The Challenges of Swimming Against the Tide

In the current issue of the Journal, Prabhu et al from Duke University report outcomes of infants with single ventricle (SV) and restricted pulmonary blood flow (PBF) who received either a systemic-topulmonary shunt or ductal stent (DS) from 2015 to 2019. They found those who received DS had significantly shorter mechanical ventilation duration (mean one vs three days) and lower extracorporeal membrane oxygenation (ECMO) need (9% vs 39%). Additionally, procedure mortality (0% vs 17%) and survival to second stage (100% vs 64%) were significantly different. Half of the patients in each group received pulmonary arterioplasty at second-stage surgery. They concluded that, at their center, DS was associated with improved survival. It’s been more than 75 years since the first Blalock-Taussig shunt was performed in 1944, and yet, the modified Blalock-Taussig shunt (mBTS) continues to be commonly performed as initial palliation in patients with cardiac defects amenable to eventual biventricular repair (although less frequently than in the past) or as first stage of palliation in SV defects associated with restricted PBF. Despite the long experience with mBTS, it continues to be associated with high operative mortality that ranges between 3% and 16%, based on several factors including underlying diagnosis, with many studies reporting higher mortality in patients with SV. Additionally, there is continuous risk of attrition prior to subsequent operation in patients with both SV or biventricular anomalies that is largely due to inherently challenging shunt physiology or development of shunt-related problems. While the shunt outcomes in the report from Duke University might seem a bit worse than current expectations, there is no denying that the management of shunts is overall challenging and associated with numerous complications. Ductal stent has been described since 1991 as a novel alternative technique to maintain PBF. However, adoption of this technique was initially very slow, until improved technology (including stent design and delivery systems) generated renewed excitement and interest, especially in the light of continued challenges in the management of patients who undergo mBTS. In the past decade, there have been a number of single-center and multi-institutional reports that compared outcomes between infants who received mBTS versus DS, and they showed that DS were associated with either equivalent or superior outcomes. Overall, it seems that patients who receive DS may be expected to recover faster than those who receive mBTS, to require shorter mechanical ventilation, intensive care unit or hospital stay durations, and to have lower complications including cardiac arrest or ECMO need. Additionally, some of these reports have shown decreased early intervention with DS compared to mBTS, and some have shown decreased procedure mortality and improved overall survival toward subsequent planned operation with DS compared to mBTS. As for pulmonary artery growth, a number of studies have examined that and have showed either equivalent or superior and more symmetrical growth of the branch pulmonary arteries following DS compared to mBTS. This new study from Duke University is definitely in line with the findings from previously published reports. Therefore, given the many single-center and multi-institutional reports, reviews of literature, and meta analyses that are increasingly being published and heavily promoted favoring DS over mBTS, does it even make sense to perform a mBTS and should we abandon these in favor of DS in all patients? Having a different opinion would definitely seem like swimming against the tide. However, what should a surgeon do if they think that the available studies have not adequately vetted the question of who should not get DS and continue to receive mBTS? This is not a similar issue to adult cardiology and coronary artery disease where the cardiologists are “the gatekeepers” and patients undergo intervention without the surgeon’s input. In the majority of pediatric programs, these cases continue to be discussed in a multidisciplinary setting with inputs from surgeons and interventional cardiologists. However, while decisions are usually made based on the best available evidence, what is the value of anecdotal experience in the face of the ample studies disseminated that say otherwise? Despite working with spectacular interventional cardiologists, my personal experience with DS is that while the majority of patients do well, a small but not negligible number of them develop significant pulmonary artery hypoplasia as a result of jailing of a branch pulmonary artery from a stent that is protruding into the artery or as a result of under-recognized “pulmonary artery coarctation” and ductal tissue that has since constricted and led to creation of stenosis or even isolation of the pulmonary artery branch (commonly left). This issue is problematic in any patient but might be especially troubling in SV patients in whom the health and quality of pulmonary arteries determine long-term outcomes. The available literature focuses on operative mortality and reintervention; however, with the lack of randomization and objective measurement of initial pulmonary artery sizes, I feel that comparison of average Nakata index in a series of patients or rate of pulmonary arterioplasty at subsequent operation might not be the necessary adequate measurement end points to determine who would be better served with a surgical approach. When we chose the initial approach in these SV patients, we should take into consideration what is the procedure that would provide not only best early survival, but best long-term outlook, and that is strongly related to pulmonary artery size and growth in this patient population. In a number of patients, that might be an initial mBTS + pulmonary arterioplasty. My current philosophy toward initial management of neonates with SV and restrictive PBF is the following: To better determine candidacy for DS versus mBTS, I personally rely on computed tomography for better assessment of ductal and pulmonary artery anatomy and potential risk of pulmonary artery obstruction or isolation. In the absence of anatomic substrate to develop these complications, I believe that DS can be an attractive and superior choice for many as it is associated with faster recovery and lower morbidity. In these who are at risk to develop the complications, I feel that an mBTS and