Abstract: A connector for a lead of a tissue stimulator such as a cardiac pacer uses a wedging element to fix the lead against inadvertent withdrawal from the pacer header. A wedge member is received in a channel which intersects a bore in the header in which the lead is inserted for connection with a pulse generator. When the wedging member is pressed into its channel, as by simple finger pressure, it engages the lead off-axis, e.g. along a tangent, and forces the lead into tight engagement with the sidewall of the header bore. A present embodiment is adapted for use with a lead which has a deformable covering. The wedge member has a concavity formed therein within which the lead seats. A first end of the wedge member has an upraised portion which is hump-shaped. This upraised portion first cams the lead into engagement with the bore sidewall, and then passes beyond the lead by deforming the lead covering. The lead then seats in the concavity.

Abstract: An active fixation mechanism for a pacemaker lead with a tissue-stimulating electrode has a rigid hook for engaging tissue pivotally fastened to the lead in the vicinity of the electrode. The tip of the hook is normally resiliently urged into a recess in the lead adjacent to the electrode. A mechanism is coupled to the lead to permit the normal bias on the hook tip to be selectively overcome to position the hook outwardly of the lead. In this position, the hook is deployed to engage tissue in the vicinity of the electrode. The force applied to deploy the hook may be removed to allow the hook to move back into the recess under the normal bias. Sufficient force applied to the hook while deployed, along the axis of the lead, will cause the hook to assume a position beyond the distal end of the lead, in which it is precluded from engaging tissue.

Abstract: A microprocessor controlled A-V responsive rate adaptive DDD cardiac pacemaker is disclosed. The pacemaker includes atrial and ventricular sense amplifiers for detecting P-waves and Q-waves respectively, atrial and ventricular stimulus pulse generators, and A-V interval timer times the interval between a P-wave and subsequent Q-wave. The timed interval is used by a pacing interval calculation algorithm to calculate an A-A pacing interval based on one of two linear functions depending upon whether atrial activity is spontaneous or induced. The pacing interval timer times the pacing interval. If no atrial activity is detected, the atrial stimulus pulse generator paces the atrium. The A-V interval timer also times a maximum A-V interval. If no ventricular activity is sensed in the interval, the ventricular stimulus pulse generator paces the ventricle.

Abstract: An implantable medical device for controlling a physiological function includes functional apparatus for controllably duplicating the selected normal physiological function of the patient's body. A sensor detects the physical orientation of the implanted medical device within the body, which is indicative of whether the patient is standing, sitting or reclining. The sensor is also responsive to forces of acceleration on the medical device within the body, indicative of the state of rest or activity movement of the patient. Apparatus in the device is responsive to the physical position and the physical state of the patient, as detected by the sensor, to control the duplication of the normal physiological function according to that position and state. In one embodiment, the medical device is a cardiac pacemaker and the physiological function is heart rate.

Abstract: An implantable cardiac stimulator integrates the functions of bradycardia and anti-tachycardia pacing-type therapies, and cardioversion and defibrillation shock-type therapies. The stimulator is programmable to provide a multiplicity of hierarchical detection algorithms and therapeutic modalities to detect and treat classes of ventricular tachycardia according to position within rate range classes into which the heart rate continuum is partitioned, and thus according to hemodynamic tolerance, with backup capabilities of defibrillation and bradycardia pacing at the higher and lower regions of the rate continuum outside the range of the ventricular tachycardia classes. Aggressiveness of the therapy is increased with elapsed time and increasing heart rate, and detection criteria are relaxed with increasing heart rate and thus with increasing hemodynamic intolerance of the tachycardia.

Abstract: A pair of defibrillation patch electrodes is adapted for close fitting placement over the ventricles of the heart, either epicardially or pericardially. One of the patches is contoured to fit over the right ventricle, and the other is contoured to fit over the left ventricle in spaced relationship to the first patch to form a substantially uniform gap between confronting borders of the two. The gap is sufficiently wide to avoid the shunting of current between edges of the patches upon delivery of defibrillation shocks, as well as to accommodate the ventricular septum and the major coronary arteries therein. The size and shape of the patches is such that they encompass most of the ventricular myocardium within and between their borders, to establish a nearly uniform potential gradient field throughout the entire ventricular mass when a defibrillation shock is delivered to the electrodes. Flat versions of the two electrodes provide ease of manufacture.

