Early- and medium-term results after aortic arch replacement with frozen elephant trunk techniques—a single center study

Introduction

The standard surgical technique for patients with extensive pathology of the thoracic aorta is still the conventional elephant trunk technique, developed by Borst in 1983 (1). However, this procedure is associated with increased operative medium term mortality, and also with a high incidence of neurological complications (2). In recent years many new technological solutions based on endovascular methods have been introduced into clinical practice, one of them being a hybrid procedure, the frozen elephant trunk technique (FET) (3).

The current study shows our 7-year institutional experience of using the FET technique for the treatment of patients with extensive thoracic aortic disease. The objectives of this study were (1) to evaluate clinical characteristics, and early, and mid-term results, and (2) to determine predictors of clinical and neurological outcome, particularly, spinal cord injury after aortic arch surgery using FET.

Patients and methods

A total of 51 consecutive patients underwent total aortic arch surgery with FET implantation between January 2006 and August 2013 and were included in our analysis. Data were prospectively collected in a database, and retrospective review was approved by the local Ethics Committee. Individual patient consent was waived.

Patients were followed-up annually with a mailed questionnaire or, when needed, by contacting the referring cardiologist or general practitioner. Follow-up was 100% complete.

Operative technique

The FET technique has been performed in our hospital since 2006. In all patients the E-vita hybrid open stent-graft (Jotec, Hechingen, Germany) was used (Figure 1). The surgical technique and indication were as previously described (4).

Figure 1 Preoperative CT scan of patient with distal aortic arch aneurysm (A) and after aortic arch surgery using FET technique (B) with completely excluded aneurysm (yellow arrow)

Definitions

In accordance with STS guidelines, early mortality was defined as all-cause mortality at 30 days. Operations were considered emergent if performed within 24 hours of hospital admission for cardiovascular instability, and urgent if performed during the same hospital admission.

All patients with suspected neurological complications on physical examination underwent computerized tomography or magnetic resonance imaging. Spinal cord injury was defined as new-onset transient or permanent paraparesis or paraplegia. Neurological complications were defined as permanent neurological deficit (PND) for patients with stroke or paraplegia, and temporary neurological deficit (TND) for patients with reversible deficits (2).

Statistical analysis

All statistical analyses were performed using SPSS 17.0 (Chicago, IL). Categorical variables were compared using the Chi-square test or Fisher’s exact test. Independent continuous variables were compared by unpaired Student’s t-test for comparison of normally distributed data between two groups or Kruskal-Wallis test for the comparison of more than two groups as appropriate. Continuous variables are expressed as mean ± SD, and categorical data as proportions throughout the manuscript.

Dichotomous adverse outcome events were analyzed using an uni- and multivariate logistic regression model with backwards stepwise elimination, and were expressed as odds ratios (OR) with 95% confidence intervals (CI). Event-free survival was calculated by Kaplan-Meier methods with 95% CI. Independent predictors of medium-term survival were determined with Cox proportional hazards analysis. P

Results

A total of 51 consecutive patients underwent total replacement of the aortic arch using the FET technique during the study period. The majority (62.7%) suffered from degenerative aortic aneurysm. Acute Type A and Type B aortic dissection was the indication for surgery in 15.7% and 13.7% of patients, respectively (Table 1).

Table 1 Demographics and preoperative clinical characteristics
Full table

Operative details and post-operative complications

All operative details are presented in Table 2. Mean core body temperature was (26±2) °C. The mean prosthesis size was 33.7±4.8 mm (24-40 mm). Prosthesis over-sizing was observed in 14% (n=7) patients. The distal prosthesis landing zone was T7 and lower in 19.6% (n=9), between T8 and T9 in 52.2% (n=24), and more than T10 in 26.1% (n=12) of patients.

Table 2 Operation data and postoperative clinical characteristics
Full table

Postoperative outcome

The 30-day and in-hospital mortality for the entire cohort of patients was 7.8% (n=4). PND occurred in 11.8% (n=26) of patients (Table 2). The incidence of PND and TND was 11.8% and 9.8%, respectively. The overall rate of paraplegia was 19.6% (n=10). Multivariate analysis identified a core body temperature of 28 °C or higher during circulatory arrest in combination with duration of circulatory arrest greater than 45 minutes, as an independent predictor of permanent spinal cord injury (OR 4.8; 95% CI, 1.1-21; P=0.04).

