Aortic arch reconstruction in the Norwood procedure using a curved polytetrafluorethylene patch

Abstract

 

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OBJECTIVES

The aortic arch enlargement in the Norwood procedure is classically carried out using a curved homograft patch on the inner curvature of the neoaortic arch. The study investigates the outcome of a newly used artificial patch from a vascular prosthesis as an alternative to a homograft patch.

METHODS

Since April 2007, we used curved polytetrafluorethylene (PTFE) patches cut out of a prosthesis as an alternative to homograft patches for the aortic arch reconstruction. The decision for either patch material was made due to anatomic reasons, preferring PTFE patches in larger aortas. In this study, 224 Norwood patients, operated between April 2007 and April 2018, were analysed. A total of 104 patients received a PTFE patch (group PTFE), and 120 patients got a pulmonary homograft patch (group homograft). A single-centre retrospective analysis was carried out concerning postoperative course and long-term follow-up regarding aortic arch interventions and reoperations and comparing the 2 material groups.

RESULTS

There were no material associated operative or postoperative complications. In-hospital mortality was 13% in group PTFE. Six children died late during follow-up (6%). One aortic isthmus dilatation (1%) was carried out 12 months after the Norwood procedure in this group, no arch reoperation was necessary during the complete follow-up.

CONCLUSIONS

The curved PTFE patch showed good qualities in operative technical demands and excellent long-term results. In selected cases of hypoplastic left heart syndrome, it can be well used as alternative to the pulmonary homograft.

INTRODUCTION

In the Norwood procedure, the large main pulmonary artery is connected to the hypoplastic aorta to warrant unrestrictive output to the systemic circulation. The aortic arch is usually enlarged with a patch at the inner curvature, which should reach as far as the proximal part of the descending aorta [1]. A resection of the isthmus is often carried out in order to shorten the reconstruction and prevent kinking [2]. Subsequent aortic arch restenoses are described as a common complication that occurs in 7–36% of Norwood patients [1–7]. They might be a consequence of design and material of the primary arch repair. As the normal aortic arch is a curved tube, the enlarging patch therefore needs to be curved in 2 planes to prevent a stenosis by kinking.

The classically used material is a patch cut out of a pulmonary bifurcation homograft that shows a similar shape. The homograft has good sewing qualities but has several disadvantages. In case, there is no suitable homograft available from the institutional allograft storage system, it has to be ordered personally for each patient, which means that the flexibility of the surgical schedule is influenced. Urgent procedures are not possible. Furthermore, there might be an immunologic reaction to this allogenic transplant. This might be of negative consequences, once a heart transplantation should be necessary. The homologous material can also be altered and calcified, which can lead to severe problems, if the aortic arch has to be crossclamped during subsequent operations. Last but not least, the high costs of the homograft have to be mentioned.

These facts lead to the search for an alternative material, that is curved in 2 planes with the correct bend and provides durability, shape stability, no antigenicity, storability and lower costs. Other sorts of material for the aortic arch repair in the neonate were mentioned before but have not gained widespread application [8–12].

The Dynaflo™ bypass graft (Bard Peripheral Vascular Inc., Tempe, Arizona) is made out of polytetrafluorethylene (PTFE), which is a commonly used vascular patch product, and has a funnel shaped end to magnify anastomoses in peripheral vascular surgery [13, 14]. A patch cut out of this funnel seems to meet the above mentioned criteria and might be used as an alternative to the homograft patch.

The aim of this single-centre study is to analyse the practicability of this new patch material comparing intra- and postoperative data as well as long-term performance regarding reinterventions and reoperations at the implantation site during follow-up between the PTFE group and a homograft control group.

