News Column

Patent Issued for Screwless Quick System for Connecting a Lead Connector to a Generator of an Implantable Medical Device

June 4, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventors D'Hiver, Philippe (Chatillon, FR); Degieux, Stephane (Sceaux, FR), filed on May 4, 2011, was published online on May 20, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8727817 is assigned to Sorin CRM S.A.S. (Clamart Cedex, FR).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Active implantable medical devices include a housing that is generally designated as 'the generator.' The generator is mechanically and electrically connected to one or more 'leads' that bear on them one or more electrodes that contact those tissues to which it is desirable to deliver electrical pulses, e.g., to apply stimulation pacing pulses, and/or to collect (detect) an electrical signal. These tissues include, for example, myocardial, nerve, and muscle tissue.

"The French standard NF EN 50077 and its international counterpart ISO 5841-3, Implants for Surgery--Cardiac Pacemakers--Part 3: Low-Profile Connectors (IS-1) for Implantable Pacemakers, defines a normalized connection system standard in the industry, which is identified as 'IS-1'. The IS-1 standard ensures interchangeability and compatibility of the leads and generators produced by different manufacturers. In this regard, it should be understood that the present invention is not limited to the particular case of a connection system according to the IS-1 standard, nor even to connection systems applicable to cardiac pacemakers.

"Typically, the connection between a lead connector--hereafter more simply referred to as 'plug'--and a connector of a generator is made by one or more screws that are tightened by the surgeon using an ad hoc tool (e.g., a screwdriver, possibly equipped with a torque limiter) at the time of implantation of the device and/or the lead. This known screw connection system has several drawbacks. First, in addition to requiring a specific tool for its implementation, this system requires the presence of caps provided with sealed slots through which the tool must pass to prevent the terminals from coming into contact with body fluids after implantation. This requirement for sealing the slots through which the tool passes increases the cost and requires a volume or size of the generator at the connector that is large enough to accommodate the tool.

"Second, a screw connection system does not prevent from a screwing oversight, whether from an insufficient screwing or from an overtightening of the screw and damaging the device, by the surgeon.

"Third, a screw connection system also introduces significant risks of damage to the silicone plug by the screwdriver with a consequent loss of insulation, of removal or stripping of the screw thread at the time of its use, of binding thereof, or of damage to the head of the screw in case of incorrect insertion of the screwdriver.

"From an economic standpoint, the use of a screw system generates certain additional costs (e.g., manufacturing of the screw, threading of inserts) and requires providing with the medical device a special tool (e.g., a screwdriver with torque limiter) for tightening the screw. From an industrial standpoint, the use of a screw connector system requires an operation for inserting and adjusting the position of screws in a predetermined position during the packaging of the device, and of addition of a spot of glue to freeze this position of the screw. From a safety standpoint, the operation of screwing the screw by the physician to secure the plug requires special attention, with an implementation time large enough to make sure that the plug is maintained in the housing, precisely and durably.

"Despite these acknowledged drawbacks, the screw connection system is still almost universally used. Indeed, the connectivity standards related to implantable medical devices require (i) minimum retention forces sufficient to prevent accidental disconnection at the time of implantation or during the product lifetime, and (ii) a high-quality and enduring electrical contact (i.e., a very low contact resistance) between the connector plug of the lead and the electrical terminal of the implantable device. These two mechanical and electrical requirements are particularly well satisfied by a conventional screw connection system, despite its many disadvantages.

"Various other systems for securing the plug into the housing of the connector head have been proposed to overcome the many difficulties and drawbacks outlined above.

"Thus, EP 0890371 A1 and its counterpart U.S. Pat. No. 6,112,120, both assigned to Sorin CRM S.A.S., previously known as ELA Medical, describe separating the electrical contact and mechanical retention functions. The electrical contact is ensured by a spring system exerting a radial pressure against the conductive surface of the plug. The mechanical retention of the plug in the housing is secured by a locking wedge inserted between the body of the plug and the housing wall at the outlet thereof.

