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.