The VSDs were repaired successfully in all patients with the use of bovine or autologous pericardial patches. No patients died or converted to median sternotomy. The average incision length was 5.1 ± 0.6 cm (range, 4.1–6.1 cm) (Fig. 1b and c). The cosmetic result was very satisfactory. The average CPB and aortic cross-clamp time was 102.5 ± 13.6 min (range, 85–127 min) and 54.6 ± 6.9 min (range, 45–66 min), respectively. No patients required blood transfusion. The mean mechanical ventilation time was 6.9 ± 1.1 h (range, 4.9–8.5 h). Average intensive care unit (ICU) stay was 17.7 ± 1.7 h (range, 15–20 h). Postoperative drainage volume within the first 24 h ranged from 20 to 102 ml (average, 65.0 ± 30.5 ml). Postoperative hospital stay ranged from 4 to 6 days (average, 5.1 ± 0. 7 days).

The average duration of follow-up was 15.4 ± 2.3 months (range, 5.4–32.3 months) after hospital discharge. During the periods of follow-up, no patients were found to have any residual shunt by transthoracic echocardiography. There were no wound infections, pericardial effusion, neurologic or other late complications.

Subarterial ventricular septal defects (VSDs) are located in the right ventricular outflow tract, which is in close proximity to the pulmonary artery valve. Usually, the upper margin of the defect lies in the fibrous ring between the pulmonary and aortic valves, and the lower margin extends to the supraventricular crest. Anatomically, subarterial VSDs are defined as conal septal defects [7]. They represent 5–7% of all VSDs [7, 8].

In this series, 27 adult patients were operated on to repair the subarterial VSDs with the use of minimally invasive cardiac surgical technique via left anterior mini-thoracotomy. The VSDs were all closed under direct visualization through a minimal skin access approximating to 4–6 cm. All the patients recovered rapidly with decreased surgical traumas and satisfactory cosmetic results. All the patients were discharged safely, with no mortality, no morbidity and no obvious postoperative complications.

Conventionally, intracardiac repair under direct visualization through median sternotomy has long been considered safe and effective treatment for subarterial VSDs, but this approach produces significant surgical traumas and leaves a long midline scarring [9]. For most adult VSD patients, the major concern is not the mortality or morbidity associated with repair surgery, but rather cosmetic problems arising from surgical scarring as a result of median sternotomy [10]. Researchers have explored transcatheter interventional occlusion and periventricular occlusion to determine whether these approaches can be feasibly applied in the treatment of subarterial VSDs [3, 11]. However, due to low success rate and increased incidence of postoperative complications, including residual shunt, arrhythmias, hemolysis, thromboemboli, aortic valve regurgitation, and translocation of closure device, the short- and long-term outcomes of these approaches are unfavorable [11–18]. Liu et al. [14] reported intraoperative device closure of subarterial VSDs in 62 cases. Overall, 16.1% of these cases were converted to full median sternotomy due to tricuspid regurgitation, aortic valve regurgitation, or residual shunt, and the overall success rate was only 83.9%. Additionally, the incidence of early- and late-stage complications of this approach was up to 19.2 and 3.8%, respectively [14].

To increase success rates, improve cosmetic results, and reduce surgical traumas, minimally invasive cardiac surgery has been increasingly applied in the treatment of VSDs, and the number of relevant literatures is increasing [1, 5]. Minimally invasive cardiac surgical techniques usually include the right anterior lateral minimal incision, right axillary minimal incision, and lower sternal minimal incision [6, 19, 20]. In addition, VSDs can also be repaired by robot via a minimally invasive access [21]. However, minimally invasive repair of subarterial VSDs via left anterior mini-thoracotomy is rarely reported. The present series adopted minimally invasive access via left anterior mini-thoracotomy for repair of adult subarterial VSDs.

