Right Ventricle-to-Pulmonary Artery Shunt in Norwood Procedure: Early Results

Abstract

The aim of this study was to evaluate experience and predictors of early mortality in patients with hypoplastic left heart syndrome (HLHS)–type defects undergoing Norwood procedure (NP) with right ventricle-to-pulmonary artery (RV-PA) shunt. Between 2001 and 2009, a consecutive series of 229 children with HLHS-type single ventricle underwent NP with application of RV-PA shunt. Demographic, echocardiographic, and clinical perioperative data were retrospectively analyzed. The mean duration of follow-up of survivors was 4.5 ± 2.1 years (60 days to 8.1 years). Follow-up was complete for 92.1% of patients. Major early postoperative complications included sepsis/generalized infection in 40 (17.5%), pericardial effusion in 9 (3.9%), and wound infection in 8 (3.5%). The early (30-day) survival was 87.8% (n = 201). In the late postoperative period, 12 (5.9%) died. Early nonsurvivors were more frequently older than 14 days (P = .045) at initial surgery, had lower operative weight (P = .024), had more frequent associated cardiac (P < .001) and/or extracardiac anomalies (P < .001), and were more likely to have a restrictive interatrial communication before operation (P = .024). Use of the right RV-PA shunt has helped to mitigate some previously described predictors of early death after NP. Longer follow-up will be required to determine whether the RV-PA shunt modification confers an important survival benefit.

Keywords

hypoplastic left heart syndrome Norwood procedure neonate congenital heart surgery

In 1980, William Norwood¹ reported on palliative surgery for children with hypoplastic left heart syndrome (HLHS), and 2 years later he performed successful application of Fontan’s procedure following his preparatory palliation.² As alternative treatment, heart transplantation was introduced in the mid-1980s by Bailey and associates at Loma Linda to provide an anatomically normal heart for these children.³ Over the last 30 years, numerous alterations in surgical technique of staged reconstructive surgery and perioperative management of children with HLHS have permitted continued improvement in early and long-term survival.^4-6 Shortages of available donor organs in this age group, as well as high mortality and morbidity on waiting lists, have limited the utility of heart transplantation for HLHS in the neonate.⁷

Staged reconstructive surgical approaches for HLHS continue to evolve. First described by Norwood et al,⁸ the use of right ventricle-to-pulmonary artery (RV-PA) shunt as the source of pulmonary blood flow in the first stage of palliation was reintroduced and promulgated in the late 1990s by Japanese surgeons: Kishimoto et al,⁹ Imoto et al,¹⁰ and Sano et al.^11,12 The evidence of favorable hemodynamics associated with RV-PA shunt has been reported by many centers.^11,13-18

The aim of this study was to describe our experience with patients undergoing Norwood procedure (NP) with RV-PA shunt and evaluate predictors of early mortality.

Methods

Between June 2001 and May 2009, 229 patients (156 males, 73 females) with HLHS and its variants underwent NP with RV-PA shunt. Informed consent was obtained from the parents of all patients. The mean age at surgery was 15.3 ± 10.9 days (range, 2-82 days), and mean weight was 3428.8 ± 550.6 g (range, 2070-4840 g); 5 neonates had low birth weight (defined as <2.5 kg). The mean gestational age was 39.1 ± 1.6 weeks (33-42 weeks). Nine children (3.9%) were born prematurely (gestational age <37 weeks).

The medical records were retrospectively analyzed for demographic, preoperative, and echocardiographic data; operative variables; and postoperative clinical data.

The diagnosis of heart defect was based on 2-dimensional and color flow Doppler transthoracic echocardiography. Hypoplastic left heart syndrome was diagnosed if mitral and aortic hypoplasia/stenosis or atresia with small left ventricle and normal segmental anatomy of the heart (visceroatrial situs solitus, ventricular D-loop, and S-position of the great arteries) were present. Variant of HLHS was defined as a functional single ventricle with systemic outflow tract obstruction and ductal dependency of the systemic circulation. Restrictive interatrial communication was considered present if the communication was smaller than 3 mm in diameter and/or the mean gradient across the foramen ovale/atrial septal defect was greater than 5 mm Hg. Ascending aorta size was measured at the narrowest part of the ascending aorta. Tricuspid or common atrioventricular valve regurgitation was graded on a scale from I to III (mild, moderate, severe) by a measurement of the ratio of regurgitant jet area to the right atrial area.

