1. Field of the Invention
This invention pertains to catheters for passage through a vasculature system. More particularly, this invention pertains to a novel construction of at least a segment of a catheter.
2. Description of the Prior Art
Catheters are widely used in medical treatment. A catheter is an elongated flexible member advanced through the vasculature system to a desired site. The catheter may be advanced over a previously inserted guide wire. Some catheter designs permit use without a guide wire. In such designs, the catheter flows through the vasculature (referred to as "flow directed" catheters).
With the catheter in place, a wide variety of substances may be passed through the catheter to the site. For example, drugs may be moved through the catheter for site-specific drug delivery. Also, implements may be passed through the catheter. The catheter may also be used to remove fluids from the site. Still further, a catheter may be equipped with implements (e.g., balloon tips) for performing procedures (e.g., angioplasty) at the site.
Catheters have long been used in cardiovascular treatment. More recently, catheters are used in neurological procedures requiring advancement of the catheter through very narrow vessels. To accomplish these advances, a high degree of flexibility is desired. Also, catheters need very thin walls in order to retain an internal bore having as large a diameter as possible.
In neurological applications, catheters preferably have extremely flexible distal tips. While a high degree of flexibility is desired, flexibility should be attained while retaining burst strength and without undue sacrifice of torque transmission response.
In certain applications, the distal tip of a catheter may be shaped for unique purposes. For example, in treating an aneurysm, the distal tip may be shaped to have a radial projection so the tip more easily enters and remains in the aneurysm upon reaching the site. A common practice is to shape the tip through steam application. The steam application softens the polymer material at the tip permitting it to be bent and retain a bent shape following the steam application. Where the distal tip is supported by a traditional coil or braid construction, the tip may not adequately retain the bent shape since the coil or braid is inclined to resume its unbent shape against the resistance of the polymer. For example, in response to body temperature, the tip may relax during use in a procedure.
In prior catheters used for neurological purposes, guide wires are used to position the catheter. Such guide wires include a deformable tip. The physician bends the tip as desired to facilitate accurate advancement of the tip. Guide wire tips can be bent without the aforementioned problems associated with bent-tip catheters since there is no coil or braid which is inclined to return the guide wire tip to its pre-bent shape.
It is also desirable to eliminate the need for guide wires. While some catheter designs may be usable without guide wires, many physicians opt to use guide wires with such catheters. Guide wires add costs, procedure steps and risks. By enhancing catheter designs to operate without the need for guide wires, physicians are more inclined to use catheters in such manner.