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. Still, 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 the replacement of an abnormal circulation with a normal 4-chambered heart in a single operation. The chief disadvantages of this approach are the limited availability of donor hearts and the requirement for lifelong immunosuppression.

In recent years, dramatic improvements have been made in staged reconstructive approaches and transplantation techniques. Both staged reconstruction and transplantation are currently involved in the management of HLHS. Staged reconstruction entails three procedures, with an overall 5-year survival rate of approximately 70%. The 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 the ongoing evolution of surgical techniques and improvements in perioperative care.

Supportive care alone, without intervention, is becoming a less acceptable alternative for neonates with HLHS. Recommendations by any given pediatric cardiac surgical unit must consider the center's results and expertise with the two approaches. This article reviews surgical techniques and results of staged reconstruction (see Surgical therapy).

History of the Procedure

Noonan and Nadas introduced the term hypoplastic left heart syndrome in 1958 to describe the morphologic features of combined aortic and mitral atresia. This followed Lev's 1952 description of congenital cardiac malformations associated with the underdevelopment of the chambers on the left side and a small ascending aorta and arch.

Frequency

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.

Etiology

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.

Pathophysiology

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.

Clinical

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.

Indications

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. Indeed, both pediatric and adult patients routinely undergo therapy for conditions with far worse prognoses 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 morphological anomalies 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 an essential 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 tiny slit with thick endocardial fibroelastosis. The ascending aorta is usually very small, ranging from 1-8 mm, as measured using 2-dimensional echocardiography; the mean diameter is 3.8 mm, and in 55% of patients, the ascending aorta is smaller than 3 mm. The portion of the 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 originates from 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 inferior 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.

WORKUP

Lab Studies

Routine laboratory studies are indicated, such as CBC, platelets, electrolytes, BUN, creatinine, liver function tests, and coagulation studies. 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 essential for balancing the relative pulmonary and systemic blood flows in patients with single-ventricle physiology (see Medical therapy and surgical therapy).

Imaging Studies

Chest radiography

Chest radiographs reveal cardiomegaly and increased pulmonary vascular markings.

In 2% of patients, a restrictive atrial septal defect causes a reticular pattern of obstructed pulmonary venous return.

Doppler/echocardiography

Diagnosis is made using 2-dimensional and color Doppler echocardiography to determine cardiac morphology and evaluate arch hypoplasia.

Color-flow Doppler images demonstrate that the blood flow in the ascending aorta is typically retrograde.

Other Tests

Electrocardiogram results demonstrate right atrial enlargement and right ventricular hypertrophy.

Diagnostic Procedures

Cardiac catheterization is rarely necessary. An exception is to obtain additional information on patients with borderline left ventricle size to assist in decision-making regarding the optimal treatment method.

TREATMENT

Medical therapy

Initial medical support in infants with HLHS requires a specific medical regimen. The goals of preoperative management are to maintain ductal patency and provide the appropriate balance between systemic and pulmonary vascular resistances. Intravenous prostaglandin E is infused at 0.05 mcg/kg/min to maintain the 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 relative hypoxemia (oxygen saturation 75-80%), preventing the pulmonary vasodilatation associated with high oxygen concentrations. Even in the neonate 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 overcirculation, hypoventilation may be used to maintain a mild respiratory acidosis (partial pressure of carbon dioxide [PCO2] 45-55 mm Hg) and elevation of pulmonary vascular resistance. Occasionally, inhaled nitrogen can be added to reduce the FIO2 to 16-18% to increase pulmonary vascular resistance. Inotropic support is advantageous in patients with depressed right ventricular function.

Nourishment is usually provided via intravenous hyperalimentation, which avoids the added risk of necrotizing enterocolitis before surgery. When pulmonary congestion becomes apparent, diuretics are added as necessary. This regimen simulates the fetal balance of pulmonary and systemic vascular resistance, stabilizing the infant while deciding therapeutic options.

Surgical therapy

Parents of children with HLHS are presented with the following three options: (1) supportive therapy only (usually leading 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 has only been challenged. The techniques and results of staged reconstruction are discussed below.

The goal of staged reconstruction is a Fontan procedure, which creates 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 an appropriately sized systemic–to–pulmonary artery shunt.

Due to the relatively high pulmonary vascular resistance 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. Preserving right ventricular function has been aided by smaller initial aortopulmonary shunts to limit right ventricular volume overload and by an interim procedure between the Norwood and Fontan operations. This staging procedure, either a bidirectional Glenn anastomosis or a hemi-Fontan procedure, is usually performed at age 6 months.

These procedures provide adequate pulmonary blood flow while decreasing volume overload to the right ventricle and improving adequate pulmonary blood flow until the patient can complete the Fontan procedure. As described in detail in Second-stage palliation: Hemi-Fontan or bidirectional Glenn anastomosis, the hemi-Fontan procedure modifies 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.

