Outcomes and Risk Factors for Morbidity and Mortality of Systemic-to-Pulmonary Shunts in a Tertiary Hospital in Thailand

Data Collection

We retrospectively collected data from the electronic medical records (EMRs) of Ramathibodi Hospital from January 01, 2013, to April 30, 2024. All patients whose primary operation was systemic-to-pulmonary shunt were included. We limited the included patients to those who were operated by a single surgeon (PS) in order to minimize bias regarding surgical techniques and postoperative care measures. Patients diagnosed with hypoplastic left heart syndrome whose systemic-to-pulmonary shunt was part of the Norwood operation and patients whose medical record data were missing significant information (lost or incomplete medical records) were excluded. Patients who were lost to follow-up within the study time frame were analyzed as alive up to the time of last follow-up period.

There were initially 56 patients eligible for our study. After exclusion, a total of 42 patients remained in the final cohort. Preoperative baseline characteristics (including age, weight, diagnosis, and comorbidities), operative details (including surgical approach, shunt type, shunt size, and cardiopulmonary bypass usage), and information on postoperative care measures (including overall and discharge mortality, overall survival time, reintervention rate, reintervention-free survival time, complications, and hospital and intensive care unit [ICU] stay duration) were collected. Discharge mortality was defined as death from any cause within the same hospital admission. Overall survival time was defined as either survival time until total correction or the end date of our study. Reintervention-free survival time was defined as survival time until the first reintervention from any cause.

Definitions and Surgical Techniques

A central shunt (Figure 1A) is defined if the systemic arterial outflow is from the ascending aorta and the pulmonary arterial inflow is from either a branch or the main pulmonary artery. A modified Blalock-Taussig-Thomas (mBTT) shunt (Figure 1B) is defined if the systemic arterial outflow is from one of the other primary or secondary branches of the aorta. In our institution, we routinely “oversized” the shunt diameter by 1 mm according to the appropriate shunt size based on the patient's body weight in kilograms. For body weight of less than 3 kg, the shunt size would be 3.5 mm. If the body weight was between 3 and 5, 5 and 10, and 10 and 15 kg, the shunt size selected would be 4, 5, and 6 mm, respectively. Lastly, if the body weight was more than 15 kg or if the patient was an adult, the shunt size selected would be either 7 or 8 mm. However, other determinants of shunt sizes included sizes of pulmonary and systemic arteries as well as the anticipated age of the patient in which total correction was planned. Baseline preoperative blood gases were not routinely obtained in every patient but only in those who were critically ill or admitted for other treatments before the operation.

OPEN IN VIEWER

Figure 1.

(A) A central shunt connecting the ascending aorta to the right pulmonary artery (N = 2) and (B) A right modified Blalock-Taussig-Thomas (mBTT) shunt connecting the right subclavian artery to the right pulmonary artery (N = 40).

Principles of operation were generally the same in every patient. Oxygen saturation at the beginning of the operation was recorded at a fraction of inspired oxygen (FiO₂) of 0.3. Bloodletting was done after anesthesia if the preoperative hemoglobin level was more than 20 g/dL. For a thoracotomy approach, a generous posterolateral thoracotomy would be performed. The systemic artery of choice would be dissected and encircled first followed by the pulmonary artery of choice. We routinely used a non-heparin-coated expanded polytetrafluoroethylene (PTFE) graft in our institution. Moderate heparinization (100 U of heparin per kilogram body weight) was done, and the systemic artery was clamped and opened. Proximal anastomosis was performed between the artery and the graft with either 6-0 or 7-0 polypropylene sutures. After proximal anastomosis completion, the proximal pulmonary artery would then be clamped while the upper and lower lobe branches were snugged separately. We typically waited for approximately 5 min to observe if there was a significant drop in oxygen saturation or hemodynamic instability. If neither occurred, a pulmonary arteriotomy would then be made and distal anastomosis performed again with either 6-0 or 7-0 polypropylene sutures. The completed shunt was palpated to assess its patency. Bleeding would be checked, a small-caliber chest drain placed, and the thoracotomy incision finally closed in layers. Heparinization was not reversed routinely. Oxygen saturation at FiO2 of 0.3 of about 85% to 90% was our acceptable target.

For a median sternotomy approach, general concepts and operative sequences were similar to the thoracotomy approach. Cardiopulmonary bypass, if needed, was commenced either before or after dissection of both systemic and pulmonary arteries depending on the difficulty of dissection. We routinely kept the ductus arteriosus open in every case.