MATERIALS AND METHODS

A single-centre retrospective study was carried out including all patients who have received a polytetrafluorethylene patch in the aortic arch during their Norwood procedure at the Children’s Heart Center Linz, Austria. The patch was cut out of the curved end of the Dynaflo™ prosthesis. This prosthesis was used for the first time in April 2007 in this indication and was used in 104 Norwood patients until April 2018. These patients form ‘group PTFE’. In the same time period, 120 Norwood patients got their aortic arch reconstructed with a pulmonary homograft patch. These patients were merged to ‘group homograft’. Six more Norwood patients had a pericardial patch or a patchless reconstruction during this period and were excluded from the study. The decision for the used patch material was made preoperatively due to anatomic reasons, weight of the patient and availability of a homograft. PTFE prostheses were preferred in patients with an ascending aorta of at least 3 mm in diameter and in children beyond newborn age. In the PTFE group available preoperative measurements of the ascending aorta showed a mean diameter of 4.7 ± 1.7 mm ranging between 1.8 and 8 mm. We started using the PTFE patch in patients with larger aortas and, encouraged by good application qualities, expanded the group where we abstained from an international homograft order in case we did not have a suitable homograft in our institutional homograft bank. Overall, this patch is used in about 50% of our Norwood cases.

The included patients were followed from birth until last observation follow-up or death. Four patients from the PTFE group are lost to follow-up. They were included until last observation end point. Data were collected retrospectively from patients’ medical records and statistically analysed. The study investigates intraoperative and postoperative material associated complications, aortic cross-clamp time and bypass time, mortality, need for reoperation because of bleeding, incidence of reintervention and reoperation for aortic arch restenosis and endocarditis during follow-up. The postoperative aortic arch development was routinely assessed echocardiographically. Catheter investigations were made in case of relevant gradients and routinely before the bidirectional Glenn and Fontan operations. Aortic arch reintervention was initiated in case of a catheter measured gradient of >10–20 mmHg depending on ventricular function according to guidelines standard. Restenoses were treated by either catheter balloon dilatation or stent implantation or surgical aortic arch reoperation. Data were compared between the 2 groups.

Ethical statement

The institutional Ethics Committee (Ethics Committee of the Medical Faculty of the Johannes Kepler University) has approved the study under the no. 1155/2018. Written patients informed consent was waived by the Ethics Committee due to the retrospective character of the investigation.

Product description

The Dynaflo™ bypass graft (Bard Peripheral Vascular Inc., Tempe, Arizona) is constructed of expanded polytetrafluoroethylene with carbon impregnated into the inner portion of the graft wall and a proprietary cuff at the distal end of the prosthesis. The graft is originally designed for peripheral vascular surgery [13, 14] and has a diameter of 7 mm before the cuff and a length of 50 cm. It is non-elastic in the longitudinal direction. Intraoperatively, a patch is cut out of the curved prosthesis end containing the complete inner bend of the cuff (see Figs. 1 and 2). The same prosthesis size was used independently of patient age.

Patients

The PTFE group contains 92 newborns and 12 infants aged between 32 and 380 days (for demographic data see Table 1). Newborn babies had their Norwood operation at a median age of 7 days without precedent palliation. One of them had a prior mitral valve plasty in attempt of a biventricular repair. The infant patients had previous pulmonary artery bandings except 2 of them, who did not have any previous procedure. Two-third of the patients were male (69 patients). The median weight was 3.4 kg, ranging from 2.3 to 7.6 kg. Thirty children had an aortic atresia, and 20 had an associated transposition of the great arteries. The control group contains 120 patients, who were treated with a homograft patch. This group contains 113 newborns and 7 infants aged between 55 and 228 days. Aortic atresia was present in 68 patients of this group (57%), which is significantly more than in group PTFE.

The 2 groups do not show a significant difference regarding age, weight or sex (see Table 1). Ninety-eight patients had a hypoplastic left heart syndrome containing aortic atresia, 66 patients had a severe aortic stenosis in either HLHS or double outlet right ventricle (DORV). Twenty-two patients had an unbalanced complete atrioventricular canal. Thirty-eight patients showed either D-TGA or L-TGA combined with tricuspid atresia or classic single ventricle anatomy.

