Imagine you are traveling in a subway, and when the train pulls into the station it misses its mark a little so that your car, at the end, ends up stuck in the tunnel. As the doors open, and passengers from other cars flow onto the platform, your door opens into the tunnel. Unfortunately it looks like you will be missing this stop!
Since this blog generally covers medical devices, and not subway malfunctions, you can guess this is a metaphor. Let's take a moment to introduce the medical device side of our analogy: endovascular aortic repair (EVAR) devices. When physicians are deciding how to treat abdominal aortic aneurysms (AAAs), one of the options at their disposal is a stent graft that is delivered to the aorta through the blood vessels and expanded to fit over the aneurysm and reinforce the vessel walls. This is a great option for about half of AAA patients. The majority of remaining patients have anatomical considerations that won?t allow for endovascular placement of these grafts.
One of the main drawbacks of these endovascular devices is that, since they are not sewn in place like traditional grafts, they are prone to shifting position. This can be a big problem if the graft shifts to block the renal arteries. Let's return to our subway analogy. If blood is traveling down the aorta, some of the blood flow will exit the aorta into the renal arteries. However, if a graft has shifted to cover the renal arteries, then the blood will be funnelled through the graft right past the renal arteries, much as you were taken right past your subway stop. Unfortunately, the consequences for blood not reaching the kidneys are much greater than missing a subway stop.
There are currently grafts available with fenestrations that fit into the renal artery, and prevent shifting of the graft. There are, however, a couple major obstacles to using these devices. First of all, because each person's vessel anatomy is slightly different, these grafts need to be custom made. It can take 6 weeks for the device to arrive, which is too long for many patients to wait. Some dedicated doctors have even been known to take a weekend to craft their own fenestrated grafts in urgent circumstances. Secondly, as with any custom product, the price for these devices is high and can be tens of thousands of dollars. Consequently, these custom fenestrated grafts are not used often.
If fenestrated grafts were available ?off-the-shelf? this would serve to instantly expand the proportion of patients that could be treated with EVAR. As it happens, several medical device companies are working on this problem, and at least one device is close to receiving approval. The first product in line for CE mark approval is Endologix's Ventana fenestrated graft; it is expected to receive device approval early this year. Cook Medical also has a fenestrated graft in clinical trials. These devices will allow immediate access to grafts for patients with juxtarenal abdominal aneurysms.
Off-the-shelf fenestrated grafts are expected to arrive this year in Europe and will usher in a new generation of EVAR devices.
For more information on off-the-shelf fenestrated grafts, check out these two articles.