunt. The distal end of the shunt is placed centrally on the pulmonary arteries, rather than onto the right pulmonary artery, to promote even distribution of blood flow to both lungs.
Second-stage palliation - Hemi-Fontan or bidirectional Glenn anastomosis procedure
The hemi-Fontan operation or a bidirectional Glenn anastomosis typically is performed in infants aged 3-10 months to minimize the period of time during which the right ventricle is subject to volume overload. Cardiac catheterization is performed prior to this procedure to evaluate pulmonary vascular resistance, pulmonary artery anatomy, tricuspid valve regurgitation, and right ventricular function.
To perform a bidirectional Glenn procedure, CPB is achieved with neoaortic arch cannulation and separate right-angle IVC and right-angle SVC cannulae. The aortopulmonary shunt is ligated and divided when CPB is initiated. If any stenosis of the pulmonary artery secondary to the prior shunt or patch exists, the stenosis is repaired with patch augmentation. The azygous vein is ligated and divided. The SVC is transected and anastomosed in an end-to-side fashion to the superior aspect of the right pulmonary artery. The cardiac end of the transected SVC is over sewn.
The hemi-Fontan procedure has the same physiologic factors as a bidirectional Glenn anastomosis, but it includes an anastomosis of the pulmonary arteries to an incision in the atriocaval junction. The cavopulmonary connection may be performed under a brief period of deep hypothermic circulatory arrest. Alternatively, cannulation of the IVC and high on the SVC can be used to perform the procedure entirely during CPB.
Whether the procedure is performed under circulatory arrest or during CPB, the remainder of the procedure is the same. The aortopulmonary shunt is divided, and the pulmonary arteries are mobilized from the right to the left upper lobe. The azygous vein is ligated. The right atrium is opened along the superior aspect of the appendage, and a corresponding incision is made transversely along the confluence of the branch pulmonary arteries (see upper left of Image 4). The posterior aspect of the right arteriotomy is anastomosed to the inferior aspect of the pulmonary arteriotomy (see upper right of Image 4).
A patch of pulmonary allograft tissue is fashioned to augment the pulmonary arteries. The allograft patch is begun at the left upper lobe, incorporating a separate end-to-side anastomosis for a left SVC, if necessary (see lower portion of Image 4). A patch is placed within the right atrium, which isolates SVC return into the pulmonary arteries and provides an unobstructed pathway for connection of IVC return during the Fontan procedure (see lower portion of Image 4). The atrial septal defect is inspected and enlarged, if necessary, which is completed best by cutting back the coronary sinus into the left atrium. Tricuspid valve repair also is performed as needed.
The advantage of the hemi-Fontan is that it shortens the length of time of CPB and dissection required for the completion Fontan procedure, which requires only the removal of the intra-atrial patch and placement of a lateral tunnel in the right atrium from the IVC to the SVC. In addition, routine augmentation of the branch pulmonary arteries helps optimize the anatomy for the completion Fontan procedure.
Third-stage palliation - Fontan procedure
The completion Fontan procedure usually is performed in children aged 18-24 months. The infant is evaluated using cardiac catheterization prior to surgery. The Fontan technique used by the authors for HLHS anatomy is the technique termed total cavopulmonary connection with a lateral tunnel. After achieving CPB, the right atrium is opened.
If a hemi-Fontan procedure has been performed, the intra-atrial baffle is resected. In bidirectional Glenn anastomosis, a right atrium–to–pulmonary artery anastomosis is created. A baffle of polytetrafluoroethylene is fashioned and placed inside of the right atrium to convey the IVC return to the cavopulmonary connection (see Image 5). This technique minimizes the possibility of obstruction of the pulmonary venous return, which can be caused by an atriopulmonary anastomosis. Fenestration of the baffle may help prevent complications in high-risk patients and shorten the period of pleural drainage. Some centers opt for an extracardiac, instead of an intracardiac, lateral tunnel Fontan.
