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Page 6 of 8 Yamanaka et al. Vessel Plus 2020;4:39 I http://dx.doi.org/10.20517/2574-1209.2020.46

Frozenix was introduced in 2014, and up to November 2016 the accumulated clinical experience has exceed
4,000 cases. Frozenix, which consists of double-layered oval- shaped nitinol stents, maintains its shape
[3]
when flexed, thus preventing undue force on the curved aortic wall . A soft polyester sheath delivery
system composes of a slippery material to prevent damage to the descending aorta wall during insertion.
Frozenix is deployed by withdrawing the sheath after the device is correctly positioned by TEE guidance.
Accordingly, these features of Frozenix enable safe and reliable device insertion. There was no FET failure
nor stent fracture of FET in this study. We have had no graft failure of Frozenix (JGOS) in the pilot study
[3]
since 2008 from 2010 . However, we have the experience of late endoleak (type Ib) in the pilot study,
which needed re-intervention by thoracic endovascular aortic repair. The selection of appropriate size of
[7]
FET (diameter and length) is very important to prevent type Ib endoleak .
The FET technique should be considered suitable for patients with extensive thoracic or thoracoabdominal
aortic disease if a second class IIa procedure (open repair or thoracic endovascular aortic repair) is
anticipated in downstream aortic segments, according to a European position statement . This way, the
[8]
operative indications of the FET for non-dissecting aortic aneurysms are still limited because TAR is gold
standard for the aortic arch aneurysm and the FET has the risk of SCI. The exact mechanism of SCI in
the FET is unknown. Thromboembolism, long stent graft, and circulatory arrest time are supposed as
[9]
factors of SCI . Presumably, the most important risk factor is the distal FET position below the level of
T8. We recommend using TEE, fluoroscope, or other modalities to deploy the FET more precisely [10,11] .
[6]
We always use TEE for the FET technique. Our three-step method by TEE guidance is easy and safe . In
our institutions, there was no permanent SCI in 113 patients with the FET (48 acute aortic dissections,
19 chronic aortic dissections, and 46 non-dissecting thoracic aneurysms. Although I trust CSF drainage,
we don’t preoperatively place CSF drain in elective cases because SCI rate was low in our institutions and
there is 5%-7% complication related CSF drainage. In the patient with paraparesis, we performed CSF
drainage postoperatively, kept more than 80 mmHg mean system pressure and administered Naloxone
and steroid. Thereafter, paraparesis disappeared and the patient discharged by foot. The maintenance of
high systemic pressure in postoperative period is another important point to prevent SCI. Our target mean
systemic pressure is more than 80 mmHg. Therefore, complete hemostasis is essential. In J-ORCHESTRA
[12]
study (Japanese multicenter study) , the rate of SCI in the FET group was 1.6%. Although the rate is still
relatively higher, Japanese surgeons mostly overcame SCI due to the FET.

Another problem is distal embolism. No patient in this study had a distal embolism. Although one of 8
patients with shaggy aorta had small cerebral infarction despite isolation technique, other patients had
no cerebral infarction and no distal embolism. It is speculated that insertion of the FET under circulatory
arrest never induce disturbed flow or dissipation of plaque and cover the shaggy aortic wall. According
to severity or location of shaggy aorta, the use of the FET may prevent distal embolism although the use
of the FET in severe shaggy aorta is presumably high risk for embolism. Some surgeons have used distal
perfusion from the femoral artery after FET deployment and fixation to remove debris/air and protect
distal function and Some surgeons have used thoracic perfusion with balloon-tipped Foley catheter into the
end of FET to reduce visceral ischemia time. Although we also tried distal perfusion by these techniques
in initial some cases, we gave up distal perfusion because it is difficult to keep bloodless field, and it makes
operative procedure more complicated and time-consuming.

As stated above, the complication of the FET technique has been declining in Japan and we suppose
the indication of FET can extend some high-risk patients of non-dissecting thoracic aortic aneurysms
as the following patients: (1) those with distal aortic arch aneurysms that cannot be treated by thoracic
endovascular aortic repair involving the left subclavian artery to the ascending aorta; (2) those in whom a
median approach extending to the upper middle descending aorta for distal anastomosis with pulmonary
complication is difficult; (3) those requiring redo operation; and (4) and those with an advanced age or
frailty who prefer to avoid left thoracotomy.