1. Field of the Invention
The present invention relates to catheters, and more directly pertains to a deployable, collapsible and retrievable filter attached to a guidewire which is tubular for filtering of blood in the vascular system during thrombectomy or other interventional vascular procedures.
2. Description of the Prior Art
Arterial disease involves damage that happens to the arteries in the body. Diseased arteries can become plugged with thrombus, plaque, or grumous material that may ultimately lead to a condition known as ischemia. Ischemia refers to a substantial reduction or loss of blood flow to the heart muscle or any other tissue that is being supplied by the artery and can lead to permanent damage of the affected region. While arterial disease is most commonly associated with the formation of hard plaque and coronary artery disease in the heart, similar damage can happen to many other vessels in the body, such as the peripheral vessels and cerebral vessels, due to the buildup of hard plaque or softer thrombus or grumous material within the lumen of an artery or vein.
A variety of vascular medical devices and procedures have been developed to treat diseased vessels. The current standard procedures include bypass surgery (where a new blood vessel is grafted around a narrowed or blocked artery), and several different types of nonsurgical interventional vascular medical procedures, including angioplasty (where a balloon on a catheter is inflated inside a narrowed or blocked portion of an artery in an attempt to push back plaque or thrombotic material), stenting (where a metal mesh tube is expanded against a narrowed or blocked portion of an artery to hold back plaque or thrombotic material), and debulking techniques in the form of atherectomy (where some type of high speed or high power mechanism is used to dislodge hardened plaque) or thrombectomy (where some type of mechanism or infused fluid is used to dislodge grumous thrombotic material). In each of these interventional vascular medical procedures, a very flexible guidewire is routed through the patient's vascular system to a desired treatment location, and then a catheter that includes a device on the distal end appropriate for the given procedure is tracked along the guidewire to the treatment location.
Although interventional vascular procedures avoid many of the complications involved in surgery, there is a possibility of complications if some of the plaque, thrombus or other material breaks free and flows downstream in the artery or other vessel, potentially causing a stroke, a myocardial infarction (heart attack), or other tissue death. One solution to this potential complication is to use some kind of occlusive device or filtering device to block or screen the blood flowing downstream of the treatment location.
The use of a protective device in the form of an occlusive device or filtering device as part of a vascular procedure is becoming more common in debulking procedures performed on heart bypass vessels. Most heart bypass vessels are harvested and transplanted from the saphenous vein located along the inside of the patient's leg. The saphenous vein is a long straight vein that has a capacity more than adequate to support the blood flow needs of the heart. Once transplanted, the saphenous vein is subject to a buildup of plaque or thrombotic materials in the grafted arterial lumen. Unfortunately, the standard interventional vascular treatments for debulking are only moderately successful when employed to treat saphenous vein coronary bypass grafts. The complication rate for a standard balloon angioplasty procedure in a saphenous vein coronary bypass graft is higher than in a native vessel with the complications including embolization, “no reflow” phenomena, and procedurally related myocardial infarction. Atherectomy methods including directional, rotational, and laser devices are also associated with a high degree of embolization resulting in a greater likelihood of infarction. The use of stents for saphenous vein coronary bypass grafts has produced mixed results. Stents provide for less restenosis, but they do not eliminate the risk of embolization and infarction incurred by standard balloon angioplasty.
In order to overcome the shortcomings of these standard nonsurgical interventional treatments in treating saphenous vein coronary bypass graft occlusion, embolic protection methods utilizing a protective device distal to the lesion have been developed. The protective device is typically a filter or a balloon. Use of a protective device in conjunction with an atherectomy or thrombectomy device is intended to prevent emboli from migrating beyond the protective device and to allow the embolic particles to be removed, thereby subsequently reducing the risk of myocardial infarction. When the protective device is a balloon, the balloon is inserted and inflated at a point distal to the treatment site or lesion site. Therapy is then performed at the site and the balloon acts to block all blood flow, which prevents emboli from traveling beyond the balloon. Following treatment, some form of particle removal device must be used to remove the dislodged emboli prior to balloon deflation. U.S. Pat. No. 5,843,022 uses a balloon to occlude the vessel distal to a lesion or blockage site. The occlusion is treated with a high pressure water jet, and the fluid and entrained emboli are subsequently removed via an extraction tube. U.S. Pat. No. 6,135,991 describes the use of a balloon to occlude the vessel allowing blood flow and pressure to prevent the migration of emboli proximally from the treatment device. While effective as a protective device, a balloon may result in damaged tissue due to lack of blood flow downstream of the treatment area due to the time required to inflate and deflate the balloon.