First-stage palliation: Norwood procedure
After weaning from CPB, an atrial-monitoring catheter is placed to measure central venous pressure, and infusion of inotropes is initiated. University of Michigan medical staff routinely use continuous infusions of milrinone and low-dose dopamine, adding epinephrine in doses of 0.02-0.06 mg/kg/min if hypotension is significant. Ventilation, with an initial FIO2 of 100% to achieve a PCO2 of approximately 35 mm Hg, is initiated and adjusted depending on the systemic arterial oxygen saturation and the systemic perfusion. If poor peripheral perfusion with systemic saturation in excess of 80-85% is noted, the FIO2 and minute ventilation are decreased to avoid excess pulmonary vasodilatation. The opposite maneuvers are used if systemic oxygen saturation is less than 70-75%.
Postoperative management is aimed at maintaining the delicate balance between the systemic and pulmonary vascular resistances and, therefore, relative systemic and pulmonary blood flow. Many regimens of ventilation, inotropic support, and vasodilatory support have been used, and multiple indicators of perfusion adequacy (mixed venous oxygen, lactate) have been measured with varying degrees of success.
Ideally, systemic arterial saturation should be maintained at 75-80%, which usually indicates that an optimal pulmonary-to-systemic blood flow ratio of less than 1 has been achieved. However, measurements of mixed venous oxygen saturation and pulmonary venous oxygen saturation are necessary to accurately assess the ratio of pulmonary blood flow (Qp) to systemic blood flow (Qs). The authors have found that serial lactate measurements provide an excellent indication of low cardiac output, and they rely on these determinations rather than mixed venous oxygen saturations.
Second- and third-stage palliation: Hemi-Fontan and Fontan procedures
For second- and third-stage operations, maintaining a low pulmonary vascular resistance is paramount. The pulmonary blood flow no longer is driven by an arterial shunt but by central venous pressure. Hypoxia and acidosis, which increase pulmonary vascular resistance, are avoided. While mild respiratory alkalosis may be beneficial for pulmonary vascular resistance, a pH higher than 7.45-7.50 decreases cerebral blood flow and, hence, SVC return. After the hemi-Fontan procedure is performed, this decrease in SVC return decreases pulmonary blood flow. Inhaled nitrous oxide (NO) also may be used to decrease pulmonary vascular resistance but is needed infrequently.
After discharge from the hospital, regular cardiovascular evaluations are important. The child should be carefully observed for aortic arch obstruction, tricuspid insufficiency, and increasing cyanosis secondary to a limited atrial septal defect, shunt stenosis, or pulmonary artery distortion. For other long-term concerns, see Complications and Outcomes and Prognosis.
Complications resulting from a procedure of the magnitude of the Norwood palliation are fairly common. Complications may include bleeding, low cardiac output syndrome, and arrhythmia in the immediate postoperative period. Aggressive correction of thrombocytopenia and coagulation factors is warranted. Poor peripheral and end-organ perfusion may represent poor cardiac output or pulmonary over circulation, which may be treated by inotropic support or manipulation of relative pulmonary and systemic resistances. Common arrhythmias include junctional ectopic tachycardiac, which can be treated either with surface cooling to 35-36°C and pacing or with amiodarone infusion.
Incidence of unexplained sudden death, both in the immediate postoperative period and after discharge, remains problematic. In the postoperative period, the authors found that serial serum lactate determinations demonstrating failure to clear lactic acidosis have been helpful in predicting patients who will do poorly despite an apparently stable clinical condition.
Shunt complications, such as thrombosis, can occur. All patients are started on low-dose aspirin when they begin enteral nutrition. Other causes of increasing cyanosis during the postoperative period include pulmonary artery stenosis or distortion and restriction at the level of the atrial septal defect.
