Norwood Procedure

Anatomy and Physiology

HLHS is the most common type of congenital heart disease observed in patients undergoing a Norwood procedure. Characterized by the underdevelopment of left-sided heart structures, HLHS manifests as an inability to supply adequate systemic outflow. HLHS often coexists with various degrees of distal outflow obstruction, such as hypoplastic aortic arch or coarctation of the aorta. Within the heart, oxygenated and deoxygenated blood is completely mixed across the atrial septum, reflecting a parallel circulation pattern rather than the series circulation observed in a normally developed heart. Consequently, the right ventricle assumes the dual role of supplying systemic blood flow through the patent ductus arteriosus while also directing pulmonary blood flow through the main pulmonary artery.[5]

HLHS subtypes are classified according to the development of the mitral and aortic valves. The most common subtype is mitral atresia with aortic atresia.[5] HLHS is associated with other congenital heart lesions, including total anomalous pulmonary venous return.[8] Other forms of congenital heart disease may also require a neonatal Norwood procedure.

The primary objective of surgery for HLHS is not curative but rather palliative, aiming to establish a stable source of systemic and pulmonary blood flow for the affected infant. The Norwood procedure, typically performed within the first week of life, is the initial step in this palliative strategy. Subsequent surgical interventions, including a second operation at 4 to 6 months and a third operation at 3 to 5 years of age, further support the single ventricle palliation approach, ultimately aiming to bridge the patient to a heart transplant.[6][7]

Immediately after birth, patients with HLHS initiate prostaglandin E1 infusion to ensure ductal patency and ductal-dependent systemic blood flow. Depending on the level of restriction of the atrial septum, neonates may also need balloon atrial septostomy to ensure adequate mixing. A prenatal diagnosis of HLHS with a severely restrictive atrial septum should prompt a planned delivery at a highly specialized center. This subgroup of patients may require emergent postnatal intervention and carries elevated morbidity and mortality risks. Additionally, if pulmonary venous return is obstructed, these infants require emergent surgical intervention.[9] 

Indications

Without surgical intervention, all patients born with single ventricle congenital heart disease face inevitable mortality due to the underlying anatomy and physiology leading to end-stage heart failure. While most commonly associated with HLHS in neonates, the Norwood procedure also holds clinical relevance for other functional single ventricle anomalies, including double-inlet left ventricle, hypoplastic right heart syndrome, and tricuspid atresia, among others.[8] Infants with variants of congenital heart disease at risk of decreased systemic cardiac output from left-sided outflow obstruction may benefit from a Norwood procedure. In some cases, uncertainty regarding the heart's ability to function with 2 separate ventricles prompts the consideration of a neonatal Norwood procedure, allowing growth into infancy and early childhood, with the potential for future septation and biventricular repair.

Stabilization immediately after birth is crucial; the Norwood procedure requires prolonged cardiopulmonary bypass and carries inherent morbidity and mortality risks. Patients may undergo balloon atrial septostomy preoperatively to enhance mixing and alleviate left atrial hypertension, particularly if the atrial septum is restrictive. Delivery at a specialized tertiary care institution equipped to manage neonatal single ventricle congenital heart disease is imperative.[8][10]

Contraindications

There are several relative contraindications to the Norwood procedure. These relative contraindication include but are not limited to poor ventricular function, extremely premature delivery or low birth weight, genetic syndromes with poor prognosis, extensive intraventricular hemorrhage, or severe concomitant extra-anatomic syndrome defects.

Family counseling is crucial, as the Norwood procedure is a high-risk surgery aimed at staged palliation toward eventual transplant.[11] Families must be prepared to provide lifelong care with close follow-up and be prepared for their child to undergo multiple operations and catheter-based interventions. Some families may opt for a nonsurgical palliative approach focusing on comfort measures. Ideally, the diagnosis of HLHS will occur in utero, and families have adequate time to understand the clinical implications of a single ventricle diagnosis.

One alternative option to the Norwood procedure for neonates with HLHS is a hybrid stage 1 palliative procedure, which typically includes atrial septostomy, patent ductus arteriosus stenting, and bilateral pulmonary artery band placement.[11] Other alternative options include primary neonatal heart transplant or palliative care.[11] Fetal intervention for HLHS remains experimental. Though rare, the neonatal mortality rate can be relatively high within the first week.[8]

Equipment

The Norwood procedure should be performed in a congenital cardiac surgery operating room with continuous hemodynamic monitoring capability, appropriate instruments, and staff trained in neonatal cardiac surgery. 

The equipment typically required for the Norwood procedure includes but is not limited to:

• Cardiopulmonary bypass pump, circuit, and cannulas appropriate to the age of the patient
• Cardioplegia solution
• Echocardiography with a transesophageal and epicardial probe
• Sterile drapes, gowns, supplies
• Surgical instruments including sternotomy saw, knives, clamps, and fine sutures
• Conduit material for planned shunt type
• Patch material for reconstruction of the aorta.

