FROZENIX FACTS

Technique and pitfalls of frozen
elephant trunk insertion:
Prevention of spinal cord injury
Department of Cardiovascular Surgery, Tenri Hospital

Kazuo Yamanaka, M.D., Ph.D.

The simplicity of the frozen elephant trunk (FET) procedure

which spinal cord injury associates with FET intervention is

has led to its increased popularity as a treatment for complex

not fully understood. Previous studies have cited stent graft

thoracic aortic pathologies. However, FET has been

length, thromboembolism, and spinal cord ischemia timeassociated with procedure-related risks, particularly spinal

during total circulatory arrest as responsible factors. In Japan,cord injury and a non-negligible postoperative paraplegia/FROZENIX first received commercial approval in February

paraparesis rate. Although this devastating complication has

2014 and was implanted in 2,216 patients between July 2014

been attributed to various mechanisms, of which spinal cord

and December 2015. Among these patients, spinal cord injury

ischemia and occlusion of the thoracic intercostal arteriesoccurred in 43 (1.9%), including paraparesis in 13 (0.6%) andappear to be the most important, the exact mechanism byparaplegia in 30 patients (1.3%). This incidence, which wasmuch lower than the 6.7% reported in the premarket trial, may
be attributable to the avoidance of implantation below T8 andFig. 1 Postoperative spinal cord injury (SCI) according toearlier distal perfusion after delivery of the stent graft. At ourthe position of the distal stent graft.

center, no spinal cord injuries were observed in more than
70 consecutive patients treated with FET according to ourtechnique, which is described in this report.
Key Point 1
The distal end of the stent graft should be positioned above
the Th8 level!!
The Adamkiewicz artery, which supplies blood to the spinalcord, generally exists below the Th8 level; therefore, werecommend that the distal end of the stent graft should bepositioned at a more proximal level (Fig. 1). For cases ofaortic dissection, we recommend selecting a stent graftwith a length of 6 or 9 cm after measuring the length froma benchmark near the Th7 level; this will allow stent graft
implantation in the straight area of the aorta, thus reducing
stress on the intima as much as possible. For this process,A distal stent graft position below Th9 was identified as a

the aortic valve, which is located near the Th7 level, is ansignificant independent risk factor for SCI. The Adamkiewicz
artery, which supplies blood to the spinal cord, is generally

appropriate benchmark (Fig. 2). After this measurement, thedistal end of the stent graft should be positioned using a three-located below the Th8 level. Therefore, the distal end of the stentgraft should be positioned at a more proximal level.

step transesophageal echocardiography (TEE) method.

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FROZENIX FACTSFig. 2 Determination of the aortic valve level via computed tomography.

The aortic valve level, located near the Th7 level, is an appropriate benchmark.

Step 1: Decisions regarding stent graft position and size (Fig. 3)

THREE-STEP METHOD FOR POSITIONING THE

The size and position of the stent graft are determined using

DISTAL END OF A STENT GRAFT

preoperative computed tomography scan data. The distance*The distal end of the stent graft is located by measuring thebetween the aortic valve and the intended distal end position

distance from the aortic valve level.

of the stent graft is also measured at this time.

Fig. 3 Step 1: Decisions regarding stent graft position and size

The stent graft size and position are determined via preoperative computed tomography. The distance
between the aortic valve and the scheduled distal end position of the stent graft are also measured at this time.

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FROZENIX FACTS

Step 2: Marking the TEE probe at the aortic valve level (Fig. 4)

Step3: TEE guidance of stent graft placement (Fig. 5)

After visualizing the aortic valve at the center of the ME AV

Upon its introduction into the aorta, FROZENIX is detected

SAX view using TEE, the probe is rotated a half-turn (DAoby TEE as a strongly echogenic line accompanied by an

SAX view of TEE) such that the descending aorta at the aortic

acoustic shadow in which the stent graft is packed. Ifvalve level is visible at the center. The TEE probe is marked

FROZENIX is directed to the aortic wall or intimal flap,

on the lips because we are unable to confirm the locationwhere it might cause damage, reshaping and reinsertion areof the descending aorta at the aortic valve level during

attempted. Initially, TEE is located at the aortic valve level

circulatory arrest.

(marking in mouth corner), with FROZENIX visible at theFig. 4 Step 2: Marking the TEE probe at the aortic valve level

After visualizing the aortic valve at the center in the ME AV SAX view of TEE, the probe is rotated a half-turn (DAoSAX view of TEE) such that the descending aorta at the aortic valve level is visible at the center. The TEE probein the corner of the mouth is marked at this position because we are unable to confirm the descending aorta at
the aortic valve level during a circulatory arrest.
Fig. 5 Step 3: TEE guidance of stent graft placement

TEE is initially used to locate the aortic valve level (marking in mouth corner), with FROZENIX visualized at thecenter. The distance from the aortic valve is defined as the difference in TEE probe depths between these twolevels. FROZENIX is deployed at the planned distance from the aortic valve level under TEE guidance.

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center (Fig. 6). The distance from the aortic valve is defined asInflation via a Foley balloon catheter is generally avoided tothe difference in TEE probe depths between these two levels.

prevent intimal injury; in addition, despite the initially small

FROZENIX is subsequently deployed at the planned distancediameter of FROZENIX, dilation occurs gradually after distalfrom the aortic valve level under TEE guidance (Fig. 7).

perfusion.