Evaluation prior to the hemi-Fontan procedure may reveal pulmonary artery stenosis, particularly of the left branch or at the insertion of the shunt. These stenosis are managed with patch augmentation during the hemi-Fontan procedure. Residual coarctation should be rare if the initial homograft patch is brought sufficiently onto the descending aorta during the Norwood procedure. Postoperative coarctation usually can be managed with balloon dilatation or, if necessary, surgical augmentation.
Long-term complications following the Fontan operation include atrial arrhythmia, thromboembolic events, and protein-losing enteropathy. Atrial arrhythmias are less common with the current techniques of cavopulmonary connections and may be treated with standard antiarrhythmic therapy. All of the authors' patients who undergo the Fontan procedure are maintained on aspirin therapy, while others have advocated low-dose warfarin as prophylaxis against thromboembolism. Patients in whom the classic atriopulmonary connection Fontan procedure is performed with a dilated right atrium may benefit from conversion to a lateral tunnel or extracardiac Fontan operation to treat both arrhythmia and thrombosis.
Protein-losing enteropathy remains a difficult problem, affecting as many as 5% of patients who undergo the Fontan procedure. Treatment with intravenous infusions of albumen and immunoglobulin are supportive but not curative. Several other methods, including intravenous heparin, Fontan takedown, and cardiac transplantation, have been used with varying success.
OUTCOME AND PROGNOSIS
Bove et al at the University of Michigan studied first-stage palliation of HLHS from January 1990 to August 1995 in 158 patients. All patients had classic HLHS, defined as right ventricle–dependent circulation, in association with atresia or severe hypoplasia of the aortic valve. Patients were subdivided into a standard-risk (n=127) population and a high-risk (n=31) population. High-risk patients included those undergoing the Norwood procedure after age 1 month, patients with severe obstruction to pulmonary venous return, and patients with significant noncardiac congenital conditions (ie, prematurity, low birth weight, chromosomal anomalies).
Hospital survivors numbered 120 (76%). The hospital survival rate was significantly better in the 127 standard-risk patients (86%) than in the high-risk group (42%). The risk factor analysis failed to reveal any effect on outcome by the morphologic subgroup, ascending aorta size, shunt size, initial pH at hospital presentation, or duration of circulatory arrest.
Among 151 patients at The Children's Hospital of Philadelphia in a report by Norwood et al, 42 (28%) early deaths and 9 (5%) late deaths occurred. In a Children's Hospital Boston series reported by Jonas et al, 78 neonates underwent palliative reconstructive surgery from 1983-1991. Hospital deaths numbered 29 (37%). Analysis of deaths revealed a greater risk of hospital death for infants with aortic atresia and mitral atresia, especially those with ascending aortic dimensions of less than 2 mm. However, in the authors' experience, these conditions have not been associated with increased risk.
Hospital records of 114 patients undergoing the hemi-Fontan procedure for HLHS between August 1993 and April 1998 at the University of Michigan Medical Center were reviewed by Douglas et al. The overall hospital survival rate was 98% (112/114). Sinus rhythm was present in 92% of patients. At the time of publication, 79 of the patients had undergone the completion Fontan procedure, with 74 survivors (94%). A similar study by Forbess et al from the Children's Hospital Boston also revealed that a cavopulmonary anastomosis performed as a second-stage procedure for HLHS reduced mortality and improved intermediate survival rates.
One hundred consecutive patients with classic HLHS underwent a Fontan procedure at the University of Michigan between February 1992 and April 1998. The survival rate in patients (n=52) undergoing surgery in the second half of the study and treated with a prior hemi-Fontan procedure at second-stage palliation was 98%, as reported by Mosca et al. No deaths have occurred in patients undergoing the last 125 consecutive Fontan procedures for HLHS. Several other centers also have reported significant improvements in survival rates following the Fontan procedure in patients with HLHS.
Similar to any patient with cyanotic congenital heart disease, patients with HLHS are at risk for neurodevelopmental delay for multiple reasons. Cyanosis, congestive heart failure, and CNS abnormalities are associated with HLHS and can contribute to developmental delay. In addition, CPB and hypothermic circulatory arrest at the time of repair can cause neurologic injury.
