EXPLANATION


Hypoplastic left heart syndrome (HLHS) is associated with significant morbidity and mortality as compared to other forms of congenital heart disease. HLHS is typically palliated with a series of three surgical procedures but may also be treated with cardiac transplantation. The Stage 1 Norwood was first described in 1979 and is comprised of a Damus-Kaye-Stansel (DKS) anastomosis to provide systemic blood flow, a systemic-to-pulmonary shunt to provide pulmonary blood flow, ascending aorta and aortic arch reconstruction, and an atrial septectomy to provide unrestricted flow of pulmonary venous blood to the right atrium and right ventricle. It remains associated with an interstage mortality of 10-15%, as parallel circulation results in a labile ratio of pulmonary to systemic blood flow with an increased risk of coronary ischemia. The Stage I Hybrid palliation (HP) was developed as an alternative to the Stage I Norwood to avoid cardiopulmonary bypass (CPB) in neonates at a higher risk for morbidity and mortality. While the specifics of the procedure vary amongst congenital cardiac surgical programs, it is typically approached via median sternotomy and consists of placement of bilateral pulmonary artery (PA) bands to restrict pulmonary blood flow and a patent ductus arteriosus stent to supply systemic blood flow, with or without stenting or balloon septostomy of the atrial septum.


There remains considerable practice variability concerning indications and execution of the Stage I HP amongst various congenital cardiac surgical programs, making comparisons of outcomes challenging. Zanaboni et al. surveyed 54 centers in North America, resulting in a 50% response rate. The majority of respondents use the Stage I HP for neonates deemed to be “high risk”. Two centers use the Stage I HP for all single ventricle patients. The most common determinants of “high risk” were prematurity, low birth weight, reduced ventricular dysfunction, severe tricuspid regurgitation, and additional cardiac or non-cardiac anomalies. Procedural techniques varied, with 95% using bilateral Gore-tex PA bands, 67% using ductal stents versus a prostaglandin infusion, and 23% routinely performing atrial septal enlargement. Interstage management was variable, with some centers opting for the Stage I Norwood at a time point four to six weeks after the Stage I HP and others opting for a comprehensive Stage II bidirectional Glenn at a time point five to six months later.


A 2024 meta-analysis by Iskander et al. analyzed 21 studies, including 1,182 patients with HLHS. The authors compared mortality and morbidity in patients who underwent the Stage I Norwood procedure to those who underwent the Stage I HP. They found no difference in in-hospital mortality or transplantation rate. Further, the authors found a statistically significant difference in one-year mortality (43.99% for the Stage I Hybrid vs 30.72% for the Stage I Norwood), which did not persist at three or five years. Five studies that specifically evaluated “high-risk” patients found an in-hospital mortality and/or transplantation rate of 19.5% for the Stage I Hybrid vs 35.59% for the Stage I Norwood group. The most common “high risk" factors included prematurity, other cardiac anomalies such as intact atrial septum and tricuspid valve insufficiency, and genetic or other non-cardiac anomalies. Nonetheless, the decrease in in-hospital mortality in the Stage I HP group did not translate into an interstage survival benefit (interstage mortality rate of 23.7% for Stage I HP vs 14.06% for Stage I Norwood). Interestingly, the Stage I HP patients experienced a higher rate of unplanned reinterventions, were less likely to reach stage II and III palliations, and had longer ICU and hospital length-of-stay. This likely reflects the fact that patients undergoing Stage I HP typically present with the above-mentioned risk factors and require a more extensive stage II palliation.


The correct answer is B. With the current available data, decreased in-hospital mortality in high-risk patients after the Stage I HP is the most likely benefit. Stage I Norwood patients had increased survival rates in the interstage period and at one year. However, it remains important to consider these conclusions in light of the fact that the hybrid procedure is most often performed in high-risk patients with a greater likelihood of morbidity and mortality. There is also considerable variation in procedural factors between congenital cardiac programs, which may impact outcomes, making direct comparisons of the two strategies susceptible to statistical error.


REFERENCES


Diaz-Berenstain L, Abbasi RK, Riegger LO, Steven JM, Nicolson SC, Andropoulos DB. Anesthesia for the Patient with a Single Ventricle. In: Andropoulos DB, Mossad EB, Gottlieb EA, eds. Anesthesia for Congenital Heart Disease. 4th edition. John Wiley & Sons, Inc.; 2023: 744-746.


Iskander C, Nwankwo U, Kumanan KK, et al. Comparison of Morbidity and Mortality Outcomes between Hybrid Palliation and Norwood Palliation Procedures for Hypoplastic Left Heart Syndrome: Meta-Analysis and Systematic Review. J Clin Med. 2024;13(14):4244. doi:10.3390/jcm13144244


Zanaboni DB, Sower CT, Yu S, Lowery R, Romano JC, Zampi JD. Practice variation using the hybrid stage I procedure in congenital heart disease: Results from a national survey. JTCVS Open. 2024;21:248-256. doi:10.1016/j.xjon.2024.07.020