Dysfunction of the right ventricular outflow tract (RVOT), whether is be due to stenosis or regurgitation, is a common and challenging condition in both children and adults with congenital heart defects. Some of these defects include pulmonary atresia, d-transposition of the great arteries with pulmonary stenosis, truncus arteriosus, double outlet right ventricle, and most commonly tetralogy of Fallot (TOF). Pulmonary valve replacement (PVR) remains the goldstandard of care for the definitive surgical treatment of progressive right ventricular (RV) failure from these defects due to long-standing pulmonary regurgitation (PR) and pulmonary stenosis. Often occurring two to three decades after surgical repair of TOF, PR has become an increasingly more common clinical situation confronting congenital and adult cardiac surgeons as outcomes and survival have improved for TOF patients over the past several decades. TOF still remains the most common type of cyanotic congenital heart defect. Surgical palliation of TOF was first popularized with the introduction of the Blalock-Taussig systemic-to-pulmonary artery shunt in 1945, and surgical management of this condition for a majority of patients has evolved over the past 50 years to include primary repair of each associated defect during infancy. With advances in surgical technique, diagnostic imaging and technology, postoperative and critical care management, and long-term follow-up capabilities, outcomes following primary TOF repair have dramatically improved with current mortality rates of 2% to 3% and 20-year survival approaching 90%. Despite these successes, significant anatomic and functional abnormalities remain following surgical treatment of TOF that confer important long-term cardiopulmonary implications.

The recognition of certain adverse functional sequelae following TOF repair has been increasingly reported and emphasized in recent years. These abnormalities include RV failure from progressive volume overload and PR, persistence of atrial and/or septal defects, RV outflow obstruction, pulmonary artery stenosis, and tricuspid regurgitation. While these lesions are often benign during childhood and adolescence, they have the potential to progress and significantly compromise patient functional status, exercise tolerance, and survival by the second or third postoperative decade. Moreover, severe, progressive chronic PR is considered a treatable cause of RV failure and has been the focus of increased study and investigation in recent years.

This chapter reviews the general principles that apply to the pathophysiology of pulmonary valve dysfunction, indications and timing for treatment of severe and clinically significant pulmonary valve lesions, selection and availability of pulmonary valve prostheses, surgical technique of PVR, and recently reported outcomes for PVR.

The pathophysiology of pulmonary valve dysfunction following TOF repair is multifactorial, and the severity of pulmonary valve dysfunction has been shown to increase over time. While for many years, the impact of PR after surgical correction of TOF was considered relatively benign, evidence has demonstrated that progressive PV dysfunction results in right heart failure. Four primary factors influence the degree of PR following TOF repair: (1) regurgitant orifice size, (2) length of diastole, (3) diastolic PA to RV pressure gradient, and (4) pulmonary artery resistance and capacitance. Early after TOF repair, the effect of pulmonary valve regurgitation is minimal due to an increased heart rate and shortened diastole, decreased RV compliance due to RV hypertrophy, and decreased pulmonary artery capacitance. However, over time, physiologic changes occur, including an increase in RV compliance and stroke volume, increased PA compliance, and slowing of heart rate with a lengthening of diastole. These changes, therefore, predispose to the eventual development of worsening PR. Moreover, the progressive development of PR results in a cyclical pattern of worsening PV and cardiac dysfunction. Increased PR results in RV dilation and increased RV compliance that serves to increase RV stroke volume, ultimately resulting in elevated PA pulse pressures, increased PA dilation, and worsening of PR.

The development of improved cardiac imaging modalities has demonstrated important changes to RV mechanics following primary TOF repair that play an important role in the progressive decline in pulmonary valve function. In fact, a close relationship between RV end-diastolic volume and percent PR exists. While the effects of RV systolic function are preserved for several years despite significant PR, eventually compensatory mechanisms fail. Failure of RV compensation results in decreased RV mass-to-volume ratios, increased end-systolic volume, and ultimately decreased RV ejection fraction. In addition, PV function is further degraded due to the effects of age of repair; RV dyskinesia due to ischemia, fibrosis, RV aneurysm, or RVOT patch; impaired RV diastolic function; and increased LV size and dysfunction.

PVR has documented beneficial effects for PV dysfunction including improved ventricular function, reduced atrial and ventricular arrhythmias, and improved cardiac functional status. These benefits notwithstanding the clinical decision as to the timing of PVR and the identification of
clinical indicators for surgical valve replacement often remain a dilemma.

Several clinical and physiologic indications exist for PVR following TOF repair. Clear clinical indication for PVR include symptomatic physical deterioration, decreased exercise tolerance, onset of clinical arrhythmia, clinical signs and symptoms of right heart failure as a result of severe PR, need for cardiac medications, and onset of syncope. However, indications for PVR in the asymptomatic patient are much less defined. In an era of advancing technology, several different cardiac functional metrics have been identified to aid in the decision to proceed with PVR. In the presence of moderate-to-severe PR, PVR is indicated in the presence of the following homodynamic factors as reported by Geva:

Other important factors include the presence of other hemodynamically significant lesions including moderate-to-severe tricuspid valve regurgitation or the presence of atrial and/or ventricular septal defects, TOF, or other congenital pulmonary outflow tract reconstruction after the age of 3 years. Moreover, an MRI-based study by Therrien and colleagues demonstrated that the optimal timing for PVR in adults following TOF repair occurred when RV end-diastolic dimension was <170 ml/m. When dealing with pulmonary stenosis, surgical indications include a RV pressure two-third of systemic regardless of symptoms.

Reconstruction of the RVOT remains a common surgical procedure in congenital heart surgery. There are several congenital heart defects that require this operation to prevent or reverse RV dysfunction that can result from long-standing pulmonary insufficiency or stenosis. Despite the high frequency of this operation, controversy still exists regarding the best valve replacement in the pulmonary position.