Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-01-19
2001-11-13
Kamm, William (Department: 3737)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06317633
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of implantable medical devices coupled with leads extending to body tissue and to the storage of lead related data, monitoring of lead functional status, and indication of lead integrity to the clinician.
BACKGROUND OF THE INVENTION
A wide variety of implantable medical devices (IMDs) for delivering a therapy or monitoring a physiologic condition which may employ one or more elongated electrical leads and/or sensors have been clinically implanted or proposed for clinical implantation in patients. A wide variety of electrical stimulation therapy delivery IMDs comprising hermetically sealed, implantable pulse generators (IPGs) and associated electrical leads are implanted in patients' bodies for delivering electrical energy to locations of the body. Such IMDs comprise cardiac pacemakers, implantable cardioverter/defibrillators (ICDs) and muscle, nerve, brain, and organ stimulators, etc.
The leads of such IMDs typically comprise a lead body extending between a proximal lead end and a distal lead end and incorporates one or more exposed electrode or sensor element located at or near the distal lead end. One or more elongated electrical conductor extends through the lead body from a lead connector element formed at a proximal lead end for connection with connector elements of the IPG or monitor and a sensor terminal or electrode located at the distal lead end or along a section of the lead body. Each electrical conductor is typically electrically isolated from any other electrical conductors and is encased within an outer sheath that electrically insulates the lead conductor from body tissue and fluids and prevents physical contact of the conductors with such body tissue and fluids.
Such leads may extend from a subcutaneous implantation site of the IPG or monitor module through a wide variety of pathways into or adjacent to various chambers of the heart, deeply into the brain, into a location within the spine, and into or adjacent other body organs, muscles and nerves. The leads must be formed with small diameter, highly flexible, reliable lead bodies that withstand degradation by body fluids and body movements that apply stress and strain to the lead body and the connections made to electrodes or sensor terminals. As lead bodies are made smaller and smaller and the number of lead conductors is increased or maintained, problems with lead insulation and integrity of lead conductors may become more prevalent. During implantation, lead body insulation can be inadvertently breached or coiled lead conductors can be crushed in minute areas and can be overlooked. Later, these defects may be magnified by exposure to body fluids and result in conductor related condition that is intermittent or which slowly or suddenly manifests itself.
For example, modern implantable cardiac pacemakers and ICDs comprise an IPG implanted subcutaneously remote from the heart and a pacing lead or leads extending from the IPG to a pace/sense electrode or electrodes located with respect to a particular heart chamber to deliver the pacing pulses and sense the cardiac P-wave or R-wave. The lead bodies of such cardiac leads are continuously flexed by the beating of the heart, and other stresses are applied to the lead body in part affected by the implantation route taken between the IPG and the heart chamber or cardiac vessel where the electrodes or sensors are located. Movements by the patient can also cause the route traversed by the lead body to be constricted, whereby shear forces are applied to the lead body sheath and electrical conductors. At times, the lead bodies can be slightly damaged during surgical implantation, and the slight damage may progress in the body environment until a lead conductor fractures and/or the insulation is breached. In most such cases, the effects of lead body damage progress from an intermittent manifestation to a more continuous lead related condition state with lead aging. In extreme cases, insulation of one or more of the electrical conductors may be breached, causing the conductors to contact one another or body fluids resulting in a low impedance or short circuit. Or a lead conductor may fracture and exhibit an intermittent or continuous open circuit resulting in an intermittent or continuous high impedance.
Other problems can arise at the proximal lead end where the electrical connection between the IPG or monitor connector elements and the lead connector elements may be intermittently or continuously disrupted, resulting in a high impedance or open circuit. Usually, such connector open circuit problems result from insufficient tightening of the connection at the time of implantation followed by a gradual loosening of the connection until contact becomes intermittent or open.
In addition, the lead distal end may become dislodged from connection or contact with cardiac tissue, resulting in intermittent or continuous loss of contact of a distal pace/sense electrode with the heart tissue. The dislodgement may leave the electrodes floating in the blood of a heart chamber. Or, “lead penetration” may occur during implantation or chronically wherein the distal end of the lead may be advanced too far into the heart tissue or advances partly through the myocardium. Alternatively, “exit block” may occur, wherein a foreign body reaction, e.g. tissue growth over the pace/sense electrode surface or inflammation of the cardiac tissue adjacent the pace/sense electrode surface increases the pacing or sensing threshold to a level that can result in loss of pacing or sensing.
When these lead problems manifest themselves, they can be collectively referred to for simplicity as a “lead related condition” event though the lead itself is intact. Such lead related conditions may also include a connector open circuit condition or lead dislodgement. It is necessary for the clinician to diagnose the nature of the lead related condition from the available data, test routines that are undertaken, and IMD and patient symptoms. Then, it is necessary for the clinician to take corrective action, e.g., to either replace the lead, reposition the electrodes or sensors or tighten the proximal connection. In severe cases, the lead related condition may result in depletion of the battery energy of the IMD, requiring its replacement.
Certain IPGs and monitors have been clinically used or proposed that also rely on lead borne physiologic sensors that monitor physiologic conditions, e.g., blood pressure, temperature, pH, blood gases, etc. Cardiac pacemakers employing such sensors use the processed sensor signals to regulate pacing characteristics, e.g., pacing rate and/or energy. Open circuit or short circuit lead conductor related conditions or connector or dislodgement related conditions can disable such sensors and compromise monitoring and/or pacing operations dependent upon true sensor output signals.
The ability to sense P-waves or R-waves accurately through a lead can be impaired by any of these lead related conditions. Complete lead breakage impedes any sensing functions, lead conductor fractures or intermittent contact can cause electrical noise that interferes with accurate sensing, and loss of contact of the pace/sense electrodes with responsive cardiac tissue can cause true cardiac signals to be distorted or attenuated.
In the context of cardiac pacing, a delivered pacing pulse “captures” the heart if its delivery through an active, cathodal, pace/sense electrode to the adjacent heart tissue causes or “evokes” a myocardial contraction and depolarization wave that is conducted through the myocardium away from that pace/sense electrode site. The increased impedance of the pacing path or the short circuit of lead conductors due to one of the above-described lead related conditions can reduce the effective pacing pulse energy below that sufficient to capture the heart, resulting in loss of capture (LOC). Commonly assigned U.S. Pat. No. 5,861,012 (Stroebel), incorporated herein by reference, describes several approaches to the determination of t
Jorgenson David J.
McVenes Rick D.
Peck Bradley C.
Starkson Ross O.
Trautmann Charles D.
Duthler Reed A.
Kamm William
Medtronic Inc.
Wolde-Michael Girma
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