Predictors of medium-term survival and freedom from thoracic endovascular aortic repair (TEVAR)

The estimated mean follow-up time for all patients was 3.4±0.4 years (0-5.1 years) with a total follow-up of 58.8 patient years. The unadjusted 1- and 5-year survival for the entire group was 80.2±5.5%, and 59.7±10.2%, respectively.

During follow-up TEVAR was performed in 8 patients. The estimate mean freedom from endovascular intervention was 4.2±0.4 years. The unadjusted 1- and 5-year freedom from TEVAR was (84.9±5.9)%, and (69.2±11.2)%, respectively (Figure 2). One patient underwent re-operative thoracoabdominal aortic surgery 5.5 years after initial surgery due to progression of extensive thoracoabdominal disease.

Figure 2 Freedom from TEVAR procedure after initial FET implantation

Discussion

The current study summarizes our 7-year institutional experience in aortic repair with “FET” for patients with extensive aortic pathology, a technique, which was introduced into clinical practice at our institution in 2006.

The 30-day mortality of 7.8%, observed in our study, is comparable to other case series reported in the literature. The in-hospital mortality, reported in 2011 by the International E-vita Open Registry, is 15% (5). The lower mortality rate in the present study must be interpreted with caution, because a lower number of patients suffered from acute type A aortic dissection. This disease has previously been identified as an independent predictor of 30-day mortality in patients undergoing aortic arch surgery (2,6).

The neurological status of patients after extended aortic arch surgery has an important impact on postoperative outcome. The most devastating complications associated with reduced quality of life and long-term survival in these patients are PND and spinal cord injury (6-8).

Permanent or transient spinal cord injury is a rare complication after extended aortic arch surgery with conventional elephant trunk implantation, with incidence rates ranging from 0.4% to 2.8% (9-11). As opposed to that, in patients who received FET, this complication was significantly higher. A multicenter study, including 240 patients with FET, reported a 9% incidence of this dreaded complication (12). Single center studies with relatively small numbers of patients have reported incidences as high as 21-24% after FET implantation (13-15). The factors influencing paraplegia are extended length of circulatory arrest (13,14), and level of the distal landing zone beyond T7 (15). Flores and colleagues identified a distal landing zone of T7 or lower, and a history of previous abdominal aortic aneurysm repair as a predictor of spinal cord injury. This observation suggests an important role of distal inflow to the paraspinous arterial collateral network via the hypogastric arteries (15). The Collateral Network Concept, investigated by Griepp’s group (10), has been used to explain and understand this phenomenon. The FET technique has the potential to impact both Collateral Network inflow pathways simultaneously: the segmental artery by insertion of the stented part of the hybrid graft into the descending aorta, and the vertebral artery due to lack of perfusion during circulatory arrest. This can explain the increased incidence of spinal cord injury to patients who underwent the FET procedure compared to those who underwent conventional elephant trunk implantation. In the current study, the incidence of spinal cord injury was 21.4%. A core body temperature of 28 °C or higher during circulatory arrest, in combination with circulatory arrest time greater than 45 minutes, was identified as an independent predictor of spinal cord injury. Five out of twelve patients, who suffered ischemic spinal cord injury, had circulatory arrest times greater than 45 minutes during which the core body temperature was 28 °C or warmer. Similar to observations of Pacini et al. (12), the core body temperature or duration of circulatory arrest alone do not have a significant impact on the incidence of postoperative spinal cord injury. In the current study we also failed to find a significant correlation between the distal FET landing zone level and the incidence of acute ischemic spinal cord injury. The landing zone of the distal end of the stent-graft was at or even proximal to the T8 level in six of ten patients with postoperative spinal cord injury.

The incidence of PND in patients undergoing aortic arch surgery has been reported to range between 1.1% and 9.8% (8,16,17). Age, acute type A aortic dissection (2), urgent status (7,16), renal insufficiency (16), operation time (16) and, prolonged circulatory arrest (2,16) were factors that influenced the occurrence of PND after surgery. PND was observed in 11.8% of our patients and was nearly twice as high among patients who presented with acute type A aortic dissection.

In conclusion, the FET technique can be performed with a relatively low mortality in patients with extensive pathology of the thoracic aorta. However, this procedure is associated with a significantly increased incidence of postoperative permanent paraplegia due to ischemic spinal cord injury. The independent predictor of paraplegia is the combination of prolonged circulatory arrest times (≥45 minutes) with mild hypothermia (≥28 °C). The FET procedure should therefore be performed using deep hypothermia, particularly in patients with prolonged aortic arch surgery, in order to prevent complications due to ischaemic spinal cord injury.

Acknowledgements

Disclosure: The authors declare no conflict of interest.

References

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