Meticulous preoperative examination for the accurate diagnosis of VSD type is mandatory for successful outcomes. The minimally invasive access via left arterial mini-thoracotomy is specially designed for simple adult subarterial VSD--the minimal access is too small to simultaneously repair other intracardiac anomalies, it is important to confirm the diagnosis of subarterial VSD and exclude other intracardiac malformations by preoperative examination, such as transthoracic echocardiography or transesophageal echocardiography (TEE). In addition, accurately choosing the skin incision access is an extremely critical step for this approach. Thus, accurate preoperative positioning of the VSD is of great significance. We adopted chest computed tomography (CT) scan combined with 3-dimensional reconstruction for positioning the VSD site. According to the positioning result of preoperative chest CT, the intercostal space nearest to the VSD was considered as the most optimal skin incision access, across where aortic cross-clamping and exposing the VSD could be simultaneously achieved. After positioning the intercostal space, we should incise the skin along the upper edge of the lower rib to avoid the intercostal vessels to decrease hemorrhage. Anatomically, regardless of the intercostal space chosen as the incision access, the sternal extremity of the third costal cartilage must be divided, without resection, to increase exposure. It should be noted that, after the heart was arrested, the transpulmonary arteriotomy should be performed and blood within left ventricular system should be suctioned out through the VSD with the use of a small soft tube to keep the operative field clean and reduce the resistance of moving the heart, making it easier to pull the VSD site up to the center of the incision, which allowed us to repair the VSD under direct visualization.

Lin et al. [2] reported a video-assisted endoscopic technique under femoro-femoral cardiopulmonary bypass for the repair of subarterial VSDs in 11 patients using a transverse incision in the third or fourth intercostal space of the left parasternal region. In his procedures, the ascending aorta was not clamped, and the operation was performed under hypothermic fibrillatory arrest. However, this approach requires special surgical instruments and a long-term learning curve, which is not conducive for promotion. Additionally, operation under hypothermic fibrillatory arrest can’t provide optimal myocardial protection [10]. In order to modify this approach, we recommend minimally invasive access via left anterior mini-thoracotomy for simultaneously clamping the ascending aorta and closing the VSD under direct visualization. According to our experiences, minimally invasive access via left anterior mini-thoracotomy could provide adequate exposure of the VSD and sufficient myocardial protection. Moreover, it doesn’t require special instruments and have no much difficulty in terms of operation.

For female patients, Jung et al. [10] advocated the anterolateral mini-thoracotomy of the breast as the incision access. Roughly starting from the sixth rib, the mammary tissues were dissected through the thoraco-fascia plane to expose the third rib. Although the incision access is hidden, it can potentially damage the mammary tissues and thus is more likely to accelerate fat liquefaction [10]. In order to avoid injury to the mammary tissues and retain cosmetic results, we chosen a longitudinal minimal incision access in the left parasternal region for female patients who present with subarterial VSDs. Most of the steps are the same as the transverse incision except for the process of the third rib cartilage. For the longitudinal incision, the sternal extremity of the third costal cartilage should be divided, fractured, and inverted interiorly to increase exposure, while the third costal cartilage only needs to be divided for the transverse incision. So, for the longitudinal incision, the third costal cartilage should be reconstructed after the VSD being closed.

The prominent advantage of minimally invasive cardiac surgical techniques is the avoidance of sternotomy [2]. The minimally invasive technique can reduce the injury to patients and postoperative complications to a minimum [2]. In this present series, we analyzed the clinical data of these 27 patients who underwent repair of subarterial VSDs via left anterior mini-thoracotomy. According to analytic results, the approach brought very few surgical traumas and haemorrhage, all the patients can obtain a fast postoperative recovery. For most patients, they can discharge the hospital 5 days after the operation. Notably, the cosmetic effect was very gratifying, which was the uppermost superiority of this approach and as well as the prime objective of the patients.

However, the new approach has potential limitations. Subarterial ventricular septal defect (VSD) accounts for 5–7% of all the VSDs, mainly prevailing in older children and adolescents, adult subarterial VSD is relatively scarce. For older children and adolescents with light body weight and small body size, some difficulties exist in constructing peripheral cardiopulmonary bypass, so the novel technique presented in this series is not appropriate for this cohort; thus its scale of application is limited. But, with the accumulation of experiences and the development of associated techniques, the novel approach might break through age, body weight, body size and other potential restrictions, and could be extensively chosen by all the subarterial VSD patients and even by patients with other types of VSD, who require surgical intervention.

The preliminary results adequately demonstrate that minimally invasive cardiac surgical technique via left anterior mini-thoracotomy can be served as a novel, safe and feasible alternative for the repair of subarterial VSDs.