Ten-Year Single-Center Experience With a Japanese Frozen Elephant Trunk Graft (FROZENIX) for Treating Thoracic Aortic Disease in 435 Patients

Abstract

Background: This study reports on a single center’s experience over 10 years with the frozen elephant trunk (FET) technique and a Japanese prosthesis. FET outcomes were compared among groups according to aortic etiology, acute aortic dissection (AAD), chronic aortic dissection (CAD), and thoracic aortic aneurysm (TAA).

Methods and Results: Between September 2014 and December 2023, 435 patients underwent total arch replacement using the FET technique for AAD, CAD, and TAA. The overall in-hospital mortality rate was 5.1% (13 patients with AAD, 3 with CAD, and 6 with TAA). Perioperative neurological deficits occurred in 5.8% of patients overall (13 patients with AAD, 2 with CAD, and 10 with TAA), and spinal cord injury occurred in 1.1% of patients overall (1 with AAD, 0 with CAD, and 4 with TAA). The respective overall 5- and 7-year survival rates were 88.8% and 83.8% for AAD, 69.2% and 67.4% for TAA, and 83.6% and 83.6% for CAD. The respective 5- and 7-year rates of freedom from distal thoracic aortic reintervention were 78.8% and 71.7% among AAD patients, and 93.7% and 93.7% among TAA patients, and 73.2% at 5 years among CAD patients.

Conclusions: The FET technique using a Japanese prosthesis for thoracic aortic disease has acceptable perioperative and long-term outcomes. Close follow-up is required after FET implantation, especially after repair of AAD and CAD.

The surgical management of extensive aortic arch pathologies is challenging. Operative outcomes have improved with recent developments in surgical techniques and management. However, in patients with aortic dissection, the reoperation rate 10 years after the first operation is around 10–20%.¹ Moreover, a persistently patent false lumen in the dissected aorta substantially reduces long-term survival and increases the risk of distal aortic events, such as enlargement of the distal aorta and rupture.^2,3 For patients with extensive thoracic aortic aneurysms (TAAs), the distal anastomosis is often located in a deep position when accessed via median sternotomy, complicating the procedure. Many surgical strategies have been developed to address this issue, including single-stage aortic arch replacement, which requires a wide skin incision.^4,5 A 2-stage approach is also commonly used, which begins with the elephant trunk technique, followed by replacement of the descending aorta or thoracic endovascular aneurysm repair (TEVAR) as the second stage.⁶

The introduction of the frozen elephant trunk (FET) technique by Kato et al.⁷ marked a significant innovation. The FET technique facilitates closure of the primary entry tear at the descending thoracic aorta, promoting false lumen thrombosis and remodeling downstream of the descending aorta.^8,9 This strategy has become an alternative for managing extensive aortic diseases, offering the advantage of addressing complex aortic lesions in a single operation via a median sternotomy.^10–12

In 2014, a Japanese commercial FET prosthesis (J Graft FROZENIX; Japan Lifeline, Tokyo, Japan) was introduced. More recently, in 2022, a hybrid FET prosthesis (J Graft FROZENIX 4branched; Japan Lifeline), combining FROZENIX with a tetrafurcated tube graft (J Graft; Japan Lifeline), was developed to enhance surgical flexibility and outcomes. The aim of this study was to evaluate the early and long-term outcomes of total arch replacement (TAR) using the FET technique with a FROZENIX prosthesis for aortic arch pathology and to demonstrate the efficacy of this procedure.

Methods

Patients and Study Design

This study was conducted in accordance with the Declaration of Helsinki. The study protocol was approved by the Ethics Committee of Saitama Medical University International Medical Center (IRB no. 2024-082). Between September 2014 and December 2023, 441 consecutive patients underwent TAR at the Department of Cardiovascular Surgery, Saitama Medical University International Medical Center using the FET technique with this type of FET. After excluding 6 patients who underwent TAR with FET for pseudoaneurysm or graft infection, data from 435 patients were analyzed.

The strategy for thoracic aortic arch pathology is as follows. Open surgery was the first choice rather than TEVAR for a TAA extending from the aortic arch to the descending aorta. FET is the first-line treatment in open surgery if a 1-stage TAR with FET can cover the aneurysm and the distal landing zone above Th8 in the thoracic spine. Staged surgery with a conventional elephant trunk or FET was performed as the first stage, followed by either replacement of the descending aorta or secondary TEVAR if the distal landing of the FET was below Th8. In addition, a 1-stage extension operation was performed if the descending aorta at the distal end of the FET was a shaggy aorta or a ruptured aneurysm.

