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.