Concomitant aortic root replacement during frozen elephant trunk implantation does not increase perioperative risk

Abstract

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OBJECTIVES

Our aim was to evaluate the risk of concomitant aortic root replacement during frozen elephant trunk (FET) total arch replacement.

METHODS

Between March 2013 and February 2021, 303 patients underwent aortic arch replacement using the FET technique. Patient characteristics, intra- and postoperative data were compared between patients with (n = 50) and without (n = 253) concomitant aortic root replacement (implantation of a valved conduit or using the reimplantation valve-sparing technique) after propensity score matching.

RESULTS

After propensity score matching, there were no statistically significant differences in preoperative characteristics including the underlying pathology. There was no statistically significant difference regarding arterial inflow-cannulation or concomitant cardiac procedures, while cardiopulmonary bypass (P < 0.001) and aortic cross-clamp (P < 0.001) times were significantly longer in the root replacement group. Postoperative outcome was similar between the groups and there were no proximal reoperations in the root replacement group during follow-up. Root replacement was not predictive for mortality (P = 0.133, odds ratio: 0.291) in our Cox regression model. There was no statistically significant difference in overall survival (log rank: P = 0.062).

CONCLUSIONS

Concomitant FET implantation and aortic root replacement prolongs operative times but does not influence postoperative outcomes or increase operative risk in an experienced high-volume centre. The FET procedure did not appear to be a contraindication for concomitant aortic root replacement even in patients with borderline indications for aortic root replacement.

INTRODUCTION

The frozen elephant trunk (FET) procedure has evolved as an effective and common treatment in patients with thoracic aortic pathologies involving the aortic arch with good postoperative outcome but a high incidence of planned and unplanned distal aortic reinterventions [1–7]. However, the procedure remains complex and still carries a high risk for adverse events [4, 7, 8]. While FET implantation in our high-volume centre is already performed as a training procedure and therefore concomitant root replacement could be carried out more liberally, the addition of cardiac and aortic root procedures still increases the complexity of the procedure further [9]. Hence, surgeons may be hesitant to perform concomitant cardiac and/or aortic root procedures during FET total arch replacement particularly in patients with borderline indications. Therefore, our aim was to evaluate the risk of concomitant aortic root replacement during FET total arch replacement, i.e. the risk of a complete proximal thoracic aortic fix from the root beyond the aortic arch.

PATIENTS AND METHODS

Ethical statement

Our institutional review committee approved this retrospective study, and the need for informed consent was waived (number: 20-1302; approval date: 4 February 2021).

Patients and follow-up protocol

Between March 2013 and February 2021, 303 patients underwent FET total arch replacement in 1 aortic centre currently performing over 60 total aortic arch procedures per annum (as of 2021). Patients were followed up for a total of 421 patient-years, with a median follow-up of 8 [first quartile: 1; third quartile 29] months. All patients were routinely followed up after 6 months, 12 months and yearly thereafter in our dedicated aortic clinic. Computed tomography angiography scans were done preoperatively, before discharge, during every follow-up visit and when clinically warranted.

Surgical approach and technique

Our standardized, integrated surgical management of the FET technique has been reported [10–12]. In short, we carry out a full sternotomy and generally cannulate the right axillary artery for arterial inflow for cardiopulmonary bypass. Any concomitant procedures (valve, aortic root, coronary artery) take place while the patients are cooled down to a target core body temperature of 25°C. We routinely apply cold-blood cardioplegia or the beating-heart technique (using 300 ml of normothermic myocardial perfusion) [12]. Bilateral cerebral perfusion is normally used and we liberally perform trilateral antegrade cerebral perfusion (additional cannulation of the left subclavian artery) when needed. For this reason, today, our preoperative work-up includes a computed tomography angiography of the supra-aortic vessels including the Circle of Willis. Zone 2 is our standard anastomosis site for FET implantation, and today, we use the short version (100 mm) of the Thoraflex (Terumo Aortic, Inchinnan, UK) hybrid-graft exclusively. In case of classical aneurysm formation, we oversize the stent graft component by 10% at the distal landing zone and in case of aortic dissections, we avoid oversizing and choose the FET stent graft size according to institutional standards. We do not routinely implant cerebrospinal fluid drainage before surgery.

Indication for aortic root replacement

In the vast majority of patients root replacement was carried out according to the 2014 ESC guidelines [13]. In selected cases of young patients or/and patients with connective tissue disease especially if the wall of the aortic root appeared considerably thin intraoperatively, root replacement was done in root diameters lower than the guideline’s threshold in an anticipative manner.

