Mortality and Survival after Norwood Procedure Comparison between Shunt Type in Patients with Hypoplastic Left Heart Syndrome or Its Variants: A Systematic Review and Meta-Analysis Study

Arnaout, Ahmad Yamen; Nerabani, Yaman; Alhaj Ali, Hassan; Shahrour, Mohamad Zaher; Fallaha, Mohamad Yahia; Arnaout, Ibrahim; Sajee, Ahmad; Morjan, Mohamad; Al-Kanj, Hussein

doi:https://doi.org/10.1155/2023/8534205

Journal of Cardiac Surgery

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Abstract Introduction Materials and Methods Results Discussion Conclusions Appendix Data Availability Additional Points Conflicts of Interest Authors’ Contributions References Copyright Related Articles

Research Article | Open Access

Volume 2023 | Article ID 8534205 | https://doi.org/10.1155/2023/8534205

Mortality and Survival after Norwood Procedure Comparison between Shunt Type in Patients with Hypoplastic Left Heart Syndrome or Its Variants: A Systematic Review and Meta-Analysis Study

Ahmad Yamen Arnaout,¹Yaman Nerabani,¹Hassan Alhaj Ali,¹Mohamad Zaher Shahrour,¹Mohamad Yahia Fallaha,¹Ibrahim Arnaout,¹Ahmad Sajee,¹Mohamad Morjan,²and Hussein Al-Kanj³

Academic Editor: Oktay Korun

Received31 Oct 2022

Revised05 Apr 2023

Accepted19 May 2023

Published31 May 2023

Abstract

Background. In the Norwood procedure, a conduit is performed either from the subclavian artery to the pulmonary artery, Blalock–Taussig shunt (mBTs), or from the right ventricle to the pulmonary artery (RV-PA shunt). There are some concerns regarding the two shunts and which one is better according to morbidity and mortality in patients with hypoplastic left heart syndrome or its variants. Methods. We systematically searched PubMed, Web of Science, Scopus, Embase, and Cochrane Library databases from inception to 04/June/2021 to collect articles reporting a comparison of RV-PA shunt and mBTs. Results. Our meta-analysis showed that the mortality rate after 6 months, 1, 2, 3, 4, 5, and 6 years for the mBTS group was 16.3%, 28.6%, 34.8%, 42.4%, 44.6%, 45.1%, and 39.6%, respectively, and for the RV-PAS, 14.8%, 26.6%, 31%, 40.1%, 36.1%, 37.5%, and 34.0%, respectively. The mortality rate was significantly higher in the mBTs group at 1 and 2 years; otherwise, there is no significance differences. Overall complications rate was higher in the mBTs group than in the RV-PAs group (17.8% vs. 8.5%). In contrast, the rate of cardiac complications was higher in the RV-PAS group. Conclusions. The RV-PA shunt had lower mortality and overall complications rate than mBT shunt at the short-term outcome within the first two years, but at the long term, there was no difference between the two shunts. On the other hand, the mBT shunt had a lower incidence of cardiac complications at the early stage after the operations. However, some studies are poor due to the difficulties in conducting original research in this field. Therefore, we recommend conducting systematic reviews and original studies to compare these and other therapeutic procedures for these patients.

1. Introduction

Hypoplastic left heart syndrome (HLHS) and its variants are rare congenital heart defects. Children born with a hypoplastic or absent left ventricle may affect the aorta, aortic valve, or mitral valve. HLHS is fatal without early intervention. There are many possible interventions used currently: either a three-stage reconstruction surgery or a heart transplant. Surgical palliation stage 1 was first described by Norwood et al. in 1983 [1].

In the Norwood procedure, the right ventricle is relied on to pump blood to the body and the lungs. To reduce the deoxygenated blood reaching the right ventricle and to make it pass directly to the lungs, a conduit is performed either from the subclavian artery to the pulmonary artery, Blalock–Taussig Shunt (mBTs), or from the right ventricle to the pulmonary artery (RV-PA shunt).

The Norwood procedure using the mBT shunt appeared as a good first procedure to save these patients, but it did not improve the survival much, so the surgeons looked for other better procedures such as RV-PA shunt, and many primary studies were conducted comparing the two procedures to find which shunt is better to survival and morbidity. Recently, a hybrid procedure appeared that reduced surgical interventions for HLHS patients in the first stage instead of Norwood, but studies and different surgical experiences between different centers are still conflicting about its importance.

