The term “STROKE” is used to describe a medical event whereby blood supply to the brain or specific areas of the brain is restricted or blocked to the extent that the supply is inadequate to provide the required flow of oxygenated blood to maintain function. The brain will be impaired either temporarily or permanently, with the patient experiencing a loss of function such as sight, speech or control of limbs. There are two distinct types of stroke, hemorrhagic and embolic. Embolic stroke may be caused by embolic material that may become dislodged after stenting.
Medical literature describes artery disease as a significant source of embolic material. Typically, an atherosclerotic plaque builds up in the arteries. The nature of the plaque varies considerably, but in a significant number of cases pieces of the plaque can break away and flow distally and, for example, block blood flow to specific areas of the brain and cause neurological impairment, plaque can also break free and flow into the lungs or heart and cause other adverse events. Treatment of the disease in the carotid artery is classically by way of surgical carotid endarterectomy whereby, the carotid artery is cut and the plaque is physically removed from the vessel. The procedure has broad acceptance with neurological complication rates quoted as being low, somewhere in the order of 5% although claims vary widely on this.
Not all patients are candidates for surgery. A number of reasons may exist such that the patients could not tolerate surgical intervention. In these cases and in an increasing number of candidates that are surgical candidates are being treated using transcatheter techniques. In this case, the evolving approach uses devices inserted in the femoral artery and manipulated to the site of the stenosis. A balloon angioplasty catheter is inflated to open the artery and an intravascular stent is sometimes deployed at the site of the stenosis. The action of these devices as with surgery can dislodge embolic material which will flow with the arterial blood and if large enough, eventually block a blood vessel and cause a stroke.
It is known to permanently implant a filter in human vasculature, such as the vena cava, to catch embolic material. It is also known to use a removable filter for this purpose. Such removable filters typically comprise umbrella type filters comprising a filter membrane supported on a collapsible frame on a guidewire for movement of the filter membrane between a collapsed position against the guidewire and a laterally extending position occluding a vessel. Examples of such filters are shown in U.S. Pat. No. 4,723,549, U.S. Pat. No. 5,053,008, and U.S. Pat. No. 5,108,419. Various deployment and/or collapsing arrangements are provided for the umbrella filter.
Improved filter devices such as those shown in U.S. Pat. No. 6,336,934 and U.S. Pat. No. 6,551,342 and US Patent Application Publication No. 2003/0065354, the entireties of which are hereby incorporated by reference, have been designed to overcome the shortcomings of the previous filters. For example, in one embodiment, the filter is freely disposed along the length to the guidewire, thereby allowing the guidewire to be moved independently of the filter assembly. U.S. Pat. No. 6,336,934 discloses in one embodiment an embolic protection filter having a collapsed state and an expanded state, the filter having a polymeric filter membrane, a support structure supporting the membrane in the expanded state and a tubular element connected to the support structure and having an aperture for disposing the filter over a delivery device, wherein the filter has a proximal inlet opening and a plurality of distal outlet openings, the outlet openings configured to allow fluid to flow through the filter but retain embolic material within the filter and the inlet opening is larger than any of the outlet openings.
After the filter has crossed the stenosed region of the vessel, the filter is deployed within the vessel to capture any emboli that may be dislodged during subsequent medical procedure(s). However, one problem associated with current embolic protection filter devices is that they must cross the stenosed area(s) before they can be deployed. In some instances the stenosed area may have a restricted diameter such that the filter may drag or knock loose some of the plaque during crossing, thereby causing emboli to be released within the lumen. The emboli may cause complications such as stroke or possibly death.
Therefore, there is a need for an improved embolic protection device, wherein the improved device reduces the risk of emboli formation while crossing a stenosed portion of the lumen.