Data collection and definition of parameters

Data were collected retrospectively relying on our prospectively maintained aortic database. Acute aortic dissection was defined as a symptom onset fewer than 14 days before hospital admission and was classified as chronic if symptoms had occurred >14 days beforehand. The TEM classification was used to categorize aortic dissections (type A, type B, type non-A non-B) [14]. The modified Rankin Scale (mRS) was used to classify the postoperative-stroke severity. Consulting neurologists evaluated all the strokes. Postoperative strokes causing no clinical symptoms (mRS 0), no significant disability (mRS 1) or slight disability (mRS 2) were classified as non-disabling postoperative strokes.

Statistical analysis

Since the data have been collected during an observational study, we applied propensity score matching. This mitigated the risk of confounding variables distorting the results. We achieved this by identifying pairs of observation that had the same propensity to experience the treatment, but which differ in their actual treatment. To estimate propensity scores, we used the following variables: aneurysm, penetrating aortic ulcer, male, age, diabetes, history of stroke, history of smoking, hyperlipidaemia, hypertension, history of renal failure, chronic obstructive pulmonary disease, coronary artery disease, bicuspid aortic valve and connective tissue disease. We used a nearest neighbour method and a calliper of 10% of the standard deviation of the propensity score logit. This approach lead to a total sample of 96 observations, with 48 patients with and without concomitant aortic root replacement. To measure treatment effects, we employed standard statistical techniques at a 5% significance level. Student’s t tests or Wilcoxon signed-rank tests were used to compare continuous variables as appropriate. McNemar tests were used for comparing frequencies. Data are presented as absolute and relative frequency or as median [first quartile, third quartile]. Cox regression analyses were performed to investigate the influence of clinically selected variables on overall mortality (selected variables: sex, age, concomitant root replacement, redo case, acute pathology) and the Kaplan–Meier method was used to analyse and compare overall survival. No primary analysis was defined; therefore, P-values may not be interpreted as confirmatory but rather descriptive. The analysis was performed with the statistical software R (version 4.1.1) and the library ‘MatchIt’ (version 4.3.4), running on MacOS x86_64-apple-darwin17.0.

RESULTS

Patient characteristics

Concomitant aortic root replacement was performed in 50 (17%) patients using a valved conduit (n = 27, 54%) or the valve-sparring reimplantation technique (n = 23, 46%). These patients were significantly younger (P = 0.002), predominantly male (P = 0.051), commonly presented with a bicuspid aortic valve (P = 0.016), underwent prior aortic valve replacement (P = 0.024) and more commonly presented with a type A aortic dissection (P = 0.018). Patient characteristics are summarized in Table 1. There were no statistically significant differences between patients with and without concomitant aortic root replacement after propensity score matching (Supplementary Material, Table S1).

Surgical details

As Table 2 shows, the right axillary artery was the preferred arterial inflow site in most patients and there were no statistically significant differences regarding the cannulation site or the incidence of additional cardiac procedures between the 2 matched groups. However, cardiopulmonary bypass (P < 0.001) and aortic cross-clamp (P < 0.001) times were significantly longer in the root replacement group significantly prolonging the duration of the surgery (P = 0.001). Unmatched data are presented in Supplementary Material, Table S2. Indications for root replacement are summarized in Table 3.

Outcome characteristics

Outcome characteristics are summarized in Table 4 and Supplementary Material, Table S3. There was no difference between the 2 groups regarding postoperative outcomes. In fact, in-hospital mortality tended to be lower in patients undergoing concomitant aortic root replacement, but the difference did not reach statistical significance (P = 0.111). In addition, overall survival tended to be higher in these patients as well but the difference did also not reach statistical significance (log rank: P = 0.062). No proximal reoperation was necessary in any patient in the root replacement group during follow-up.

Regression analysis

Concomitant root replacement was not identified as a significant variable in our Cox regression model. The full model is shown in Table 5.

DISCUSSION

Our study’s most important findings can be summarized as: (i) concomitant FET implantation and aortic root replacement is common particularly in patients with type A aortic dissection and in redo scenarios; (ii) concomitant aortic root replacement prolongs operative times, but does not impact postoperative outcomes or increases operative risk; and (iii) the FET procedure should not be a contraindication for concomitant aortic root replacement by itself, particularity in patients with borderline indications for aortic root replacement.

