Surgery – Diagnostic testing – Flexible catheter guide
Reexamination Certificate
2001-05-22
2004-09-21
Marmor, Charles (Department: 3736)
Surgery
Diagnostic testing
Flexible catheter guide
C600S466000, C604S525000
Reexamination Certificate
active
06793634
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to medical devices and more particularly to an improved catheter system having a work element coupled to a drive cable disposed within a lumen of a flexible tubular catheter body.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both the peripheral blood vessels, which feed the limbs of the body, and the coronary vessels, which feed the heart. When deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits are known, including balloon angioplasty, in which a balloon-tipped catheter is used to dilate a region of atheroma; atherectomy, in which a blade or cutting bit is used to sever and remove the atheroma; spark gap reduction, in which an electrical spark burns through the plaque; and laser angioplasty, in which laser energy is used to ablate at least a portion of the atheroma. In order to facilitate treatment of the stenosis, it is often desirable to obtain a visual image of the interior of the blood vessel within the region of interest. Catheters having imaging elements such as ultrasonic transducers are often used to obtain these images.
In many cases, catheter systems having imaging or interventional devices will include a rotatable drive cable disposed within the flexible catheter body. Catheters of this type will have some type of work element fixed to the distal end of the drive cable. In imaging systems, the work element is typically an ultrasonic transducer or a movable mirror associated with an ultrasonic transducer.
An exemplary catheter system having a rotating ultrasonic transducer coupled to a drive cable is disclosed in U.S. Pat. No. 4,794,931, the disclosure of which is incorporated herein by reference. In this system, a drive cable disposed within a flexible tubular catheter body is used to rotate an ultrasonic transducer about an axis parallel to the catheter body. The ultrasonic transducer is thereby caused to scan a region of the blood vessel in a plane normal to the catheter body.
In yet another exemplary catheter system of particular importance to the present invention, a catheter body is provided with a guidewire engagement sheath design, where the catheter is introduced over a separate (moveable) guidewire. A catheter system of this type is disclosed in U.S. Pat. No. 5,203,338, which is fully incorporated herein by reference. In this particular catheter system, the catheter body has a guidewire lumen attached at the distal end of the catheter body. The guidewire lumen and the primary lumen are separated by a wedge, which ensures that the drive cable does not proceed beyond the primary lumen and into the guidewire lumen.
A catheter of the type having a guidewire engagement is used as follows. A guidewire is advanced into the patient until it lies within a region of interest, typically a region of stenosis within the blood vessel. After the guidewire is positioned, the proximal end of the guidewire is fed into the guidewire lumen of the catheter. The catheter is then advanced into the patient over the guidewire. Advancement of the catheter into the patient continues until the primary lumen distal region lies within the blood vessel in the region of interest. A suitable work element, such as a rotatable imaging core, may be delivered while positioned in the primary lumen.
A general concern in the development of each type of catheter system described above, and in catheter system development in general, is the ability to achieve consistency in reliability and performance among catheters employing a particular system. In response to this concern, approaches have been identified which may provide techniques for improving common components of these catheter systems to provide consistent reliability and performance.
One such approach of particular interest to the present invention, includes improvement of the hub assembly. The hub assembly provides, among other things, electrical coupling to the rotating transducer or other work element. Rotation of the transducer element makes it necessary to transmit an electrical signal through a fixed ferrite wire to a transducer lead wire disposed within the rotating drive cable. The signal is transmitted between the fixed and rotating wires through the well-known electrical process of induction. Generally, this process includes using two ferrites separated by a small air gap, where the first ferrite rotates relative to a second fixed ferrite. The first ferrite, when charged, produces an electromagnetic field. The second ferrite, in close proximity to the first ferrite and its electromagnetic field, causes the introduction of inductance into the circuit. The gap is generally necessary to remove the negative effects of friction which occur whenever a rotating body contacts a fixed body. However, as in most rotary transformers, there are losses of power and other inefficiencies inherent in this transmission. For example, it is generally difficult without labor intensive and expensive manufacturing processes, to provide a consistent gap size. Without a consistent gap, the output performance of the transformer can vary between hub assemblies. Moreover, it can be difficult to ensure that the rotating ferrite rotates with enough precision to avoid inadvertently contacting the fixed ferrite.
A number of other approaches for improving catheter systems are directed at the drive cable. The drive cable is coupled via a drive shaft to a drive motor. The drive cable runs substantially the length of the catheter body, and serves as a flexible, torque-transmitting element to rotate the electrical transducer. The drive cable is constructed with coils in order to provide torsional stiffness and flexibility. This enables the drive cable to traverse the tortuous lumen of the human vascular system. A drive cable, which may include transducer lead wires surrounded in a coaxial fashion by a coiled cable body, is disclosed in U.S. Pat. No. 5,503,155, the disclosure of which is incorporated herein by reference.
One potential drawback to the drive cable described above is its susceptibility to stretching. Stretching of the drive cable is typically encountered during removal procedures, during pullback sequences, where the imaging core is retracted within the flexible catheter body to obtain longitudinal imaging sequences, or else during flushing operations. Upon removing the catheter from the intravascular lumen, the user must “pull back” on the proximal end of the catheter body. Generally, movement of the catheter can be restricted when the catheter body encounters friction between the catheter body and the walls of the intravascular lumen. When movement of the catheter body is restricted in this manner, the coils of the drive cable can stretch in a manner similar to coils of a spring. The coils can also be stretched apart when the catheter body is being flushed-out with a flushing fluid. In this case, the flushing fluid creates a piston effect on the coils and work element, thus spreading the coils apart.
While a stretchable drive cable may be advantageous for some purposes, it can also be problematic. Transducer lead wires, disposed and anchored within the drive cable lumen, do not have the ability to stretch and when subjected to tensile forces, the transducer lead wires tend to break which creates a break in the electrical continuity of the system.
Other improvements to catheter systems may include re-directing flushing fluids from exiting through a side port positioned at the distal end of the primary lumen. Generally, the side exit port works well, however, the side exit port can be a nuisance in a clinical setting since it is difficult to know whi
Belef William M.
Jabba Ronald J.
Wasicek Lawrence
White David A.
Marmor Charles
Sci-Med Life Systems, Inc.
Townsend and Townsend / and Crew LLP
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