Abstract: In a method and apparatus for defibrillating a heart in fibrillation, the onset of fibrillation of the heart is detected, and a biphasic waveform having only a first phase and a second phase is applied to the fibrillating heart. Each phase of the waveform is characterized by a predetermined time duration and by a predetermined polarity and magnitude of voltage, the duration of the first phase being greater than the duration of the second phase, and the initial voltage magnitude of the first phase being greater than that of the second phase. The biphasic waveform is applied by delivering it to a pair of patch electrodes affixed over and contoured to conform substantially to the surface of the right and left ventricles, respectively. The patch electrodes are affixed to either the epicardium or the pericardium. The left ventricular patch electrode is used as the cathode for the first phase of the applied biphasic waveform, and as the anode for the second phase.

Abstract: A controller for variably controlling the pacing rate of a cardiac pacer responsive to temperature which includes a logic and control unit, a parameter communication unit, an analog to digital converter and a temperature sensor. The temperature sensor in the right ventricle or atrium communicates a value related to blood temperature through the analog to digital converter to the logic and control unit. The logic and control unit operates under control of the rate algorithm to calculate a pacing rate value related to variations in the blood temperature. The pacing rate value is calculated as the sum of a reference rate, a natural rate response term, and a dynamic rate response term which contributes rate only in response to physical activity. A step rate response is also added to the calculated pacing rate when predetermined criteria related to the blood temperature and calculated pacing rate indicate the onset of physical activity.

Abstract: An apparatus suitable for use in an implantable automatic defibrillation system for automatically generating a multiphasic defibrillation pulse waveform in response to sensed fibrillation has first and second series charge-storing capacitors having a common terminal and two other terminals each at different potentials. A controller senses cardiac fibrillation and generates a control signal which causes a charging circuit to charge the capacitors to selected voltage levels in sequentially alternating charge generation and charge coupling cycles. A voltage level detector senses the stored voltage level, disables the charging circuit when the sensed voltage reaches a predetermined level, and informs the controller that the capacitors are fully charged.

Abstract: A stimulus generator for a stimulation rate-adaptive cardiac pacemaker has a detector for sensing a first physiological parameter in the pacemaker patient, selected on the basis that heart rate is a function of that parameter, such as central venous blood temperature, and another detector for sensing a second physiological parameter in the patient representative at any given time of either patient activity or patient inactivity, such as a motion sensor. Two different algorithms are stored relating heart rate to the first physiological parameter, one for patient inactivity and the other for patient activity, in which the activity algorithm specifies a greater rate of change of heart rate than that specified by the inactivity algorithm relative to a unit change of said first physiological parameter. A decision rule is implemented based on the measurement of the second physiological parameter, by which a decision is to be made for selecting between the two different algorithms.

Abstract: An electrode for use in cardiac pacing has a substrate composed of a material conventionally employed for pacing electrodes, and a surface layer or film of iridium oxide overlying the substrate. For use as a stimulating cathodic electrode and a sensing electrode, the iridium oxide layer is arranged to be in cardiac tissue stimulating relationship when the electrode is in proper position with respect to the patient's heart. The electrode impresses electrical stimuli on the excitable myocardial tissue, and at the completion of each stimulus, the electrode is capable of abruptly sensing, within an interval less than 100 ms thereafter, the electrical activity of the heart in response to the stimulus to verify capture. The surface of the electrode may be provided with recesses to which the iridium oxide layer may be confined.

Abstract: An electrical circuit is connected in series with a lead of an implantable heart pacemaker between the pacemaker and the heart to protect the pacemaker against high voltages and currents produced by defibrillators and other sources. The electrical circuit has a sensing resistor arranged between two normally conducting field effect transistors (FETs) all in electrical series with the pacemaker lead. When the voltage drop across the sensing resistor exceeds a predetermined positive or negative amplitude, a transistor becomes conductive and turns off the normal conduction channels of the FETs. An alternate, electrically conductive high-impedance path is switched in to limit the current flow to the pacemaker until the magnitude of the voltage across the sensing resistor drops to a safe level. The transistor then becomes non-conductive and the FETs become conductive re-establishing the normal low-impedance conduction path and effectively switching the alternate high-impedance path out of the circuit.