There were statistically significant differences regarding the baseline characteristics between the 2 unmatched groups, in particular, patients undergone concomitant aortic root replacement were significantly younger and more commonly men in our cohort. Both difference may be associated with the significantly higher incidence of patients with bicuspid aortic valves in this study. In fact, a bicuspid aortic valve is generally more common in male patients and patients with bicuspid aortic valve have a significantly higher risk for adverse aortic events at younger ages with lower cardiovascular risk factors present [15, 16]. This fact may also explain the significantly higher incidence of type A aortic dissections (acute or residual after prior repair) in patients with concomitant aortic root replacement. According to previous reports of patients with acute type A dissections, the need for concomitant root replacement has been reported to be higher in patients with a bicuspid compared to patients with a tricuspid aortic valve [16, 17]. In residual aortic dissection cases after previous repair for acute type A aortic dissection, it seems plausible that surgeons tend to aim for a complete aortic repair when performing the FET technique as a redo case to prevent any third step intervention for any residual root pathology and because the FET procedure has been shown to be safe in redo scenarios [18, 19].

Intraoperative data reflect our standardized, integrated surgical approach to the FET procedure with the right axillary artery as our routine choice for arterial inflow. The carotid artery remains a back-up option for arterial inflow in stable patients with compromised supra-aortic perfusion due to an acute dissection of the brachiocephalic trunk, even though we usually also cannulate the right axillary artery, as we did not see a higher risk for cerebral malperfusion in these patients [20, 21]. In selected scenarios (haemodynamically unstable patients, severe risk for spinal cord ischaemia, redo cases with retrosternal adhesions), the femoral artery may also be used. We generally switch to central perfusion or establish concomitant axillary and femoral artery perfusion (e.g. in atherosclerotic scenarios with risk for spinal cord ischaemia, when iliac artery perfusion is compromised preoperatively).

The beating-heart technique is liberally performed in our centre and may simply be performed when an artificial graft is present in the ascending aorta [12, 22]. This may explain the numerically higher rate of beating-heart procedures in patients with concomitant root replacement, since the procedure is usually carried out during cooling of the patient. Cardioplegia may then be stopped for the arch procedure and the FET can be implanted with a beating heart. The benefits of the beating-heart technique during FET total arch repair have been shown by the Hannover group and by us previously [12, 22, 23].

The addition of a concomitant root replacement obviously caused longer operative times but did not affect postoperative outcomes. In fact, while there were not statistically significant difference in postoperative outcome, there was a numerically better outcome in patients with concomitant root replacement. Similar results have previously been reported in isolated type A aortic dissection populations [23]. Hence, in patients with borderline indications for root replacement, these data suggest that the procedure can be performed safely.

Limitations and strengths

Our study is limited by its small sample size and retrospective nature. Of note, concomitant root replacement revealed favourable results in our and other high-volume centres, but these results may not be reproducible in less-experienced centres. However, this investigation contributes valuable knowledge on outcomes after concomitant aortic root replacement during FET total arch replacement.

CONCLUSION

Concomitant FET implantation and aortic root replacement prolongs operative times but does not influence postoperative outcomes or increase operative risk in an experienced high-volume centre. The FET procedure did not appear to be a contraindication for concomitant aortic root replacement even in patients with borderline indications for aortic root replacement. Further prospective multicentre studies or registry data are needed to confirm our results and their reproducibility.

SUPPLEMENTARY MATERIAL

Supplementary material is available at EJCTS online.

Funding

No funding was received for this work.

Conflict of interest: Bartosz Rylski performs proctor activities for Terumo Aortic. Martin Czerny is a consultant for Terumo Aortic, Medtronic and Cryolife, received speaking honoraria from Bentley and is a minority shareholder of TEVAR Ltd. Bartosz Rylski and Martin Czerny are shareholders of Ascense Medical. Maximilian Kreibich has received speaking honoraria from Terumo Aortic. The other authors report no conflict of interest.

Data availability

The datasets presented in this article are not readily available because of the requirements of our institutional review board. Individual reasonable requests will be evaluated by the corresponding author.

Author contributions

Tim Berger: Data curation; Methodology; Writing—original draft. Salome Chikvatia: Data curation; Writing—review & editing. Matthias Siepe: Conceptualization; Methodology. Stoyan Kondov: Data curation; Investigation; Writing—review & editing. Dominic Meissl: Data curation; Writing—review & editing. Roman Gottardi: Conceptualization; Supervision; Writing—review & editing. Bartosz Rylski: Conceptualization; Project administration; Supervision; Writing—review& editing. Martin Czerny: Conceptualization; Investigation; Methodology; Supervision; Validation; Writing—review & editing. Maximilian Kreibich: Conceptualization; Data curation; Investigation; Methodology; Visualization; Writing—original draft.

Reviewer information

European Journal of Cardio-Thoracic Surgery thanks Erik Beckmann, Joseph S. Coselli and the other, anonymous reviewer(s) for their contribution to the peer review process of this article.

REFERENCES

ABBREVIATIONS

ABBREVIATIONS
 
• FET

  Frozen elephant trunk

 
• mRS

  modified Rankin Scale