Conventional full sternotomy in cardiac surgery has the disadvantages of a long incision, more bleeding and the risk of mediastinitis. Although partial sternotomy shortens the incision, sternal stability is damaged and the patient will require several months to recover back to normal life after surgery. In the last two decades, various minimally invasive techniques were applied in congenital cardiac surgery [14]. Liu et al. from Fuwai Hospital have reported their experience of oblique lateral thoracotomy in 683 children with congenital heart disease [3]. The ages ranged from 4 months to 7 years, and the main diseases in this series were ASD and VSD. A few patients with tetralogy of Fallot were also operated using this technique. However, the length of this incision was not small, and the incision was close to mammary tissue. Bleiziffer et al. have followed 72 female adolescent patients and found that 61% of the patients developed asymmetric breasts in adulthood; therefore, they recommended not using such an incision in adolescent females [15]. To avoid such complications, this group modified their techniques and reported their results in 2005. The modified incision was at the midaxillary level and the length was approximately 5 cm. Thirty-six children with isolated ASD were included in this study, and the outcomes were excellent. The youngest patient in this study was 4 years old [5]. Pretre et al. from Switzerland have reported their experience of using right posterolateral thoracotomy in 80 patients with simple congenital heart disease [4]. In most patients in this group, femoral arterial and venous cannulations were used (87.5%). The mid-term results were good [16]. Palma et al. from Italy have reported excellent outcomes of 132 open-heart surgeries using right anterolateral mini-thoracotomy [17]. Recently, several heart centers from China have reported various modified minimally invasive methods for repairing simple congenital heart diseases. The most commonly used incision was the RSAVI. The incision was modified from an oblique shape to the vertical direction, and its length was also shortened. The indications for such minimally invasive surgeries were expanded, and there was a trend of using a soft tissue retractor instead of a rigid spreader [9, 13, 18, 19]. The safety and efficacy of such strategies were validated, and the outcomes of MICS in children were not inferior to conventional heart surgery.
The indication of MICS and the choice of incision in children are not yet consistent. In the past, the indication was simple ASDs, and the exposure usually was excellent. However, in patients with VSD, surgical exposure was not as good as that in patients with ASD because the VSDs are deep and blocked by tricuspid tissues. With the advancement of instruments and techniques in MICS, the indication was expanded recently. In our opinion, all isolated ASDs of any size or location can be repaired using minimally invasive approaches; however, patients with ASD who have concomitant anomalous pulmonary vein drainage should be evaluated carefully and may not be suitable for this minimally invasive surgery. The most common type of VSD in this study was peri-membranous or inlet muscular VSD because they are usually easily repaired through the tricuspid valve from a right atriotomy. The size of VSD is not crucial for decision making, and both direct suturing and patch closure techniques were used in our patients. In our institution, we prefer to operate on patients whose age is over 8 months and weight is over 8 kg since tissue in infant is fragile. However, Anzhen Hospital recently reported a group of infants less than 5 kg operated via RSAVI, and the outcomes were the same as those operated from median sternotomy [20]. Furthermore, CAVSD repair was reported from lateral mini-thoracotomy in infants as well [9].
An uneventful establishment of cardiopulmonary bypass is fundamental to perform MICS. The diameters of femoral vessels in infants are small, and femoral cannulation may lead to a high incidence of vascular complications; therefore, central cannulation is preferred in such patients. The RSAVI can expose the ascending aorta, SVC and IVC excellently. The arterial cannulation site is usually deep, and aortic cannulation is the most difficult step in most patients. In the literature, some authors have used forceps to grab the tip of the curve arterial cannula which facilitated cannulation [8, 13]; however, mastering this technique is not easy, especially when surgical exposure is limited. In our center, we used a straight arterial cannula with a rigid inner cylinder; and put it inside through an arterial incision. The keys of this step are to open the adventitia within the aortic purse string as much as possible and to rotate the cannula back and forth slightly if we feel resistance. In some older patients with deep thoracic cavities and small incisions, the aorta is punctured using a needle, and a guiding wire is inserted; then an arterial cannula is placed by Seldinger technique. The SVC and IVC cannulas can be either curved or straight, and we prefer using cannulas with thin-walled wire reinforcement, which is flexible to be positioned.