All operations were performed by the same surgeon in 2 centers: Department of Paediatric Cardiac Surgery (Collegium Medicum, Jagiellonian University, Cracow, Poland) and Department of Cardiac Surgery (Klinikum Grosshadern, Ludwig Maximilians University, Munich, Germany). The same preoperative, intraoperative, and postoperative protocols were applied in both institutions, and the study was approved by the Institutional Review Boards of both institutions. Systemic outflow tract reconstruction was performed by pulmonary homograft patch augmentation of the aortic arch and ascending aorta, without aortic transection, with side-to-side connection between the aortic root and main pulmonary artery in 167 (72.9%) children (“classic technique”) or by direct association of the aortic arch and main pulmonary artery posterior walls, with homograft patch enlargement of the anterior walls anastomosis in 62 (27.1%) children (“modified technique”) (Figure 1). The interatrial communication was enlarged if needed by excision of the septum primum. A polytetrafluoroethylene shunt (IMPRA ePTFE Vascular Graft, BARD, Tempe, Ariz; Gore-Tex Vascular Graft, W.L. Gore & Associates, Dundee, Scotland, UK) was used to provide pulmonary blood flow (size: 4 mm in 3 [1.3%], 5 mm in 221 [96.5%], and 6 mm in 5 [2.2%] children). Patient weight/shunt ratio (g/mm) was calculated by dividing the patient’s weight (in grams) by the shunt size (in millimeters). The proximal end of the shunt was anastomosed to a small right ventriculotomy made with a coronary punch bioptome. The distal end was connected to the confluence of the pulmonary arteries, which was patched with pulmonary homograft tissue. The RV-PA shunt was placed to the left of the neoaorta in 205 (89.5%) and to the right in 24 (10.5%) children. The chest was routinely closed primarily. Delayed chest closure was applied in patients who required support with extracorporeal membrane oxygenation (ECMO) or if hemodynamic changes were observed at the time of sterna approximation. The sternum was then secondary closed when hemodynamics were stable and tissue edema had subsided, usually on postoperative day 2 to 4.

Inotropic support was started during termination of cardiopulmonary bypass, only as needed. The most common inotropic drug was dopamine hydrochloride (3-6 μg/kg/min); occasionally epinephrine was additionally used (0.01-0.05 μg/kg/min). Sodium nitroprusside (0.5-2 μg/kg/min), milrinone (0.75 μg/kg/min), or both were used when vascular resistance needed to be decreased.

Extracorporeal membrane oxygenation was used as needed. The indication for ECMO was failure to wean from cardiopulmonary bypass or, more commonly, noneffective resuscitation after cardiac arrest during the postoperative course. Routine anticoagulation included heparin (Heparin Biochemie, Biochemie, Austria) (5 U/kg/h) during the few first days after the operation and acetylsalicylic acid (2-3 mg/kg/d) applied between Norwood and second-stage procedure, started few days after operation.

The early postoperative period was defined as the first 30 days after the operation. The operative mortality was defined as any death within 30 days after surgery or after 30 days during the same hospitalization subsequent to the operation. Data were presented as the mean ± standard deviation (SD) and range for continuous variables. For qualitative data, count and percentage were given. Time-dependent analysis of overall survival was calculated using Kaplan-Meier method. The statistical analysis was carried out by means of V test, χ² test, χ² test with Yates correction, and t Student’s test. Differences were considered statistically significant at P < .05. All analyses were performed using Statistica 8.0 statistical software (StatSoft, Cracow, Poland).

Results

The mean duration of follow-up for hospital survivors was 4.5 ± 2.1 years (60 days to 8.1 years). Follow-up was complete in 92.1% patients (19 children were lost to follow-up).

Hypoplastic left heart syndrome was diagnosed in 208 (90.8%) children, and variants of HLHS were identified in 21 (9.2%) children. Specific anatomical diagnosis and associated cardiac and extracardiac (genetic) anomalies are listed in Table 1. Intact atrial septum or restrictive interatrial communication was diagnosed in 79 (34.5%) children. The mean ascending aortic size was 3.80 ± 1.9 mm (1.4-9.5 mm). In 38 (16.6%) children, the smallest diameter of the ascending aorta was less than or equal to 2 mm. The incidence of moderate or severe tricuspid or common atrioventricular valve regurgitation on preoperative echocardiographic study was 17 (7.4%).The mean weight to shunt ratio for the whole series was 679.4 ± 94.5 g/mm (414.0-968.0 g/mm).

Table 1.