"Another solution is proposed by EP 0900577 A1 (assigned to Sorin CRM S.A.S., previously known as ELA Medical), which implements a locking system with a retractable spring-loaded eccentric, locally applied against the plug and bearing against it response to an attempted extraction.

"These solutions are functionally effective, but they involve relatively complex, and therefore expensive to produce, mechanical systems (e.g., including elements such as a spring, eccentric, and slide). They also require a specific release mechanism for the removal of the plug, typically requiring the use of a special tool for removing the holding or retraction force provided by the eccentric. Finally, they require special precautions to durably ensure the efficient sealing required at the connector.

"Other known efforts at alternative connection systems implement deformable elastic elements such as metal blades with one or more orifices through which the plug passes when inserting it into the slot, and exerting a radial point of contact between the edge of the orifice and the surface of the plug.

"Thus, U.S. Pat. No. 5,252,090 (Giurtino et al.) proposes to block the plug with an elastically deformable metal piece, extending around the plug in a plane substantially radial to the axis of the plug. Deformable tabs formed in the part produce by stemming an anti-kickback effect, preventing any withdrawal or pulling of the plug once it is inserted in the metal part. For disassembly, the part is extended laterally by two symmetrical ears that, by pinching, deforms the piece enough to remove the tabs of the plug and release it. This device is very effective in terms of mechanical retention. However, unlocking the device requires having two entrances on each side of the part, to ensure a symmetrical pinching, and therefore requires providing two release buttons (one on each side of the head connector).

"FR 2 662 310 A (Darby et al.), refers to an elastic clamp whose ends of the two arms are folded against one another and are provided with holes corresponding to the diameter of the plug. The holes are shifted when the clamp is in the free state, and they can be aligned by moving the two arms of the clamp. The plug can then be introduced through the two holes, and be retained in the clamp after release of the force exerted to bring the two arms together. This connection system is very effective in terms of mechanical retention of the plug, but it is not designed to be integrated with a generator. Rather, it is presented to serve as a dispensing connector between several leads, this connector being placed away from the generator."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "It is therefore, an objective of the present invention to provide a generator for an active implantable device including a connector head provided with a connecting system for the plug of a lead that is both simple and effective and that would: allow connection and disconnection of the plug to the connector terminal without screws and without ad hoc tools; establish a strong mechanical connection ensuring an effective and permanent retention of the plug, even in the case of plugs with smooth surfaces such as those carried out in accordance with the IS-1 standard mentioned above; and be integrated into the very small volume of the connector head of an implant, so as to be minimally invasive for the patient.

"Broadly, the present invention is directed to a leaf spring system which, by its geometric characteristics and the nature of the material used, can provide a tool-free system for securing a plug when it is inserted into the connector housing of the generator of the device with a specific geometry for ensuring the mechanical action of locking/unlocking the plug from one only side of the generator.

"One embodiment of the invention is a device in which the connector head includes, in a manner in itself known, for example, according to the FR 2 662 310 A cited above, at least one female housing provided with an electrical connection terminal and able to receive a plug, the plug having, for example, a smooth surface of a cylindrical or prismatic lead connector, and locking means for the mechanical immobilisation of the plug in the housing. The locking means preferably has a resilient member adapted to be deformed and placed under elastic tension when inserting the plug into a slot in the housing in which the resilient member is disposed. The resilient member also is adapted to be deformed after insertion of the plug, the elastic deformation then being in an axial direction, such that the resilient member comes to exert a retention force on the plug. This retention force in the radial direction exerts contact pressure against the smooth surface of the plug far exceeds the force of insertion of the plug into the housing, and opposes an extraction force applied to the plug. The device also includes structure for releasing the locking means, able to apply to the resilient member, due to an external force, a mechanical force to neutralize the retention force and thereby permit an extraction of the plug from the housing.

