Definition, Pathophysiology and Clinical Symptoms
Absent pulmonary valve syndrome (APVS) is characterized by a combination of atresia of the pulmonary artery valve, underdevelopment of the right ventricular outflow tract, a large malalignment VSD and an aorta overriding the VSD. In view of the comparable anatomy (although usually without cyanosis) the APVS is seen as an extreme variant of tetralogy of Fallot (TOF) and occurs in 3-6% of all patients with TOF. Massive aneurysmatic enlargement of the pulmonary arteries can lead to tracheobronchial compression with respiratory failure and bronchomalacia. The symptoms depend on the degree of respiratory insufficiency, heart failure and infections: 40-50% of the patients develop a postnatal obstructive ventilation disturbance such as tachypnea, stridor or intercostal retraction or even respiratory insufficiency requiring mechanical ventilation or implantation of an ECMO (extracorporeal membrane oxygenation) device. In the case of less pronounced bronchial obstruction the clinical symptoms are similar to those of TOF.
Diagnosis
- by ECG: signs of right ventricular and right atrial hypertrophy.
- by chest X-ray: clog-like cardiac configuration with raised apex and a pronounced pulmonary artery segment, asymmetrical pulmonary vascular markings.
- by echocardiography: large malalignment VSD (location in relation to tricuspid, pulmonary and aortic valve), overriding aorta, right aortic arch, diameter of the right ventricular outflow tract (RVOT), function and diameter of the pulmonary valve, diameter of the right and left pulmonary artery, coronary anomalies, persistent ductus (usually not present).
- by heart catheterization: in particular cases to measure the pulmonary vascular resistance and excluded coronary anomalies.
- by CT / MRI/ bronchoscopy: diameter of the pulmonary arteries and their position in relation to the main bronchi (in the case of symptoms of bronchial obstruction).
- by chromosome analysis: DiGeorge syndrome, particularly likely with right aortic arch.
Indication
The diagnosis represents the indication for surgical correction. The timing of the operation depends on the clinical symptoms. Patients without signs of bronchial compression should be operated upon electively at the age of 3-6 months. Patients with a large VSD and those with pronounced bronchial compression are operated upon earlier, i.e. before the development of bronchomalacia.
Operation
Access is by median thoracotomy and the heart-lung machine is used. The right and left pulmonary arteries are mobilized up to the lung hilum. The heart is arrested by cardioplegia. Transtricuspid patch closure of the ventricular septal defect is performed and an atrial septal defect, if present, is closed directly. If signs of bronchial compression are present the ascending aorta is transected and the pulmonary artery transposed to before the ascending aorta. The diameter of the pulmonary arteries is reduced to normal size by performing a reduction plasty of the anterior wall and longitudinal plication of the posterior wall. Continuity between the right ventricle and the pulmonary artery is created with a valve-bearing conduit.
Possible Complications in the Long Term
The prognosis of the child with this heart defect in the short and mid-term is good. The most important risk factor for elevated mortality and morbidity is the need for preoperative mechanical ventilation. There is usually no significant gradient across the right ventricular outflow tract. In the further course stenosis or insufficiency of the pulmonary valve may make a reintervention or the placement of a right ventricle to pulmonary artery (RV-PA) conduit necessary.