The invention relates generally to electrical leads used with implantable medical devices, and more particularly, to an implantable electrical lead incorporating a novel, secure, and readily manufactured coupling between electrical conductors inside the lead.
Implantable electrical leads are used with implantable medical devices to provide electrical contact between the implantable medical device and a region of a patient""s anatomy that is remote from the device.
Cardiac pacemakers include batteries and controllers to deliver regular patterns of electrical signals to the tissues of the heart to help maintain a patient""s normal pulse. Because the batteries and controllers must be of considerable size, and because it is generally undesirable to perform highly invasive surgeries on the heart itself, the batteries and controllers are generally implanted in a more accessible region somewhat remote from the heart. A sealed package containing the batteries, processor, and other components of the pacemaker may be implanted, e.g., in a space created in the region of the patients shoulder. This package is then electrically connected to the patient""s heart by a thin, flexible electrical lead implanted between the main body unit of the pacemaker and the tissue of the heart. The pacing signals are then delivered to the heart from the main unit over the electrical lead.
Implantable cardiac defibrillators are implantable devices that continuously monitor electrical signals from a patient""s beating heart. When the defibrillator detects a predetermined adverse signal pattern, for example, signals indicating cardiac arrhythmia, the defibrillator delivers a strong electrical impulse to reestablish the normal electrical rhythmxe2x80x94and thus a regular pulsexe2x80x94in the patient""s heart.
In an implantable cardiac defibrillator, the package containing the batteries, monitor, controller, and the other components of the main body unit may be implanted remotely from the heart, usually again in the region of the patient""s shoulder, but sometimes elsewhere. In a device of this type, not only are electrical impulses delivered through the lead, but the controller monitors signals from the heart through the lead as well.
Other devices are known in which electrical signals are delivered between a main unit and region of the body somewhat away from the main unit, and still more such devices will likely be made in the future.
In all such devices that transmit signals or impulses over an implantable lead, it is generally desirable for the lead to be thin and flexible so that the lead can be implanted into the body conveniently and with minimal discomfort and distress. At the same time, the lead must provide a highly reliable and secure connection between the electrical base unit and the target location inside the patient""s body. Perhaps less obviously, it is sometimes desirable to design a degree of xe2x80x9cpushabilityxe2x80x9d or xe2x80x9ctorqueabilityxe2x80x9d into certain regions of such leads to facilitate the leads"" delivery to their remote destinations inside the body.
Leads have been developed that include helical metal coils as conductors. In some such leads, one relatively thin conductor coil is disposed inside another coil of slightly larger diameter with an insulator layer between them. In other leads, helical conductor coils run parallel to one another along the body of the lead. Such coils have been found reliable and deliverable, and have been widely adopted by medical practitioners.
In some cases, though, leads having coaxial or otherwise parallel helical coils are neither as thin nor as flexible as might be desired. Some attention has been paid, therefore, to potential new leads in which one or more flexible wire conductors might be used in place of one or more of the helical coils of a known lead. Each such flexible wire conductor might be a single strand of wire, or it might include multiple strands of a very thin and highly flexible conductor material, such as in a wrapped wire cable. Such flexible wire conductor leads might then be thinner and provide greater flexibility than known leads, which might be highly advantageous in many applications.
Lead designers know, however, that reliability and failure resistance are key criteria in the performance of these electrical leads. An implantable electrical lead remains intact and functional inside the patient""s body for long periods, perhaps many years. At best, lead failure can require a painful and dangerous surgical explantation to replace the failed lead. If the lead fails to deliver a crucial signal at a critical time, the patient may very well die.
It is vital to avoid compromising a lead""s robustness and reliability in the quest for flexibility and small size. The lead conductors themselves must obviously provide sufficient strength and failure resistance, including resistance to mechanical fatigue. Connections between components within the lead must also perform satisfactorily.
It would be desirable, therefore, to devise new lead constructions that offer desired combinations of flexibility and thinness in certain regions of the lead, while avoiding any undue impairment of the lead""s reliability or performance. The present invention attempts to meet these objectives in a lead that has good performance characteristics and that is readily, reliably, and conveniently manufactured. Representative embodiments of leads incorporating the invention are depicted in the accompanying figures and described in detail below.
The invention provides electrical leads suitable for implantation in a human patient and electrical couplings for providing secure electrical connections between components in such leads.
A representative embodiment of such a lead includes an electrically conductive connector at a proximal end of the lead. The connector may be a standard connector commonly used with implantable medical devices, or it may be a custom connector. An electrically conductive transitional coil is electrically connected to the electrical connector, with a wire conductor electrically connected by an electrically conductive coupling to the transitional coil. This construction provides a particularly advantageous construction featuring robust and secure electrical connections between the electrical components, with high flexibility provided at the lead""s distal end by the wire conductor.
A preferred embodiment of the electrical coupling includes an electrically conductive coupling body. The coupling body in this embodiment includes structure defining a connector sleeve receiver. A corresponding connector sleeve fits over an end of the wire conductor and is attached to the wire conductor to hold it in secure electrical contact with the coupling body. The coupling body also includes a coil receiver configured to receive and hold a distal end of the transitional coil in secure electrical contact with the coupling body. Secure electrical contact is thereby insured between the transitional coil and the wire conductor. Electrical contact is thus ensured between the connector at the proximal end of the lead and an electrode or another electrical element at the lead""s distal end.
An alternative lead features multiple coil conductors fixed by multiple couplings to multiple wire conductors in a single lead.