Personnel

The personnel typically required to perform the Norwood procedure includes but is not limited to:

• Congenital cardiac surgeon
• Pediatric cardiac anesthesiologist
• First surgical assistant
• Surgical technician or operating room nurse
• Circulating or operating room nurse
• Pediatric perfusionist
• Pediatric cardiologist with or without an echocardiographer.

Perioperative care should ideally be performed in a specialized congenital cardiac intensive care unit where pediatric intensivists and nurses are familiar with the unique care required for single ventricle neonates. 

Preparation

When preparing for a Norwood procedure, all relevant clinical imagining, including a transthoracic echocardiogram, should be reviewed. Particular attention should be paid to the size of the ascending aorta, ventricular function, level of atrioventricular valve regurgitation, size and level of restriction of the atrial septum, and anatomy of the aortic arch and isthmus.

Given the parallel circulation in these patients, achieving balanced systemic (Qs) and pulmonary (Qp) blood flow is crucial before surgery; a Qp:Qs ratio approximating or equaling 1 is desirable. Oxygen saturations ideally should range between 75% to 85%. Supplemental oxygen and invasive respiratory support should be limited, as too much blood flow into the pulmonary circulation will cause a decrease in systemic cardiac output. Prostaglandin E1 infusion is initiated to maintain ductal patency.[8]

Technique or Treatment

The ultimate goal of the Norwood procedure is to provide adequate atrial level mixing, unobstructed systemic and coronary blood flow through the aorta, and a stable source of pulmonary blood flow that prevents overcirculation and protects the pulmonary vasculature. There are 2 shunt choices for establishing pulmonary blood flow: the mBTT shunt or the Sano shunt.[4][11] See StatPearls' companion reference, "Modified Blalock-Taussig-Thomas Shunt," for more information about that procedure.

Before beginning the operation, neonates are intubated with general anesthesia. Monitoring during the procedure typically involves using standard arterial lines for hemodynamic monitoring and cerebral near-infrared spectroscopy to assess cerebral oxygenation. The choice of central venous access will vary with institutional protocols. Neonates are small, and transesophageal echocardiography may not always be feasible; preparation for epicardial echocardiography after initiating cardiopulmonary bypass is recommended. A median sternotomy provides optimal exposure and is the standard surgical incision utilized in neonates requiring cardiopulmonary bypass. There is institutional variability regarding cerebral protection strategies, with some institutions employing antegrade cerebral perfusion or deep hypothermic circulatory arrest (DHCA) during procedures involving the aortic arch.[11] This activity describes a technique for cannulation and conduct on cardiopulmonary bypass with the creation of an mBTT, as outlined by Drs John and McKenzie.[12] 

Following the creation of the pericardial window, one cannulation strategy involves right atrial venous and right subclavian arterial cannulation using a graft. Subsequently, the neonate is cooled to 18 °C in preparation for DHCA, and the large patent ductus arteriosus is ligated. Once cooled, the heart is arrested with cardioplegia delivered through the aortic cannula, enabling the atrial septectomy to be performed under DHCA via a right atriotomy. Aortic arch reconstruction follows using a patch accompanied by low-flow cerebral perfusion via the graft on the right subclavian artery. The ascending aorta is then amalgamated with the transected proximal main pulmonary artery in the manner of a Damus-Kaye-Stansel procedure. The arterial cannula is transferred to the ascending aorta, and full flow is resumed with rewarming. The final anastomosis connects the graft to the pulmonary artery to complete the mBTT shunt.[12] 

Alternatively, if using a Sano shunt to establish pulmonary blood flow, a right ventriculotomy is performed, and the proximal end of the conduit is secured to the ventricle, with the distal end anastomosed to the main pulmonary artery at its bifurcation. Routine monitoring lines, chest tubes, and temporary pacing wires are inserted. Some centers opt to leave the chest open at the conclusion of the operation, with plans for delayed sternal closure.[11]

The selection of shunt type during the Norwood procedure varies by institution.[11] The SVR trial studied the differences between the mBTT and Sano shunts in more than 500 patients undergoing the Norwood procedure. The initial results, first published in 2010, noted that at 12 months, transplant-free survival was higher in the Sano shunt cohort. However, the Sano shunt cohort also had more unintended interventions and complications. At 3-, 6-, and 12-year follow-up visits, there remained no difference in transplant-free survival between the 2 cohorts.[5][13][14]

Complications

Postoperative hemodynamic challenges in patients with single ventricle physiology underscore the necessity of specialized care provided by centers experienced in caring for these infants. Despite the increased utilization of interventions like the Norwood procedure for neonates with single ventricle anatomy and physiology, there has been only a marginal improvement in overall mortality rates for patients with HLHS undergoing this procedure; mortality rates decreased from 25% in 1998 to approximately 21% in 2005.[15] 

The risk of developing a major postoperative complication that can cause significant morbidity or mortality is highest in the 48 hours directly following a Norwood procedure. These complications include but are not limited to: 