For acute aortic dissection (AAD), TAR with FET was performed in patients who had and entry tear located distal to the aortic arch, were young (age <75 years), or had supra-arch vessel dissection. Descending or thoracoabdominal aortic replacement via a left thoracotomy was the first choice for chronic aortic dissection (CAD). FET was only selected for patients with concomitant procedures in the proximal arch or undergoing heart surgery or for patients who could not tolerate left thoracotomy because of chronic obstructive pulmonary disease (COPD), prior left lung surgery, or older age (>75 years). Computed tomography (CT) to identify the artery of Adamkiewicz was only performed in patients with CAD.

Surgical Techniques

The indications and surgical techniques for the FET procedures have been described previously.^9,11 The primary features of the standard approach used in the present study are summarized below.

Central cannulation was primarily in the ascending aorta or right axillary artery, with cannulation on one side of the femoral artery for retrograde flushing of debris after deployment of the FET. Patients were cooled to moderate hypothermia with a target temperature of 26℃ after cardiopulmonary bypass was established. The aorta was opened under circulatory arrest, and 3 supra-aortic vessels were cannulated from their ostia inside the aortic arch with balloon-tipped cannulas for antegrade selective cerebral perfusion with a target flow rate set to 12 mL/kg/min. The FET device was inserted blindly into the descending aorta and deployed. A distal stump was created, and a 4-branched graft was anastomosed to the distal stump. After distal anastomosis, antegrade systemic perfusion through the side branch of the arch graft was resumed, and the proximal aorta and 3 cerebral vessels were sequentially reconstructed. Cerebrospinal fluid drainage was not routinely performed before surgery. FET devices were not deployed in patients with preoperatively diagnosed Marfan syndrome, who underwent conventional TAR instead.

Stent length was determined using preoperative CT, which was used to calculate the distance between the distal anastomosis and the target of the distal end of the stent. The target level at the end of the stent graft was the straight part of the descending aorta, below the curvature of the aortic arch, and above the Th8 level.

Stent graft size was planned using preoperative multiplanar reconstruction CT. In the case of an AAD, the selected stent graft was >10% smaller than the total aortic diameter of the target distal end of the FET in the dissected descending aorta. In patients with preoperative shock, as well as in those without CT data, the FET graft size was determined intraoperatively using transesophageal echocardiography. For patients with TAA, the FET prosthesis diameter was selected as 110–120% of the diameter of the descending aorta. In CAD, the size of the stent graft was almost the same when measuring the area of the true lumen at the target distal landing zone.

Definitions

Mortality is reported as 30-day mortality, and hospital death was defined as death before hospital discharge. Late mortality was defined as all-cause mortality, and the time of origin was defined as the time of surgery. Aortic-related death was defined as procedure-related mortality and included hospital death after primary and secondary procedures, death due to rupture or aortic infection, and death due to an unknown cause. Distal thoracic aortic reintervention was defined as reintervention of the downstream aorta, including the descending, thoracoabdominal, and abdominal aorta. Intended staged TEVAR for TAA, defined as an FET procedure following TEVAR that was planned before FET, was excluded from the aortic reintervention procedures.

Endpoints and Follow-up

The primary endpoints were hospital mortality, late mortality, and freedom from distal thoracic aortic reintervention. Data were recorded prospectively, and patients were followed up in the outpatient unit of Saitama Medical University International Medical Center. Contrast-enhanced CT was performed before discharge, with plain CT performed annually thereafter. If the subsequent annual CT showed aortic enlargement, contrast-enhanced CT was performed to determine the reason for the aortic enlargement. In cases where the patient underwent follow-up at another hospital, telephone interviews or emails were exchanged. The mean (±SD) duration of follow-up was 46.6±32.8 months.

Statistical Analyses

Continuous data are expressed as the mean±SD or as the median with interquartile range (IQR) and were compared among the 3 groups (AAD, CAD, and TAA) using 1-way analysis of variance. Categorical data are presented as frequencies and were compared among groups using the χ² test. Cox proportional hazards regression analysis was used to estimate hazard ratios (HRs) for risk factors for late mortality and aortic reintervention. Survival and aortic reintervention-free rates were estimated using Kaplan-Meier curves and were compared among groups using the log-rank test. All data were analyzed using JMP 17.0.0 (SAS Institute Inc., Cary, NC, USA). Statistical significance was set at P<0.05.

