Surgery – Instruments – Internal pressure applicator
Reexamination Certificate
2001-11-07
2004-04-27
Truong, Kevin T. (Department: 3731)
Surgery
Instruments
Internal pressure applicator
Reexamination Certificate
active
06726701
ABSTRACT:
The invention relates to an embolic protection device.
INTRODUCTION
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, haemorrhagic and embolic. This invention addresses embolic stroke.
Medical literature describes caroitid artery disease as a significant source of embolic material. Typically, an atherosclerotic plaque builds up in the carotid 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 block bloodflow to specific areas of the brain and cause neurological impairment. Treatment of the disease 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 6% 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 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 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, No. 5,053,008, No. 5,108,419, WO97/17100 and WO 98/33443. Various deployment and/or collapsing arrangements are provided for the umbrella filter. However, as the filter collapses, the captured embolic material tends to be squeezed outwardly towards an open end of the filter and pieces of embolic material may escape from the filter with potentially catastrophic results. More usually, the filter umbrella is collapsed against the guidewire before removal through a catheter or the like. Again, as the filter membrane is collapsed, it will tend to squeeze out the embolic material. Further, the umbrella filter is generally fixed to the guidewire and any inadvertent movement of the guidewire during an interventional procedure can dislodge the filter.
The insertion of such known filters in the human vasculature which comprises very small diameter blood vessels may result in inappropriate haemodynamics which can exacerbate damage to the flowing blood and may result in haemolysis.
This invention is therefore directed towards providing an embolic protection device which will overcome these major problems.
STATEMENTS OF INVENTION
According to the invention there is provided a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings sized to allow through-passage of blood, but to retain embolic material within the filter body;
the distal outlet portion of the filter body in the region of the outlet openings having means for reducing shear stress on blood passing through the outlet openings.
In a preferred embodiment of the invention the shear stress reducing means includes lead-in radiussed portions of the filter body leading to the outlet holes.
In a particular embodiment of the invention the shear stress reducing means includes lead-out radiussed portions of the filter body leading from the outlet holes.
Most preferably the outlet holes are generally circular.
In another preferred embodiment of the invention the proximal inlet portion of the filter body in the region of the inlet openings has means for reducing shear stress on blood passing through the inlet openings. Preferably the shear stress reducing means includes lead-in radiussed portions of the filter body leading to the inlet holes. Ideally, the shear stress reducing means includes lead-out raduissed portions of the filter body leading from the inlet holes.
In a particularly preferred embodiment the filter is of a polymeric material. Preferably the filter body defines a three dimensional matrix. Most preferably, the filter body is of a resilient elastomeric material. The filter body may be of a polyurethane elastomer. Most preferably the filter body is of a polycarbonate urethane material.
In an especially preferred embodiment of the invention the filter body is covered with a hydrophilic coating, the openings being provided in the coating.
Preferably the filter is of a polymeric material and the raduissed portions are formed by solvent polishing of the polymeric material.
In a preferred embodiment the porosity of the distal portion of the filter body decreases towards the distal end of the filter. Ideally, the overall porosity of the distal portion of the filter element is from 5% to 40%. Preferably the overall porosity of the distal portion of the filter element is form 8% to 21%.
In a preferred embodiment in the transverse cross sectional areas at longitudinally spaced-apart locations of the distal portion are substantially the same.
Preferably the distal portion is of generally conical shape having a radial dimension which decreases towards a distal end of the filter element.
In one embodiment the distal portion includes a blind section adjacent to the distal end of the filter element. Preferably the blind portion extends longitudinally for at least 5% of the length of the distal portion, ideally for less than 30% of the length of the distal portion.
In a preferred arrangement the number of outlet holes increases towards an outer edge of the distal outlet portion of the filter body.
Most preferably there are between 200 and 1000 outlet openings with an average diameter of between 50 and 200 microns. Ideally, there are between 200 and 300 outlet openings with an average diameter of approximately 150 microns. There may be at least 200 outlet openings with an average diameter of no more than 200 microns.
Preferably there are less than 1000 openings with an average diameter of at least 50 microns.
In a particularly preferred embodiment the openings are sized such that shear stress imparted to blood flowing through the filter body at physiological flow rates is less than 800 Pa, most preferably less than about 400 Pa and ideally less than about 200 Pa.
The openings are ideally generally circular openings.
In a preferred embodiment said filter body, when in a deployed configuration includes a generally cylindrical intermediate section between said proximal and distal portions. The filter body is generally tapered when in a deployed configuration. Preferably said distal section of said filter body comprises at least
Brady Eamon
Gilson Paul
Gilvarry Michael
Finnegan Henderson Farabow Garrett & Dunner
Salviac Limited
Truong Kevin T.
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