There are still some concerns regarding the two shunts and which one is better. Randomized controlled trials and cohort studies show that RV-PA conduit improves transplant-free survival, but morbidity did not affect the outcome between two shunts [2, 3]. A meta-analysis suggested an early survival advantage of RV-PA conduit over the mBTs shunt [4]. In contrast, other studies demonstrated that there is no significant difference between the two shunts [5, 6] and other studies suggest that the mBTs shunt is better [7].

Accordingly, we decided to conduct a systematic review and meta-analysis to try to answer this question comprehensively according to the medical literature.

2. Materials and Methods

We conducted our systematic review and meta-analysis following to recommendations of Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 (PRISMA 2020) [8].

2.1. Eligibility Criteria

We include in this systematic review full-text articles reporting a comparison of the RV-PA shunt and mBT shunt in patients with hypoplastic left heart syndrome or its variants who underwent Norwood procedure. We exclude any study that did not mention primary outcome data for both groups. Any study that did not mention mortality, survival, or transplantation was also excluded. The exclusion criteria also contain review articles, case reports, and case series of less than 10 patients. Book chapters, abstract conferences, articles with no full text or missing information, and studies published in languages other than English or Arabic were also excluded.

2.2. Information Sources and Search Strategy

We systematically searched PubMed, Web of Science, Scopus, Embase, and Cochrane Library databases from inception to 04/June/2021 to collect articles reporting a comparison of right ventricle to pulmonary artery conduit and modified Blalock–Taussig shunt. The search terms of our search strategy were showed in Appendix A, and the search strategy was modified to fit each database. No restrictions were applied regarding the date of publication. The reference sections of the included full-text articles were manually evaluated to find more studies eligible for inclusion.

2.3. Selection Process

The title/abstract and full-text screening processes were conducted by two authors separately, and disagreements were resolved by a third author.

2.4. Data Collection Process

Data were extracted from the eligible studies including first author’s name, year of publication, journal, country, the intervention and control procedures, number of participants in mBTS shunt/Sano shunt groups, gestational age (weeks), birth weight (kg), surgery stage 1 age (days), sex, ascending aorta diameter (mm), surgery weight (kg) at stage 1, aortic atresia, mitral atresia, aortic stenosis, mitral stenosis, noncardiac anomalies, genetic syndrome, cardiopulmonary bypass time (minutes), aortic cross clamp (minutes), and primary outcome that contain mortality or transplantation, and transplant free survival. Secondary outcomes were reoperation, post-Norwood complications, pacemaker placed, protein-losing enteropathy, and adjudicated cause of death. Data extraction process was performed by one author separately and reviewed by another.

2.5. Quality Assessment of the Studies

For each eligible study, the quality assessment was performed by one investigator and reviewed by another. We assessed the risk of bias in including studies based on Cochrane Collaboration Handbook [9] for RCT studies and the criteria of the Newcastle–Ottawa scale [10] for non-RCT studies. Conflicts are resolved through discussion among authors or the involvement of a third author if necessary.

2.6. Effect Measures and Synthesis Methods

Our primary outcomes were analyzed using the random effect model because of the high level of heterogeneity and with the risk ratio (RR) used as the summary statistic in the forest plots. In our analysis, we used the I² statistics to estimate the percentage of total variation in each outcome, owing to heterogeneity rather than chance, with values > 50% considered as substantial heterogeneity. Sensitivity analysis was performed. Publication bias was assessed by funnel plots; any extremity result was excluded from the analysis. All statistical analyses were performed using MetaXL software tool. We could not do meta-analysis for our secondary outcomes because they were reported from one or two studies. We calculated the mortality percentage at 6 months, one, two, three, four, five, and six years by aggregating the number of death events at each time point reported by the included studies divided by the total number of children reported by the included studies.

3. Results

3.1. Identification and Selection of Reviews

We identified 70 articles accepted in our review, after searching in four databases, doing a manual search, screening title/abstract and full text, and applying our criteria on full-text articles. Thirty-four studies have overlap between patients with other studies, so 36 studies were selected for statistical synthesis including two RCTs and 30 retrospective and four prospective cohort studies. Our PRISMA flow diagram is shown in Figure 1. The main characteristics of the accepted studies are shown in Table 1.