Anatomical Characteristics and Associated Cardiac and Extracardiac Anomalies

Anatomy	No. (%)
Hypoplastic left heart syndrome	208 (90.8)
MS/AS	84/208 (40.4)
MS/AA	70/208 (33.6)
MA/AA	49/208 (23.6)
MA/AS	5/208 (2.4)
Variants of HLHS	21 (9.2)
Unbalanced AVC, hypoplastic LV, AS/AA, hypoplastic AoArch	8/21 (38.1)
VSD, AA/AS, hypoplastic AoArch	5/21 (23.8)
DORV, hypoplastic LV, VSD, AS/AA, hypoplastic AoArch	4/21 (19.0)
DILV, hypoplastic RV, d-TGA, AS/AA, hypoplastic AoArch	3/21 (14.3)
DOLV, TA, hypoplastic RV, VSD, AA, hypoplastic AoArch	1/21 (4.8)
Associated cardiac anomalies	60/229 (26.2)
VSD	27/229 (11.8)
L-SVC	14/229 (6.1)
PAPVR	12/229 (5.2)
Agenesia IVC (azygos continuation)	8/229 (3.5)
Anomalies of aortic arch branches	8/229 (3.5)
LV-CA fistulae	7/229 (3.1)
IAA	4/229 (1.7)
Others	4/229 (1.7)
Extracardiac anomalies	20/229 (8.7)
Kidney anomalies	5/229 (2.2)
DiGeorge syndrome	3/229 (1.3)
Esophageal atresia	2/229 (0.8)
Dysmorphia	2/229 (0.8)
Polysplenia	2/229 (0.8)
Others	6/229 (2.6)

AA, aortic atresia; AoArch, aortic arch; AS, aortic stenosis/hypoplasia; AVC, atrioventricular canal; DILV, double inlet left ventricle; DOLV, double outlet left ventricle; DORV, double outlet right ventricle; d-TGA, d-transposition of great arteries; IAA, interrupted aortic arch; IVC, inferior vena cava; L-SVC, left superior vena cava; LV, left ventricle; LV-CA, left ventricle-coronary artery; MA, mitral atresia; MS, mitral stenosis/hypoplasia; PAPVR, partial anomalous pulmonary venous return; RV, right ventricle; TA, tricuspid atresia; VSD, ventricular septal defect.

Delayed chest closure was used in 35 patients (15.3%) and ECMO support in 23 patients (10.0%). Inotropic support with dopamine hydrochloride was administered in 207 children (90.4%), with epinephrine in 35 children (15.3%). The mean duration of ventilatory support time was 170.4 ± 223.6 hours (20-1296 hours), mean length of intensive care unit stay was 16.3 ± 15.8 days (3-91 days), and mean length of hospital stay was 42.6 ± 30.6 days (9-155 days). At the time of discharge, the mean oxygen saturation was 77.2% (68%-87%). Medications prescribed at discharge included acetylsalicylic acid (2-3 mg/kg/d) in all children, furosemide (1 mg/kg/d) in 102 children (52.8%), diuretic therapy with 2 or more medications in 8 children (4.1%), digoxin (10 µg/kg/d) in 85 children (44.0%), and angiotensin-converting enzyme inhibitors (enalapril, 0.2 mg/kg/d) in 60 children (31.1%). Two children remained in the hospital until their second stage operation. All others were discharged to home. Two children required tube feeding, and none were treated with supplemental oxygen at home.

Major postoperative complications included sepsis/generalized infection in 40 children (17.5%), pericardial effusion in 9 children (3.9%), wound infection in 8 children (3.5%), supraventricular tachycardia in 7 children (3.1%), hydrothorax in 6 children (2.6%), intracranial hemorrhage in 3 children (1.3%), and coxitis in 2 infants (0.9%). Reoperations included reexploration for hemostasis in 8 children (3.5%), shunt revision in 4 children (1.7%), and atrial septectomy in 3 children (1.3%). Between first and second stage procedures, 38 infants (18.9%) required balloon aortoplasty to address recoarctation with gradient ≥20 mm Hg). Seven infants (3.5%) underwent balloon atrial septostomy, and 2 infants (1.0%) underwent stent implantation within the RV-PA shunt.

Mortality at 30 days was 12.2% (28/229). Operative mortality was 14.8% (34/229). Late mortality after discharge was 2.6% (6 children). The causes for operative mortality were cardiac dysfunction in 22 children (64.7%), sepsis in 8 children (23.5%), shunt complications in 3 children (8.8%), and pulmonary embolism in 1 child (2.9%). Among the discharged infants, there were 4 late deaths with unknown reasons and 2 related to intracranial hemorrhage. The Kaplan-Meier survival curve of the entire group, including second and third stage results, is presented in Figure 2.