Fig. 6 TEE image obtained while positioning the distal end of FROZENIX

Upon introduction into the aorta, FROZENIX is depicted on TEE as a strongly echogenic line accompanied byan acoustic shadow, with the stent graft packed inside.

Fig. 7 TEE view during deployment

FROZENIX was deployed at the planned distance from the aortic valve level under TEE guidance.

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FROZENIX FACTS

After the stent graft is inserted and deployed, the prosthesis isKey Point 2

sutured to the proximal end of the descending thoracic aorta.

Selective left subclavian artery (LSA) perfusion and distal

Anastomosis should be performed to ensure a high level ofbody circulatory arrest within 60 min

accuracy, as the arch can be difficult to reach once it has been
replaced. For this procedure, we use a 3-0 Prolene suture

Leontyev et al. reported a body core temperature of ≥28 °C

and a strong needle, although the suture line could also be

to be an independent predictor of paraplegia for patients inreinforced with Teflon felt. Distal perfusion (500 ml/min) is

whom distal body arrest exceeds 40 min. In accordance withthen initiated via the femoral artery, with an occlusion balloon

these findings, we recommend moderate hypothermia during

catheter placed into the stent graft. Our experience has led

FET procedures, especially if a prolonged lower body arrest

us to define a distal body circulatory arrest time with LCA

time is expected or if additional risk factors are present.

perfusion of <60 min as acceptable. Therefore, we recommend

A prolonged lower body arrest time may increase the risk

additional distal perfusion if the distal body circulatory arrestof spinal cord injury, especially under conditions of mild

exceeds 60 min.

hypothermia. Accordingly, additional antegrade perfusion ofthe LSA is crucial for increasing the blood supply to the spinal

Key Point 3cord. We describe two types of antegrade LSA perfusion:

Mean blood pressure should be maintained at ≥70mmHg.

Type 1: Retrograde cerebral perfusion is performed when thebladder temperature falls to 25 °C before a circulatory arrest.

To ensure adequate spinal cord perfusion pressure, stable

After the aortic arch is opened, balloon catheters are inserted

hemodynamics, with a mean arterial pressure of ≥70 mmHg,

into the brachiocephalic artery, left common carotid artery,should be sought after stent graft deployment together withand left subclavian artery. After retrograde cerebral perfusiona central venous pressure (CVP) of <10 mmHg, if possible.

is stopped, selective antegrade perfusion is initiated at a rate

Although an increased mean arterial pressure may renderof 800 ml/min and FET is deployed (Fig. 8).

hemostasis more difficult, hemostasis should not be achieved

Type 2: After perfusion (200 ml/min) via an 8-mm graftby reducing the blood pressure. Therefore, diligent surgicalanastomosed to LSA, the proximal LSA is ligated and FET istechniques and adequate administration of coagulation

implanted to the proximal LSA. This procedure may reduce

products are important.

the risk of recurrent laryngeal nerve damage (Fig. 9).

Fig. 8 Type 1 left subclavian artery perfusion

Fig. 9 Type 2 left subclavian artery (LSA) perfusion

After opening the aortic arch, balloon catheters are inserted into
the brachiocephalic artery, left common carotid artery, and leftsubclavian artery. Selective antegrade cerebral perfusion is theninitiated at a rate of 800 ml/min.

After perfusion via an 8-mm graft anastomosed to the LSA, theproximal LSA is ligated and the FET is implanted into the aorta
proximal to the LSA in an attempt to reduce the risk of recurrent
laryngeal nerve damage.

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REFERENCES
1)Kato M, Ohnishi K, Kaneko M, Ueda T, Kishi D, Mizushima T et al. New graftimplanting method for thoracic aortic aneurysm or dissection with a stented
graft. Circulation 1996; 94(Suppl):II188-93.
2)Katayama K, Uchida N, Katayama A, Takahashi S, Takasaki T, Kurosaki T,Imai K, Sueda T. Multiple factors predict the risk of spinal cord injury after thefrozen elephant trunk technique for extended thoracic aortic disease. Eur J
Cardiothorac Surg. 2015;47:616-20.
3)Uchida N, Katayama A, Higashiue S, Shiono M, Hata M, Minami K, Yamanaka
K, Miyamoto S, Sawa Y, Kuratani T, Kato M. A new device as an open stentgraft for extended aortic repair: a multicentre early experience in Japan. Eur J
Cardiothorac Surg. 2016;49:1270-8.
4)Ma W-G, Zheng J, Sun L-Z, Elefteriades JA. Open stented grafts for frozen
elephant trunk technique: Technical aspects and current outcomes. AORTA(Stamford). 2015;3:122-35.
5)Orihashi K, Matsuura U, Sueda T, Watari M, Okada K, Sugawara Y, Ishii O.
Echocardiography-assisted surgery in transaortic endovascular stent grafting:Role of transesophageal echocardiography. J Thorac Cardiovasc Surg. 2000;
120(4):672-8.

Higashishinagawa, Shinagawa-ku, Tokyo 140-0002 Japan
http://www.japanlifeline.com
2021-07-00-01