Surgery For Congenital Heart Disease

Eric L. Ceithaml, M.D., Chief of the Division of Pediatric Cardiovascular Surgery, University of Florida / Jacksonville

Ross Procedure

The Ross procedure involves using the patient's own pulmonary valve (pulmonary autograft) to replace the aortic valve. The pulmonary valve is removed as a cylinder, which includes the arterial wall, valve leaflets, adjacent right ventricle, and proximal pulmonary artery. This cylinder is then used as the replacement for the aortic root. The origins of the coronary arteries are excised from the native aorta and then reimplanted in the corresponding positions on the pulmonary autograft. The right ventricle to pulmonary artery connection is reestablished with a cryopreserved pulmonary homograft (cadaver valve).

There are several distinct advantages of the Ross procedure over prosthetic or homograft aortic valve replacement in children and young adults. The longevity of the pulmonary autograft in the aortic valve position has been shown to be excellent with 97% freedom from valve degeneration at 10 years. Aortic homografts fare less well: the freedom from valve degeneration is approximately 80% over the same time frame. Bioprosthetic valves undergo early calcification in children and have very high failure rates (30% freedom from reoperation at 10 years), so they are unsuitable for young patients. Mechanical prosthetic valves theoretically have a 100% freedom from valve degeneration in the long term, but carry significant rest and exercise transvalvular gradients in smaller sizes. In addition, all mechanical valves require life-long anticoagulant therapy to reduce the risk of thromboembolism. Long term anticoagulant therapy carries a risk of bleeding complications which is not insignificant, and diligence is required to monitor and adjust the anticoagulant levels. Pulmonary autografts, as well as homografts, do not require anticoagulant therapy.

One of the major advantages of the pulmonary autograft in children is the demonstrated growth of the pulmonary autograft valve after the procedure. Early findings indicate that this growth may even keep pace with somatic growth, limiting or even eliminating the need for surgically "up-sizing" the valve as the child grows. The homograft used to replace the pulmonary valve is cadaveric tissue and does not grow. An oversized homograft can be placed during the procedure to accommodate the growing patient. However, homograft degeneration can still occur and replacement may be necessary in the future.

Complex Single Ventricle

Complex single ventricle anomalies require some of the most innovative reconstructions of any of the congenital heart defects. In these defects, both ventricles are often represented, but one is usually incomplete or diminutive. The dominant ventricle may be morphologically a right ventricle, a left ventricle, or indeterminate, but it must be utilized for systemic arterial perfusion. Systemic venous blood must be routed to the pulmonary arteries and flow passively through the pulmonary arterial bed without the benefit of ventricular assistance. For this to occur, venous pressure must be elevated and pulmonary vascular resistance must be low. If venous pressure is too high, or pulmonary vascular resistance becomes elevated, sequellae of venous hypertension, including ascites, pleural effusions, and facial swelling, can occur. Furthermore, the decreased pulmonary blood flow causes decreased oxygen saturation, reduced systemic atrial and ventricular filling, and decreased cardiac output.

The surgical application of the above concepts has been credited to Fontan.¹ Blood flow from the superior vena cava was directed to the right pulmonary artery and that from the inferior vena cava (via the right atrium) was directed to the left pulmonary artery. The left atrium and dominant ventricle were used for systemic perfusion. This massive hemodynamic rearrangement carried a significant morbidity and mortality.

Over the years there have been numerous modifications of the original Fontan procedure which have markedly reduced complications and improved survival. Staging the Fontan operation by performing the superior vena cava procedure first, followed 6 - 18 months later by the inferior vena cava procedure, has favorably impacted mortality. Furthermore, the superior caval procedure has been modified so that blood flow is directed to both lungs: this is known as the bi-directional Glenn shunt. Patients tolerate the shunt procedure very well and recovery is usually rapid.

At the second stage, the inferior caval blood flow is directed to the pulmonary artery. This represents a more significant hemodynamic impact on the patient. A number of procedural modifications have been used to improve outcome. Fenestration of the atrial septum has proved to be a very useful adjunct, especially in high-risk patients. In this procedure, a small orifice is created between the two atria, which allows blood to flow from the high-pressure right atrium to the low pressure left atrium, in essence a right-to-left shunt. This reduces the systemic venous pressure and improves systemic preload and cardiac output. The shunted blood is low in oxygen and a small reduction in systemic saturation occurs but with a significant gain in systemic cardiac output. In addition, the reduction in systemic venous pressure reduces the risk of ascites and pleural effusions.

Recent attention has focused on creating a tubular connection from the inferior vena cava to the pulmonary artery. This has been found to preserve laminar flow and venous kinetic energy, thus helping to reduce venous pressure and enhance pulmonary blood flow. The tubular connection can be created by suturing a cylindrical patch to the lateral atrial wall inside the heart (lateral tunnel). Another technique involves interposing a prosthetic tube graft (e.g. Gore-Tex®) between the inferior vena cava and the pulmonary artery outside the right atrium (extracardiac conduit). This isolates the systemic venous blood flow from the right atrium. Using a tubular connection has additional advantages over a direct right atrial to pulmonary artery anastomosis. The procedure avoids high right atrial pressures that can cause right atrial dilatation and troublesome atrial arrhythmias. Furthermore, these connections often can be made without utilizing cardiopulmonary bypass, thus eliminating the associated inflammatory reactions.

