Timing and Outcome of Surgical Pulmonary Valve Replacement

Abstract

The physiological role of the pulmonary valve (PV) is to allow one-way flow of blood from the right ventricle (RV) to the pulmonary vasculature. An incompetent PV results in varying degrees of pulmonary regurgitation (PR). Isolated trace or mild PR is considered physiologically normal, and has no long-term consequences. Isolated moderate or severe PR is considered pathological and over time results in volume overloading of the RV. Chronic volume overloading leads to RV dilatation and systolic dysfunction, and right-sided congestive heart failure. Tetralogy of Fallot (TOF) is the most common form of cyanotic congenital heart disease with a prevalence of 0.18–0.26 per 1000 live births [1, 2]. If left untreated, it carries 33% mortality in the first year of life; and a 50% mortality in the first 3 years of life [3]. Primary repair of TOF in the neonate and young infant began in the early 1970s and consisted of ventricular septal defect patch repair and relief of the right ventricular outflow tract (RVOT) obstruction via a transannular patch, valvectomy, and/or valvotomy [4]. Surgical repair is currently considered the standard of care for patients born with TOF. It has an operative mortality below 2% [5, 6], and a 5-year and 36-year survival of 93%and 85%, respectively [7, 8]. Although, the long-term outcome of patients with repaired TOF is favorable, the initial repair to relieve the RV outflow tract obstruction often results in significant PR. PR in the repaired TOF patient is usually well tolerated for long periods of time. The low-resistance, highcapacitance reservoir of the pulmonary circulation minimizes the actual regurgitant volume in the face of free PR. However, over time, chronic PR results in volume overloading of the RV. Volume overloading of the RV eventually leads to an increase in right ventricular end-diastolic volume (RV-EDV), right ventricular end-systolic volume (RV-ESV), and RV systolic dysfunction. The ensuing RV dilatation and dysfunction predisposes the patient to exercise intolerance, congestive heart failure, atrial and ventricular arrhythmias, and may contribute to sudden cardiac death (SCD) [9, 10]. There is a direct relationship between poor exercise capacity and the severity of pulmonary insufficiency and its effects on RV. Carvalho et al. [11], demonstrated that residual PR after complete repair of TOF correlated with impaired exercise capacity. They prospectively evaluated 10 asymptomatic patients more than 5 years after TOF repair. There was a significant negative correlation between the severity of PR and exercise duration. Patients with an abnormal maximal oxygen uptake were statistically more likely to have more severe residual PR. Wessel et al. [12], also demonstrated that in repaired TOF a statistically significant relationship exists between reduced work performance and residual disease. Rhythm disturbances in patients with repaired TOF are relatively common and it is related to surgical scar and RV enlargement. Chronic PR leads to RV enlargement, which in turn leads to tricuspid annular dilatation and subsequent tricuspid regurgitation. Right atrial enlargement ensues, which predisposes the patient to atrial flutter/fibrillation. Atrial tachyarrhythmias, including atrial fibrillation and atrial flutter occurs in up to one-third of all patients postrepair and contributes significantly to patient morbidity. Right ventricular dilatation results in delayed right ventricular depolarization (wide QRS complex on ECG) and inhomogeneous repolarization patterns, which may serve as a trigger for ventricular reentry tachycardias. There is a mechanico-electrical relationship described in these patients where the degree of RV dilatation corresponds to the width of QRS duration on surface ECG and patients with QRS width > 180 ms are at greater risk of syncope and SCD. The incidence of SCD (presumably from VT) is reported to be between 0.5% and 6%. [9, 13, 14, 15] G. Martucci (*) MAUDE Unit, McGill University, Montreal, QC, Canada