In a recent study from the University of Michigan Medical Center, Goldberg and colleagues evaluated 51 patients with single ventricle physiology, 26 patients with HLHS, and 25 patients with other cardiac anomalies. The primary testing methods were the Wechsler Preschool and Primary Scales of Intelligence, revised for children aged 34-87 months, and the Wechsler Intelligence Scale, third edition, for children aged 72 months to 17 years. Additional tests included the Bayley Scales of Infant Development, the Vineland Adaptive Behavior Scales, and the Child Behavior Checklist.
Results indicated that children with HLHS scored statistically lower than children without HLHS with single ventricles. However, neither group scored significantly differently than population standards. As has been seen in children with congenital heart disease in general, patients in this study scored significantly better on tests of verbal intelligence than on tests of motor skills. Socioeconomic status, hypothermic circulatory arrest, and perioperative seizures were significant risk factors for impaired neurodevelopmental outcome. Duration of CPB, cardiac arrest requiring resuscitation, and clinical shock or pH less than 7.10 did not correlate with a poor neurodevelopmental result.
FUTURE AND CONTROVERSIES
Several groups have begun to use the techniques of regional cerebral perfusion for aortic arch reconstruction in lieu of deep hypothermic circulatory arrest. For this technique, the proximal anastomosis of the modified Blalock-Taussig shunt is performed prior to arresting the heart. Then, the arterial cannula can be placed into the shunt, and perfusion administered to the innominate artery. Whether these techniques will improve perioperative survival rates or long-term neurodevelopmental outcomes has yet to be determined.
Currently, a number of groups are advocating the use of an extracardiac conduit to complete the Fontan procedure. This technique may offer significant advantages, yet patients may be exposed to the risks of thromboembolic complications inherent in prosthetic conduits in the venous system.
Future considerations for the Fontan procedure in this subgroup of patients include minimization of thromboembolic events, preservation of right ventricular and tricuspid valve function, and prevention of arrhythmias.
Figure 1. Hypoplastic left heart syndrome and the staged Norwood procedure. The main pulmonary artery and ductus arteriosus have been divided. Dashes indicate the line of incision on the hypoplastic ascending aorta. Image courtesy of Edward L. Bove, MD.
Figure 2. Hypoplastic left heart syndrome and the staged Norwood procedure. The ascending aorta is opened and sutured to the adjacent proximal main pulmonary artery. A patch of pulmonary homograft is fashioned to create the neoaorta (inset). Image courtesy of Edward L. Bove, MD.
Figure 3. Hypoplastic left heart syndrome and the staged Norwood procedure. Completed Norwood procedure showing reconstructed neoaorta and modified Blalock-Taussig shunt from the innominate artery to the confluence of the branch pulmonary arteries. Image courtesy of Edward L. Bove, MD.
Figure 4. Hypoplastic left heart syndrome and the staged Norwood procedure. Hemi-Fontan procedure. The modified Blalock-Taussig shunt is ligated, and incisions are made in the right atrial appendage and pulmonary arteries (upper left). The posterior aspect of the right atriotomy is anastomosed to the inferior aspect of the pulmonary arteriotomy (upper right). A patch of polytetrafluoroethylene is placed to prevent the superior vena cava return from entering the right atrium. The cavopulmonary connection is roofed with a patch of pulmonary homograft (lower). Image courtesy of Koji Kagasaki, MD.
Figure 5. Hypoplastic left heart syndrome and the staged Norwood procedure. Fontan procedure. Through a right atriotomy, the polytetrafluoroethylene (PTFE) patch has been removed. A new PTFE patch is placed to baffle the inferior vena cava return to the cavopulmonary connection constructed during the hemi-Fontan procedure (left). The arrows indicate the systemic venous return bypassing the right heart to directly enter the pulmonary arteries (right). Image courtesy of Edward L. Bove, MD.