Results

Baseline Characteristics

The characteristics of patients in the 3 groups are presented in Table 1. The main indications for surgery were AAD in 237 (54.5%) patients (type A in 231, type B in 6), CAD in 44 (10.1%) patients, and TAA in 154 (35.2%) patients. Compared with patients with AAD and CAD, patients with TAA had high-risk preoperative characteristics, were older, and had higher rates of comorbidities, such as coronary artery disease, diabetes, cerebrovascular disease, and COPD. Cerebrovascular disease was defined as a history of stroke, intracerebral or subarachnoid hemorrhage, or transient ischemic attack. Of the patients with AAD, 21 (8.9%) experienced cerebral malperfusion, including 4 cases of coma and 1 case of preoperative paraplegia.

Table 1.

Patient Characteristics

	Overall (n=435)	AAD (n=237)	CAD (n=44)	TAA (n=154)	P value
Age (years)	66.5±10.3	61.4±11.6	66.0±12.4	74.4±7.1	<0.0001
Male sex	325 (74.7)	157 (66.2)	36 (81.8)	132 (85.7)	<0.0001
Marfan syndrome	2 (0.5)	1 (0.4)	1 (2.3)	0 (0)	0.218
Coronary disease	51 (11.7)	12 (5.1)	8 (18.2)	31 (20.1)	<0.0001
Diabetes	49 (11.4)	13 (5.6)	2 (4.6)	34 (22.1)	<0.0001
Hypertension	328 (76.3)	179 (77.2)	38 (86.4)	111 (72.1)	0.114
Hyperlipidemia	137 (31.9)	60 (25.9)	15 (34.1)	62 (40.3)	0.012
COPD	36 (8.4)	4 (1.7)	5 (11.4)	27 (17.5)	<0.0001
CKD (serum creatinine ≥1.5 mg/dL)	69 (15.7)	33 (14.1)	7 (15.9)	28 (18.2)	0.562
CKD requiring HD	14 (3.2)	5 (2.1)	2 (4.6)	7 (4.6)	0.357
Cerebrovascular disease	50 (11.5)	20 (8.4)	3 (6.8)	27 (17.5)	0.016
Reoperation	27 (6.2)	8 (3.4)	13 (30.0)	6 (3.9)	<0.0001

Unless indicated otherwise, data are given as the mean±SD or n (%). AAD, acute aortic dissection; CAD, chronic aortic dissection; CKD, chronic kidney disease; COPD, chronic obstructive pulmonary disease; HD, hemodialysis; TAA, thoracic aortic aneurysm.

Operative details are summarized in Table 2. The FET prostheses used for AAD were smaller and shorter than those used for CAD or TAA (size 27.0±2.7, 29.2±4.1, and 32.2±2.8 mm, respectively [P<0.0001]; length 80.5±19.1, 93.8±18.4, and 100.7±18.3 mm, respectively [P<0.0001]). The distal end of the FET graft was placed below the level of the Th9 in 1 (0.4%) patient with AAD, 1 (2.3%) with CAD, and 6 (3.9%) with TAA (P=0.044). Thirty-nine (25.3%) patients with TAA underwent simultaneous coronary artery bypass grafting with TAR using the FET technique owing to concomitant coronary artery disease, and 7 (15.9%) patients with CAD underwent aortic root replacement. Although the operation and cardiopulmonary bypass times were longer in the AAD group, there was no significant difference in circulatory arrest time for distal anastomosis among the 3 groups. In the TAA group, intended staged TEVAR was performed in 15 (9.7%) patients, and the mean duration between FET and TEVAR was 49 days.

Table 2.