Postoperative Care Protocols and Follow-up

Ventilatory support at FiO2 of 0.3 was continued until at least the next postoperative day for all patients. The highest oxygen saturation level was recorded and blood sample for arterial blood gas analysis were collected as soon as the patient was hemodynamically stable after arrival at the intensive care unit (ICU). Blood gas analysis would then be obtained every 6 h thereafter on the first postoperative night. Complete blood count analysis was obtained also after the patient arrived at the ICU and again on the following morning. Therapeutic doses of low-molecular-weight heparin (LMWH) would be administered subcutaneously within 6 h postoperatively if there was neither significant bleeding or bleeding concern and then continued for three days. Aspirin would be given orally the next day. Chest drain would be removed when the content was at least serosanguinous in consistency, and the output was less than 4 mL/kg body weight per day. Our pediatric cardiologists performed a full-study echocardiography on every patient one day before discharge to confirm shunt patency.

After discharge from the hospital, patients were followed on an outpatient basis at a one-week interval from the hospital-discharge date. If clinically satisfactory, a one-month follow-up would then be arranged and a half-yearly appointment would be made thereafter. General physical examination (including auscultation of shunt murmur and measurement of cutaneous oxygen saturation) and chest x-rays were performed at every visit.

Statistical Analysis

Patient characteristics, operative, and postoperative details with continuous variables were compared using Wilcoxon rank-sum test while categorical variables were compared with χ² and Fisher exact tests for values with balanced and imbalanced distributions, respectively. The statistical software used was Stata version 14.1.

Our Overall Results

Systemic-to-pulmonary shunts have been around for decades, and there have been many contemporary reports regarding their short- and long-term outcomes.^3–9 There were only three cases of shunt thrombosis requiring placement of a new contralateral shunt in our study. We opted for a reoperation rather than an interventional treatment because we believed that a shunt that had already thrombosed was compromised and would have a higher tendency to rethrombose despite appropriate catheter-based treatment. Our results also satisfactorily demonstrated that there was only one exceptional mortality in our cohort. The patient who died presented to us at a considerably advanced age with a diagnosis of dextro-transposition of the great arteries with left ventricular outflow tract obstruction (d-TGA/LVOTO) and multiple organ dysfunctions. The patient received an 8-mm mBTT shunt which resulted in significant overflow and heart failure with bilateral pleural effusions. Initial treatment included placement of chest drains, diuretics, and adjustment of heart failure medications. The patient died following total corrective operation from postoperative cardiac failure, being unable to separate from bypass. We should state that, from our study, a systemic-to-pulmonary shunt was a considerably safe operation and should be strongly considered when necessary. Considering only data from neonates in our cohort, the end results were also satisfactory without any discharge or overall mortality. These findings demonstrated that our results of systemic-to-pulmonary shunts performed in neonates were at least comparable to the current STS database.

Another point of interest was the median age at operation of our patients, which was roughly ten months old (307.5 days). According to the STS database of systemic-to-pulmonary shunts, the high operative risk was calculated solely from neonates.¹ We believed that postponing the operation past the neonatal period would result in more favorable overall outcomes, especially discharge and overall mortality. From our earlier experience, neonates would require placement of a considerably smaller shunt (probably 3 mm), resulting in a higher incidence of shunt thrombosis and early death. Therefore, prostaglandin would be continuously administered throughout this waiting period if necessary to maintain acceptable pulmonary blood flow until surgery was deemed appropriate. None of these significantly cyanotic neonates died during this interval in our cohort. Only six neonates had persistent desaturation despite continuous prostaglandin infusion and had to undergo early intervention. Again, our results proved to be favorable, with no discharge and only one overall mortality as stated.

Diagnosis as a Predictor of Outcomes

Some studies^4,8 stated that certain clinical diagnoses had negative impacts on mortality following systemic-to-pulmonary shunt procedures. Our study included patients with TOF, double outlet right ventricle with pulmonary stenosis, pulmonary atresia with ventricular septal defect, d-TGA/LVOTO, as well as hearts with univentricular physiology. We had one mortality from the d-TGA/LVOTO group as stated but we did not find the differences in mortality between all other groups to be statistically significant. This may be due to the limited number of patients in our study. With that said, we could still imply from our results that diagnosis alone should not be the only factor contributing to morbidity and mortality but other factors such as surgical techniques and postoperative care measures should have more important roles.

Shunt Size and its Effects on Outcomes

Smaller shunt sizes were associated with a higher incidence of shunt thrombosis and reduced survival according to Ahmad and colleagues. ⁸ In our study, we divided the patients into two groups with shunt sizes of 5 mm or less in one and more than 5 mm in the other. We did not find shunt sizes of 5 mm or less to be associated with reduced shunt patency or increased mortality. We believed that shunt size alone should not have a negative impact on morbidity and mortality if the size was already appropriately chosen according to body weight and arterial inflow and outflow sizes. Moreover, proper and meticulous surgical techniques rather than placing larger shunts should contribute more to improved outcomes.