• Hemorrhage
• Arrhythmias
• Low cardiac output syndrome
• Atrioventricular valve regurgitation
• Aortic valve insufficiency
• Pulmonary artery distortion
• Ventricular dysfunction
• Seizures
• Stroke
• Shunt thrombosis
• Vocal cord dysfunction
• Infection
• Cardiac arrest
• Death

Intrinsic patient risk factors for mortality following Norwood palliation include prematurity and low birth weight, genetic syndromes, and extracardiac anomalies. Concurrent genetic syndromes and extracardiac anomalies correlate with heightened morbidity, marked by prolonged mechanical ventilation and extended hospital stays. Despite comparable extracorporeal membrane oxygenation (ECMO) and reoperation rates, patients with these risk factors exhibit higher hospital mortality rates.[16] Risk factors for mortality or transplant include total anomalous pulmonary venous return, small patient size, restrictive interatrial septum, small aortic size, genetic syndromes, moderate to severe preprocedural tricuspid valve regurgitation, need for ECMO, and surgeon annual volume.[13][17]

Postoperative complications in Norwood patients have been extensively quantified with long-term follow-up at 1, 3, and 6 postoperative years. Notably, ventricular function and complications showed no significant differences between shunt types. At the 6-year mark, the estimated risk of post-Norwood morbidities includes thrombosis (20%), seizures (15%), and stroke (7%).[5][13] Ventricular arrhythmias were prevalent at 6 years, with no apparent disparities based on shunt type.[18] 

For infants with HLHS unable to undergo their stage 2 palliative operation, risk factors include combined ventricular dysfunction and atrioventricular valve regurgitation following the Norwood procedure. A retrospective study highlighted additional clinical factors such as prematurity, total bypass minutes, and ECMO use contributing to attrition, defined as death or heart transplant.[19] Certain anatomic subtypes may also pose risks post-Norwood procedure, although generalization across institutions is challenging.[20][21] Furthermore, research suggests that full-term patients with aortic atresia may exhibit improved survival with a Sano shunt, whereas preterm subjects may fare better with an mBTT shunt.[21]

For single ventricle patients undergoing sequential staged palliation, the highest risk of death occurs after the first-stage Norwood procedure, termed interstage mortality. Mortality rates are notably higher following the Norwood procedure compared to the subsequent second-stage Glenn/Hemi-Fontan procedure or third-stage Fontan operation. Up to 15% of infants may die after discharge from the Norwood procedure while awaiting their second-stage operation.[15]

Clinical Significance

Despite its widespread adoption as an operative strategy in staged palliation for infants born with single ventricle heart disease, neonatal mortality after the Norwood procedure remains at 15%, regardless of shunt type.[3] Interstage mortality, encompassing mortality between all 3 stages, is highest after the first-stage Norwood procedure. However, before Norwood pioneered his strategy, all neonates born with HLHS faced imminent death.[1] His groundbreaking work initiated the paradigm shift towards staged palliation for neonates with otherwise fatal congenital heart disease. This innovative approach has since facilitated palliative surgery for thousands of neonates, enabling them to reach adolescence and adulthood, with many ultimately undergoing cardiac transplantation.

Enhancing Healthcare Team Outcomes

The Norwood procedure demands a multidisciplinary approach to ensure patient safety and optimal outcomes. Physicians, advanced practice providers, nurses, pharmacists, respiratory therapists, echocardiographers, and other health professionals are crucial in delivering patient-centered care throughout the perioperative period, ideally beginning during the fetal period. Physicians are responsible for assessing patient eligibility for the Norwood procedure, meticulous surgical execution, and postoperative care. Advanced practitioners, such as physician assistants and nurse practitioners, provide invaluable support in perioperative care, including preoperative evaluation, intraoperative assistance, and postoperative monitoring. Nurses are integral members of the care team, overseeing patient assessments, administering medications, monitoring vital signs, and providing essential patient education and emotional support to families. Pharmacists ensure appropriate medication management, including sedation, pain control, and maintenance of hemodynamic stability.

Interprofessional communication among team members is essential for effective care coordination, facilitating seamless transitions between perioperative phases, promptly identifying and addressing potential complications, and ensuring alignment of care goals with patient and family preferences. By fostering collaboration and leveraging the expertise of each team member, healthcare professionals can enhance patient-centered care, improve outcomes, ensure patient safety, and optimize team performance.

Nursing, Allied Health, and Interprofessional Team Interventions

The findings from a randomized controlled trial underscore the significance of surgical volume in outcomes following the Norwood procedure, with low-volume centers posing a heightened risk for mortality and cardiac transplantation.[5] Given these patients' complex anatomy and physiology, their hospital course can be particularly challenging, necessitating the expertise of interprofessional healthcare teams. Each healthcare professional must recognize their specific responsibilities and possess the requisite experience to manage the intricacies of perioperative care effectively. Effective interprofessional communication among nurses, advanced practice providers, perfusionists, cardiologists, intensivists, anesthesiologists, and surgeons is paramount. Collaborative communication ensures a comprehensive understanding of patient status, facilitates timely decision-making, promotes adherence to best practices, and ultimately enhances patient outcomes and safety throughout the Norwood procedure and subsequent care phases.