Does Volume Matter: Outcomes After Norwood Procedure?
Susan Nicolson, James DiNardo, Lindsey Loveland, Viviane Nasr
Original article
Schäfer M, McFarland C, Amula V, Truong D, Lambert LM, Griffiths ER, Eckhauser AW, Husain SA, Hobbs RD. Volume-Outcome Relationship of Norwood Procedures: Insights from the National Pediatric Cardiology - Quality Improvement Collaborative Database. Ann Thorac Surg. 2025 Jan 21:S0003-4975(25)00071-2. doi: 10.1016/j.athoracsur.2025.01.007. Epub ahead of print. PMID: 39864776.
Investigations of the effect of center-specific and surgeon-specific case volume on outcomes using data from The Society of Thoracic Surgeons Congenital Heart Surgery Database (STS-CHSD) and other databases have produced conflicting results.1,2 Case-mix variability explains these differences in part, but disagreement persists even when outcomes isolated to patients with hypoplastic left heart syndrome (HLHS) undergoing the Norwood procedure are considered.3
Today’s PAAD4 utilized the National Pediatric Cardiology Quality Improvement (NPC-QIC) registry to explore center volume outcome relationships in infants who underwent the Norwood procedure between 2016-2023 with consideration of pre-operative high-risk features. NPC-QIC is a contemporary multi-national registry of pediatric cardiac care centers with comprehensive clinical and outcome data in infants with single ventricle disease through 1 year of age (https://www.npcqic.org/). Centers were categorized by number of Norwood procedure performed annually into low (1-5 per year), medium (6-10 per year) and high-volume centers (> 10 per year). The authors compared high-risk features between center volume categories and assessed survival at both 30 days and one year.
There were 3397 infants identified from 69 participating institutions with 2964 infants (87.3%) having complete data sets through one year of life.Twenty-nine centers were classified as low, 20 as medium and 20 as high-volumes centers. Only a single center performed more than 20 Norwood procedures (see graph). The variability of case volume across centers coupled with the extensive data collection provides a unique opportunity to examine the impact of high-risk features on neonates undergoing palliation for HLHS at low, medium and high-volume centers.
Overall, 56.8% of infants had a Norwood with pulmonary blood flow supplied by a right ventricle to pulmonary artery conduit, 23.9% had pulmonary blood flow via a Blalock- Tausig-Thomas shunt and 10.8% underwent a Hybrid Norwood procedure. Low volume centers performed a more significant proportion of Hybrid procedures.
There were no differences in the frequency of pre-operative high-risk features among centers. High-risk features included prematurity, low birth weight (< 2.5 kg), ascending aorta size of < 2 mm, intact or restrictive atrial septum, pre-operative aortic valve regurgitation, greater than moderate AV valve regurgitation and greater than moderate ventricular dysfunction. This finding is contrary to the common belief that surgical care of high-risk neonates with HLHS is more commonly undertaken at higher volume centers. The presence of pre-operative risk factors in patients with HLHS are known to impact their outcomes in the interstage period and beyond.5 There was no association between volume categories and 30-day mortality, but first stage palliation of HLHS at low and medium volume centers was associated with both the highest incidence (low volume mortality 21.2%, p=0.01, medium volume mortality 19.3%, p=0.02 and high-volume mortality 15.5%) and odds of 1-year mortality. This difference in odds was present in both unadjusted analysis and in analysis adjusted for known risk features.
The reason for the difference in longer-term outcome is not clear. One possible explanation is that low volume centers may have fewer resources for interstage monitoring which has been shown to improve long term outcomes.
Post-operative morbidity continues to be significant but was similar among all volume-center sizes with the exception of performance of post-procedure cardiac catheterization with or without intervention which was significantly lower in high-volume centers. The need for ECMO in the low, medium and high-volume centers was 18.1%, 21.3% and 15.4 % respectively. The re-operative rate for the low, medium and high-volume centers was 20.1%, 27.5% and 20.3% respectively.
Infants undergoing Norwood procedures in low and medium-volume centers have worse 1-year mortality and increased morbidity as compared to those receiving care in high-volume centers. These outcome differences persist following adjustment for high-risk features.
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References:
1. Pasquali SK, Thibault D, O'Brien SM, et al. National Variation in Congenital Heart Surgery Outcomes. Circulation 2020;142(14):1351-1360. (In eng). DOI: 10.1161/circulationaha.120.046962.
2. Chauhan D, Mehaffey JH, Hayanga JWA, Udassi JP, Badhwar V, Mascio CE. Volume Alone Does Not Predict Quality Outcomes in Hospitals Performing Pediatric Cardiac Surgery. Ann Thorac Surg 2024;117(6):1187-1193. (In eng). DOI: 10.1016/j.athoracsur.2024.01.006.
3. Checchia PA, McCollegan J, Daher N, Kolovos N, Levy F, Markovitz B. The effect of surgical case volume on outcome after the Norwood procedure. The Journal of thoracic and cardiovascular surgery 2005;129(4):754-9. (In eng). DOI: 10.1016/j.jtcvs.2004.07.056.
4. Schäfer M, McFarland C, Amula V, et al. Volume-Outcome Relationship of Norwood Procedures: Insights from the National Pediatric Cardiology - Quality Improvement Collaborative Database. Ann Thorac Surg 2025 (In eng). DOI: 10.1016/j.athoracsur.2025.01.007.
5. Kaplinski M, Ittenbach RF, Hunt ML, et al. Decreasing Interstage Mortality After the Norwood Procedure: A 30-Year Experience. J Am Heart Assoc 2020;9(19):e016889. (In eng). DOI: 10.1161/jaha.120.016889.