Our rationale on oversizing the shunt diameter by 1 mm from the appropriate size according to body weight proved to be more favorable in terms of delaying or rreducing future reoperations due to recurrent desaturation. Somatic growth of the patient would ensue that a new shunt placement would be inevitable unless the patient had undergone early total correction. By placing a slightly larger shunt, we have eliminated the incidence of shunt reoperations due to inadequate shunt flow. The setback of this strategy was that some patients would be more in need of diuretics early postoperatively in order to treat pulmonary congestion. However, none of the patients demonstrated signs of congestive heart failure and all of them adjusted well clinically on late-postoperative terms.

Aspects on Shunt Type, Surgical Techniques, and Postoperative Protocols

Shunt types did not seem to have an effect on outcomes in our study. Although some would argue that a central shunt with its larger arterial inflow might possibly cause a higher incidence of shunt overflow, we believed there were many other factors involved in deciding on which type of shunt should be placed. A central shunt would still be needed if the peripheral arterial inflow size was deemed too small for an mBTT shunt. Also, if the shunt size was chosen appropriately, there should be minimal to no problem of shunt overflow. In our institution, an mBTT shunt was preferred over a central shunt if the situation permitted due to the ease of shunt placement and if the shunt flow could be better controlled. Also, an mBTT shunt would allow placement of a larger shunt at a similar shunt flow rate as a smaller shunt in the central position. We believed this would allow for less incidence of shunt thrombosis and subsequent revision. Heparin-coated shunts were associated with a lower incidence of shunt thrombosis according to some studies.^10,11 We did not use heparin-coated vascular grafts in our patients but our postoperative protocols dictated that all patients received therapeutic doses of LMWH, unless contraindicated, as soon as bleeding subsided which was usually within 6 h postoperatively. Aspirin was also given on postoperative day 1 unless contraindicated. Several studies^12–17 emphasized the importance of strict and clinically feasible postoperative care protocols to maximally improve outcomes. We strongly agreed with this point because our protocols significantly improved our standard of care and provided a standardized and reproducible guideline for any medical personnel involved in providing care for our patients.

We had very few cases that required reintervention due to shunt thrombosis and we had no bleeding complications following LMWH and aspirin administration. Moreover, the three cases of shunt thrombosis previously mentioned presented in patients with very small and thin pulmonary arteries, potentially compromising shunt flow albeit with optimal surgical techniques. Therefore, we could firmly state that, along with good surgical techniques, postoperative anticoagulant and antiplatelet therapy^18–23 should be recommended as part of the postoperative protocols. Improvement in surgical planning could now theoretically be obtained from virtual simulations of blood flow using computer programs,^24–26 and this might in fact be the future of surgical planning for systemic-to-pulmonary shunt operations.

Is Median Sternotomy Really Superior to Thoracotomy?

Median sternotomy has several theoretical advantages compared with thoracotomy according to some studies.^27,28 It permits rapid initiation of cardiopulmonary bypass in case of hemodynamic collapse or significant desaturation during operation, allows placement of the shunt more proximally to larger arterial inflow and outflow, requires no lung traction, and causes only one scar after total correction. Also, a patent ductus arteriosus could be ligated after shunt completion only through a median sternotomy approach. Thus, the incidence of steal and shunt thrombosis could be reduced. Taking down an intrapericardial shunt at total correction would also be significantly easier than if the shunt is intrapleural. Resternotomy for a second corrective procedure may be of concern but this is usually not severely problematic or dangerous. However, most of the patients in our study underwent a thoracotomy approach mainly due to surgeon's preference and familiarity. Thoracotomy, in fact, was the original approach and we believed that preserving the mediastinum for the next total correction are helpful for the safety and effectiveness of the next operation. We also had remarkable results from our cohort regarding morbidity and mortality although the vast majority of our patients received systemic-to-pulmonary shunts through a thoracotomy approach.

Emerging Interventional Treatment for Maintaining Ductal Patency

Ductal stenting has emerged as a new and interesting option for providing pulmonary blood flow in this group of patients. It provides comparable overall mortality to systemic-to-pulmonary shunts but with less surgical morbidity and shorter hospital and ICU stay duration.^29–32 However, procedure-related complications as well as stent migration and embolization still prove to be a concern. In our institution, there are very few cases that underwent successful ductal stenting procedures due to our limited resources. Therefore, we did not include this patient population in our study. We are currently working with our pediatric cardiologists in order to further pursue this aspect and hopefully include this in our future study.