Shunt Type in the Norwood Procedure

Abstract

Source: Ohye RG, Sleeper LA, Mahony L, et al. Comparison of shunt types in the Norwood procedure for single-ventricle lesions. N Engl J Med. 2010; 362(21): 1980– 1992; doi: 10.1056/NEJMoa0912461The Pediatric Hear t Network conducted a clinical trial at 15 North American centers of infants with hypoplastic left heart syndrome (HLHS) or related single right ventricle anomalies who were scheduled for a stage I repair (Norwood procedure) and were randomized to have either a Sano (right ventricle to pulmonary artery [RVPA]) shunt or a modified Blalock Taussig (MBT, subclavian artery to PA) shunt to provide pulmonary blood flow. The primary outcome was death or cardiac transplantation within 12 months following the intervention. Secondary outcomes included morbidity during the hospitalizations for the Norwood and the stage II (Bidirectional Glenn) procedures; unintended cardiovascular interventions involving the shunt; function and volume of the right ventricle; and the amount of tricuspid-valve regurgitation at discharge following the Norwood procedure, before stage II, and at 14 months of age.The study enrolled 555 infants but six were excluded from the analysis (5 did not receive the intervention and 1 was lost to follow-up). The two equally divided groups did not differ in initial clinical characteristics. Twelve months after randomization, primary outcome events occurred in 72 (68 deaths and 4 transplantations) of the 274 infants (26.3%) assigned to the RVPA group as compared to 100 events (91 deaths and 9 transplantations) of the 275 infants (36.4%) assigned to the MBT group. However, there was no difference in transplantation-free survival between the two groups with continued follow-up to a mean of 32 months after the stage I procedure.During the 12 months following the Norwood procedure, infants in the RVPA shunt group underwent more unplanned cardiovascular interventions (92 vs 70 per 100 infants, P=.003) primarily due to the higher need for balloon dilation or stent placement in the shunt or a branch of the PA. The rate of complications was also higher in the RVPA shunt group (5.3 vs 4.7 complications per infant, P=.002), although the proportion of infants with at least one complication was the same (91%). The authors concluded that continued follow-up beyond 12 months is needed to determine which of the two shunts to establish pulmonary blood flow is superior.HLHS occurs in 1 of 5,000 live births.1 Infants with HLHS require surgical therapy to establish adequate systemic blood flow that is separate from the pulmonary circulation. The risk of death is high, especially during the initial Norwood surgery and the interstage period until a bidirectional cavopulmonary anastomosis (Stage II procedure) is performed. This time period encompasses the duration the child has single ventricle physiology — approximately the first six months of life.Much interest was generated when Sano and colleagues first described their success modifying the source of pulmonary blood flow from an arterial (MBT) to a ventricular (RVPA) shunt for the first stage palliation pioneered by Norwood and colleagues.2,3 Results from several institutions demonstrated that an RVPA shunt improved survival through the period of single ventricle physiology compared to a MBT shunt, perhaps due to better coronary perfusion associated with higher diastolic blood pressure. However, concern persisted that the physiologic advantages of a RVPA shunt for early survival may be offset by the adverse effects of the required ventriculotomy on long-term cardiac function and arrhythmogenesis.To address these concerns, in the current study the Pediatric Heart Network completed a randomized trial of shunt type for initial surgical palliation. The results validate the survival advantage of the ventricular shunt for the first year after the initial surgery, but found no difference in transplant-free survival between groups after one year.Echocardiography is the primary method for assessment of ventricular function over time. Previous data comparing ventricular function between shunt types is limited, and in the current trial echocardiography findings at 14 months post initial palliation did not differ between the two shunt types. Nonetheless, other reports of concerning findings, including pathological specimens showing fibrosis and collagen changes4 and catheterization findings suggesting decreased cardiac contractility5 in RVPA shunts are concerning. Additional follow-up of the population in this study should further elucidate whether a RVPA shunt negatively impacts ventricular function in the long term compared to the MBT. Thus far there have been few reports of arrhythmias in HLHS patients with either shunt type.6Congenital heart research teams plan a more detailed analysis of data from this trial and continued follow-up of this population. The important message for primary care physicians who take care of patients with HLHS and their families is that the morbidity and mortality do not vanish after the stage II procedure regardless of shunt type. Close follow-up is required to allow timely interventions.