The present invention relates to medical devices in general, and in particular to catheter ablation systems for revascularizing occluded vein grafts.
One of the most commonly used techniques for treating partially or totally occluded cardiac vessels is cardiac bypass surgery. With this procedure, a surgeon obtains a vessel from another portion of the patient""s body and grafts the new vessel to healthy sites in the cardiac vessels in order to direct blood flow around a blockage. One of the most common vessels used in bypass surgery is a portion of the saphenous vein, which is a large superficial vein found in the leg. Such grafts are often referred to as saphenous vein grafts or SVGs.
One of the problems with SVGs is that they also tend to become occluded within three to five years of being grafted onto the heart muscle. For some physiological reason which is not completely understood, the material that occludes such grafts tends to be more loosely organized and brittle than the material that occludes native cardiac arteries. As a consequence, treating occluded SVGs can be more difficult because the occluding material tends to break off and can flow downstream wherein it may cause the onset of a heart attack.
One method of treating vein graft lesions is set forth in U.S. Pat. No. 5,681,336 to Clement et al. and assigned to the assignee of the present invention. The ""336 patent, which is herein incorporated by reference, discloses a system of ablating vein graft lesions including proximal and distal balloons that isolate the treatment area. In addition, the system provides for the aspiration of ablated material and/or infusion of liquids to maintain vascular pressure. In the ""336 patent, the ablation burrs are designed to abrade a lesion in the vein wherein the abraded material can be aspirated through a catheter that extends into the treatment area.
While it is believed that the system described in the ""336 patent works well, additional benefits may be obtained using ablation burrs that are optimized for particle aspiration and removal of the type of blocking material found in saphenous vein grafts.
To improve the treatment of occluded saphenous vein grafts, the present invention comprises a system for aiding in the aspiration of ablated material from a vessel. The system includes a guide wire which is advanced into a treatment area and an ablation mechanism that is routed over the guide wire. The ablation mechanism includes an ablation burr that is rotated by a driveshaft, and a hollow sheath that extends over the driveshaft. The position of the guide wire and ablation mechanism are controlled by an advancer that moves these elements within a patient""s vasculature. Rotation of the driveshaft is controlled by a prime mover, typically an electric motor or air turbine. The guide wire, driveshaft and sheath extend through a Y connector. One port of the Y connector is connected to a vacuum source that draws ablated material into a collection jar. The other port of the Y connector is coupled to the advancer.
According to one aspect of the present invention, an ablation burr is designed to propel ablated material proximally into an aspiration lumen. The ablation burr includes one or more channels on the surface of the burr that direct ablated material and fluid in the vessel to the aspiration lumen as the burr is rotated. In another embodiment of the invention, the one or more channels on the burr direct fluid and ablated material and fluid in the vessel proximally and radially outward to provide a scouring action of the interior vascular wall.
In accordance with another aspect of the invention, an ablation burr has a proximal and distal section with the distal section having a point of maximum diameter where the proximal and distal sections meet. The diameter of the distal section tapers down to a distal tip of the burr such that the distal section is ovoidal in shape. The distal section includes one or more channels that direct ablated material and fluid towards an aspiration lumen and/or toward the interior vascular wall. The proximal section comprises a cylindrical tube of a smaller diameter than the maximum diameter of the burr. The cylindrical tube may include one or more spiral channels that direct ablated material toward an aspiration lumen. In accordance with another aspect of the invention, the distal section has a diameter that decreases linearly from the point of maximum diameter to the distal tip such that the distal section of the burr has a conical configuration.
In accordance with another aspect of the present invention, an ablation burr has a diameter that tapers between the point of maximum diameter and the point where the distal section of the burr joins the proximal section. This tapered section includes a number of channels that direct fluids and ablated material towards the interior vascular wall to provide a scouring action in the vessel.
In accordance with another aspect of the present invention, the atherectomy burr fits within a protective shroud. The atherectomy burr has a relatively flat distal face that is covered with an abrasive material. The burr has one or more tapered blades that extend proximally from the distal face that move the ablated material and liquid proximally as the burr rotates.
