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.