Surgical Details

	AAD (n=237)	CAD (n=44)	TAA (n=154)	P value
FET size
23 mm	19 (8.0)	2 (4.5)	0
25 mm	76 (32.1)	10 (22.7)	0
27 mm	82 (34.6)	8 (18.2)	6 (3.9)
29 mm	32 (13.5)	3 (6.8)	29 (18.8)
31 mm	15 (6.3)	8 (18.2)	46 (20.0)
33 mm	8 (3.4)	7 (15.9)	34 (22.1)
35 mm	3 (1.3)	0	23 (14.9)
37 mm	1 (0.4)	1 (2.3)	11 (7.1)
39 mm	1 (0.4)	2 (4.5)	5 (3.3)
Mean±SD (mm)	27.0±2.7	29.2±4.1	32.2±2.8	<0.0001
FET length
60 mm	97 (40.9)	5 (11.4)	9 (5.8)
90 mm	118 (49.8)	24 (54.5)	83 (53.9)
120 mm	22 (9.3)	10 (22.7)	60 (39.0)
150 mm	0	0	2 (1.3)
Mean±SD (mm)	80.5±19.1	93.8±18.4	100.7±18.3	<0.0001
Distal end of FET
Th4	1 (0.4)	0	0
Th5	23 (9.7)	2 (4.5)	7 (4.5)
Th6	89 (37.6)	12 (27.3)	45 (29.2)
Th7	94 (39.7)	12 (27.3)	74 (48.1)
Th8	20 (8.4)	6 (13.6)	18 (11.7)
Th9	1 (0.4)	1 (2.3)	6 (3.9)	0.044
Distal anastomosis of 4-branched graft				<0.0001
Zone 0	26 (11.0)	1 (2.3)	19 (12.3)
Zone 1	5 (2.1)	1 (2.3)	11 (7.1)
Zone 2	109 (46.0)	37 (84.1)	108 (70.1)
Zone 3	97 (40.9)	5 (11.4)	16 (10.4)
Operation time (min)	444±145	428±138	390±98	0.0004
Cardiopulmonary bypass time (min)	223±73	199±58	195±45	<0.0001
Circulatory arrest time (min)	57±21	52±14	56±14	0.427
Concomitant procedures	56 (23.6)	16 (36.4)	47 (30.5)	0.120
CABG	19 (8.0)	7 (15.9)	39 (25.3)	<0.0001
Aortic valve replacement	4 (1.7)	2 (4.6)	5 (3.3)	0.437
Aortic root replacement	17 (7.2)	7 (15.9)	1 (0.7)	<0.0001

Unless indicated otherwise, data are given as the mean±SD or n (%). CABG, coronary artery bypass grafting; FET, frozen elephant trunk. Other abbreviations as in Table 1.

Early Outcomes

The surgical outcomes are presented in Table 3. The overall 30-day mortality rates in the AAD, CAD, and TAA groups were 2.5%, 6.8%, and 2.0%, respectively (P=0.301), with corresponding overall in-hospital mortality rates of 5.5%, 6.8%, and 3.9%, respectively (P=0.666). The causes of death included multiple organ failure (6 patients), stroke (5 patients), pulmonary disease (3 patients), sepsis (2 patients), myocardial infarction (2 patients), intestinal necrosis (2 patients), acute kidney failure (1 patient), and low-output syndrome (1 patient). Neurological dysfunction developed in 13 (5.5%) patients in the AAD group, 2 (4.6%) in the CAD group, and 10 (6.5%) in the TAA group (P=0.857). Spinal cord injury (SCI) developed in 1 (0.4%) patient in the AAD group and in 4 (2.6%) patients in the TAA group (P=0.110). Patients with AAD had longer intubation time, ICU stay, and hospital stay than those with CAD or TAA.

Table 3.

Surgical Outcomes

	Overall (n=435)	AAD (n=237)	CAD (n=44)	TAA (n=154)	P value
30-day death	12 (2.7)	6 (2.5)	3 (6.8)	3 (2.0)	0.301
In-hospital death	22 (5.1)	13 (5.5)	3 (6.8)	6 (3.9)	0.666
Neurologic dysfunction	25 (5.8)	13 (5.5)	2 (4.6)	10 (6.5)	0.857
PND	13 (3.0)	8 (3.4)	1 (2.3)	4 (2.6)	0.819
TND	11 (2.5)	4 (1.7)	1 (2.3)	6 (3.9)	0.342
SCI	5 (1.1)	1 (0.4)	0 (0)	4 (2.6)	0.110
Paraplegia	2 (0.5)	0 (0)	0 (0)	2 (1.3)
Paraparesis	3 (0.7)	1 (0.4)	0 (0)	2 (1.3)
Renal failure on HD	21 (4.8)	15 (6.3)	1 (2.3)	5 (3.3)	0.260
Re-exploration for bleeding	17 (3.9)	10 (4.2)	1 (2.3)	6 (3.9)	0.808
Prolonged intubation (≥72 h)	138 (31.7)	102 (43.0)	6 (13.6)	30 (19.5)	<0.0001
ICU stay (days)	9.8±12.6	11.5±15.5	6.4±5.0	8.1±7.9	0.0072
Hospital stay (days)	29.5±33.7	35.4±43.0	20.4±9.1	22.4±13.0	0.0003

Unless indicated otherwise, data are given as the mean±SD or n (%). ICU, intensive care unit; PND, permanent neurologic deficit; SCI, spinal cord injury; TND, temporary neurologic deficit. Other abbreviations as in Table 1.

