Obstructed TAPVC was found in 25% to 50% of patients with TAPVC, and represents a life-threatening neonatal emergency warranting immediate surgery [8–10]. The incidence of PVO was highest in the infracardiac and lowest in the cardiac type [11, 12]. Generally, the longer of the drainage vein connecting to RA, the higher incidence of PVO. The infracardiac and cardiac types have the longest and shortest drainage vein respectively of four types. In this study, PVO was found in 42.9% of patients, and the PVO occurred in 87.5% of infracardiac, 52.4% of supracardiac, but none of cardiac type presents PVO (0%). In supracardiac, the most common sites of PVO were at the level of VV, especially at the place where the VV step over the left PA and bronchus, and the VV was often oppressed by them. In infracardiac, the drainage veins were usually connected to PV, and obstruction resulted from the high resistance of PV flow needing to traverse through the liver parenchyma before returning to RA [7, 13, 14].
Our study showed the patients with TAPVC had normal birth weight, and there was no significant difference in birth weight between obstructed and unobstructed TAPVC. The reason may be the unique nature of fetal hemodynamics allows the fetus with TAPVC to be well tolerated in utero. Pulmonary blood flow of the fetus was a small portion of the combined ventricular output, so the physical growth of the fetus will not be affected in utero. However, there was complete mixing of the pulmonary and systemic circulations in the right heart after birth. The patients will be cyanotic and may have difficulty feeding in the first weeks or months of life. If there was a PVO, it resulted in elevated pulmonary pressures and decreased systemic oxygen delivery, and severe respiratory distress and decompensation may ensue very early in the neonatal period. The patient’s conditions can deteriorate rapidly and become life threatening unless the cause was promptly recognized and treated . Our study demonstrated that the first admission age of obstructed TAPVC was earlier than the unobstructed type, and patients with PVO were usually hospitalized during neonatal period. We believed that the presence of PVO led to earlier symptoms and thus to be discovered earlier.
For patients with TAPVC, a right-to-left intracardiac shunt is obligatory for survival, and it almost always occurs at atrial level through an ASD that is rarely restrictive. ASD size is one of the most important factors affecting the survival period. The presence of a large ASD allows some of the excessive venous return in RA to reach LA. Several cases of adult untreated TAPVC have been reported, even a few cases were diagnosed after 50 years of age, and they have very similar pathophysiology to a large ASD [16–18]. All our patients presented ASD of various sizes except a case with common atrium, and unobstructed TAPVC had a larger ASD size than obstructed type. The first admission age of unobstructed TAPVC was later than obstructed type, so a larger ASD size maybe resulted in later admission age. PDA was the common concurrent abnormality with an incidence of 44.3% in this study. The direction of PDA flow was right to left or Bi-directional shunt in 26 of 31 patients. We found that obstructed TAPVC had a higher incidence of PDA than unobstructed type, and the patients with PDA had a smaller ASD than that without PDA. The presence of PDA may relate to pulmonary pressure. Obstruction of drainage vein caused elevated pressure in pulmonary venous territory, elevated pressure in pulmonary capillary bed, pulmonary edema, pulmonary hypertension, and right heart failure with leftward shift of the interventricular septum and low systemic output. Remaining a PDA can alleviate the pulmonary hypertension and provide more blood flow for systemic circulation.
Pulmonary arterial blood flow velocity was related to right ventricular function, pulmonary arterial pressure, blood flow and arterial diameter and so on. Right ventricular volume overload and pulmonary hypertension were common findings in patients with TAPVC , and patients with TAPVC were often found having abnormal pulmonary artery flow velocity. Our study demonstrated that PA Vmax significantly higher in patients with unobstructed TAPVC than obstructed type. Obstructed type had a lower PA Vmax, which maybe resulted from increased pulmonary vascular resistance and decreased compliance due to obstructed drainage veins. However, unobstructed type had an accelerated PA Vmax, we speculated that the increase of pulmonary circulation blood flow was not compatible with the expanding pulmonary artery itself, resulting in functional pulmonary artery stenosis, then led to an accelerated PA Vmax.
Enlargement of the right heart was a common feature to patients with TAPVC. The RV was disproportionately larger than the LV in most of our cases. The LA was frequently small and the LV was compressed by the dilated RV. The ratios of RD/LD of obstructed and unobstructed TAPVC were larger than normal, but there was no significant difference between obstructed and unobstructed type. For patients with TAPVC, the blood of left heart was almost always obtained by an ASD, so the size of ASD could often affect the LV volume. The presence of PVO reduced the blood flow returning into the RA, the obligatory right-to-left shunt was also attenuated and the LV volume became small. The obstructed TAPVC had a smaller ASD than unobstructed type, which resulted in decreasing of SV in patients with obstructed TAPVC. Our study demonstrated that the obstructed TAPVC had a higher LVFS and LVEF than unobstructed type. The main reason may be that obstructed TAPVC need to increase cardiac output through strengthening the ventricular systole.
TAPVC has an excellent outcome if detected early and corrected surgically in due time, but the prognosis is poor when TAPVC is associated with a PVO . The presence of PVO was significantly associated with an increased risk of death [3, 8]. Therefore, an important part of preoperative diagnosis of TAPVC was to determine whether there was a PVO. Echocardiography can detect the PVO by measuring the blood velocity of the stenotic pulmonary vein . But incorrect diagnosis might occur because of an insufficient spatial resolution, restricted acoustic window or an interpretation error by the operators. The role of echocardiography was limited in the evaluation of obstruction, especially in patients with infracardiac and mixed TAPVC . We tried to predict PVO by some familiar, easily obtained echocardiographic and clinical parameters. The ROC curve analysis was used to predict PVO in this study. To the best our knowledge, it was the first time to determine PVO using this method. The first admission age of obstructed TAPVC was earlier than the unobstructed type. The ROC curve analysis for the first admission age showed the area under the curve was 0.805, and the sensitivity and specificity were 76.7%, 80% respectively at the optimal cut-off value of 0.64 (months). Therefore, we can make a preliminary judgment whether there was a PVO according to the first admission age, which was the easiest parameter to obtain. If the first admission age was less than 0.64 months, then a suspicion of PVO was strongly suggested, and further imaging examination was necessary. For both clinicians and echocardiographer, this was a convenient and quick way to understand the patient’s conditions. Among echocardiographic parameters, the PA Vmax had 88.5% sensitivity and 67.6% specificity at the optimal cut-off value of 1.11(m/s), and the area under the curve was 0.841. The other separate parameters appeared to be limited in its predictive ability. Compared to a single parameter, the comprehensive utilization of multiple echocardiographic parameters can greatly improve the efficiency of diagnosis. There was an excellent value in predicting PVO when a logistic model was created using the seven echocardiographic parameters. The area under the curve was 0.936, and the sensitivity and specificity were 82.6%, 100% respectively at the optimal cut-off value of 0.5774. This was a simple method to predict PVO, and it required measurements of only some familiar and easily obtained data.