Intraoperative details

First-stage palliation - Norwood procedure

Cardiopulmonary bypass (CPB) is established through a midline sternotomy. For deep hypothermic circulatory arrest, a minimum of 20 minutes of cooling to a core temperature of 18°C is begun. Alternatively, some groups have reported using regional low-flow cerebral perfusion instead of deep hypothermic circulatory arrest (see Future and Controversies).

Regardless of the technique, 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 it reaches the level of the previously divided main pulmonary trunk (see Image 2).

A cryopreserved pulmonary allograft is trimmed to fashion a patch that will 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. During rewarming, a polytetrafluoroethylene shunt is placed from the innominate artery to the central pulmonary artery (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 is typically performed in infants aged 3-10 months to minimize the time the right ventricle is subject to volume overload. Cardiac catheterization is performed before 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 pulmonary artery stenosis 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 oversewn.

The hemi-Fontan procedure has the same physiologic factors as a bidirectional Glenn anastomosis, but it includes anastomosis of the pulmonary arteries to an incision in the aortocaval junction. The cavopulmonary connection may be performed during a brief period of deep hypothermic circulatory arrest (CPB). Alternatively, cannulation of the IVC and high on the SVC can be used to perform the procedure entirely during CPB.

The remainder of the procedure is the same whether the procedure is performed under circulatory arrest or during CPB. 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 the 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 is also performed as needed.

The advantage of the hemi-Fontan is that it shortens the time of CPB and dissection required to complete the Fontan procedure. This procedure 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 of the Fontan procedure.

Third-stage palliation - Fontan procedure

The completion of the Fontan procedure is usually performed in children aged 18-24 months. The infant is evaluated using cardiac catheterization before surgery. The Fontan technique used by the authors for HLHS anatomy is 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. A right atrium–to–pulmonary artery anastomosis is created in bidirectional Glenn anastomosis. A baffle of polytetrafluoroethylene is fashioned and placed inside 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 an atriopulmonary anastomosis can cause. 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.

Postoperative details:

First-stage palliation: Norwood procedure

After weaning from CPB, an atrial-monitoring catheter is placed to measure central venous pressure and an infusion of inotropes is initiated. University of Michigan medical staff routinely use continuous milrinone and low-dose dopamine infusions, 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 above 80-85% is noted, the FIO2 and minute ventilation is decreased to avoid excess pulmonary vasodilatation. The opposite maneuvers are used if systemic oxygen saturation is less than 70-75%.

Postoperative management aims to maintainlicate 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 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 is no longer 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 benefit pulmonary vascular resistance, a pH higher than 7.45-7.50 decreases cerebral blood flow and, hence, SVC return. After the hemi-Fontan procedure, this decrease in SVC return decreases pulmonary blood flow. Inhaled nitrous oxide (NO) may also decrease pulmonary vascular resistance but is needed infrequently.

Follow-up care

After discharge from the hospital, regular cardiovascular evaluations are essential. 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, Outcomes, and Prognosis.

COMPLICATIONS

Complications resulting from a procedure of the magnitude of the Norwood palliation are relatively 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 helped predict patients who will do poorly despite an stable clinical condition.

Shunt complications, such as thrombosis, can occur. When they begin enteral nutrition, all patients are started on low-dose aspirin. 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 before the hemi-Fontan procedure may reveal pulmonary artery stenosis, particularly of the left branch or at the insertion of the shunt. These stenoses 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 can usually 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 familiar 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 arrhythmia and thrombosis.

Protein-losing enteropathy remains a complex problem, affecting as many as 5% of patients who undergo the Fontan procedure. Treatment with intravenous infusions of albumen and immunoglobulin is supportive but not curative. Several other methods, including intravenous heparin, Fontan takedown, and cardiac transplantation, have been used with varying success.

OUTCOME AND PROGNOSIS

First-stage palliation

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).

The number of hospital survivors was 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, according to 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.

Second-stage palliation

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 of the 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.

Third-stage palliation

Between February 1992 and April 1998, the University of Michigan treated 100 consecutive patients with classic HLHS with a Fontan procedure. As reported by Mosca et al., 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%. No deaths have occurred in patients undergoing the last 125 consecutive Fontan procedures for HLHS. Several other centers have also reported significant improvements in survival rates following the Fontan procedure in patients with HLHS.

Neurodevelopmental outcomes

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 with HLHS, and 25 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 outcomes. 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 using regional cerebral perfusion techniques for aortic arch reconstruction instead of deep hypothermic circulatory arrest. In this technique, the proximal anastomosis of the modified Blalock-Taussig shunt is performed before arresting the heart. Then, the arterial cannula can be placed into the shunt, and perfusion can be administered to the innominate artery. Whether these techniques will improve perioperative survival rates or long-term neurodevelopmental outcomes has yet to be determined.

Several groups are advocating the use of an extracardiac conduit to complete the Fontan procedure. This technique may offer significant advantages, but 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 TEXT

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 polytetrafluoroethylene patch 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. The polytetrafluoroethylene (PTFE) patch has been removed through a right atriotomy. 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 enter the pulmonary arteries (right) directly. Image courtesy of Edward L. Bove, MD.

References

http://emedicine.medscape.com/article/904137-overview