Spiral Flow peripheral vascular graft for treating peripheral arterial disease

Introduction

Peripheral arterial disease (PAD) is a form of cardiovascular disease caused by a build‑up of fatty deposits in the arterial walls of the leg. These fatty deposits, called atheroma, narrow the arteries in a process known as atherosclerosis. PAD is estimated to affect 1 in 5 people aged over 60 years in the UK and its incidence increases with age, according to NICE's quality standard on peripheral arterial disease. It is more common in people with type‑I and type‑II diabetes, those with high blood pressure or high cholesterol and in those who smoke. PAD is more common in men, with an overall incidence of 8.2% compared with 5.5% in women (Kroger et al. 2006).

Although some people with PAD may have no symptoms, it often causes muscle pain and aching (known as claudication) in the affected leg. PAD can cause severe claudication, making walking painful and reducing quality of life. In approximately 1 in 5 people with PAD, the narrowing of the arteries leads to increasingly severe symptoms with the development of critical limb ischaemia (CLI). Symptoms of CLI include gangrene and ulcers (NHS Choices 2014) and it is the most common cause of leg amputation in the UK (NICE quality standard 52).

PAD is also a risk factor for other cardiovascular events, such as heart attack and ischaemic stroke; people with PAD have a 3–4 fold increased risk of one of these events (NICE quality standard 52).

Peripheral vascular (PV) grafts are used during vascular bypass procedures carried out to restore blood flow to the lower limbs. This is achieved through bypass of the diseased (blocked) portion of the blood vessel with a portion of healthy vessel (first‑line choice) or, if no healthy vessels are available, with an artificial graft.

During bypass surgery, a healthy vein is taken from another part of the leg and joined, or grafted, above and below the blocked artery. This procedure, referred to as an autologous graft, allows the flow of blood to be rerouted to avoid the blockage and maintain an efficient blood supply. A vascular surgeon assesses whether a vein is available and suitable for the procedure. Autologous grafts have a lower failure rate than prosthetic grafts and are used wherever possible. When it is not feasible to use a healthy vein, an artificial graft may be used.

Blood naturally flows through the arteries in a spiral pattern, which has been reported in an in vitro model to increase the pressure and velocity of the blood flow (Paul et al. 2009). Standard artificial PV grafts can interrupt this spiral flow, causing turbulence in the flow of the blood. Over time, this turbulence can lead to neointimal hyperplasia (NIH), an accumulation of vascular smooth muscle cells at the furthest attachment of the graft (the distal anastomosis). NIH causes thickening of the graft walls and restenosis or narrowing of the vessel, which reduces blood flow and can lead to graft failure. Further surgery may be needed to salvage or re‑open the graft using techniques such as endovascular thrombolysis, angioplasty, stent placement or mechanical thrombectomy to restore blood flow. If this is unsuccessful, and if all other revascularisation options have been exhausted, the affected limb may have to be amputated. Artificial grafts that are designed to mimic a more natural blood flow may be less prone to failure than standard prosthetic grafts.