To overcome this disadvantage, most development in relation to occlusive devices has focused on devices that screen the blood through a filter arrangement. An early arterial filtering system utilizing a balloon catheter with a strainer device is described in U.S. Pat. No. 4,873,978. The strainer device is inserted into a vessel downstream of the treatment site. The strainer device responds to actuation of a separately introduced control cable to open and close a plurality of tines capable of retaining dislodged particles. After treatment, the strainer device is collapsed and the entrapped emboli are removed from the body. The additional wire, however, creates additional complexity for the user.
More recently, filter designs have been deployed through the use of a single guidewire in which the filter device is transported to the deployment area within a sheath or catheter. Typical filters have either an umbrella shape to capture emboli or a tube shape in which the proximal end contains larger openings than the distal end so as to allow the blood and debris to enter the filter. The filter thus presents an operational face to the flow of blood within the vessel as provided by the distal end of the tubular filter that is concave in orientation. Particles are captured within the concave face of the filter and are then retracted out of the vessel when the entire device is removed from the body.
One of the challenges regarding filters is the manner in which it is transported to and from the area of interest. U.S. Pat. Nos. 6,042,598, 6,361,546, 6,371,970, 6,371,971 and 6,383,206 describe various examples of filter arrangements that are to be deployed through a sheath, while U.S. Pat. Nos. 6,080,170, 6,171,328, 6,203,561, 6,364,895 and 6,325,815 describe filters that are deployed by a catheter. For example, U.S. Pat. No. 6,371,971 describes a blood filter positioned by way of a single guidewire covered by a sheath for advancement through the channel. The sheath compresses the struts of the filter while in transit. An interventional procedure requires deployment of the sheath along a guidewire downstream of the vascular occlusion. The sheath is retracted and the filter expands to a predetermined size. The filter is retrieved after the procedure by deploying the sheath back down the guidewire, capturing the filter and removing the system from the patient. The disadvantage associated with this type of filter is that re-insertion of the sheath for the collapsing and removal of the filter offers an opportunity to damage the vessel during additional routing and during removal.
Another disadvantage associated with many prior art filters is that dislodged or loosened thrombotic particulate is successfully filtered by the filter, but remains in the filter to clog the filter to the flow of blood through the filter. Additionally, thrombotic particulate which may cling to the filter or which is in loose association with the filter may be lost into the vasculature during retraction of the filter. Thrombotic particulate which is lodged within the filter mesh can hamper suitable collapsing of the filter for removal due to the additional bulk. Ideally, cleansing of the filter by a thrombectomy catheter, such as an Angiojet®, during the procedure would be desirable, but often structure which is incorporated to maintain the opening at the proximal end of the filter could prohibit or interfere with introduction of the thrombectomy catheter therein for the purpose of such cleansing, wherein thrombotic particulate is dislodged from the filter and urged proximally within the thrombectomy catheter as waste product.
There is a need then for a protective device capable of embolization protection for vascular and arterial procedures without the design limitations of the existing approaches. Occlusive balloons can remain in place too long, increasing the risk of vessel damage downstream of the occlusion. Protective filters avoid this problem but suffer from complicated deployment structures and retraction schemes and from introduction of particulate matter into the vasculature due to operational considerations. Moreover, existing filters are limited in range due to the filter support framework, which also may result in vessel damage.
It would be desirable to provide an occlusive filter device on a guidewire which collapses to a reduced and thin profile which facilitates removal of thrombotic particulate matter which is engaged by such a protective occlusive filter. It would also be desirable to provide a protective occlusive filter device as part of a guidewire which is accessibly cleansable and thereby facilitates removal of thrombotic particulate matter which is engaged by such a protective occlusive filter.