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Outcomes of different aortic arch replacement techniques

Abstract Background Consensus on the best treatment for aortic arch pathology is unresolved due to an emerging variety of procedures. We aimed to compare the outcomes of two major techniques for open aortic arch replacement involving the supra‐aortic branches and to identify the risk factors for specific adverse events. Methods Between 1974 and 2017, 172 patients were treated with either the en bloc (island, n = 59; 34.3%) or branched graft technique (n = 113, 65.7%). Most of the patients were treated in an emergent/urgent setting (52.4%). Results Patients who underwent the en bloc procedure had significantly shorter cardiopulmonary bypass (median: 241 vs 271 minutes, P = .041) and aortic cross clamp times (median: 124 vs 168 minutes, P = .005) than patients who underwent the separate graft technique. Overall, the hospital mortality was lower in the en bloc group, 8.5% vs 19.5%, although the difference was not significant (P = .077). No difference was found in the survival between the separate graft and en bloc groups at 1 (77.0 vs 86.3%), 5 (67.7 vs 66.3%) and 10 years (42.4 vs 51.3%), (P = .63). The postoperative stroke rate was comparable between the en bloc and separate graft cohorts (14.3 vs 19.6%, P = .52). Diabetics and those who underwent an elephant trunk procedure were at a higher risk for reintervention. Conclusions The separate graft technique, which is more common today, showed no difference from the en bloc technique with regard to hospital mortality and morbidity. Furthermore, the late survival and reintervention rates were similar after both procedures.

efforts to formulate and provide more uniform guidance for reporting the clinical results of aortic arch surgery. 4 The current study is aimed to clarify the contemporary outcomes of open surgical aortic arch replacement involving the supra-aortic branches and to evaluate the predictive risk factors of adverse events of different reimplantation techniques.

| Operative technique
Over the last two decades, the surgical technique for an aortic arch replacement has been standardized at our institution. 5 To approach the aortic arch, a median sternotomy was used in 156 (90.7%) patients, a posterolateral thoracotomy in 14 (8.1%) patients and a thoracolaparotomy in 2 (1.2%) patients.
In most of the patients, cardiopulmonary bypass (CPB) was initiated with arterial cannulation of the ascending aorta (48.8%) or femoral artery (41.3%), whereas CPB initiation through the axillary artery or other sites was used in only 5.8% or 4.3%, respectively. The Following institutional policy, cold crystalloid cardioplegia was used for myocardial protection in all cases. Cerebral perfusion with cold blood (18°C) was initiated at a flow of 10 mL/kg/min. For partial arch repair, only one cannula was used, and ACP was delivered at a flow of 7 mL/kg/min. The right radial arterial pressure was maintained between 40 and 70 mmHg. Cerebral monitoring was secured with a right radial arterial pressure line and cerebral oxygen saturation by using nearinfrared spectroscopy. Control of pH balance was carried out by integrating the pH-stat method during moderate to deep hypothermia and α-stat method for temperatures higher than 28°C. The left side of the heart was vented through the right superior pulmonary vein. Over the study period, two different techniques were used to replace the aortic arch: brachiocephalic vessel implantation using an island technique or a branched prosthesis (Plexus 4; Vaskutek Ltd, Renfrewshire, Scotland, UK) with separate revascularization of arch vessels.
Over time, the choice of a certain surgical technique depended on the patient's characteristics, for example, the presence of connective tissue disorder or extensive atherosclerotic disease and the surgeon's preference. According to the surgical plan, over the last 2 decades, either an "elephant trunk" (ET) or a "frozen elephant trunk" (FET) was placed through the opened aortic arch in the descending aorta in patients with extensive pathology of the thoracic aorta.

| Data collection and clinical endpoints
The Medical Ethics Committee of Erasmus Medical Center in Rotterdam granted approval for this study (MEC 2011-064). The data were extracted from our institutional Aortic Surgery Database, a prospectively maintained clinical registry of all patients undergoing thoracic aortic surgery at our institution and double-checked for accuracy (D.A. and J.B.).
All operative survivors were followed up regularly and recommended to undergo computed tomography (CT) at the time of discharge, after 6 months and annually thereafter. Follow up was complete in 100% of patients.
All clinically gathered data, including the occurrence of events during follow-up and cause of death, were registered and reported according to the expert consensus recommendation for reporting treatment results in the thoracic aorta. 6 Any surgical or percutaneous interventional catheter procedure that repaired or otherwise adjusted any part of the aorta was defined as an aortic reintervention.

