Abstract: An implantable medical device for generating a cardiac pressure-volume loop, the implantable medical device comprising a pulse generator including control circuitry, a first cardiac lead including a proximal end and a distal end and coupled to the pulse generator at the proximal end, a first electrode located at the distal end of the cardiac lead and operatively coupled to the control circuitry, a sound sensor operatively coupled to the control circuitry, and a pressure sensor operatively coupled to the control circuitry, wherein the implantable medical device is adapted for measuring intracardiac impedance. A method of using the implantable medical device to optimize therapy delivered to the heart.

Abstract: Lead Tracking of Implantable Cardioverter-Defibrillator and Cardiac Resynchronization Therapy Devices improve upon the process of implantation of ICD-CRT devices, placing their leads, and improving the information fed back to the device and/or clinician. Tracking of the placement of the leads during implantation is accomplished along with monitoring the leads once implanted. Benefits include reducing the risk and complication rate, simplifying implantation procedure, and enabling the extraction of vital data not previously available. Leads are tracked to at least minimize the need to use fluoroscopy. Three dimensional tracking (10) is employed to facilitate obtaining of data that allows the surgeon to better visualize lead insertion and placement. Placement of the leads during a procedure requires use of an external tracking component along with means and method for tracking the implantable leads.

Abstract: A method for determining a physiologic characteristic associated with cardiac function in a subject comprising the steps of providing at least one electromagnetic radiation absorption measurement, providing demographic information reflecting the subject's physical condition, determining a temporal plethysmographic value from the electromagnetic radiation absorption measurement, and determining at least one physiologic characteristic from the temporal plethysmographic value and demographic information by using a predetermined phenomenological model that is adapted to provide an estimate of a blood volume-time relationship proximate the heart and compute at least one physiologic characteristic associated with cardiac function based on the estimated blood volume-time relationship.

Abstract: A method and device for delivering cardiac function therapy on a demand basis. An implantable device for delivering cardiac function therapy is programmed to suspend such therapy at periodic intervals or upon command from an external programmer. Measurements related to hemodynamic performance are then taken using one or more sensing modalities incorporated into the device. Based upon these measurements, the device uses a decision algorithm to determine whether further delivery of the cardiac function therapy is warranted.

Abstract: A method of treating a heart with an implantable cardiac stimulation device involves transiently disturbing the steady state hemodynamic parameters by altering a cardiac cycle timing interval sufficient to reduce end diastolic volume for that cycle. The cardiac cycle timing interval is then adaptively controlled for successive cardiac cycles to achieve a second set of hemodynamic parameters.

Abstract: An exemplary method includes introducing current between a first pair of electrodes configured for placement internally in a patient, triggering a potential measurement between a second pair of electrodes configured for placement internally in a patient wherein communication of a signal through the patient allows for proper triggering, measuring potential between the second pair of electrodes and, based at least in part on the measuring and the introducing, determining a cardiac condition. Other exemplary methods, devices, systems, etc., are also disclosed.

Abstract: Exemplary methods for decreasing workload, maintaining or increasing cardiac output and/or achieving a desirable autonomic balance by stimulating one or more parasympathetic nerves. Various exemplary methods include delivering one or more stimulation pulses postinspiration and/or based at least in part on detection of one or more cardiac event. Other methods and/or devices are also disclosed.

Abstract: An implantable subcutaneous cardiac device includes at least two subcutaneous electrodes adapted for placement external to a heart beneath the skin of a patient. The device further includes an arrhythmia detector that detects a sustained tachyarrhythmia of the heart and a pulse generator that delivers anti-tachycardia pacing pulses to the subcutaneous electrodes in response to detection of a sustained tachyarrhythmia. The pacing pulses preferably have waveforms devoid of any exponential voltage decay and include rounded or substantially constant portions to minimize pain.

Abstract: A method of data management for optimizing the patient outcome from the provision of cardiac resynchronization therapy (CRT) is described. This method describes a process by which sets of dynamic cardiopulmonary dependent variables are measured during steady-state conditions, displayed, and translated into quantitative and qualitative measurements while the independent variables of CRT, device lead placement and atrial-ventricular and interventricular delay settings of bi-ventricular pacemaker systems, are altered by a physician. In combination with visual observation and computer-assisted ranking of the dependent variables, a physician can utilize the resulting information to render decisions on the optimal choice of the independent variables.

