Abstract: In a method and apparatus for automatically adjusting the threshold detection level of a detector unit for detecting physiological events, e.g. heart contractions, a cardiac signal is sensed and sampled, the samples of the cardiac signal are stored in a memory. A timer starts the sampling and stops the sampling after a predetermined time. An analysis unit analyzes the stored cardiac signal samples to generate a first set of values which represent physiological events, such as average peak signal value, the average maximum signal slope or an integrated signal value. The analysis unit calculates at least one derived parameter from the whole of the first set of values and automatically determines a new threshold detection level for the sensor as a function of this at least one derived parameter.

Abstract: In a magnetic field detector as well as in a combined telemetry and magnetic field detector unit in a medical implant, a magnetic field sensor with a coil and a diode are employed for determining the presence of a magnetic field. For making such a determination, the coil is charged by a source of voltage for a defined period of time, the time for the discharge of the coil through the diode depending on whether a magnetic field is present. A detection signal indicating the presence of a magnetic field is generated if the discharge time is less than a defined time threshold value.

Abstract: An implantable heart defibrillator includes a pulse generator controlled by a control unit for emitting defibrillation pulses. The pulse generator is controllable to emit a number of low-energy defibrillation pulses, having a lower pulse amplitude and a shorter pulse duration than a conventional defibrillation pulse, with the total energy in the number of low-energy defibrillation pulses being less than the energy in a conventional defibrillation pulse. Each pulse in the number of low-energy defibrillation pulses, however, contains enough energy to depolarize heart cells oriented favorably in relation to the direction of the electrical field of the low-energy defibrillation pulse.

Abstract: A defibrillator having a housing for enclosing and containing defibrillation pulse generator circuitry, particularly adapted to allow for ease of manufacture and use. At least one surface of the housing is electrically conductive and may be connected to the defibrillation pulse generator circuitry for delivering defibrillating energy to the heart. The defibrillator is provided with two case-activating setscrew blocks isolated from two contacts. By tightening the first setscrew onto its contact, the can is activated and is positive for defibrillation. By tightening the second setscrew instead, the can is activated and is negative for defibrillation. Tightening neither setscrew maintains the inactive status of the can. By using this system, various electrode configurations can be used as required to provide the optimum system for a given patient. The defibrillator generator housing is preferably implanted in the left pectoral region proximate the heart with the conductive surface facing the heart.

Abstract: A lead for use with an implanted pulse generator which may be a pacemaker or defibrillator or combination thereof. The lead can deliver an electrical charge to cardiovert or defibrillate the ventricles of the heart via a large surface area defibrillation electrode which is passively implanted in the ventricle. The defibrillation electrode is designed to produce a uniform defibrillation charge distribution.

Abstract: A device for preventing a fixation element on the distal end of an implantable lead, during introduction into a body cavity, from coming into contact with and damaging the cavity has a protective body, which completely encloses the fixation element, and which is made of a gel-forming material. After introduction and contact with body fluid and when pressure is applied to the material against body tissue, the material permits mechanical penetration of the protective body by the fixation element, whereupon the fixation element can be affixed to the body cavity.

Abstract: A device for detecting a state of imminent cardiac arrhythmia, relative to a normal state for a heart, in response to activity in nerve signals conveying information from the autonomic nerve system to the heart, contains a sensor body for sensing neural activity, a comparator with a threshold value forming a condition for the presence of an arrhythmia, the comparator emitting an arrhythmia-indicating output signal depending on whether neural activity meets the condition, and the sensor body being placeable in an extracardiac position for at least one of the sympathetic and vagus nerves. The sensor body directly senses activity in the nerve at that location in direct contact with the nerve. An implanted blood pressure sensing cuff also can be provided which generates signals indicative of blood pressure which can be evaluated in combination with the nerve signals for identifying the state of imminent cardiac arrhythmia.

Abstract: A DDI pacemaker detects when a pacemaker mediated retrograde rhythm (PMRR) occurs, and automatically alters the DDI operation to terminate the PMRR. The PMRR is detected by measuring the P-to-V time interval in a DDI pacing cycle that terminates in the generation of a ventricular stimulation pulse (V-pulse). A PMRR is presumed to be present whenever the measured P-to-V interval exceeds a prescribed time interval, or whenever a programmed number of consecutive P-to-V time intervals, e.g., ten, are greater than the prescribed time interval. Once a PMRR is detected, the pacemaker automatically extends the post-ventricular atrial refractory period (PVARP) of the pacemaker to block any retrograde P-waves that may be occurring as part of the PMRR. As soon as the extended PVARP terminates, an alert time interval, T.sub.ALERT, begins that is selected to be of sufficient length to allow atrial tissue to repolarize and/or to detect a normal P-wave. If a P-wave is not sensed during the T.sub.

Abstract: A programmable pacemaker that allows both noninvasive electrophysiological ("EP") testing for atrial tachycardias and ventricular pacing support, by allowing operation in the atrial channel to be decoupled from operation in the ventricular is provided. Many patients require EP testing to evaluate a predisposition to tachycardias. Many of these patients also have dual-chamber pacemakers for cardiac support. These systems can be noninvasively coupled to a external programmer enabling the already implanted system to serve as an in vivo EP laboratory. When performing noninvasive atrial EP testing with current dual-chamber pacemakers, the device must first be programmed to a single-chamber triggered mode. The present system allows the pacemaker to maintain ventricular pacing during EP testing.

