Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical energy applicator
Reexamination Certificate
2002-04-17
2004-11-02
Schaetzle, Kennedy (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical energy applicator
C607S127000, C600S375000
Reexamination Certificate
active
06813521
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Cross-reference is hereby made to commonly assigned related U.S. Applications, filed concurrently herewith, Ser. No. 10/124,802, entitled “INSULATING MEMBER FOR A MEDICAL ELECTRICAL LEAD AND METHOD FOR ASSEMBLY”; 10/124,185, entitled “DRIVE SHAFT SEAL FOR A MEDICAL ELECTRICAL LEAD”; 10/124,530, entitled “IMPLANTABLE MEDICAL LEAD HAVING A RETRACTION STOP MECHANISM”; and 10/124,160, entitled “APPARATUS FOR TRANSFERRING TRACTION FORCES EXERTED ON AN IMPLANTABLE MEDICAL LEAD”.
FIELD OF THE INVENTION
The present invention relates to a medical electrical lead, and, more specifically, relates to an implantable medical lead system that is readily manufactured with improved reliability.
BACKGROUND OF THE INVENTION
A wide assortment of automatic, implantable medical devices (IMDs) are presently known and in commercial use. Such devices include cardiac pacemakers, cardiac defibrillators, cardioverters, neurostimulators, and other devices for delivering electrical signals to a portion of the body and/or receiving signals from the body. Pacemakers, for example, are designed to operate so as to deliver appropriately timed electrical stimulation signals when needed, in order to cause the myocardium to contract or beat, and to sense naturally occurring conduction signals in the patient's heart.
Devices such as pacemakers, whether implantable or temporary external type devices, are part of a system for interacting with the patient. In addition to the pacemaker device, which typically has some form of pulse generator, a pacing system comprises one or more leads for delivering generated stimulation pulses to the heart and for sensing cardiac signals and delivering sensed signals from the heart back to the pacemaker. As is known, pacemakers can operate in either a unipolar or bipolar mode, and can pace the atria or the ventricles. Unipolar pacing requires a lead having only one distal electrode for positioning in the heart, and utilizes the case, or housing of the implanted device as the other electrode for the pacing and sensing operations. For bipolar pacing and sensing, the lead typically has two electrodes, a tip electrode disposed at the distal end of the lead, and a ring electrode spaced somewhat back from the distal end. Each electrode is electrically coupled to a conductive cable or coil, which carries the stimulating current or sensed cardiac signals between the electrodes and the implanted device via a connector.
Combination devices are available for treating cardiac arrhythmias that are capable of delivering electrical shock therapy for cardioverting or defibrillating the heart in addition to cardiac pacing. Such a device, commonly known as an implantable cardioverter defibrillator or “ICD”, uses coil electrodes for delivering high-voltage shock therapies. An implantable cardiac lead used in combination with an ICD may be a quadrapolar lead equipped with a tip electrode, a ring electrode, and two coil electrodes. A quadrapolar lead normally requires four conductors extending the length of the lead body in order to provide electrical connection to each electrode, potentially resulting in a substantial increase in lead body diameter.
Other leads used with ICDs may be tripolar or bipolar. A tripolar lead that is also known as a “dedicated bipolar” lead is configured with a tip electrode, a ring electrode and a coil electrode. The tip and ring electrodes serve as a bipolar sensing pair. The coil electrode serves as the defibrillation electrode, and the tip electrode serves as the pacing electrode. An “integrated bipolar” lead, also used with ICDs, is configured with a tip electrode and a coil electrode but no ring electrode. The tip and coil electrodes serve as a bipolar pair for sensing and each serve individually as unipolar pacing and defibrillation electrodes, respectively. Each of these types of leads has different advantages related to the size of the lead, the location of the electrodes after implantation, and the characteristics of the sensed cardiac signals.
In order to work reliably, cardiac leads need to be located at a targeted cardiac tissue site in a stable manner. One common mechanism for securing an electrode position is the use of a rotatable fixation helix. The helix exits the distal end of the lead and can be screwed into the body tissue. The helix itself may serve as an electrode or it may serve exclusively as an anchoring mechanism to locate an electrode mounted on the lead adjacent to a targeted tissue site. The fixation helix may be coupled to a drive shaft that is further connected to a coiled conductor that extends through the lead body as generally described in U.S. Pat. No. 4,106,512 to Bisping et al. A physician may rotate the coiled conductor at its proximal end to cause rotation of the fixation helix via the drive shaft. As the helix is rotated in one direction, it is secured in the cardiac tissue. Rotation in the opposite direction removes the helix from the tissue to allow for repositioning of the lead at another location.
One problem that can arise with the use of a fixation helix is over-retraction of the helix during lead repositioning. Repositioning of the lead may be required during an implant procedure if poor electrical contact is made with the targeted cardiac tissue, resulting in higher than desired stimulation thresholds or poor sensing. The physician must retract the helix by applying turns to the coiled conductor in the appropriate direction. The physician may not have tactile feedback or fluoroscopic image indicating when the helix has dislodged from the heart tissue and is fully retracted. In many cases, the physician will perform additional turns of the coiled conductor in order to ensure the helix is safely removed from the heart tissue before applying tension to the lead to relocate it. Excessive turns, however, can cause deformation of the fixation helix rendering it unusable. In such cases, the lead must then be removed and replaced by a new lead.
To address the problem of over-retraction, a retraction stop mechanism may be provided within the distal lead head. An exemplary retraction stop mechanism that includes a fixed stop formed of a plurality of fixed cam and axial stop surfaces and a movable stop formed of a like plurality of rotatable cam and axial stop surfaces is disclosed in U.S. Pat. No. 5,837,006 to Ocel et al.
When using a lead having an open tip to allow for advancement and retraction of a fixation helix, it is desirable to prevent the ingress of body fluids into the lead body. Blood or other body fluids entering the lead body can create a pathway for infection, a serious complication with implantable devices. Furthermore, the entrance of blood into the lumen of a lead body can interfere with the insertion of a stylet, used for lead positioning during implantation, and with the final connection of the lead to an implantable medical device.
Methods for sealing the distal end of the lead body while still allowing a coiled conductor and drive shaft to rotate for advancing or retracting a fixation helix are known. One method is to provide a sealing membrane within the lumen of the distal lead tip. Reference is made to U.S. Pat. No. 4,311,153 issued to Smits. When the helix is advanced, the pointed tip of the fixation helix punctures the sealing membrane, which then provides a seal around the fixation helix. When used during implantation, multiple turns of the coil may be required in order to build up enough torque to overcome the friction encountered when rotating the helix through the membrane. The helix may not advance by the same amount with each turn applied to the coil. Therefore, the extension or retraction of the helix may be somewhat unpredictable. The punctured membrane may not always form a fluid-tight seal around the fixation helix. Another method for sealing the lumen of a medical lead involves positioning a sealing ring such that it encircles the drive shaft connected to the fixation helix. This type of seal may be maintained in a desired location by retainers mounted pro
Bischoff Thomas C.
Helmick Marc R.
Huepenbecker George M.
Parsons Kathryn R.
Shoberg Bret R.
Medtronic Inc.
Schaetzle Kennedy
Soldner Michael C.
Wolde-Michael Girma
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