Abstract: An implantable cardiac stimulation device comprises a physiologic sensor and one or more pulse generators. The physiologic sensor is capable of sensing a physiologic parameter. The pulse generators can generate cardiac pacing pulses with a timing based on the physiologic parameter. The timed cardiac pacing pulses can prevent a sleep apnea condition. In one example, a cardiac stimulation device has a physiologic sensor and can be configured to pace a patient's heart according to a rest mode of operation. The cardiac stimulation device uses measurements from the physiologic sensor to prevent and treat sleep apnea using a revised rest mode of operation. The revised rest mode operates under a presumption that sleep apnea is primary to a reduced heart rate, rather than secondary, so that pacing at a rate higher than the natural cardiac rate during sleep will prevent sleep apnea.

Abstract: A pacing system for providing optimal hemodynamic cardiac function for parameters such as ventricular synchorny or contractility (peak left ventricle pressure change during systole or LV+dp/dt), or stroke volume (aortic pulse pressure) using system for calculating atrio-ventricular delays for optimal timing of a ventricular pacing pulse. The system providing an option for near optimal pacing of multiple hemodynamic parameters. The system deriving the proper timing using electrical or mechanical events having a predictable relationship with an optimal ventricular pacing timing signal.

Abstract: Techniques are provided for performing internal measurement of heart sounds to estimate patient cardiac function in terms of stroke volume, cardiac output, or a maximum rate of change of aortic pressure with time (max dP/dt). Control parameters of the medical device are then automatically adjusted so as to optimize overall cardiac function or to provide for ventricular resynchronization therapy. In one example, heart sound signals are derived from acceleration signals received from an accelerometer. The heart sound signals are analyzed to identify S1 and S2 heart sounds as well as ejection period and isovolumic interval (ISOV). Proxies for max dP/dt, stroke volume and cardiac output are then derived from the S1 and S2 heart sounds, the ejection period and the ISOV. Alternative techniques, not requiring detection of ISOV, are employed for use if the patient has heart value regurgitation.

Abstract: An implantable medical device delivers augmentation therapy to intervene in a pattern of sleep-disordered breathing. Augmentation therapy includes the delivery of electrical stimulation to cardiac tissue above and/or below a capture threshold. PESP and NES/CCM are possible augmentation therapies that are used alone or in combination. In addition, augmentation therapies can be used with other pacing therapies such as atrial overdrive pacing and atrial coordinated pacing as a therapy for sleep-disordered breathing.

Abstract: Methods and devices for improving ventricular contractile status of a patient suitably exploit changes in ventricular pressure and/or dP/dtmax to provide and/or optimize a response to a patient. The ventricular pressure may be appropriately correlated to intracellular calcium regulation, which is indicative of contractile status. To assess ventricular contractile status, the device suitably observes a cardiac perturbation of the patient and measures force interval potentiation following the perturbation. The contractile potentiation can then be stored and/or quantified in the implantable medical device to determine the ventricular contractile status of the patient, and an appropriate response may be provided to the patient as a function of the ventricular contractile status. Examples of responses may include administration of drug or neuro therapies, modification of a pacing rate, or the like.

Abstract: A minute ventilation sensing device in which transthoracic impedance is measured with a excitation current waveform at a specified amplitude and frequency. In order reduce interference with the impedance measurement from external noise sources, a noise detection operation may be performed with the amplitude and/or frequency of the excitation current waveform adjusted accordingly.

Abstract: A cardiac rhythm management device is configured to detect mechanical oscillations in cardiac rhythm. Upon detection of such oscillations, the device may adjust its operating behavior to compensate for the deleterious effects of the condition.

Abstract: Techniques are described for estimating a rate of blood flow from a heart, such as a stroke volume or a cardiac output, as a function of a pressure in the heart. A pressure monitor may measure pressure values, and identify the times at which pressure values and valve opening and closing occur. The pressure monitor may estimate a velocity-time function as a function of the measured pressures and identified times, and may calculate a velocity-time integral by integrating the velocity-time function. The pressure monitor may also calculate an estimated velocity-time integral directly as a function of the measured pressures and the identified times. The pressure monitor may calculate the stroke volume or cardiac output using the velocity-time integral. The pressure monitor may control a delivery of therapy by an implantable medical device as a function of the stroke volume or cardiac output.