| Statistical analysis
Continuous data were presented as the means ± standard deviation or medians with interquartile range (IQR) depending on the data distribution. Categorical variables were presented as frequencies and percentages. The patients were divided into 2 categories according to whether they were treated with an en bloc or a separate graft technique. The short-and long-term outcomes of the two patient groups were then compared. Continuous variables were examined using the two-sample t test or the Mann-Whitney U test, where appropriate. Categorical variables were compared using the χ² test or Fisher's exact test, when applicable.
The preoperative and intraoperative variables were first analyzed using univariate logistic regression, and then a ridge-penalized logistic regression model was used to assess independent predictors of hospital mortality and neurologic outcome. 7 Univariate and multivariate Cox proportional hazard regression analyses were used to identify predictors for the predefined adverse events: all-cause mortality and aortic reintervention. Due to the low frequencies of the aforementioned events, a penalized likelihood approach was used in the multivariate Cox model. 8 Patient survival was estimated using the Kaplan-Meier method and log-rank test. The cumulative incidence of aortic reintervention in both groups was calculated by accounting for death as a competing risk. 9,10 All statistical tests were two-sided with an α level set at 0.05 for statistical significance.
Statistical analyses were performed with IBM SPSS Statistics for Mac, version 25.0 (IBM Corp, Armonk, NY) and R software, version 3.5.1 (R Foundation for Statistical Computing, Vienna, Austria).  Table 1).

| Study population
The only significant difference in the preoperative characteristics between the two study groups was a higher baseline serum creatinine level in the separate graft group. However, no difference was noted in the number of patients affected by chronic kidney disease.

| Intraoperative data
The extent of surgery depended on the extent of aortic arch disease and coexistence of other cardiac pathologies (Table 1, Complete results are presented in Table S3). Arch repair involving all 3 arch arteries (total aortic arch), 2 arch arteries or 1 arch artery was performed in 91 (52.9%), 46 (26.7%) and 35 (20.3%) patients, respectively. The extent of aortic pathology required additional replacement of the ascending aorta in 112 (65.1%) patients. In 24 (14.0%) patients with subsequent disease of their descending aorta, conventional ET was deployed. A FET procedure was performed in 6 (3.5%) patients (Table S3).  (Table 1).

| Hospital mortality and morbidity
Overall hospital mortality was 15.7% (n = 27), with rates of 7.3% (6/82 patients) after elective surgery and 23.3% (21/90 patients) after urgent/ emergent surgery (P = .006). Nine patients (5.2%) died in the operating theater during the urgent surgical procedure due to acute aortic dissection. The hospital mortality tended to be higher for the separate graft cohort than for the en bloc reimplantation cohort, though no statistically significant difference was found (19.5 vs 8.5%, P = .077).
Several variables were identified as risk factors by means of univariate analysis for in-hospital mortality and the occurrence of postoperative stroke (Table S4). None of these predictors maintained their significance in the multivariate penalized regression model (Table S5).
The two reimplantation techniques of the supra-aortic vessels were not associated with an increased risk of the postoperative development of stroke or hospital mortality.
During the follow-up, 58 more deaths occurred, thus resulting in a total of 85 (49.4%) deaths. The longest survival was 26 years in a patient who underwent total aortic arch replacement with reimplantation of all three supra-aortic vessels with the en bloc technique.

| Reinterventions
Two patients required aortic reintervention due to acute dissection during the in-hospital stay after initial separate reimplantation of the supra-aortic branches.
In competing risks analysis, no difference was found in the cumulative probability of aortic reintervention, accounting for death as a competing risk, between the en bloc and separate graft operative

| Study strengths and limitations
The current study was limited by several weaknesses. Although allinclusive, it was a retrospective, single-center, and observational study. This study included only patients, whose replacement of aortic arch involved supra-aortic vessels, providing certain homogeneity.
Nevertheless, the differences in presenting pathology and status may account for heterogeneity.
It's also important to emphasize the strength of the statistical approach. The penalized regression model used in this study is a more evolved method that is particularly suited when the number of covariates is large relative to the number of observations in the data set. Thus, the problem of overfitting was avoided.

| CONCLUSIONS
Although the current study was limited by the shortcomings of