SCTIMST Developed Affordable Stent Graft and its Delivery System

THIRUVANANTHAPURAM:
Sree Chitra Thirunal Institute of Medical Science and Technology (SCTIMST) developed affordable Stent Graft and its delivery system for the treatment of Thoracic Aortic Aneurysm.

The stent graft is made up of Polyester fabric seweird in tubular form and are scaffolded by NiTi (Nickel Titanium Alloy) rings (stents), which are sewed in to the tubular fabric. The NiTi rings were made in collaboration with National Aerospace Laboratories, Bangalore (CSIR-NAL). The stent graft is crimped to a lower diameter and is inserted in to the Catheter Sheath (small diameter delivery tube) of the delivery system.

During the EVAR procedure the sheath along with the crimped stent graft are inserted through the femoral artery (in the groin area) and to reach the aneurysm. The catheter sheath is then retrieved using a mechanism provided in the delivery system after deploying the stent graft at the correct position. The stent graft expands and fixes firmly on the inner aortic wall because of the super elastic property exerted by the NiTi rings. Once the stent graft in place, blood flow occurs only through the conduit created by the stent graft .Thus excluding the aneurysm
and preventing its rupture.

The imported stent graft and the delivery system are designed for the anatomy of aorta of Europeans, and has a larger diameter catheter which is difficult to insert and pass through the femoral artery of Indian patients ( Asian Population in general) and often injuries to the blood vessels. In this context SCTIMST developed a new asymmetric design or the NiTi rings (stents), which is crimpable to a lower diameter and can be inserted in to a lower diameter catheter sheath.

This asymmetric design helps the stent graft to affix itself to the inner aortic wall, so that it resists displacement of stent graft during the flow of blood.

Endoleak (Type-1) is a defect which occurs after after the deployment of the stent graft in the aneurysm area.Blood enters through the gap
between the inner aortic wall and the upper end of the graft fabric. To prevent this defect SCTIMST developed a braided endcuff made of NiTi, which when sewed at the proximal end of the tubular graft eradicates the gap between the inner aortic wall and prevents the occurrence of Endoleak (Type-1).

A tip capture mechanism is also provided at the end of delivery catheter, which helps in positioning the stent graft in aorta and releases while deploying the stent graft ,thus aid by accurate positioning of the stent graft during delivery. The delivery system incorporates a new feature for the fast release of the stent graft and accurately deployment of the device during the EVAR procedure. Six patent applications and five design registrations were filed for the above said features.

Thoracic aortic aneurysms (TAAs) have an estimated incidence of at least 5-10 per 100,000 person-years. In India currently Thoracic surgeons uses the imported Stent grafts for the Endovascular Aortic Repair (EAR). Thoracic aortic aneurysm, as there is no indigenous device available in the market. The imported stent graft (along with its delivery system) costs at least 3.5 lakhs. It is this context there SCTIMST decided to develop an indigenous affordable Stent graft and its delivery system for a thoracic aortic aneurysm .

The project team include Dr. Sujesh Sreedharan, Engineer-F, Division of Artificial Internal Organs, Biomedical Technology Wing, Dr. Jayadevan ER, Additional Professor, Imaging Sciences and Interventional Radiology, Dr. Santhosh Kumar K. Additional Professor, Imaging Sciences and Interventional Radiology and Dr. Unnikrishnan M, Professor (Senior Grade, Rtd), Cardiovascular and Thoracic Surgery.

An aortic aneurysm is a ballooning or enlargement of the aorta. Aortic aneurysm is a disease affecting about 5% of the population in their late sixties and can be fatal in case of rupture. Most patients with aortic aneurysms do not have any symptoms at all. The aneurysm is usually discovered by X-ray during a routine health exam for some other, unrelated condition.

When symptoms do occur, pain in the chest or abdomen is most common, depending on the aneurysm’s location. Some people describe a pulsing sensation in the abdomen as a symptom of an abdominal aortic aneurysm. A thoracic aortic aneurysm may cause back pain,shortness of breath or difficulty swallowing.

Smoking, High blood pressure, High Cholesterol, Old age, Hardening of the arteries (atherosclerosis), Diabetes, and Hereditary factors are the major causes of Aortic aneurysm.

An aneurysm can be treated with open surgery or minimally invasive techniques. Endovascular Aortic Repair or EVAR is a minimally invasive technique which involves the insertion of stent grafts in the diseased vessel, by a delivery catheter which enters the central circulatory system through the femoral artery. Stent Graft is a tube consisting of a fabric supported by a reinforcing metallic mesh, which redirects the blood flow through it. The principle of aneurysm treatment in endovascular repair is to produce a sealed conduit for blood to pass through the affected segment of aorta without leaking into (and pressurizing) the aneurysm sac, preventing the aneurysm wall from rupturing.