Surgical technique

All procedures were done in double arterial cannulation technique using 2 similar 8 French soft cannulas for the newborns. The first cannula was inserted into a 3.5-mm PTFE prosthesis anastomosed to the brachiocephalic artery, and the second cannula was inserted into the descending aorta above the diaphragm. A single venous cannula was used in the right atrium. Patients were cooled to 25°C, lately only to 28°C. Circulatory arrest was used only for the excision of the atrial septum.

The aortic arch reconstruction was done in a classical and identical manner no matter what kind of patch was used. The patch material was tailored before crossclamping. The aortic isthmus was resected and an extended end to end anastomosis between the aortic arch and the descending aorta was performed routinely. The proximal part of the descending aorta was incised to enable a thorough enlargement. The patch was then sewn from the distal ending until the pulmonary artery. The PTFE patch was sewn with a PTFE suture (GORE-TEX^® suture CV-7 by W. L. Gore & Associates, Inc.), the homograft patch with 6/0 polypropylene. Great attention was paid to the correct anatomical shape of the patch to prevent kinking, keeping in mind that the PTFE patch does not stretch under tension as the homograft. As the curve of the prosthesis is not very long, nearly all of the funnel is needed for the patch curvature. In case of transposition of the great arteries, the ascending aorta was divided and reconnected to the front of the patched reconstruction in an end to side fashion. Before opening the aortic cross-clamp, the stitches in the PTFE prosthesis were sealed with fibrin glue (2 ml Tisseel™ from Baxter AG, Vienna, Austria) to minimize bleeding. The majority of children received a right-sided 5-mm Right ventricle to pulmonary artery (RV–PA) PTFE conduit; older children after pulmonary artery banding underwent a comprehensive stage II with a bidirectional Glenn anastomosis.

Statistical analysis

All data of continuous variables were checked for normal distribution (test of normality: Kolmogorov–Smirnov with Lilliefors significance correction, type I error = 10%) and in the case of normal distribution also for heteroscedasticity (Levene test, type I error = 5%). For the comparison of Heart transplantation (HTX)-free survival, depicted by Kaplan–Meier plots, the log-rank test was used. The influence of the used material in the aortic arch (PTFE/homograft), age at Norwood procedure, weight at Norwood procedure, sex, cross-clamp time, bypass time, aortic atresia, transposition of the great arteries and status post precedent procedure on HTX-free survival and on the occurrence of reintervention was investigated by Cox regression analyses (multivariable and stepwise forward based on the likelihood ratio approach).

The type I error was not adjusted for multiple testing. Therefore, the results of inferential statistics are descriptive only. Statistical analysis was performed using the open-source R statistical software package, version 3.6.1 (The R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

The arch augmentation with the prosthetic material could be carried out in all 104 preoperatively selected patients. One patient intraoperatively encountered a rupture of the implanted homograft patch, which was replaced by a PTFE patch. The patient now belongs to group PTFE. There were no material associated operative or postoperative complications as could be rupture, aneurysm formation, bleeding or infection of the patch in the PTFE group. The median bypass time in group PTFE was 202 min. ranging from 152 to 461 min. The median aortic cross-clamp time was 71 min, ranging from 45 to 178 min (for detailed perfusion data see Table 2). Postoperative Extracorporeal membrane oxygenation (ECMO) therapy was used more often in group homograft (20% vs 14% in group PTFE).