3.2. Characteristic and Quality of the Included Studies

A total of 6183 patients (3144 (50.8%) with RV-PA shunt vs. 3039 (49.2%) with mBTs) were included in all studies. Baseline statistics were between the RV-PA shunt and mBTs groups including gender (RV-PA shunt 890/1431 (60%) male vs. mBTS 749/1180 (59%) male), gestational age (weeks) (RV-PA shunt; mean = 38.68 and SD = 1.48 and N = 534 vs. mBTs; mean = 38.95 and SD = 1.42 and N = 616), and mean birth weight (kg) (RV-PA shunt; mean = 3.16 and SD = 0.38 and N = 1160 vs. mBTs; mean = 3.23 and SD = 0.40 and N = 1254).

The other surgical characteristics of the patients were surgery stage 1 age (days) (RV-PA shunt; mean = 7.52 and SD = 3.80 and N = 1262 vs. mBTs; mean = 7.26 and SD = 4.21 and N = 1270), ascending aorta diameter (mm) (RV-PA shunt; mean = 3.10 and SD = 1.34 and N = 962 vs. mBTs; mean = 3.89 and SD = 1.64 and N = 875), and cardiopulmonary bypass time (minutes) at stage 1 (RV-PA shunt; mean = 138.46684 and SD = 36.374885 and N = 582 vs. mBTs; mean = 132.67 and SD = 40.04 and N = 497) Table 2.

The patient’s cardiac abnormalities were as follows: hypoplastic left heart syndrome (RV-PA shunt; 1057/1121 (94.3%) vs. mBTs; 1085/1230 (88.2%)), other single ventricle abnormalities (RV-PA shunt; 63/1079 (5.8% vs. mBTs; 146/1160 (12.6%)), and genetic syndrome (RV-PA shunt; 23/388 (5.9%) vs. mBTs; 33/398 (8.3%)). These results are only for studies that mentioned these characteristics in Table 3.

A total of 36 studies were assessed as described above. The only two randomized controlled trials included in our meta-analysis (Single Ventricle Trial and Frommelt et al 2007 study) had a high risk of bias, as selection bias, performance bias, and detection bias were high due to the difficulty of randomization and blinding. Twenty-one of the 29 observational studies we included were considered to be at high quality. In contrast, the remaining eight observational studies were judged to be at poor quality because these studies did not report a comparison of surgery stage 1 age, birth weight, or gestational age between the two groups (Table 4).

3.3. Primary Outcome Results

3.3.1. Mortality

Early mortality is defined as the mortality post operation or in the first 30 days after stage 1 patients (S1P) or prior to hospital discharge. Early mortality was higher in the mBTs group than the RV-PAS group (20.9% from 1410 vs. 13.2% from 1620), (RR, 0.62; 95% CI, 0.50 to 0.75; ). Our pooled estimate showed mild heterogeneity (I² = 28%).

Mortality by 6 months, 1, 2, 3, 4, 5, and 6 years for the mBTs group is 16.3%, 28.6%, 34.8%, 42.4%, 44.6%, 45.1%, and 39.6%, respectively, and for the RV-PAs 14.8%, 26.6%, 31%, 40.1%, 36.1%, 37.5%, and 34.0%, respectively. The difference in survival between the two shunt groups is significantly different at 1 and 2 years; otherwise, there is no significance difference.

All meta-analysis forest plots for this outcome are shown in Figure 2.

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3.3.2. Interstage Mortality

The mortality rate after discharge from the hospital after S1P and before stage 2 patients (S2P) was higher in the mBTs group (24.8% from 1264 vs. 16.8% from 1202) (RR, 0.70; 95% CI, 0.58 to 0.83;), and the pooled estimate showed mild heterogeneity I² = 19%. There was no significant difference between the two groups mortality after S2P and before stage 3 patients (S3P) (7.54%, 6.79%) in the mBTs and RV-PAs cohort, respectively, (RR, 0.93; 95% CI, 0.53 to 1.62; ) and there was a moderate heterogeneity I² = 48%. All meta-analysis forest plots for this outcome are shown in Figure 3.

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3.3.3. Duration of Hospital and ICU Stay

There was no significant difference at stage1P (hospital: SMD = 0.08, , 95% CI: (−0.26–-0.41)) (mean hospital days RV-PAs = 32.5, SD = 18.8 vs. mean hospital days mBTs = 29.4, SD = 16.7); ICU: SMD = 0.22, , 95% CI: (−0.27, 0.71) (mean ICU days RV-PAs = 18.85, SD = 15.3 vs. mean ICU days mBTs = 17.6, SD = 12.95), S2P (hospital: SMD = 0.12, , 95% CI: −0.09, 0.33 (mean hospital days RV-PAs = 24.4, SD = 4.7 vs. mean hospital days mBTs = 28.9, SD = 26.3); ICU: SMD = 0.29, , 95% CI: −0.52, 1.09) (mean ICU days RV-PAs = 11.6, SD = 6.6 vs. mean ICU days mBTs = 11.3, SD = 6.9), and higher in the RV-PAs group at S3P (ICU: SMD = 0.36, , 95% CI: −0.15, 0.57) (mean ICU days RV-PAs = 12.5, SD = 7.1 vs. mean ICU days mBTs = 11.4, SD = 6.9) (Figure 3).