Abstract: A rate adaptive pacemaker comprises a means (2) for determining the demand of the patient's organism, a pacing rate controlling means (16) for controlling the pacing rate in response to the patient's demand, and a pacing rate limiting means (20) for preventing the pacing rate from becoming too low. The pacing rate limiting means is adapted to limit the pacing rate downwards such that a first predetermined relation is satisfied between actual cardiac output (CO) and cardiac output (COrest) for the patient in rest conditions and a second predetermined relation is satisfied between actual stroke volume (SV) and rest stroke volume (SVrest).

Abstract: A body implantable system employs a lead system having at least one electrode and at least one thermal sensor at a distal end. The lead system is implanted within a patient's heart in a coronary vein of the left ventricle. The thermal sensor can be attached to a catheter that is disposed within an open lumen of the lead system. The thermal sensor senses a coronary vein temperature. The coronary vein temperature can be measured at a detector/energy delivery system and used as an activity indicator to adaptively control pacing rate. The measured coronary vein temperature can be also used with a left ventricular flow measurement to determine hemodynamic efficiency of the heart. A detected change in hemodynamic efficiency can be used by the detector/energy delivery system to modify the delivery of electrical pulses to the lead system.

Abstract: A rate adaptive pacemaker has a measuring unit which interacts with a patient to determine a demand, a pacing rate controller connected to the measuring unit for controlling the pacing rate in response to the demand, and a pacing rate limiter connected to the pacing rate controller which upwardly limits the pacing rate so as to always maintain the energy supplied to the myocardium at a level which exceeds the energy consumed by the myocardium.

Abstract: Method and device for the diagnosis and therapy of chronic heart failure comprising continuous monitoring of the patient and continuous determination of significant decompensation parameters during a sample period of normal patient life, recording the data determined, continuously monitoring these data during therapy, comparing the memorized data with those determined during the same time span of the sample period and comparing the duration of periods in which decompensation is present with the total duration of those periods during which decompensation is absent or conforms to that determined during the sample period.

Abstract: A method and system for setting the operating parameters of a cardiac rhythm management device in which a plurality of parameter optimization algorithms are available. A measured feature of an electrophysiological signal such as QRS width has been shown to be useful in selecting among certain parameter optimization algorithms.

Abstract: A system for automatic manipulation of a transcranial Doppler probe device designed for placement on a patient's head comprising a bi-temporal probe hanger, a cylindrical probe housing having an inner electrical wiring, an ultrasound transducer with cable affixed on the probe cylindrical base having a coil, said probe cylindrical base placed within the cylindrical probe housing, a spring system affixed to provide perpendicular pressure on the probe cylindrical base, a system of roller balls, a locking system to affix the cylindrical probe housing to the frame of the bi-temporal probe hanger, a system software program and microprocessor for controlling the probe position, and a removable handle attached to the said probe cylindrical base. The system software ‘learns’ probe angulations after initial manual manipulations and then performs cerebral vessel insonation using electromotive force independent of operator.

Abstract: A pacing system for providing optimal hemodynamic cardiac function for parameters such as contractility (peak left ventricle pressure change during systole or LV+dp/dt), or stroke volume (aortic pulse pressure) using system for calculating atrio-ventricular delays for optimal timing of a ventricular pacing pulse. The system providing an option for near optimal pacing of multiple hemodynamic parameters. The system deriving the proper timing using electrical or mechanical events having a predictable relationship with an optimal ventricular pacing timing signal.

Abstract: Determining the cardiac output of a patient uses first and second electrodes disposed with the peri-aortic adventitia or fat pad of the patient. Third electrode is disposed on the cardiac atrial area of the patient. Fourth electrode is placed either externally on the body surface or internally superior to electrodes one and two. A bioelectrical impedance recorder is coupled to the third and fourth electrodes to pass a current between the electrodes. A bioimpedance recorder is coupled to the first and second electrodes to measure the resulting voltage. The output of the bioelectrical impedance recorder is processed to compute a metric corresponding to the patient's cardiac output. The third electrodes are adapted to be the cardiac pacing electrodes.

Abstract: The invention relates to a cerebral blood flow velocity monitoring system and method that comprises a transcranial Doppler ultrasound device that is adapted to be implanted in the human body, an oximeter, an external handheld computer and a drug delivery system. The system provides for monitoring of microembolic signals and operatively activates the drug delivery system for infusion of medication into the blood circulation for thrombolysis and neuroprotection.