The comparison between early survivors and nonsurvivors revealed that nonsurvivors were more frequently older than 14 days (P = .045) at initial surgery, had lower operative weight (P = .024), had more frequent associated cardiac (P < .001) and extracardiac anomalies (P < .001), and had higher prevalence of restrictive interatrial communication before operation (P = .024) (Table 2).

Table 2.

Comparison Between Stage I Early Survivors and Nonsurvivors

	Survivors (n = 201)	Nonsurvivors (n = 28)	P Value
Age, d, mean ± SD (range)	15.0 ± 10.9 (3-82)	17.0 ± 10.1 (2-43)	.345^a
Age ≥14 d, n (%)	75 (37.3)	16 (57.1)	.045^d
Weight, g, mean ± SD (range)	3465.3 ± 529.0 (2070-4840)	3204.4 ± 527.6 (2330-4380)	.024^a
Gestational age, wk, mean ± SD (range)	39.2 ± 1.6 (33-42)	38.9 ± 1.2 (37-41)	.355^a
Gender: female/male, n	63/138	10/18	.643^c
HLHS variants, n (%)	19 (9.5)	2 (7.1)	.962^b
HLHS MS/AA/HLHS other MV/AV forms, n	60/122	10/16	.580^c
Associated cardiac anomalies, n (%)	41 (20.4)	19 (67.9)	<.001^c
Extracardiac anomalies, n (%)	9 (4.5)	11 (39.3)	<.001^b
Restrictive interatrial communication, n (%)	64 (31.8)	15 (53.6)	.024^c
Ascending aortic size, mm, mean ± SD (range)	3.83 ± 1.9 (1.4-9.5)	3.38 ± 1.3 (2.0-6.0)	.475^a
Ascending aortic size ≤2 mm, n (%)	36 (17.9)	2 (7.1)	.245^b
TV or CAVV regurgitation II° or III° before surgery, n (%)	13 (6.5)	4 (14.3)	.274^b
Weight/shunt ratio, g/mm, mean ± SD (range)	686.4 ± 94.7 (414-968)	635.6 ± 82.7 (536-876)	.045^a
Aortic reconstruction type: classic/modified, n	145/56	22/6	.474^c

AA, aortic atresia; AV, aortic valve; CAVV, common atrioventricular valve; MS, mitral stenosis; MV, mitral valve; TV, tricuspid valve.

^a t-Student test,

^b χ² test with Yates correction,

^c V test,

^d χ² test.

One hundred seventy-two children have proceeded to stage II surgery (hemi-Fontan operation, 138; right bidirectional Glenn operation, 25; hemi-Fontan + left bidirectional Glenn, 4; left and right bidirectional Glenn, 3; biventricular correction, 2 children) and 95 to Fontan operation (fenestrated lateral tunnel, 86; extracardiac conduit, 9). Five patients are on the waiting list for stage II and 53 for stage III.

Discussion

Although the NP remains one of the highest risk operations performed in the neonatal period, postoperative survival continues to improve and has been reported to be 90% to 95% in some centers.^15,19,20 Apart from technical advances, modern perioperative management, and better understanding of single-ventricle physiology, new surgical modifications have been associated with improved outcomes. Recently, one of the more intriguing technical modifications, RV-PA shunt, has been adopted in many centers.

The RV-PA shunt was reintroduced as an alternative to the modified Blalock-Taussig (BT) shunt. Proponents of this technique describe favorable postoperative hemodynamics after the NP. The purported positive effects include hemodynamic stability, higher postoperative diastolic blood pressure (which theoretically improves coronary and peripheral organ perfusion), more balanced and predictable pulmonary to systemic flow (Qp:Qs) ratio, and decreased ventricular volume loading due to lower pulmonary blood flow. Numerous reports cite improved survival following the NP with RV-PA shunt.^{9,10,12,13,15,19} In children with BT shunt, acute elevation of systemic vascular resistance may cause acute elevation of the pulmonary to systemic flow ratio and significant reduction in systemic cardiac output. The location of the proximal end of the RV-PA shunt beneath the level of the systemic arterial valve eliminates the aortopulmonary runoff²¹ and reduces diastolic steal of coronary blood flow. We believe that improved coronary perfusion is likely to be the main reason for early hemodynamic stability, less complicated postoperative course, and decreased mortality.