3.4. Secondary Outcome Results (Complications and Adjudicated Causes of Death)

Overall complications rate was higher in the mBTs group than in the RV-PAs group (17.8% Vs. 8.5%). The RV-PAs group had less gastrointestinal complications than the mBTs group (3.9% vs. 8.47%). In contrast, the rate of cardiac complications, respiratory complications, neurological complications, infectious complications, and renal complications were higher in the RV-PAs group than in the mBTs group as shown in Table 2. As for the other complications, there was no significant difference between the two groups. Furthermore, pacemakers placing rates were slightly higher in the mBTs group (2.5% vs. 2.90%), whereas RV-PAs patients were more likely to develop the protein-losing enteropathy (3.3% vs. 1.59%). Only one study reported the adjudicated causes of death. Mortality from pulmonary, neurological, gastroenterological, and infectious causes was higher in the RV-PAs group, whereas participants in the mBTs group were more likely to die of cardiac or complex/multisystem causes. On the other hand, the death rate from unknown causes was equal between the two groups (1.8% vs. 1.81%), while there was no study reported the death of organ failure cause. The details of the complications and the adjudicated causes of death data are shown in Table 5.

4. Discussion

The Norwood procedure is the first of the series of three operations which involve performing two different systemic to pulmonary shunts to ensure pulmonary blood flow in children with HLHS, either mBT shunt or RV-PA shunt. The advantage of either shunt over the other has long been a matter of debate, especially with regard to the long-term outcomes. The results of our meta-analysis indicate the advantage of using the RV-PA shunt to reduce early mortality after S1P and interstage mortality after S1P and before S2P. As for interstage mortality after S2P and before S3P, there was no preference for either of the two shunts over the other. Our meta-analysis provides a look at the mortality after 6 months, 1, 2, 3, 4, 5, and 6 years, in which there was significant difference at 1 and 2 years; otherwise, there is no significance difference.

Furthermore, mBT shunt was accused of causing higher overall complications rate, and this was confirmed by the results of our study, with varying incidence of these complications in both groups; while the patients who received mBT shunt are more likely to develop gastrointestinal complications, and the patients who received RV-PA shunt are more likely to develop cardiac, respiratory, neurological, infectious, and renal complications, and maybe this is what made some centers use the mBT shunt until now. Because of the small number of studies that reported this outcome, the differences in complications between the two groups cannot be explained and can be attributed to the difference in medical centers and surgical experience in performing these two procedures.

As for the causes of death, our review found only one paper that reported the various causes of death in both groups, [14] where children with mBT shunt were more likely to die of cardiac or complex/multisystem causes, while children in RV-PA shunt group were more likely to die from other causes.

The RV-PA shunt is associated with a lower mortality rate in the first 30 days after S1P or prior to hospital discharge. [4] In addition, the results of the single ventricle trial, which was conducted on 549 children, have shown that the transplantation-free survival at one year was better with the RV-PA shunt. In contrast, the current evidence shows similar results between the two groups after one year of age [3, 7]. Although studies have indicated that patients of the RV-PA shunt group are relatively less likely to develop complications, caution should be taken against shunt failure, especially during the first week [6]. This is in addition to the serious neurological complications associated with this type of shunt, such as seizure, bleeding, and stroke [7, 22]. On the other hand and in the context of constant attempts to develop care for patients with HLHS, the Hybrid procedure has emerged in recent years to be sometimes an alternative to the Norwood procedure [77]. Hybrid procedure shows a good midterm survival in high risk patients [77, 78].

There are several limitations to the current study. These limitations include the lack of high-quality randomized controlled trials due to the nature of the surgical procedure that limits the application of blinding and randomization, there are also some observational studies of poor quality in our review. The heterogeneity that is sometimes present in some pooling operations, also limits this study. In addition, many of the studies included in the review did not discuss many important details for HLHS patients after the procedure such as the diameter of the artery, pulmonary artery reoperation at S2P, and incidence of pulmonary artery stenosis prior to S2P.