Patient selection plays an important role in the ultimate success of the modified Fontan or total cavopulmonary connection. Ideal candidates have low pulmonary vascular resistance with low pulmonary artery pressures, absence of pulmonary artery stenoses and good function of the single ventricular chamber. The presence of significant AV valve regurgitation or subaortic obstruction must be addressed at the time of repair and will increase the overall morbidity and mortality.

Timing of the procedures is also important. Prior to 4 to 6 months of age, there is increased risk of performing a bi-directional Glenn shunt. If pulmonary blood flow is not adequate, then a systemic artery to pulmonary artery shunt (such as a Blalock-Taussig shunt) is recommended as a temporizing maneuver. In patients with the opposite problem, unrestricted pulmonary blood flow, early disconnection of the pulmonary artery from the high-pressure ventricle can protect the pulmonary vasculature from excess pulmonary blood flow, elevated pulmonary arterial pressure, and pulmonary vascular obstructive disease. Of course, some pulmonary blood flow is required, and this can be established with a systemic to pulmonary arterial shunt. The shunt should be converted to a systemic to pulmonary venous shunt (i.e. bi-directional Glenn shunt) after approximately 6 months of age to reduce the volume load on the single ventricle.

Staging and modification of the Fontan procedure, along with advances in surgery, cardiopulmonary bypass, pharmacology, and intensive care, have led to survival rates of 90% or better for complex single ventricle anomalies.

Hypoplastic Left Heart Syndrome

One of the most complex congenital heart anomalies where utilization of staged procedures has been particularly gratifying has been with hypoplastic left heart syndrome (HLHS). As the name implies, the left ventricle is poorly developed, but this is not the only problem. During gestation, there is little blood flow from the left ventricle through the aortic valve and into the ascending aorta and arch. As a result, all of these structures are hypoplastic at birth. The right ventricle is dominant and ejects through a large pulmonary artery to both lungs, and to the descending aorta via a large patent ductus arteriosus. At birth, these patients have good pulmonary blood flow, are pink and well saturated, belying the grave nature of their defects.

The prognosis of HLHS without surgical palliation is poor: the disease is uniformly fatal within several months of birth. Attempts to reconstruct this collection of defects with a single operation have been unsuccessful. Even early multi-staged surgical procedures carried a very high combined mortality of approximately 70-80%. This prompted many physicians to either abandon attempts at surgical reconstruction and provide comfort measures only, or to refer patients for heart transplant. However, with refinements of surgical techniques over the years, patients with HLHS now benefit from a multi-staged approach.

In HLHS, the right ventricle is adequate for systemic requirements, but the ascending aorta, transverse arch, and proximal descending aorta are too small to provide adequate systemic perfusion. Therefore a large systemic artery must be constructed before any Fontan procedures can be applied. This is done by enlarging the entire diminutive aorta with a patch of homograft pulmonary artery. The main pulmonary artery is severed from the right and left branch pulmonary arteries and joined to the newly enlarged aorta to restore continuity between the ventricle and the systemic circulation. Blood flow to the lungs is established by a systemic to pulmonary arterial shunt. The inter-atrial septum is removed to allow pulmonary venous blood entering the left atrium to flow unobstructed to the right atrium and right (systemic) ventricle. This procedure was first popularized by Norwood² and bears his name. Initially, the survival rate was approximately 50 %. However, with improvements in surgical technique, anesthesia, cardiopulmonary bypass, and intensive care, the mortality for the Norwood procedure has been dramatically reduced with one center reporting a survival of 77 %.³ More recent information from these centers indicates a survival of 80 - 90%.

Following the Norwood procedure, reconstruction is similar to other forms of complex single ventricle. The second stage (bi-directional Glenn shunt) is performed at approximately 6 months of age and the third stage (Fontan) at 12 to 24 months of age.

Cardiac transplantation remains an option for patients with HLHS. A number of series show survival rates similar to that for the three-stage palliative reconstruction. Transplant gives the patient a fully functional, two-ventricle system. However, a number of patients will die while waiting for a donor heart. Once a patient is transplanted, the issues of rejection and infection are of continuing concern. Transplant coronary disease does develop in these patients and its role in limiting long term survival is unclear. The procedure of choice for patients with HLHS remains controversial.

Summary

1. The Ross procedure (pulmonary autograft) offers the advantages of valve growth and avoidance of anticoagulation in pediatric patients with aortic valve disease.
2. Staging the reconstruction of complex single ventricle anomalies has resulted in reduced morbidity and mortality.
3. For hypoplastic left heart syndrome, the Norwood operation and subsequent staged Fontan reconstruction carry acceptable morbidity and mortality.

References

1. Fontan F, Baudet E. Surgical repair of tricuspid atresia. Thorax 1971;26:240.
2. Norwood WI, Lang P, Hansen DD. Physiologic repair of aortic atresia - hypoplastic left heart syndrome. N Engl J Med 1983;308:23-26.
3. Mahle WT, Spray TL, Wernovsky G, et al. Survival after reconstructive surgery for hypoplastic left heart syndrome. A 15-year experience from a single institution. Circulation 2000;102:III-135-41.

October, 2001/ Jacksonville Medicine

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