Late Outcomes

Figure 1 shows the overall long-term survival assessed using the Kaplan-Meier method. Long-term survival was worse in the TAA group than in the AAD and CAD groups (P=0.0003). The survival rates at 3, 5, and 7 years postoperatively were 91.7%, 88.0%, and 84.3%, respectively, in the AAD group; 90.7%, 83.6%, and 83.6%, respectively, in the CAD group; and 79.7%, 69.2%, and 67.4%, respectively, in the TAA group. Multivariate analysis demonstrated that the risk factors for mortality after surgery were age (HR 1.04; P=0.006), CAD (HR 2.85; P=0.0006), chronic kidney disease (serum creatinine ≥1.5 mg/dL; HR 2.99; P<0.0001), and COPD (HR, 2.18; P=0.020). No aortic pathology was a risk factor for postoperative mortality (Table 4).

Figure 1.

Survival curves after the frozen elephant trunk technique for patients with acute aortic dissection (AAD), chronic aortic dissection (CAD), and thoracic aortic aneurysm (TAA).

Table 4.

Cox Proportional Hazards Regression Analysis for Mortality After Surgery

	Univariable		Multivariable
	HR (95% CI)	P value	HR (95% CI)	P value
Age	1.05 (1.03–1.08)	<0.0001	1.04 (1.01–1.07)	0.006
Male sex	2.33 (1.16–4.69)	0.009	1.89 (0.89–4.01)	0.100
AAD	0.41 (0.25–0.68)	0.0004	1.26 (0.52–3.09)	0.602
CAD	0.95 (0.42–2.02)	0.844
TAA	2.54 (1.58–4.11)	0.0001	1,23 (0.53–3.09)	0.628
Coronary artery disease	4.05 (2.33–7.02)	<0.0001	2.85 (1.57–5.19)	0.0006
COPD	3.73 (2.06–6.78)	0.0001	2.18 (1.13–4.20)	0.020
CKD (serum creatinine ≥1.5 mg/dL)	3.15 (1.91–5.20)	<0.0001	2.99 (1.13–4.20)	<0.0001
Smoker	0.87 (0.54–1.40)	0.562
Hyperlipidemia	0.75 (0.44–1.27)	0.271
Previous sternotomy	1.15 (0.64–3.41)	0.388
Cerebrovascular disease	2.14 (1.17–3.92)	0.022	1.46 (0.77–2.74)	0.244

CI, confidence interval; HR, hazard ratio. Other abbreviations as in Table 1.

Rates of freedom from aortic-related death did not differ significantly among the 3 groups (P=0.852). The rates freedom from aortic-related death were 94.3% in the AAD group, 93.2% in the CAD group, and 95.0%, 91.5%, and 91.5% at 3, 5, and 7 years postoperatively, respectively, in the TAA group (Figure 2). The causes of aortic-related death were graft infection in 3 patients, rupture of the descending aorta in 1 patient, and rupture of the abdominal aorta in 1 patient. Figure 3 shows that the rates of freedom from distal thoracic aortic reintervention were 86.1%, 84.8%, and 82.6% at 3, 5, and 7 years, respectively, in the AAD group; 81.3% and 73.2% at 3 and 5 years, respectively, in the CAD group; and 95.5%, 93.7%, and 93.7% at 3, 5, and 7 years, respectively, in the TAA group (P=0.014). Freedom from distal thoracic aortic reintervention rates were worse in the CAD and AAD groups than in the TAA group (CAD vs. TAA, P=0.0015; AAD vs. TAA, P=0.038; and AAD vs. CAD, P=0.13). In the AAD group, 28 (12.0%) patients underwent distal aortic reintervention.

Figure 2.

Kaplan-Meier curves showing freedom from aortic-related death curves after the frozen elephant trunk technique for patients with acute aortic dissection (AAD), chronic aortic dissection (CAD), and thoracic aortic aneurysm (TAA).

Figure 3.