In accordance with another aspect of the invention, the ablation burr comprises an auger-type bit that cuts occluding material from the vessel and moves it proximally to an aspiration lumen.
In accordance with another aspect of the present invention, the ablation burr is designed as a hub of cutting blades that fit within a canister. The blades are joined at the center of the burr and extend radially outward from a central axis to the inner wall of the canister. A central lumen extends through the point at which the blades are joined so the burr can be passed over a guide wire. Each of the blades includes a tab that fits into a corresponding slot on the canister to secure the blades in the canister.
In accordance with yet another aspect of the present invention, the ablation burr has a xe2x80x9cdumbbellxe2x80x9d shape having proximal and distal radially expanded portions. Each of the expanded portions moves liquid and abraded material radially outward as the burr is rotated. An aperture positioned between the distal and proximal radially expanded portions is in an area of low pressure so that the aperture acts as an aspiration port to aspirate material through a driveshaft that rotates the burr.
In accordance with yet another aspect of the present invention, the ablation burr has a bell shape with a large central lumen that is expanded at the distal end. A distal rim of the burr is covered with an abrasive material. The central lumen of the burr allows abraded material to be gathered and directed proximally to an aspiration sheath that is positioned near the proximal end of the burr and in fluid communication with the central lumen.
In accordance with yet another aspect of the present invention, the ablation burr includes a series of radial holes that extend into a center lumen of the burr. A vacuum is applied to the center lumen such that occluding material in the vessels is drawn into one or more holes and is sheared off the vessel wall by rotation of the burr. The ablated material may flow through the holes and into the center lumen of the burr where it is aspirated out a center of a driveshaft or may be drawn over the burr into another aspiration lumen.
In accordance with another aspect of the invention, the plurality of holes are coupled to one or more fittings that mate with corresponding lumens in a catheter sheath. The additional lumens are used to aspirate ablated material drawn into the holes and to provide vacuum pressure.
In accordance with yet another aspect of the present invention, an ablation device comprises an outer shell having an abrasive leading surface and a core that fits within the outer shell. Liquid and material disposed between the core and the inner surface of the shell are propelled proximally by the rotation of the core and shell.
In accordance with yet another aspect of the present invention, the ablation burr is maintained at a fixed distance from the distal end of a sheath by a coupler having a threaded end that mates with threads on the distal end of the sheath. The ablation burr is secured to the coupler via a post having a proximal cap with a diameter that is larger than the diameter of a hole at the distal end of the coupler.
The post also includes a distal shaft to which the ablation burr is secured. In accordance with yet another aspect of the invention, an ablation burr includes one or more holes that eject fluid that pumped through a sealed driveshaft radially outward to scour the internal vessel walls in which the burr is being used.
In accordance with yet another aspect of the present invention, a driveshaft that rotates an ablation burr includes a conically shaped section at its distal end. Fluid entering the space between the conically shaped section of the driveshaft and a surrounding sheath is pushed radially outward and proximally by the rotation of the driveshaft thereby aiding in the aspiration of ablated material and liquid from a vessel.
In accordance with yet another aspect of the invention, an expandable sleeve fits within the sheath surrounding the driveshaft. During an ablation procedure, the sheath is extended from the distal end of the sheath and expands to seal the proximal portion of the treatment site and to aid in the aspiration of material from the vessel.
In accordance with yet another aspect of the invention, a method is disclosed for isolating a treatment area by routing a catheter having an inflatable balloon through a native coronary artery to the point where a bypass vessel is attached to the native artery. The balloon is inflated to seal the bypass artery so that ablation can take place without ablated material being pumped downstream.
Finally, the present invention is a method for treating occluded native arteries by routing a catheter having an inflatable balloon through a bypass vessel and into the native artery in order to seal a treatment area such that the original blockage in the native artery can be ablated.