The 30-day mortality rate was 6% (6 patients) in group PTFE [95% confidence interval: 2.2–12.1%] and 8% (9 patients) in group homograft [95% confidence interval: 3.5–13.8%]. In-hospital mortality was 13% in group PTFE and 12% in group homograft. The incidence of a rethoracotomy because of postoperative bleeding was 4% in the PTFE group versus 6% in the homograft group. There was no bleeding reported in the area of the PTFE patch. The median intensive care unit (ICU) stay and median hospital stay did not show relevant differences between the 2 groups. Reduced ventricular function at time of discharge from hospital was documented in 5 out of 91 discharged PTFE patients. One patient showed a substantial tricuspid regurgitation, which was addressed with tricuspid valve repair at the age of the bidirectional Glenn operation. During the follow-up time after the Norwood procedure of up to 11.4 years (median 3.8 years), there was a late mortality rate of 6% in group PTFE and 9% in group homograft. The 10-year survival expectancy was 80.8% in group PTFE [95% confidence interval: 73.4–89.0%] and 78.1% in group homograft [95% confidence interval: 70.8–86.2%]. For long-term follow-up data, see Table 3. Exitus occurred at a median age of 0.2 years. The analysis of the causes for death was as follows: in the PTFE group, 9 patients died due to cardiorespiratory failure or chronic failure of the univentricular circulation, one more patient due to isolated respiratory failure, 2 due to multiorgan failure, 3 due to sepsis, 1 due to a pulmonary hypertensive crisis, 1 due to a cerebral sinus vein thrombosis, 1 had a severe congenital cerebral malformation and 1 died due to bleeding at the rethoracotomy for the Glenn procedure. In the homograft group, 20 children died due to cardiorespiratory failure or chronic failure of the univentricular circulation, 1 had a severe tricuspid insufficiency, 1 had a sudden death at home and another one a documented acute rhythm disturbance. Two children died due to an infection, 1 had a severe intracerebral haemorrhage and 1 an unknown severe congenital cystic malformation of the lungs.

Cox regression analysis regarding exitus revealed only longer extracorporeal bypass time to be a significant risk factor for exitus. The stepwise forward model based on the likelihood ratio approach showed additionally the anatomic variant of transposition of the great arteries to be of positive influence regarding survival (see Table 4). The transplant free survival expectancy is depicted by Kaplan–Meier plots (see Figs. 3 and 4). Four patients are lost to follow-up but are included until last follow-up date. In total, only 5 out of 224 Norwood patients (2%) showed an aortic arch restenosis during follow-up. Only one of them belongs to group PTFE (1%). This stenosis was treated by an interventional balloon dilatation at the age of 12 months. Four patients out of group homograft (3%) encountered an aortic arch restenosis during follow-up. Three of these patients underwent aortic arch reoperation, one of them early during stage I (10 days after the Norwood procedure) and the other 2 combined with their bidirectional Glenn operation at the age of 3 months. There is no residual gradient after the reoperation at last controls. The fourth patient of group homograft underwent catheter intervention with stent implantation at the age of 3 months. Cox regression analysis was used to look for influence on the occurrence of reintervention regarding the following parameters: used material in the aortic arch (PTFE/homograft), age at Norwood procedure, weight at Norwood procedure, sex, cross-clamp time, bypass time, aortic atresia, transposition of the great arteries and status post precedent procedure, but none of these parameters showed significant independent influence (P > 0,05).

There was no case of endocarditis or aneurysm formation during follow-up in any of the patient groups.

DISCUSSION

The classical material for the aortic arch reconstruction within the Norwood procedure is a patch cut out of a pulmonary homograft bifurcation, which is also practice at our centre [1]. Limited availability of homografts made us search for an additional material that can be used in at least a subgroup of Norwood patients to spare scarce homografts for advanced reconstruction cases.

Overall recoarction rates after the Norwood procedure are described also in large multicentre trials in 7–36% of Norwood cases [1–7]. Several groups have reported their experiences using autologous or heterologous pericardium as alternative to a homograft patch, but the rate of restenosis in the patch area due to intima proliferation or kinking is concerningly high. Vitanova et al. [4] compared homograft patches with autologous and equine pericardium and other material and found significant different restenosis rates. They advised against equine pericardium. Ashcraft et al. [8] also demonstrated that the type of patch material used for the arch reconstruction influenced the long-term risk of aortic arch recoarctation identifying bovine pericardium to be associated with greatest risk in their group of patients. Coarctectomy and the interdigitating technique were described to lower the risk for recurrent arch obstruction [1, 2].

