DISSCUSION
Unilateral absence of pulmonary artery (UAPA) is a rare malformation
that can present as an isolated lesion or may be associated with other
congenital heart defects. Although TOF is the most common combined
deformity of UAPA, the literature available is limited to small case
series or case reports. Due to the scarcity of cases and the anatomical
variation, the diagnostic criteria, embryological origin, and clinical
classification of UAPA are still very controversial [2, 5]. Although
there is a hypothesis that UAPA is caused by the failure of the sixth
aortic arch to connect with the pulmonary trunk during embryologic
development [6], it still cannot explain that TOF combined with UAPA
is more common in the left pulmonary artery. Barram and his colleagues
[1] classified TOF combined with UAPA into four types. However,
according to Congenital Heart Surgery Nomenclature and Database Project
[7], those cases of the unilateral pulmonary artery originating from
the ascending aorta or supplied by the arterial duct should be included
in the category of aortopulmonary window. Therefore, these patients were
not included in this study. In addition, we also found occlusion of the
left pulmonary artery in the pericardium in some cases, usually with a
noticeable arterial ligament. Waldman et al[8] believed that this is
a spontaneous acquisition of pulmonary artery discontinuity related to
the degeneration of the arterial duct tissue. The clinical
manifestations and surgical protocols of these patients are the same as
those of conventional TOF, so we excluded such patients in this study.
The treatment strategy of TOF combined with UAPA is still very
controversial. Surgeons often face the challenge of whether to
reconstruct bilateral pulmonary arteries to achieve the ideal ”
two-lungs repair”. At present, there are only sporadic reports on
two-lungs correction. Most of the literature is “single-lung repair”
or palliative treatment, in which the operative mortality rate was
reported to be 44%-48% in the early stage, and recently reduced to
5%-8.3% [1, 3, 4, 9, 10]. Normal-sized contralateral pulmonary and
a well-developed left ventricle are the basis of “single-lung repair”
[1]. But due to the inherent pulmonary circulatory dysplasia in TOF
patients, even if the unilateral pulmonary artery can meet the criteria
of TOF correction and successfully complete the single-lung repair, it
is obvious that the damage of the right ventricular function in the
procedure and the postoperative pulmonary valve regurgitation will have
a huge impact on the long-term prognosis. This is the biggest difference
with the isolated UAPA patients.
With the experience in the application of unifocalization technique in
the pulmonary atresia with ventricular septal defect, we believe that it
is feasible to implement bilateral pulmonary artery reconstruction in
TOF with UAPA. It is very important to analyze the computed tomography
carefully and to judge the anatomical morphology of the “missing”
pulmonary artery with three-dimensional reconstruction. The filling
degree and timing of the contrast medium may lead to an underestimation
of the development of the pulmonary artery in a CT scan. Cardiovascular
MRI may be more helpful for these patients to assess the pulmonary
artery. In this group of 8 patients, the left hilar confluence is still
present, and despite the presence of major aortopulmonary collateral
arteries, the inherent left pulmonary artery system covers all lung
segments. Neither McGoon nor Nakata Index could meet the criteria of
one-stage TOF repair. However, if the left pulmonary artery can be
effectively reconstructed, one-stage bilateral pulmonary artery TOF
repair could be achieved.
Due to the length of the lacking segment and few available blood vessels
tissue, how to reconstruct the connection between the left pulmonary
artery and the main pulmonary artery is a challenge for surgeons.
Various techniques and reconstructive materials have been reported [9,
10, 11, 12, 13]. In our institute, different surgeons have chosen
different techniques and strategies. During the postoperative follow-up,
we found that the proportion of thrombosis after the use of the Goretex
vessel was very high and the diameter of the vessel was limited, so it
was almost inevitable to replace the vessel again. Although an
autologous pericardial patch was used to widen the anterior wall in the
direct anastomosis technique, vascular distortion and stenosis of the
left pulmonary artery may occur postoperatively because of the greater
tension of the anastomosis, and requiring further intervention. We
applied a modified technique of extension of the main pulmonary artery
sidewall to reconstruct the connection of the left pulmonary artery to
the main pulmonary artery, ensuring anastomosis without tension. The
short-term results are good, and the long-term results need further
follow-up. So far, our institute has not treated patients with TOF
combined with the absence of right pulmonary artery, or the absence of
left hilar confluence requiring the unifocalization of the collateral
arteries.