Abstract: A method of accurately determining if ectopic beats are occurring in the heart by detecting the time interval, T, between a point Q* defined is the onset of the QRS complex and the peak value of R (T=Q*R) during a heart beat cycle and comparing that time with a running mean value calculated from normal heartbeats. A beat is identified as an ectopic beat if the Q*R time interval for a current beat is at least four standard deviations from the mean Q*R time interval of normal preceding beats. The electrodes for detecting the ectopic beats may be inside the patient's heart or on the patient's skin. If more than one electrode is used for monitoring the depolarization of the heart, then by combining the Q*R intervals (e.g. using a triangulation method) calculated from different electrodes, the location of the ectopic excitation can be determined and identified.

Abstract: Systems and methods examine heart tissue morphology using three or more spaced apart electrodes, at least two of which are located within the heart in contact with endocardial tissue. The systems and methods transmit electrical current through a region of heart tissue lying between selected pairs of the electrodes, at least one of the electrodes in each pair being located within the heart. The systems and methods derive the electrical characteristic of tissue lying between the electrode pairs based, at least in part, upon sensing tissue impedances. The systems and methods make possible the use of multiple endocardial electrodes for taking multiple measurements of the electrical characteristics of heart tissue. Multiplexing can be used to facilitate data processing. The systems and methods also make possible the identification of regions of low relative electrical characteristics, indicative of infarcted tissue, without invasive surgical techniques.

Abstract: A pacing system for providing optimal hemodynamic cardiac function for parameters such as contractility (peak left ventricle pressure change during systole or LV+dp/dt), or stroke volume (aortic pulse pressure) using system for calculating atrio-ventricular delays for optimal timing of a ventricular pacing pulse. The system providing an option for near optimal pacing of multiple hemodynamic parameters. The system deriving the proper timing using electrical or mechanical events having a predictable relationship with an optimal ventricular pacing timing signal.

Abstract: A method for the delivery of substances to a cell is disclosed. In a preferred embodiment, one administers continuous wave ultrasound or pulse-wave ultrasound to a cell bathed in a cocktail containing macromolecules and monitors the ultrasound using reflected echos of the ultrasound. One then observes incorporation of the substances into the cell. In a preferred embodiment of the present invention, macromolecules are combined in a cocktail solution comprising bubble micronuclei.

Abstract: A system for controlling end diastolic volume of the heart is disclosed. The system includes an EDV sensor constructed and arranged to measure a parameter related to the end diastolic volume of the heart, and a heart stimulator, responsive to the EDV sensor, constructed and arranged to invoke systole when the measured parameter reaches a predetermined level, the parameter reaching that level prior to termination of diastole. Preferably, the heart stimulator may be a pacemaker. The EDV sensor may be any sensor constructed to measure a parameter related to the end diastolic volume of the heart, or another selected physiological or patho-physiological condition of the heart, including a strain sensor, a stress sensor, a dimension sensor, an impedance sensor, an optical sensor, a microwave sensor, or another sensor constructed to measure a parameter related to the end diastolic volume of the heart, or another selected physiological or patho-physiological condition of the heart.

Abstract: A heart stimulator has a circuit for determining cardiac output and for producing a control signal corresponding to the determined cardiac output, and a controller for controlling cardiac stimulation dependent on the control signal. The circuit for determining cardiac output includes a pressure sensor which measures pressure in the right ventricle and which generates an electrical pressure signal corresponding to the measured pressure, and an integrator supplied with the pressure signal which integrates the pressure signal between a start time and stop time to produce an integration result corresponding to the cardiac output, which is used to form the control signal. The pressure signal is bandpass filtered during a systolic phase to identify opening of a valve at the right ventricle as the start time, and to identify closing of the valve as the stop time.

Abstract: In the determination of an optimal rate for the delivery of stimulation pulses to a heart, the stroke volume (SV) of a heart ventricle is measured as a function of heart rate (HR), e.g. by determination of impedance in individual heart cycles whose duration is varied from the duration corresponding to the prevailing rate or the basic rate regarded as optimal for stimulation. The optimal rate should lie at the knee of this function. A corresponding knee is also found in the curve for cardiac output (CO). This rate is determined by calculation of an auxiliary function, e.g. HF=HR.times.CO, which displays a peak at the heart rate at which the knee is located, and the heart rate is determined which yields this maximum. The heart rate determined in this manner is subsequently employed as a basic rate.