"In one embodiment, the resilient member is a leaf spring folded to have a generally U-shaped portion including a central region at the base of the U and two legs or branches of the U extending from the central portion. A first branch preferably extends in a plane in a first direction forming a first angle with respect to an axial direction of insertion of the plug into the slot, and a second branch preferably extends in a plane in a second direction forming a second angle with respect to the axial direction of insertion. The two branches are elastically connected in the central region of the U and extend from the central region to a respective end, and each branch is provided with a respective hole sized so that the plug can pass through the holes when the plug is inserted into the slot.

"The leaf spring is thus deformable between a free state or unstressed position, in the absence of a plug, and a deformed state or stressed position, with the plug inserted. In the free position, the projections of the two holes in the first and second branches in the plane perpendicular to the axial direction of insertion are overlapping but misaligned, while in the stressed position the projections are aligned, so that one edge of each hole crossed by the plug exercises, by a reaction effect of the deformed leaf spring, a radial stress force against the smooth outer surface of the plug, thereby producing said contact pressure and a retention force.

"The first branch may in particular extend in a direction primarily perpendicular to the axial direction of insertion and the second branch in a direction, primarily oblique to, forming, for example, an angle between 45.degree. and 75.degree. from, the axial direction of insertion.

"In a first embodiment, the end of one branch of the U-shaped portion is a stationary end relative to the head of the connector, and the end of the other branch is a free end that is extended by a flange which serves as a support element. In an alternate embodiment, an auxiliary elastic body may be interposed between the connector body and the central region of the U at the junction of the two branches.

"In a second embodiment, the end of one of the branches of the U-shaped portion is a free end extended by a flange serving as a support element, the end of the other branch is a pivoting end moving over the head of the connector, about an axis perpendicular to the axial direction of insertion, and a resilient return member is further inserted between the connector body and the central region of the U at the junction of the two branches.

"In either embodiment, the flange is advantageously a flat push-button extending in a plane generally or substantially parallel to the axial direction of insertion, which can notably extend into an internal cavity of the connector head, this cavity being isolated in a sealed manner from the outside environment. The flange may also include an element causing a tactile response to the change of state between the free and stressed positions.

"Preferably, the leaf spring is a metal blade connected to a terminal for making an electrical connection, between the lead and the generator, so as to achieve simultaneous mechanical immobilization of the plug in the housing and electrical connection of this plug to the connection terminal of the generator.

"Advantageously, the present invention provides a quick screwless connector system that is handled via a single support, located on only one side of the connector head (for the lock as well as for the unlock operation). Further, the present invention locking means is sealed vis-a-vis the outside world, that is to say that no bodily fluid that would promote a loss of electrical insulation or corrosion can leak into the housing through the locking means. It also is simple to manufacture and inexpensive to industrialize. In addition to providing a mechanical connection, it also provides an electrical connection between the terminal of the generator and the plug with, in this case, a sufficiently low contact resistance (in accordance with the industry standards in force for electrical contact resistance, for example, for stimulation/detection below 5 Ohms for static and below 10 Ohms for dynamic resistance, and for defibrillation below 0.5 Ohm for static and 1 Ohm for dynamic resistance), and during the useful life of the product. The present invention also is well suited to manual use by a doctor equipped with gloves, with appropriate forces needed to lock or unlock the plug, and a use that is not affected by the environment in which the device is used (blood medium in particular). Moreover, the invention realizes a reduction of the metal mass used, providing an improved electromagnetic compatibility of the device, and a lever arm effect of reducing the effort needed from the doctor for locking and unlocking the plug and, conversely, producing with an equal force a greater contact force between the connector and the plug, therefore less electrical resistance at the point of contact."

URL and more information on this patent, see: D'Hiver, Philippe; Degieux, Stephane. Screwless Quick System for Connecting a Lead Connector to a Generator of an Implantable Medical Device. U.S. Patent Number 8727817, filed May 4, 2011, and published online on May 20, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=114&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=5654&f=G&l=50&co1=AND&d=PTXT&s1=20140520.PD.&OS=ISD/20140520&RS=ISD/20140520

Keywords for this news article include: Sorin CRM S.A.S.

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Source: Journal of Engineering


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