Abstract: An implantable cardiac stimulation device that has automatic functions in each of two different sets of microprocessor operating code. Following implantation, a first mode of operation executes a first set of operating code, stored primarily in RAM, and performs software error detection. Upon detection of an error, the microprocessor is caused to enter a second (backup) mode of operation, where it executes a second set of operating code, which is retained in read-only memory (ROM). Thus, in the unlikely event of error detection, the implantable device is still fully functional in its second mode to provide automaticity, e.g., to select therapies for different heart condition and provide rate-responsive pacing that tracks physiological requirements. If an error is detected in the second mode, than a third mode of operation (e.g., fixed-rate VVI pacing) is enabled.

Abstract: A method and apparatus for calculating and monitoring the impedance of an implanted pacemaker lead, and in particular to such a method and apparatus for monitoring the impedance to determine whether a lead fault, such as a lead rupture or a lead dislocation, has occurred. In order to avoid reprogramming the implanted pacemaker to deliver a pulse having known parameters in order to permit an impedance measurement to be made, the method and apparatus operate on the basis of the system formed by the pulse generator, the electrode leads and body tissue being considered to behave as an RC circuit, with the pulse generator emitting an ideal square wave pulse which then exhibits an exponential decay in the body tissue having a decay time constant associated therewith. From surface ECG measurements, the decay time constant is estimated, and since the capacitance of the pulse generator is known, the lead impedance can then be calculated.

Abstract: In a method and apparatus for stimulating and/or diagnosing the heart, a voltage is applied to the heart over at least a selected portion of the heart during an activation interval with a rise and fall, with the voltage having a first derivative with an absolute value that is less than the value of the derivative which, for a patient in question, would trigger the patient's heartbeat, and with a duration from beginning to end of each applied voltage signal of at least 30 ms.

Abstract: An apparatus for preventing an anchoring element on the distal end of an implantable medical electrical conductor from coming into contact with and damaging the wall of a body cavity during advancement of the conductor into the cavity has a sleeve element attachable to the outer surface of the distal end of the conductor to enclose the entire length of the anchoring element, and a pulling element attached to the distal end of the sleeve element. Pulling on the pulling element from the proximal end of the conductor retracts the sleeve element after introduction of the conductor has been concluded, to expose the anchoring element for active fixation to adjacent body tissue. An implantable electrode cable equipped with such an end protector.

Abstract: A device for indicating that an electrode cable is correctly connected to a medical implant for emitting electrical pulses, the implant being equipped with a connection part for the electrode cable's proximal end, has a contact for making electrical connection with the proximal end of the electrode cable and an indicator, the contact electrically causing the indicator to emit at least one indication signal which is perceptible outside of the implant when the electrode cable is correctly attached to the implant.

Abstract: An implantable medical device lead assembly has an electrode head including a flexible tip of elastomeric material embedding at least one rigid or flexible electrode. The at least one electrode and the elastomeric material define a curved tip surface adapted to contact the tissue to be stimulated. The compliance of the tip surface preferably approaches that of the body tissue to be stimulated so as to minimize the stress applied to the heart thereby reducing the adverse reaction of the heart to the presence of the electrode head. By way of example, the at least one electrode may take the form of a metallic or conductive polymer pin or may be made of wire. The elastomeric material may take the form of an envelope disposed about the electrode head and having formed integrally therewith anchoring means preferably comprising a plurality of pliant tines.

Abstract: A single-pass A-V lead for cardiac pacing comprises a lead body having an atrial electrode and a right ventricular outflow tract (RVOT) electrode. Preformed bends in the lead body are configured such that the atrial and RVOT electrodes are biased against walls of the right atrium and the RVOT respectively. Biasing forces generated by the preformed bends help to maintain the atrial and RVOT electrodes in their respective positions following implantation. The lead advantageously permits ventricular stimulation in the RVOT, resulting in an improved sequence of ventricular activation and a corresponding increase in cardiac output. Branched and unbranched embodiments of the lead are disclosed.

Abstract: The cardiac output of a paced heart is optimized by measuring a parameter indicative of the volume of blood in a heart chamber as a function of a pacing parameter. The pacing parameter is adjusted so that the heart pumps the maximum volume at different rates for hearts with debilitating pathologies. This pacing parameter is then used for controlling the pacing pulses for pacing the heart. Preferably the volume parameter is the paced depolarization integral and the pacing parameter is the A-V delay.

Abstract: An implantable heart defibrillator contains a pulse generator controlled by a control unit for emitting a number of heart stimulation pulses at a rate of several Hertz or more. The control unit causes the pulse generator to emit heart stimulation pulses with an energy content of the same, or somewhat greater, magnitude than conventional pacemaker pulses for a period of time long enough for the entire heart to become refractory.

Abstract: A method for making an electrical contact for a vitreous carbon electrodes includes the steps of making a bore in an electrode blank of a cross-linked artificial resin forming the electrode blank into an electrode body. A solid or hollow pin, or a sleeve, composed of a biocompatible, refractory metal is introduced into the bore. If a pin is to be used, the bore is made to extend only partially into the electrode body, if a sleeve is used the bore extends completely through the body. The pin or sleeve has smaller dimensions than the bore; if a pin is used it projects from one side of the electrode body and if a sleeve is used it projects from both sides of the electrode body. The electrode blank is subjected to a pyrolysis, whereby the cross-linked artificial resin is converted into vitreous carbon and the electrode body shrinks onto the pin or sleeve.

Abstract: A suture sleeve for anchoring the lead body of an implantable medical device is fabricated of a biocompatible, polymeric material to which has been added color pigment in clear contrast with the bodily tissue adjacent the sleeve. The sleeve is therefore readily visible to the naked eye to aid the physician in locating the sleeve during lead implant or lead revision. Furthermore, the tubular body may be radiopaque and, therefore, easily seen on a fluoroscope through the addition of a radiologically dense material, such as tantalum powder, to the plastic from which the sleeve is molded.