Abstract: A dual chamber cardiac pacemaker is programmable for either unipolar or bipolar pacing of the atrium or the ventricle, independently of the pacing mode for the other chamber. Transistor switches are utilized for selectively connecting the various anodic electrodes to ground such that one of those electrodes is grounded at all times and isolation is maintained from circuit paths for non-selected modes. Switch control is effected using signals having the highest voltage level of proper polarity in the system, to assure maintenance of the selected switch states despite possible random voltages arising from external influences. Cumulative buildup of charge on coupling capacitors is prevented by selectively and actively discharging them after the respective chamber is paced.

Abstract: A passive stabilizer for an electrode lead of a cardiac pacemaker for maintaining the electrode tip in interstitial contact with the endocardium until a sufficient amount of tissue ingrowth has occurred to secure the electrode tip in place. The passive stabilizer is secured to the lead of the cardiac stimulating device adjacent the electrode tip and comprises a sleeve having at least two groups of resilient tines, each group of tines being longitudinally displaced along the axis of the conductive lead with a first group being disposed between the second group and the electrode tip. The tines extend radially outwardly from the lead at a substantially right angle, with the tines of the first group extending outwardly a distance less than that of tines of the second group. Additionally, the tines of the first group are circumferentially staggered with respect to the tines of the second group.

Abstract: A temperature driven rate responsive cardiac pacemaker adapted to distinguish between physiologically determined changes of the patient's blood temperature under conditions of exercise and non-exercise, and to adaptively vary the rate at which stimuli are generated accordingly, is also capable of recognizing the blood temperature dip which is characteristic of the commencement of exercise. In response to such a temperature dip, the pacemaker initiates a rapid and physiologically beneficial increase in the stimulation rate. To assure the proper selective initiation of a rate increase, the pacemaker discriminates between a blood temperature drop indicative of the onset of exercise and those temperature drops which occur for other reasons, such as upon cessation of exercise or as normal phasic variations, including respiration and circadian fluctuations.

Abstract: A microprocessor-controlled pacemaker is programmed to extend an atrial refractory interval in response to the detection of events which could initiate a pacer sustained tachycardia. The extended atrial refractory interval ensures that a spurious atrial event resulting from retrograde conduction of a ventricle event will not cause a pace of the ventricle. The pacer is also programmed to break out of a pacer sustained tachycardia by inhibiting a ventricular pace when a predefined number of previous successive ventricular paces have occurred at the ventricular rate limit. The pacer is further programmed so that in response to a high atrial rate, the ventricle is paced at either a predefined ventricular upper rate limit value or at a rate limit value that is decremented to a fallback rate limit value. The pacer further increases the VA interval when the ventricle is paced at the ventricular rate limit.

Abstract: An exercise responsive cardiac pacemaker (1) has a stimulation electrode (3) for introduction into the atrium or ventricle of the heart, a temperature sensor (4) situated in proximity to the electrode (3) for detecting the blood temperature, and a control circuit (8, 9, 10, 11) connected to the electrode (3) and the temperature sensor (4) by which the stimulation rate of the pacemaker is adaptively adjusted depending on the blood temperature. To ensure that the cardiac pacemaker works reliably in all physiological conditions of a patient, the stimulation rate is determined with reference to a field of characteristic curves (K1, K2), the individual characteristic curves constituting distinct algorithms relating heart rate to blood temperature for different physiological conditions of the pacemaker patient. A basic characteristic curve (K2) relates distinct heart rates to absolute blood temperatures under conditions without physical stress on the pacemaker patient.

Abstract: An electrode for use in cardiac pacemaking has a conductive tip portion including a substrate composed of a material conventionally employed for pacing electrodes, and a layer of film of iridium oxide overlying the surface of the substrate. The tip portion may be provided with recesses to which the iridium oxide surface layer may be confined. An iridium oxide layer may be formed on both the cathode and the anode for efficient transduction at the electrode-electroyte interface in the environment of the pacemaker patient's body.

Abstract: An improved voltage level shifter circuit employs pairs of P and N-channel devices which are operated in response to control signals to generate a voltage shifted output signal that corresponds in timing and polarity to an input data signal. The P and N-channel devices interact in latched pairs to maintain logic levels for the output signal. The P-channel and N-channel devices of each pair are disconnected prior to each logic level change for the output signal so that the devices of each pair do not oppose one another in changing the logic level of the output signals.

Abstract: A cardiac pacemaker lead has a structure which provides an enhanced sensitivity to atrial P-waves. The distal end of the lead has two sensing electrodes disposed thereon to contact atrial cardiac tissue and to detect near field P-waves with greater sensitivity than far field R-waves.