Corresponding Author:
Dr. A. Mohammed Idhrees MBBS, MS MCh, FAIS
Cardiovascular Surgeon
Institute for Cardiac and Aortic Disorders
SRM Institutes for Medical Science (SIMS Hospitals)
Chennai, India – 600 026
Phone: +919962268787
E-Mail:a.m.idhrees@gmail.com
Key Words: Aortic dissection, Frozen Elephant Trunk, Size of
hybrid prosthesis, Spinal cord ischemia, paraplegia
No. of words: 1124 (including references, abstract, title page)
No. of reference: 8
Conflict of Interest: Nil
Ethic committee clearance: N/A
The management of Acute Type A aortic Dissection (ATAAD) has evolved
over the years. Resection of the primary tear in the ascending aorta
with/without addressing the aortic root has remained the gold standard.
The major concerns of these patients during follow-up are the expanding
distal false lumen which can cause compression of the true lumen or
rupture. Frozen elephant trunk (FET) has been suggested to attenuate the
negative phenomena of distal false lumen. Experts from Europe have
recommended FET for clinically stable ATAAD patients (1). Spinal cord
deficit (SCD; postoperative paraplegia or paraparesis) has been
considered the ‘Achilles heel’ of FET. A recent metanalysis showed that
the pooled prevalence of paraplegia was 3.5 %(2). Wang et al (3)
reported an incidence of SCD of 4.4% in 158 ATAAD patients. They have
implanted longer (150mm) Cronus hybrid prosthesis (HP) in patients who
are taller than 160cm and they found there was no statistical difference
between the long and short (100mm) HP in regards to SCD. Further the
longer HP helps in positive remodelling of the distal thoracic aorta
In the recent times there are several papers in literature favouring FET
in multiple aortic pathologies, but there are no general consensuses in
regards to the size (diameter and length) of the stent graft to be used.
A short HP may not be adequate enough to cover the entry tear in the
descending thoracic aorta (DTA), while a longer HP may invoke a risk of
paraplegia. So the aortic team have to balance between the risk of
reintervention (endoleak or partial thrombus) with shorter HP, and risk
of paraplegia with longer HP (4). Most of the centers/surgeons opt for
the former stratergy.
No authors have studied the application of the longer versus shorter HP
in regards to height of the patient. The average height of the Asian
male (166-174cm) is approximately 7 to 8 cm shorter than the European
population (179-182cm) (5). Wang et al (3) have used 150mm Cronus HP in
45 patients with height great than 160cm tall and reported SCD in 1
patient (2.2%). Theoretically, this is equivalent to using 150mm HP in
average European men who are 180cm tall. In similar context, earlier in
2017 (6), a team from India has presented their experience with FET. The
authors performed antegrade Thoracic endovascular aortic repair
(TEVAR ) in the DTA and anastomosed a four branch graft to the
zone 2/3. The authors reported zero incidence of SCD in their cohort.
Figure 3 of the article (6), shows the extend of the endograft – a few
inches from the origin of coeliac artery.
It is very intriguing to know the difference between the European and
Asian population. So when someone is asked, “Does the anatomy of
spinal circulation differ in Asian population as compared to
Europeans?” The answer is ‘May be yes’. The incidence of SCD in an
average Asian (166-174cm) with longer HP is almost equal to an average
European (179-182cm) with a shorter HP. A larger study to understand the
difference in spinal circulation between different Ethnic is needed.
It is very intriguing to ask, “Is the length of HP the sole
culprit of SCD? Or it is one of the culprit”. In our experience,
length of the HP is just one of the culprits of SCD. The overall results
depends on several other factors which includes
(i) Lower body protection during circulatory arrest: Adequate cooling of
the patient and maintain a short circulatory arrest period. If need
intermittent perfusion of lower body with a Foley’s catheter
(ii) Continuous perfusion of left subclavian artery: Continuous
perfusion through the left subclavian artery would encourage collateral
circulation to the spinal cord during the circulatory arrest period
(7,8)
(iii) Minimal Handling of the atherosclerotic plaques on the aorta
(iv) Through deairing of the descending thoracic aorta, prior to
restarting lower body circulation.
A decade ago, when FET was evolving, surgeons used long HP at zone 3,
resulting in a high incidence of SCD. Over the years the surgical
techniques of FET have tremendously evolved, graft deployment takes
place in zone 2 and surgeons prefer shorter HP. This resulted in a
reduction of SCD in the recent reports. With evolved techniques in FET
and zone 2 implantation, is longer HP still an apprehension among
surgeons? The answer is probably ‘May not be’. Zone 3 to Zone 2
proximalization has helped us gain 2-3cm, and a deployment of 150mm HP,
is effective 2cm more than 100mm HP implanted in zone3. A randomized
trial is definitely necessary to ascertain the fact.
Longer HP helps in better positive remodelling of DTA, but the
apprehension of SCD still looms around us. A randomised trail to study
the incidence of paraplegia in regards to height of the patient and
length of HP is needed.