Discussion

In our interim analysis comparing a 5 cm left anterior mini-incision to redo median sternotomy for pulmonary valve replacement, left anterior mini-incision was shown to be largely comparable to redo median sternotomy. Minimally invasive approaches have previously been associated with longer cardiopulmonary bypass times. This relates to the early peripheral bypass strategy utilised by a majority of minimally invasive techniques. ^{Reference Dieberg, Smart and King2,Reference Doenst, Diab, Sponholz, Bauer and Farber14} In our early analysis, trends suggest that left anterior mini-incision patients may have longer cardiopulmonary bypass times with comparable operative times when compared to redo median sternotomy. There were no postoperative complications in either group, and the quality of valve replacement was not compromised by the minimally invasive approach. Given overall similar perioperative outcomes for left anterior mini-incision and redo median sternotomy in this patient population, technical considerations of each approach, patient preference, and limitations of the left anterior mini-incision should serve as a guide in determining which approach is best for a given patient.

Redo median sternotomy presents unique challenges. Following the first sternotomy, adhesions form between the mediastinal structures and the sternum. This distorts the underlying anatomy, which necessitates extensive and careful dissection prior to the start of any operation. The increased technical difficulty of a redo sternotomy is associated with increased bypass time, cardiac and aortic injuries, and increased blood transfusion requirements when compared with an initial sternotomy. ^{Reference Yin, Yan, Li, Li, Wang and Wang15–Reference Holst, Dearani and Burkhart17} It is also well established that increasing age, a phenomenon of the current congenital cardiac population, is an independent risk factor for sternal non-union. ^{Reference Wang, He and Wang18} In patients with a prior sternotomy, we have found that the left anterior mini-incision is appropriate for a majority of individuals requiring intervention near the pulmonary artery. In such cases, the right ventricular outflow tract is often positioned anteriorly and can be accessed through a 5 cm incision which requires less dissection than redo median sternotomy to achieve a safe exposure and complete the repair. ^{Reference Nellis, Vekstein, Meza, Andersen, Haney and Turek9,Reference Nellis, Wojnarski, Fitch, Andersen and Turek10}

Beyond the technical advantages of the left anterior mini-incision, patients tend to prefer a minimally invasive approach over redo median sternotomy. All eleven patients offered the mini-incision chose the procedure and expressed a preference for a smaller incision despite this representing an additional incision from their prior sternotomy. Additionally, patients receiving a median sternotomy require sternal precautions which limits their activity for 6 weeks. Patients who receive a left anterior mini-incision, however, can avoid these restrictions. This allows resumption of activities as tolerated and is the primary advantage of a minimally invasive approach. ^{Reference Glower, Landolfo and Clements19} This is particularly important in the congenital cardiac population where patients tend to be younger and more active than their adult cardiac surgery counterparts. The median patient in our cohort was 15 years old, underscoring the importance of considering the impact of sternal precautions on postoperative quality of life in the congenital population. Based on our experience, patients seem to view the left anterior mini-incision as appealing. And while prior studies have shown a reduction in pain with minimally invasive strategies, our study shows no difference, potentially owing to small sample size and the inclusion of converted mini-incision patients who received both thoracotomy and sternotomy. ^{Reference Iribarne, Easterwood and Chan1,Reference Walther, Falk and Metz3}

Despite our observed unanimous patient preference for the left anterior mini-incision, and the overall similar outcomes, there are limitations to this approach. The first limitation is a reduction in the size of the operative field of view, a salient factor in paediatric patients where the surgical field is already small. This reduced operative view necessitates a near bloodless field to maintain adequate visualisation which may require additional venous drainage from the left subclavian. ^{Reference Nellis, Vekstein, Meza, Andersen, Haney and Turek9,Reference Nellis, Wojnarski, Fitch, Andersen and Turek10} Our practice is to obtain such venous access percutaneously. Increased patient size can also compound this effect. To help facilitate an adequate workspace, peripheral cannulation strategies are employed. Ultrasound is utilised to evaluate patency and size of the femoral vessels prior to making the mini-incision. The risk of distal limb ischaemia is reduced in paediatric patients by establishing the arterial circuit through a 6 mm end-to-side Dacron graft with the femoral artery. Postoperatively, the graft is removed, and the artery is repaired with bovine pericardium. Lastly, the left anterior mini-incision leaves redo patients with a second, albeit smaller, scar. Preoperatively this point is discussed with patients, and in our experience, they seem to care more about the size and location of the planned incision rather than whether it is within the prior scar.

In this series, two patients required conversion from thoracotomy to sternotomy. This underscores the importance of appropriate patient selection, which is expected to mitigate the risk of conversion compared to this cohort where the procedure was offered without exclusion criteria. Based on these findings, we now consider two or more prior sternotomies and mesocardia as well as dextrocardia to be contraindications for the left anterior mini-incision. These situations lead to poor exposure secondary to dense adhesions and anatomic constraints, respectively. Early trends also indicate that patients with a body mass index above 30 have increased likelihood of conversion and are counselled accordingly. Since these early cases, we now perform preoperative CT for all patients being considered for the mini-incision, a process that can also be of value for patients undergoing redo sternotomy. CT scans help ensure that the pulmonary valve is accessible through a minimally invasive approach and demonstrate which intercostal space should be accessed to perform the mini-incision. Placement is confirmed in the operating room with transthoracic echocardiogram. Additional data may reveal more factors relevant to patient selection and help lower conversion rates.

We believe that the single left anterior median incision patient requiring redo PVR due to a perivalvular leak did so because of sewing into a fenestrated muscle bar and feel that visualisation was not an issue, though this cannot be definitively stated. Perivalvular leaks are not uncommon during valvular intervention. Surprising, however, was the fact that the leak was not detected during the post-bypass TEE, which we routinely perform in the operating room. Thus, rather than repairing the leak during the initial intervention, the patient returned to the operating room the next day. They recovered well, and we have had no such complications since.

The small sample size limits our power of detection for statistical significance in this interim analysis comparing pulmonary valve replacement outcomes for patients undergoing left anterior mini-incision and median sternotomy. Still, while early trends suggest longer bypass times, outcomes between the two groups are otherwise comparable. We believe that public reporting of early results and an open discussion of minimally invasive outcomes in congenital cardiac surgery are essential. It ensures that the balance of risks and benefits continues to favour patients by facilitating a public review of innovative approaches for low-volume operations. This is critical to ensuring patient safety and accelerating the surgeon’s learning curve. The retrospective nature, along with unanimous patient preference for left anterior mini-incision since it was offered, resulted in longer follow-up for the sternotomy cohort. Attention should be given to the durability of repair in left anterior mini-incision patients as their follow-up increases. Future prospective studies should specifically address patient satisfaction with the overall procedure experience via survey data, whether they would make the same decision again, and if their preference is based on perceptions about cosmesis or anticipated postoperative pain.

In conclusion, our experience demonstrates a strong patient preference for minimally invasive approaches to pulmonary valve replacement, despite prior sternotomy, and similar outcomes with slightly longer bypass times for the mini-incision group. The key benefit conferred by the left anterior mini-incision is avoidance of sternal precautions in appropriately selected patients. Additionally, patients express a desire for a smaller incision and scar. The costs and benefits to the patient and surgeon should be considered carefully. Left anterior mini-incision should continue to be offered to patients while comparable outcomes are achieved. Ongoing reporting of these outcomes will promote patient safety and surgeon education. As the left anterior mini-incision cohort expands and their duration of follow-up is increased, we anticipate additional insights into patient selection, a lower conversation rate, and advancements in operative technique.