Abstract: In an implantable pacemaker or cardioversion/defibrillation device, the optimal electrodes for determining a pacing parameter are found. A test signal is sequentially switched and a response from each of the remaining electrodes is determined. From those responses an optimal electrode or electrode pair is selected and used for pacing parameter determination. If an optimal electrode (a pair) is not found, then a fall back pacing rate is used.

Abstract: A dual-chamber implantable pacemaker configured to operate in the DDD or DDDR mode automatically sets its AV (or PV) interval to an amount that is equal to the natural conduction time of a patient plus or minus a small prescribed amount, e.g., 1-100 msec. When set to a value that is less than the natural conduction time, preemptive ventricular pacing thus occurs at a time in the patient's cardiac cycle that is near when a natural ventricular contraction (an R-wave) would occur. Such ventricular pacing causes a mechanical contraction sequence of the patient's heart that differs from the natural contraction sequence following a natural depolarization, resulting in improved cardiac output. The pacemaker includes a pulse generator that generates ventricular stimulation pulses (V-pulses) at the conclusion of a pacemaker-defined AV (or PV) interval if no natural ventricular activity (an R-wave) is sensed during such AV (or PV) interval.

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 arrangement is provided for controlling a stimulation frequency of a pacemaker. The arrangement includes an atrial bipolar electrode system and a ventricular bipolar electrode system. A first electrode pair comprises an electrode from each of the atrial and ventricular bipolar electrode systems, with the electrodes of the first electrode pair being disposed intracardially in the atrium and ventricle, respectively. A pacemaker control unit generates stimulation pulses for stimulating the heart. A constant current source impresses a constant current to a second electrode pair, comprising at least one electrode from one of the atrial and ventricular bipolar electrode systems being disposed intracardially in one of the atrium and ventricle, for developing an electrical potential between the electrodes of the first electrode pair during predetermined cardiac phases.

Abstract: A system and method for a pacemaker are provided, for using cardiac wall motion sensor signals to provide hemodynamically optimal pacing therapy to patient at rest, and for providing rate-responsive pacing therapy. The cardiac wall motion sensor signals are provided by an implantable lead that incorporates an accelerometer for measuring cardiac mechanical activity. The cardiac wall motion sensor signals are processed to derive cardiac wall velocity signals and cardiac wall displacement signals. The derived signals are further processed to derive physiologic parameters indicative of cardiac performance, including stroke volume, contractility, pre-ejection period, and ejection time. The physiological parameters, in turn, are used by the pacemaker to provide hemodynamically optimal pacing therapy at rest, and rate-responsive pacing therapy.

Abstract: An implantable, rate responsive pacemaker, sensitive to impedance changes in the heart as an indicator of cardiac stroke volume or minute volume, wherein common interfering signals such as the intracardiac electrogram, myoelectric signals, pacing artifacts and other pacing after potentials are reduced or eliminated from the measurement of the impedance by the use of a biphasic test signal. The cardiac pacemaker has a signal injector which produces biphasic test pulses of similar duration and magnitude and of constant current, though of opposite polarity. The pacemaker also has a detector which senses voltage resulting from the applied biphasic current pulses in each phase. Since the injector and detector are separate circuits, they can be used with a variety of electrode configurations.

Abstract: An arrangement, in particular a heart pacemaker, has a measuring device for recording a heart activity measurement parameter. In order to record the measurement parameter in such a way that it is rid of disturbing signals, and can thus be used to evaluate the physiological functions of the heart pacemaker, the arrangement contains switching means which evaluate the signal curve of a measurement parameter during a heart cycle (n+1) as a function of the frequency (f) or duration (t.sub.S) of the previous heart cycle (n).

Abstract: A processing system and method are provided for deriving an improved hemodynamic indicator from cardiac wall acceleration signals. The cardiac wall acceleration signals are provided by a cardiac wall motion sensor that responds to cardiac mechanical activity. The cardiac wall acceleration signals are integrated over time to derive cardiac wall velocity signals, which are further integrated over time to derive cardiac wall displacement signals. The cardiac wall displacement signals correlate to known hemodynamic indicators, and are shown to be strongly suggestive of hemodynamic performance. An implantable cardiac stimulating device which uses cardiac wall displacement signals to detect and discriminate cardiac arrhythmias is also provided.