In our opinion, apart from shortening the aortic arch and excision of all ductal tissue by an isthmus resection, the shape of the patch is the most important factor influencing good and durable growth of the neoartic arch (see Fig. 3). A short, but curved patch is necessary to achieve a near normal postoperative anatomy of the aortic arch with a low restenosis rate. The funnel shaped end of the Dynaflo™ bypass graft (Bard Peripheral Vascular Inc., Tempe, Arizona) provides such a curve that can be used for a patch reconstruction anatomically similar to a homograft patch. We used this material in Norwood patients with an ascending aorta of at least 3 mm in diameter. As the PTFE material is stiffer and thicker than a homograft, we were reluctant in using the new prosthesis in very thin and tiny native aortas. This fact is illustrated by the lower rate of cases with aortic atresia in the PTFE group, which was nevertheless 29% compared to 57% in the homograft group. Additionally, patients beyond newborn age, who had prior pulmonary artery bandings, were more often selected for the PTFE group.

The subgroup analyses between our PTFE group and the homograft group did not reveal any negative perioperative effects of the newly used material as could be a higher rate of rethoracotomies, rupture, infection or aneurysm formation. The technique was easily adopted by all experienced members of the surgical team. The aortic arch restenosis rate of 1% in the PTFE group underlines the appropriate material qualities without mentionable neointima proliferation. Aortic cannulation during subsequent procedures was performed in the area of native tissue in both groups. Preparation close to the PTFE patch at time of the bidirectional Glenn and Fontan operation was possible without any problems as there was no sign of calcification or unpleasant tissue growth in the patched area.

A further advantage of the synthetic product is the absence of any immune reaction, which will be of positive effects once heart transplantation should be necessary later in life.

The prize of the prosthesis in our country is about one-tenth of the prize of internationally available homograft bifurcations. The usage of this prosthesis might therefore enable also easier access to single ventricle palliation in countries where homograft application is not warranted or too expensive.

In summary, in our cohort of selected patients with aortas of reasonable size and wall thickness, we did not encounter negative effects of the newly used product. But it has to be clearly stated that due to the small number of adverse events in both groups and the short follow-up period, we can still not exclude the possibility that the PTFE patch could perform worse than the homograft patch on the long run.

Limitations

A limitation of the study is the retrospective character of the investigation. The fact that patients were selected preoperatively due to their aortic anatomy and were not randomized is a bias towards a patient cohort with potentially better outcome. Therefore, better results have to be seen with caution, as the application of the new material is maybe not applicable to the whole cohort. The stiffness of the artificial material may also be of negative effect regarding cardiac workload and should be investigated in further studies [15, 16].

In addition, longer follow-up time and a larger sample size of adverse events are needed to exclude inferiority of the PTFE material compared to the homograft patch especially regarding the aortic arch restenosis rate. A prospective multicentre investigation would be of great advantage to provide evidence of reproducible results.

ACKNOWLEDGEMENTS

The authors thank Dr. Wolfgang Schimetta and the Working Group for Systemic Optimization of Clinical Research Projects (ASOKLIF) for data analysis and statistics.

Conflict of interest: none declared.

Data availability statement

All relevant data are within the manuscript and its supporting information files.

Author contributions

Eva Sames-Dolzer: Conceptualization; Data curation; Methodology; Project administration; Writing—original draft. Gregor Gierlinger: Data curation. Michaela Kreuzer: Data curation. Roland Mair: Data curation. Roland Gitter: Data curation. Christoph Prandstetter: Data curation. Gerald Tulzer: Supervision. Rudolf Mair: Conceptualization; Writing—review & editing.

Reviewer information

European Journal of Cardio-Thoracic Surgery thanks Emile Bacha, Katarzyna Januszewska, Joachim O.M. Photiadis and the other, anonymous reviewer(s) for their contribution to the peer review process of this article.

REFERENCES

ABBREVIATION

 
• PTFE

  Polytetrafluorethylene