Potential disadvantages of using the RV-PA shunt include the theoretical risk of ventricular dysfunction and late arrhythmias due to ventriculotomy and risk of hypoxemia due to lower Qp:Qs ratio.^15,22 Volume overload due to diastolic regurgitation through the valveless RV-PA shunt seems to be only a theoretical danger. On the contrary, it is our opinion that the lower Qp:Qs ratio (antegrade flow though the RV-PA shunt occurs only during systole) should reduce the ventricular volume overload. This opinion seems to be supported by the observations of Frommelt and coworkers.²¹ They compared the right ventricular end-diastolic areas before and after bidirectional Glenn (BDG) anastomosis in patients after NP with either RV-PA shunt or BT shunt. The investigators noticed a significant decrease in RV end-diastolic area after BDG operation and shunt removal compared with immediately before BDG in the BT group. This was not observed in the RV-PA group. The investigators estimated the RV-PA regurgitant fraction at less than 25%.

The anatomical subset of HLHS with mitral stenosis or hypoplasia with aortic atresia (MS, AA) is prone to the development of the multiple ventriculocoronary artery connections to the left ventricle, which may affect survival.^23-25 We did not find any association between the anatomical subset (MS, AA) and increased risk of mortality in children after NP with RV-PA shunt. Others have described similar observations.²⁰ Small diameter of the ascending aorta has also been considered by some to be a risk factor for mortality after the classic NP.⁵ In our series, there was no difference in ascending aortic size between early survivors and nonsurvivors. Other studies have presented similar observations.²⁰ We believe that use of the RV-PA shunt has helped to mitigate some of the previously described predictors of early death after NP, such as younger gestational age, smaller ascending aorta size, variant of HLHS (aortic atresia with mitral stenosis) and regurgitation of the atrioventricular valve. Our opinion reflects our experience reported here, together with inferences supported by experiences reported by others.^12,16,26,27 Tabbutt and associates²⁸ compared outcomes of their Norwood stage 1 patients with both BT shunt with RV-PA shunt, in which both shunt types were performed during the same era. In that series, shunt type was not randomized and the shunt selection was at the discretion of the surgeon. The investigators observed no difference in overall mortality based upon shunt type but observed a trend toward choice of RV-PA shunt for higher risk patients (eg, with higher incidence of aortic atresia, single right ventricle, or extracardiac anomalies). We acknowledge that some purported risk factors for mortality after Norwood stage 1, such as lower weight,^4,20,28,29 associated cardiac and extracardiac anomalies,^4,28 or restrictive interatrial communication before the operation,³⁰ still have a significant impact on the results, irrespective of the shunt type.

RV-PA shunt-related complications such as stenosis and sudden shunt occlusion^20,26,31 or development of a right ventricle aneurysm¹⁷ are relatively rare. Shunt stenosis is usually located in the proximal end, where it may be caused by fibrointimal hyperplasia. Dynamic myocardial narrowing can cause hypercyanotic spells. All these complications preceded by intensification of the cyanosis can be easily diagnosed and successfully treated (stent implantation, surgical revision, earlier stage II procedure). Some studies have reported a higher incidence of interstage surgical shunt interventions in the RV-PA shunt group compared with the BT shunt group (with no differences regarding the transcatheter shunt interventions).²⁸ We have to be aware that this is a comparison between an “old” (BT) and a “new” (RV-PA) method, and the potential effect of a learning curve associated with optimal shunt placement should be taken into account.

For almost 10 years now, the RV-PA connection in Norwood operation has been the subject of many studies. There is still no consensus regarding the terminology: is it a shunt^{11,12,20,26,32,33} or is it a conduit?^{9,15,17,19,21,27,28,31} The term shunt is usually used to describe a connection between the systemic and pulmonary circulations (eg, Blalock-Taussig shunt). The term conduit is generally used to describe a surgically created connection within 1 circulation (eg, conduit between right ventricle and pulmonary artery in patients with pulmonary artery atresia after biventricular repair). We prefer to call the RV-PA connection in NP a shunt, because this is a connection between 2 circulations: systemic ventricle and pulmonary artery.

The continuous improvement in early survival of patients undergoing the NP is widely documented, and because of this fact it is difficult to justify either nonintervention or primary transplantation as a medical choice for these children. Although promising in our hands, longer follow-up will be required to determine whether the RV-PA shunt modification confers an important survival benefit. Much information will be provided by the ongoing multi-institutional trial on right ventricular versus modified Blalock-Taussig shunt in infants with single ventricle defect undergoing staged reconstruction.³²

Footnotes

Presented at the Meeting of the World Society for Pediatric and Congenital Heart Surgery, June 22-24, Cairns, Australia.

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

The authors received no financial support for the research and/or authorship of this article.

Abbreviations and Acronyms

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