Shunt choice in single right ventricle patients: an update

Abstract

Hypoplastic left heart syndrome, the most common complex congenital heart malformation, is characterized by underdeveloped left-sided heart structures. The Norwood procedure followed by two-staged operations has permitted the extended survival of many of these patients. Survival, however, remains suboptimal with most of the morbidity and mortality occurring during the Norwood procedure hospitalization. The modified Blalock–Taussig shunt has been implicated in contributing to the mortality risk due to decreased systemic diastolic blood pressure and coronary perfusion. Therefore, the right ventricle-to-pulmonary artery shunt was recently reevaluated as a lower-risk source of pulmonary blood flow in the Norwood procedure. The Pediatric Heart Network Single Ventricle Reconstruction trial, sponsored by the NIH National Heart, Lung and Blood Institute, evaluated the two types of shunts during the Norwood procedure. This randomized clinical trial has yielded important insight into the effects of shunt selection on morbidity, mortality, hemodynamics and overall current outcomes for hypoplastic left heart syndrome.

Keywords:

• clinical trial
• hypoplastic left heart syndrome
• Norwood procedure
• shunt

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• • While tremendous progress has been made in the care of the single ventricle patient over the past three decades, survivals remain limited. It has been postulated that the traditional modified Blalock-Taussig shunt utilized during the Norwood procedure is one of the potential sources of these suboptimal outcomes.

• • The National Heart, Lung and Blood Institute-sponsored Pediatric Heart Network Single Ventricle Reconstruction trial compared the modified Blalock-Taussig shunt and the right ventricle-to-pulmonary artery shunt (RVPAS) for the Norwood procedure. One-year transplant-free survival was found to be superior for the right ventricle-to-pulmonary artery shunt (74 vs 64%, p = 0.01).

• • However, the Single Ventricle Reconstruction trial also found that the survival advantage was lost (log-rank p = 0.06) when all available data were analyzed at the point where the last subject reached the 12-month endpoint (mean follow-up 32 ±11 months). In addition, there were more complications and unintended cardiovascular interventions in the RVPAS group.

• • Obstructed pulmonary venous return, non-hypoplastic left heart syndrome diagnosis compared to hypoplastic left heart syndrome subtypes aortic stenosis/mitral stenosis and aortic atresia/mitral atresia, lower socioeconomic status and smaller ascending aorta were risks for early/acute phase mortality. The late/constant phase analysis identified lower gestational age and presence of a genetic syndrome as significant risk factors for death. Shunt type was not a significant risk factor in the late/constant phase.

• • The overall interstage mortality was 12%, with the RVPAS group demonstrating a significant survival advantage (6 vs 18%, p < 0.001). Independent risk factors for interstage mortality by multivariable analysis were gestational age less than 37 weeks, Hispanic ethnicity, aortic atresia/mitral atresia, greater number of post-Norwood complications, census block poverty level (5.4–13% poverty) and MBTS only in the setting of no or mild postoperative atrioventricular valve regurgitation.

• • Echocardiographic studies revealed that average right ventricular ejection fraction was abnormally low in both the groups and identical at all time intervals, except after the Norwood procedure where it was higher in the RVPAS group (49 vs 44%).

• • Neurodevelopmental impairment in patients who have undergone the Norwood procedure is associated with inherent patient factors rather than intraoperative factors.

• • Practice pattern variation existed in the Single Ventricle Reconstruction trial and has been postulated as a potential source of primary and secondary endpoint variability within the trial.