Abstract: An implantable cardiac stimulator for detecting and treating cardiac arrhythmias includes a sense amplifier responsive to sensed cardiac signals for detecting and distinguishing normal and abnormal cardiac activity within the sensed signals. The sense amplifier includes an automatic gain control amplifier, a filter and quad comparator having a pair of signal channels for processing the sensed signals according to different frequency bandpass characteristics to establish sensing thresholds, margins and signal gain. The sense amplifier has a feedback loop containing a microprocessor which implements preselected algorithms in conjunction with the outputs of the quad comparator to variably adjust the amplifier gain and to programmably control the sensing margin.

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 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 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: 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 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 implantable microprocessor-controlled dual chamber heart pacemaker is programmed to control the timing of the pacing of the ventricle in response to high rate atrial signals. The microprocessor operates in conjunction with an atrial timer to detect atrial signals which occur at a rate in excess of a predefined atrial rate limit. The microprocessor paces the ventricle at a predefined desirable demand rate and inhibits pacing of the atrium in response to the high rate atrial activity. The microprocessor also controls the timing of an atrial refractory interval which includes an absolute refractory portion during which atrial signals are not detected and a relative refractory portion during which atrial signals are detected but are not tracked. The combined absolute and relative atrial refractory portions insure that relatively high rate atrial signals are detected and spurious signals conducted from the ventricle are ignored.

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.

Abstract: An external command device and an internal decoding and verification device are used to non-invasively alter the operating parameters of a programmable device implanted in an animal body. Thus, physiological changes can be easily accommodated by the implanted device. In a preferred embodiment, pulse position modulation is used to externally encode the command information. A resulting string of current pulses generates voltage spikes (in the internal decoding device) through inductively coupled coils. Each incoming data bit is verified and the entire command word is verified. After verification, the decoded command is transferred to a command register for simultaneously altering the selected operating parameters. The internal receiver circuitry may conveniently utilize energy from the induced voltage spike, using passive components for forming an output suitable for processing.

Abstract: A method and apparatus are provided for detecting and arresting a condition of tachycardia. Stimulating pulses are provided in a search routine within a selected time interval after a tachycardia beat. The heart is monitored after each pulse application and the search is terminated when a normal heartbeat is detected. In a preferred search routine, the refractory interval of the heart adjacent the electrode is determined during a first search routine. If the first search routine does not terminate the tachycardia, the refractory interval found during the search is stored. A second pulse is then applied in a time interval following the refractory interval pulse to break the tachycardia. The breaking interval is determined through a second search routine generated in an interval following the refractory interval pulse.