The key point to ensure precise repair is well surgical exposure, especially when the infra-axillary incision is tiny. To obtain better surgical exposure, recently, Heinisch et al. have reported percutaneous cannulation of the IVC in 38 pediatric patients; however, 13.5% of the cases had thrombosis at the cannulation site [21]. In some patients in the RSAVI group, the IVC cannula was placed through the sixth intercostal space, and this puncture site was used to place chest tube at the end of surgery. After cardioplegia was given, the cardioplegia needle and tube were removed, since most simple cardiac defects can be repaired within the protection time of a single dose of cardioplegia. In a few patients with VSD, an ice-cold saline-rinsed gauze was placed behind the heart in the pericardial cavity, which helped push the heart close to the incision; with appropriate retraction, the VSD was exposed well. In case of unrestrictive VSD, patch closure using interrupted stitches was preferred.
We found that the infra-axillary incision was convenient in infants and children; however, it was limited in adolescents and adults since the incision is too far away from the heart. Therefore, we used RALT in such patients. Giordano et al. have reported using similar incision to replace aortic valve in adolescents with bicuspid aortic valve [22]. In this study, the mean age and body weight of the RALT group is significantly higher than those of the RSAVI group. The RALT incision from the fourth intercostal space is close to the heart, and the surgical view is similar to the view from sternotomy. Peripheral cardiopulmonary bypass established by femoral cannulations helps obtain better exposure from the mini-thoracotomy. Recently, the SVC cannula was placed through the right jugular vein, and a Chitwood aortic cross-clamp was used in this study. Furthermore, thoracoscopy assistance and a soft tissue retractor helped us reduce the incision to as short as 4 cm in length. To be noticed, the skin incision should be at the lower margin of the breast tissue in adult females and should be far away from the mammary tissue in prepubescent female children.
The aforementioned two incisions expose ASD and peri-membranous VSD well enough to repair; however, they can hardly expose subpulmonary VSD. A few heart centers have reported their experience of repair doubly committed subarterial VSD using subaxillary incision. VSD was repaired either through the tricuspid valve or through the main pulmonary artery; however, the number of such cases is very limited, and the surgeons are experienced in this field, so the reproducibility is not easy [13, 18]. In this study, only one infant with subpulmonary artery VSD underwent repair using a right subaxillary incision, and the exposure was not good enough for precise repair. Intraoperative transesophageal echocardiography demonstrated residual VSD, and a second cross-clamp was applied to repair the residual defect. After this case, we preferred median sternotomy in infants with subpulmonary artery VSD. Meanwhile, in adolescents and adults with subpulmonary artery VSD, a LALT from the second intercostal space was used. In this study, we reported our preliminary experience in five cases. Femoral arterial and venous cannulations were used. Single IVC cannulation usually achieves adequate drainage, and SVC cannulation is unnecessary in most patients; however, SVC cannulation is possible through the incision if needed after the patient is on bypass. In 2017, authors from China have used this approach to repair subpulmonary artery VSD; however, it was used only in adults, not in children [23]. In 2019, authors from Guangzhou have reported an alternative method using minimal mid-partial sternotomy in 13 patients [24]. Minimally invasive per-ventricular closure of doubly committed subarterial VSD has also been reported, but this technique lacks long-term follow-up results [2]. In our opinion, surgical closure using LALT is preferred in such patient groups. Recently, the LALT incision was also applied to replace the pulmonary valve in seven patients following tetralogy of Fallot repair by Nellis et al. [25].
The lowest weight limit of femoral cannulation is inconsistent. Most surgeons prefer using peripheral cannulation in patients over 30 kg; however, surgeons from Switzerland have dissected the iliac artery in infants with a body weight as low as 10 kg [16]. The reported lowest body surface area using a femoral venous cannulation was approximately 0.3 m2, however, the patency of the femoral vein was compromised in 13.5% of the patients [20]. The cutoff body weight is 20 kg in our institution, and preoperative femoral vessels were evaluated using ultrasonography to determine the possibility of femoral cannulation.
This study is limited by its retrospective nature in a single institution, and no comparison was performed between minimally invasive approaches and sternotomy. Pain scores were not evaluated in these patients, and the follow-up time was relatively short. The minimally invasive approaches reported here are unsuitable for all congenital heart diseases, especially in complicated diseases. In infants less than 6 months old, we still prefer median sternotomy due to the fragile heart and lung tissues in infants, whereas a few centers summarized their experience in such patients [19, 20]. In low body weight patients with doubly committed subarterial VSD, we prefer median sternotomy, and finally, if the patient has prior thoracic surgery or has significant adherence in the thoracic cavity, sternotomy is preferred as well.