Abstract: An implantable monitor/stimulator is disclosed that monitors and assesses indices of cardiac function, including the strength and timing of cardiac contraction, then automatically executes a physician-selected mode of therapy. It accomplishes this by assessing impedance, electrocardiogram, and/or pressure measurements, then calculating various cardiac parameters. The results of these calculations may be stored within the device, telemetered to an external monitor or display and/or may be used by the physician to determine the mode of therapy to be chosen. If indicated, therapy is administered by the device itself or by telemetering control signals to various peripheral devices for the purpose of enhancing either contraction or relaxation of the heart. The cardiac parameters that are calculated all provide an assessment of level of cardiac function by monitoring changes in ventricular filling and ejection or by calculating isovolumic phase indices of heart contraction.

Abstract: A dual-chamber implantable pacemaker configured to operate in the DDD or DDDR mode automatically adjusts its AV (or PV) interval to an amount just less than the natural conduction time of a patient, thereby assuring that ventricular pacing occurs in a patient's cardiac cycle at a time near when a natural ventricular contraction (an R-wave) would occur. The pacemaker includes a pulse generator that generates ventricular stimulation pulses (V-pulses) at the conclusion of a pacemaker-defined AV (or PV) interval if no natural ventricular activity (an R-wave) is sensed during such AV (or PV) interval. The AV (or PV) intervals are automatically adjusted by the pacemaker to be just less than the natural conduction time sensed by the pacemaker, where the natural conduction time is the time between atrial activity (a sensed P-wave or a delivered A-pulse) and the subsequent natural ventricular activity (R-wave).

Abstract: A cardiac rhythm management device includes a dual-chamber pacemaker especially designed for treating congestive heart failure and a defibrillator as a back-up measure. The device incorporates a programmed microcontroller which is operative to adjust the AV delay of the pacemaker to a minimum or maximum length consistent with optimal cardiac function. The cardiac stimulator includes apparatus for sensing cardiac function from cycle-to-cycle and determining whether incremental changes made to the AV delay interval enhances or worsens the measured cardiac function. On each iterative cycle, the AV delay interval is changed, either incremented or decremented, until a cross-over point is reached in which it is noted that the cardiac function ceases to improve and this is followed with a further incremental adjustment in an opposite direction to compensate for any overshoot.

Abstract: A cardiac pacemaker, whose stimulation rate is controlled dependent on an impedance signal acquired between two electrodes, has one of the two electrodes disposed in an atrial electrode catheter and the other electrode being disposed in a separate, ventricular electrode catheter. Catheters carrying only a single electrode can thus be used, thereby avoiding the use of a bipolar electrode catheter. The two electrodes are respectively connected to two different stimulation pulse generators within the pacemaker housing, constructed as a dual chamber pacemaker.

Abstract: The implantable device, of the Holter intervention type, permits the detection and the polygraphic analysis (ECG, TA, haemodynamics, resonant frequencies), of the cardiovascular parameters, especially in the active sequence of current cycles, permitting the instantaneous activation of a cardiac electrical or neurovegetative or pharmacological stimulation. The device comprises automatic adaptation means permitting the active permanent monitoring of the hearts treated, repaired by prosthesis (especially valvular, arterial or myocardial), or repaired by transgenic tissue graft (including a graft in the presence of specific growth factors such as FGF).

Abstract: An endocardial lead having first and second spaced apart electrodes resides in a patient's heart. The first electrode is a sensing electrode and the second electrode is a carrier signal driving electrode. The lead has a conductor coupling a source of alternating current carrier signals of a predetermined frequency to the second electrode. A third electrode is in electrical contact with body tissues. A cardiac pacer apparatus includes a pacer can which functions as a fourth electrode and has a plastic top wherein the third electrode is located. Said third electrode acts in cooperation with the first electrode to form a pair of sensing electrodes. The sensing electrode pair is further coupled to a sense amplifier for receiving an amplifying modulated electrical signals developed across the sensing electrode pair. A demodulator and filters circuit for demodulating the modulated carrier signal and recovering the modulating signal therefrom is connected to the output of the sense amplifier.