Kaplan-Meier curves showing freedom from distal thoracic aortic reintervention after the frozen elephant trunk technique for patients with acute aortic dissection (AAD), chronic aortic dissection (CAD), and thoracic aortic aneurysm (TAA).

Additional operations were performed for distal stent graft-induced new entry (dSINE; which involves the formation of a new intimal tear at or just beyond the distal end of the stent graft) in 12 (5.2%) patients with acute dissection and in 5 (8.9%) patients with chronic dissection. In the AAD group, the duration from the initial surgery to the additional operation for dSINE was <1 year in 6 patients, 1–3 years in 3 patients, 3–5 years in 2 patients, and >5 years in 1 patient. In the CAD group, the duration from initial surgery to the additional operation for dSINE was <1 year in 0 patients, 1–3 years in 2 patients, 3–5 years in 2 patients, and >5 years in 1 patient.

Another reason for enlargement of the false lumen was retrograde flow into the re-entry. In the AAD and CAD groups, 14 (6.1%) and 2 (3.6%) patients, respectively, underwent additional operations after the FET procedure. In the AAD group, only 3 patients required open surgery. In the TAA group, 9 (6.3%) patients underwent distal aortic reintervention (open surgery in 1 patient, TEVAR in 8 patients). In the CAD group, 11 (19.3%) patients underwent distal aortic reintervention (open surgery in 5 patients, TEVAR in 6 patients).

Aortic diameter at the downstream aorta is presented in Table 5. In the AAD group, the aortic diameter at the distal arch level was smaller 1 year after the operation. However, there was no significant difference between the preoperative diameter and the diameter 1 year after the operation in the CAD group.

Table 5.

Size of the Aorta at the Level of the Distal Arch and the Celiac Artery at Before and 1 Year After Surgery

	Distal arch (mm)			Celiac artery (mm)
	Before surgery	1 year after surgery	P value	Before surgery	1 year after surgery	P value
AAD	34.0±3.1	29.7±2.3	<0.0001	28.0±0.4	29.4±0.4	0.010
CAD	50.6±6.5	48.7±10.4	0.449	32.6±5.6	34.1±6.2	0.399

Unless indicated otherwise, data are given as the mean±SD. AAD, acute aortic dissection; CAD, chronic aortic dissection.

Discussion

The first study on the FROZENIX FET device was published in 2016.¹³ That multicenter prospective comparative study demonstrated the effect of the FROZENIX device on the early outcomes of TAR. A subsequent multicenter prospective comparative study, published in 2022, further investigated the efficacy of the FROZENIX device compared with conventional repair techniques, demonstrating acceptable early outcomes.¹⁴ Notably, to the best of our knowledge, the present study is the first to report long-term outcomes with this device over a period of 10 years, highlighting its acceptable durability and effectiveness. Although this study reports a single-center experience, it includes the largest patient cohort to date.

The stent of the FROZENIX device has a Dacron polyester fabric vascular prosthesis integrated with nitinol wire, a superelastic shape memory alloy. The stent is fixed inside the graft, which may reduce the risk of intimal damage compared with other FET devices that have externally fixed stents. The delivery system features a soft sheath wrapped with a polyester-based mesh, providing a flexible and smooth surface, unlike the hard sheath used in conventional self-made devices. Furthermore, the open stent graft used in the FROZENIX device demonstrates better trackability in the curved aortic arch than devices using the Z stent graft. The FROZENIX device is expected to become useful for open-style stent graft placement in cases of AAD. In addition, the design of the prosthesis allows the FET graft to serve as a proximal graft during secondary descending or thoracoabdominal aortic repair.

Comparative studies of aortic pathology following FET have shown that although endovascular treatment of type B aortic dissection provides good mid-term protection against aortic-related death,^15,16 there is also a high rate of aortic reintervention.¹⁷ False lumen thrombosis and aortic remodeling occur more frequently in AAD than in CAD, leading to an increased rate of aortic reintervention in the chronic phase. Another contributing factor is dSINE, which occurs more frequently in the chronic than acute phase, necessitating a higher reintervention rate in CAD.¹⁸ In the present study, freedom from distal thoracic aortic reintervention after FET were lower in the CAD group, but the difference was not statistically significant.