5. Conclusions

The RV-PA shunt had lower mortality and overall complications rate than mBT shunt at the short-term outcome within the first two years, but at the long term, there was no difference between the two shunts. On the other hand, the mBT shunt had a lower incidence of cardiac complications at the early stage after the operations. However, some studies are poor due to the difficulties in conducting original research in this field. Therefore, we recommend conducting systematic reviews and original studies to compare these and other therapeutic procedures for these patients.

Appendix

A. Search Strategies

PICO

P: children with HLHS or single ventricle.

I: Sano shunt or its synonymous.

C: modified blalock taussig.

Primary outcome: heart transplant or death. PubMed Terms: (“Sano shunt” OR “initial shunt” OR “RV-to-pulmonary artery shunt” OR “Systemic-to-pulmonary artery shunt” OR “modified blalock taussig” OR “aortopulmonary shunt” OR “Norwood” OR “right ventricle-to-pulmonary artery conduit” OR “Blalock Taussig” OR “Subclavian Pulmonary Artery Shunt”) AND (“hypoplastic left heart syndrome” OR “single heart” OR “univentricular heart” OR “Dominant right ventricular” OR “Left Heart Hypoplasia Syndrome”) No of results: 1306 Web of Science Terms Results: 1210 Embase Terms: TITLE-ABS-KEY “Sano shunt” OR “initial shunt” OR “RV-to-pulmonary artery shunt” OR “Systemic-to-pulmonary artery shunt” OR “modified blalock taussig” OR “aortopulmonary shunt” OR “Norwood” OR “right ventricle-to-pulmonary artery Shunt” AND TITLE-ABS-KEY “hypoplastic left heart syndrome” OR “single heart” OR “univentricular heart” OR “Dominant right ventricular” OR “Left Heart Hypoplasia Syndrome”. Results: 1458 Cochrane Clinical Trials Library Term: “Sano shunt” OR “initial shunt” OR “RV-to-pulmonary artery shunt” OR “Systemic-to-pulmonary artery shunt” OR “modified blalock taussig” OR “aortopulmonary shunt” OR “Norwood” OR “right ventricle-to-pulmonary artery conduit” OR “Blalock Taussig” OR “Subclavian Pulmonary Artery Shunt” AND “hypoplastic left heart syndrome” OR “single heart” OR “univentricular heart” OR “Dominant right ventricular” OR “Left Heart Hypoplasia Syndrome”. Results: 65 Scopus Term: (“Sano shunt” OR “initial shunt” OR “RV-to-pulmonary artery shunt” OR “Systemic-to-pulmonary artery shunt” OR “modified blalock taussig” OR “aortopulmonary shunt” OR “Norwood” OR “right ventricle-to-pulmonary artery conduit” OR “Blalock Taussig” OR “Subclavian Pulmonary Artery Shunt”) AND (“hypoplastic left heart syndrome” OR “single heart” OR “univentricular heart” OR “Dominant right ventricular” OR “Left Heart Hypoplasia Syndrome”). Results: 1948 All results: 5987

B. Funnel Plots for Each Outcome

Funnel plots for each outcome are present in Figure 4.

Data Availability

The total detailed data for the characteristics of accepted studies and patients are available from the corresponding author. For those who want to view them, they must contact the corresponding author.

Additional Points

This umbrella review was performed according to the protocol previously published on PROSPERO (CRD42021282120).

Conflicts of Interest

The authors declare that they have no conflicts of interest to report regarding the present study.

Authors’ Contributions

Mr Ahmad Yamen Arnaout is the study leader and performed the screening, data extraction, analysis, quality assessment, and writing. Mr Yaman Nerabani performed the screening, data extraction, quality assessment, and writing. Mr Hassan Alhaj Ali performed the screening, data extraction, quality assessment, and writing. Mr Mohamad Zaher Shahrour performed the screening, data extraction, quality assessment, and writing. Dr Mohamad Yahia Fallaha performed the screening, data extraction, quality assessment, and writing. Mr Ibrahim Arnaout performed data extraction and writing. Mr Ahmad Sajee performed data extraction and writing. Professor Mohamad Morjan performed scientific supervising and reviewed the manuscript. Professor Hussein Al-Kanj performed scientific supervising and reviewed the manuscript.

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Copyright © 2023 Ahmad Yamen Arnaout et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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