Discussion
APVS is characterized by a rudimentary PV and aneurysmal dilatation of central pulmonary arteries.5 It occurs in 2.4% to 6.3% of patients with TOF.6 Compression of airways secondary to pulmonary dilatation can cause early presentation and portray dismal prognosis. Co-existence of absent APV with complete absence of the LPA in TOF is an extremely rare combination.
The absence of LPA is believed to be the result of a continued link between the fetal ductus arteriosus and the intrapulmonary aspect of the pulmonary artery during the in utero phase, as well as the involution of the 6th aortic arch (the extrapulmonary portion of pulmonary artery). Severe hypoplasia occurs in the pulmonary artery due to closure of the ductus after birth.7 Only 18 patients with APVS and TOF with complete absence of left PA has been reported.3, 8 Complete absence of RPA in association with APVS has not been reported.3
Asymmetric lung field with reduced vascularity on left side can provide a clue to the diagnosis. Cardiac catheterization and angiography are usually diagnostic. Combination of pulmonary regurgitation and a single pulmonary artery may ultimately result in pulmonary hypertension. Pulmonary hypertension will in turn worsen pulmonary regurgitation, creating a vicious cycle ultimately leading to early onset of right ventricular dysfunction.9 We expect increased overall mortality in this subset of TOF patients owing to high pulmonary vascular resistance (PVR), free PR, and significantly less cross sectional area of RVOT.
Timing of surgical intervention is usually dictated by clinical status and onset of RV dysfunction. As the entire right ventricular stroke volume is directed to the unilateral pulmonary artery, aneurysmal dilatation of connected PA can occur early and be more pronounced, leading to increased symptomatology. In symptomatic newborn and infant, with involvement of airway, morbidity and mortaility rise considerably.2
Total correction, including construction of a durable PV, will be the most appropriate surgical approach. TOF with absent pulmonary valve with dilated PA, have PVR on the higher side. Considering unusual spectrum of PA morphology in which RV has to eject against higher PVR, we strongly believe in construction of valve in RVOT. This would have both short term and long term benefits.
Conduit repair is possibly indicated in patients with airway obstruction, but it has inherent problems. For those without airway obstruction, valves created from pericardium or 0.1-mm PTFE membrane is always an option. The competence of valve created depends upon surgeon’s skill. Long term durability of the pericardium is extremely doubtful. Graham et al reported that all the pericardial valves constructed by them for RVOT developed free PR whereas the bileaflet polytetrafluoroethylene (0.1-mm) valves have remained competent with regurgitant fractions of only 5% to 30% (as evaluated on magnetic resonance imaging) and this has remained stable with time.4 To our knowledge, creation of a bileaflet PV using PTFE membrane in a TOF patient with absent LPA and APV syndrome has not been reported in the literature until now. In our patient, with two years follow up, there is only mild PR with preserved RV function.
To conclude, TOF with APV with UAPA is a very rare congenital anomaly, with high mortality rate. Early surgical intervention, with provision of durable valve in RVOT, can preserve RV function. Onset of RV dysfunction in the follow-up mandates aggressive intervention, which might include conduit replacement, to eliminate any degree of PR.