Risks associated with FET include SCI, dSINE, and graft kinking. In the present study, spinal cord ischemia occurred in 6 patients: 1 with AAD, 1 with CAD, and 4 with TAA. In 1 patient with acute dissection, the stent graft was not deeply inserted (ending at Th7), yet complete false lumen thrombosis resulted in spinal cord infarction owing to occlusion of an intercostal artery originating from the false lumen. Four patients treated with FET for true aneurysms had spinal cord injury 3 with distal landings at or below Th8 had spinal cord infarctions, all of whom had shaggy aortas with poor vascularity at the landing site. The mechanism of spinal cord injury may differ between AAD and thoracic aneurysms. Another risk factor for SCI after FET is long coverage of the descending aorta.¹⁹ In previous studies, the reported rate of SCI is 3–20%.^15,20–22 In the present study, the rate of SCI was lower incidence than that reported previously. The Hannover group¹⁵ used 150-mm grafts more frequently, including in cases of aortic dissections, and the Bologna group²¹ used 100-mm grafts and reported a lower rate of paraplegia (4.3%). The rates of SCI in the present study were lower than in those studies, possibly because shorter FET grafts were used. Even in patients with TAA, grafts shorter than 90 mm were used in 84 patients. To mitigate the risk of SCI in patients with thoracic aneurysms, a 2-stage treatment strategy was adopted: TAR followed by TEVAR when the distal landing zone extended beyond Th8. In the case of a shaggy descending aorta, conventional TAR through a median sternotomy with distal anastomosis at the distal side of the aneurysm was performed without using the FET technique. In addition, maintaining a low mean blood pressure (<70 mmHg) is a significant independent risk factor for spinal cord ischemia.²³ To address this, precise hemostasis and stable perioperative hemodynamics following FET surgery were prioritized.

After surgery for aortic dissection, many patients are at risk of progressive dilatation of the dissected descending or thoracic abdominal aorta. Some studies have reported that the rate of reoperation of the distal aorta is 16–24% within 10 years.^24,25 This progressive dilatation is often attributed to dSINE or retrograde flow into the re-entry sites. dSINE is a recognized complication of the FET procedure, with the reported incidence varying according to study and patient population, typically ranging from 4% to 30%^26,27 and most commonly between 10% and 20%.²⁸ Factors influencing dSINE include graft oversizing, aortic pathology, and stent design. In our experience, 5.2% of patients with AAD and 8.9% of patients with CAD underwent additional operations for dSINE. Similarly, reoperations for false lumen enlargement due to retrograde flow into re-entry sites occurred in 6.1% of AAD patients and 3.6% of CAD patients. Specifically, only 2 patients underwent open thoracic surgery, 16 underwent TEVAR for dSINE, 3 underwent open thoracic surgery, and 13 underwent TEVAR for false lumen dilatation caused by re-entry flow.

The FET procedure offers the advantage of establishing a stable landing zone for future TEVAR interventions, facilitating treatment if the downstream aortic aneurysm enlarges. TEVAR can be performed without significant concerns regarding retrograde type A dissection or type Ia endoleaks,²⁹ further enhancing the effectiveness and safety of the FET approach. Consequently, the risk of reoperation is reduced, highlighting the role of FET as a robust strategy for addressing complex aortic pathologies.

The FET approach may be considered a first-line treatment for AAD. For TAA, shaggy aortas should be avoided, and patients with short treatment lengths can be treated safely. Chronic dissection often requires reintervention of the aorta and, because aortic remodeling is not expected, exclusion of the aneurysm by descending or thoracoabdominal replacement with left open thoracotomy seems to be the preferred option for radical treatment.

This study has some limitations. First, it was a retrospective study lacking a control group. In addition, up until 2022, FROZENIX was the only FET graft approved for use in Japan, and a few patients in whom other FET devices were deployed were excluded from this study.

Conclusions

The FET technique using a Japanese prosthesis addresses thoracic aortic disease with acceptable perioperative and long-term outcomes. However, close follow-up is needed after FET implantation, especially after the repair of acute and chronic dissection. Future research could focus on refining the FET technique and developing strategies to further reduce complications such as dSINE and spinal cord ischemia.

Acknowledgments

The authors thank Mayuka Okada and Katsuya Ohori for collecting the data and Editage (www.editage.jp) for English language editing a draft of this paper.

Sources of Funding

This study did not receive any specific funding.

Disclosures

The authors declare that there are no conflicts of interest.

IRB Information

The study protocol was approved by the Ethics Committee of Saitama Medical University International Medical Center (IRB no. 2024-082).

Data Availability

The deidentified participant data will not be shared.

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