Participants and Setting
All procedures in this study involving human participants were performed in accordance with the Declaration of Helsinki (as revised in 2013). This study was approved by the ethics board of Xijing Hospital (approval No. KY20182066-C-1), and informed consent was obtained from all of patients. We selected 118 pediatric patients aged from 1 day to 18 years old from Sep. 1, 2016, to Sep. 31, 2021[7], who were diagnosed with total, partial or mixed SAPVC by TTE or CT, as shown in Fig. 1. Among them, 13 cases were newborns, 61.5% of whom were male, aged from 2 to 28 days, with an average age of 18.8±7.9 days. Fifty patients were infants, 64% of whom were male, aged from 1 to 10 months, with an average age of 4.0±2.4 months. Twenty-five cases were young children, 44.0% of whom were male, aged from 1 to 3 years old, with an average age of 1.6±0.9 years old. Sixteen cases were preschool children, 75.0% of whom were male, aged from 4 to 6 years old, with an average age of 5.1±0.9 years old. Eight cases were school-age children, 62.5% of whom were male, aged from 8 to 13 years old, with an average age of 9.5±1.9 years old. Six cases were adolescents, 66.7% of whom were male, aged from 13 to 18 years old, with an average age of 14.7±1.8 years old.
Methods
TTE in the diagnosis of SAPVC.
Philips iE33 (Philips Ultrasound; Bottell Everett Highway Bothell; USA), GE E9 (GE Medical systems Ultrasound & Primary Care Diagnostic, LLC; Wauwatosa. WI 53226,
USA) and EPIQ-7C (Philips Ultrasound; Shanghai; China) were selected as the echocardiography diagnostic instruments, with an S5-1 transducer (frequency 1-5 MHz) and an S8-3 transducer (frequency 3-8 MHz). All results were compared with the CT results. The TTE diagnosis of SAPVC was made by an experienced sonographer who has more than 8 years of experience in evaluating congenital heart disease in children. The following ultrasound features should be noted when applying different echocardiographic scan views to determine the classification of SAPVC: (1) The four pulmonary veins do not flow back into the left atrium, and there are abnormal blood vessels behind or outside the left atrium to help track the paths and drainage sites of the veins. (2) There is an abnormal vein adjacent to the descending aorta or ascending aorta that flows up into the LIV, SVC or AV. (3) The SVC could have a widened inner diameter and an increased flow velocity. (4) The size or ratio of the atria and ventricles are generally normal or abnormal. (5) The atrial septum might not be continuous and complete. (6) Tricuspid regurgitation is estimated to assess the pulmonary artery pressure. (7) It is important to rule out other malformations.
Standard views for complete visualization of the pulmonary veins and superior vena cava include the long axis of the parasternal left ventricle, the short axis of the high parasternal fundus, the four and five chambers of the apical heart and so on. In addition, nonstandard views, such as the long axis of the superior apical vena cava in the high position, at the apex of the heart, below the xiphoid process, or at the right supraclavicular fossa, are also important supplementary views to show the veins. Some nonstandard views are shown in Fig. 2.
MSCT diagnosis of SAPVC
Multilayer spiral CT (MSCT) is an examination method that provides additional information when SAPVC is diagnosed or suspected by TTE. The patients completed the image acquisition, such as axial, multiplanar reconstruction and VR reconstruction of the MSCT. According to the CT heart protocol, the measurement parameters, including 0.75 mm diameter, 1 mm layer thickness, and 0.8 mm layer interval, were set. The whole scan is administered by percutaneous injection into the peripheral veins in the foot or elbows. The dose of contrast agent was calculated according to 0.8-1 ml/kg under 1 year old, 1-1.5 ml/kg over 1-5 years old, and 2-5 ml/kg for 5-18 years old. The injection speed was 0.8 ml/s for children under 1 year old, 1-2 ml/s for children 1-5 years old and 2-5 ml/s for children 5-18 years old. The scanning radiation dose of MSCT was in accordance with the automatic milliamp control technology, and the scanning range was from the thoracic entrance to the top of the liver. Subsequently, all data were transmitted to the workstation, and the image reading was completed by a radiologist with 8 years or more experience in cardiac assessment.
Determination of the different classifications of SAPVC and the drainage sites of the ectopic pulmonary veins
According to the pulmonary veins connected to the left atrium, SAPVC can be classified as a total SAPVC (TSAPVC), in which none of the four pulmonary veins connect with the left atrium; partial SAPVC (PSAPVC), in which one, two or three pulmonary veins do not converge into the left atrium; and mixed SAPVC (MSAPVC), in which two or more types of APVC are present simultaneously. The most common drainage sites for the veins include the left innominate vein (LIV) and the right superior vena cava (SVC), and a rarer site is the azygos vein (AV) (Figure 3).
Determination of the numbers of ectopic pulmonary veins
TTE shows that a normal pulmonary venous system consists of 4 veins, 2 on each side, draining into the left atrium. In contrast, the anomalous pulmonary veins of SAPVC tend to converge posteriorly or laterally in the left atrium to form a common pulmonary venous trunk. When determining the number of veins, we first focus on judging the veins that enter the left atrium and then clarify the veins that do not flow back into the left atrium through multiple views. Subsequently, we follow up to find the drainage paths and sites of these veins. The methods of using TTE to determine the veins through multiple views are as follows: ① If no pulmonary veins are found to open in the wall of the left atrium, the 4 veins are all ectopic pulmonary veins. We consider this to be total or mixed SAPVC. ② If one pulmonary vein converging into the left atrium is visible in the left atrial wall, which can show any of the superior left, inferior left or superior right and inferior right branches, the patient is considered to have partial SAPVC with 3 ectopic pulmonary veins. ③ If two pulmonary veins can be found in the wall of the left atrium, they can show that two left or two right or one left and one right veins merge into the left atrium. We consider this to be the partial SAPVC of two ectopic pulmonary veins. ④ If three pulmonary veins can be found in the wall of the left atrium, two left and one right or two right and one left veins merge into the left atrium. We consider this to be the partial SAPVC of one ectopic pulmonary vein. ⑤ If four pulmonary veins can be found in the wall of the left atrium, we basically rule it out as not SAPVC. The judgment of the number of ectopic pulmonary veins is shown in Fig. 4.
Statistical analysis
SPSS 22.0 statistical analysis software was used to analyze all data, and the normally distributed measurement data are expressed as the mean ± standard deviation. Categorical data are expressed as frequencies, and Fisher’s exact probability method was used to compare the intergroup countable data. P<0.05 was considered to indicate a statistically significant difference.