Abstract: A system and method for preventing atrial competition during sensor-driven operation of a dual-chamber pacemaker includes means for sensing atrial activity during an atrial refractory period. Atrial competition is avoided by either: (1) generating an atrial competition prevention (ACP) interval upon the detection of any atrial activity during the relative refractory portion of an atrial refractory period, and preventing any atrial stimulation pulses from being generated for the duration of such ACP interval; or (2) shortening the atrial refractory period in the event that the sensor-driven rate of the pacemaker begins to approach a rate that might place atrial stimulation pulses near the end of the unshortened atrial refractory period.

Abstract: A low-power band-pass filter for use in a cardiac pacer includes a single operational amplifier connected in circuit relationship with a plurality of switched capacitors that function as bilinear resistors. Each bilinear resistor comprises a switch for coupling a first lead of a capacitive element to a first terminal and for coupling a second lead of the capacitive element to a second terminal in response to a first state of a control signal, and for coupling the first lead of the capacitive element to the second terminal and for coupling the second lead of the capacitive element to the first terminal in response to a second state of the control signal. Thus, the bilinear resistor switches or oscillates the electrical orientation of the capacitive element between the first terminal and the second terminal in response to the first and second states of the control signal. The invention also includes a method of operating such an implantable filter circuit.

Abstract: A dual-chamber implantable pacemaker automatically adjusts its AV interval so that any ventricular stimulation pulses generated by the pacemaker at the conclusion of the pacemaker-defined AV interval occur at a time in the cardiac cycle that avoids fusion with the natural ventricular depolarization of a patient's heart. The AV interval is set using a search sequence that sets the AV interval value to be on one side or the other of the natural conduction time of the heart, and incrementally changes the AV interval value until it crosses over the natural conduction time interval. The cross-over point is manifest by the occurrence of an R-wave, where an R-wave had previously been absent, or the absence of an R-wave, where an R-wave had previously been present. A final AV interval value is then set as the AV interval value at the cross-over point, adjusted by appending an AV margin thereto.

Abstract: A bifurcated lead adapter or lead used with an implantable stimulation device, such as a pacemaker, forms part of a stimulation system and method that senses depolarization of the ventricular muscle tissue, and in response thereto, generates a stimulus (composed of a single pulse or multiple closely-spaced pulses) that is delivered to translocated muscle tissue wrapped around the ventricle of the heart, thereby causing the translocated muscle tissue to contract in synchrony with the sensed ventricular depolarization. In one embodiment, a pacemaker operates in the single-chamber triggered stimulation mode analogous to VVT mode. A bifurcated bipolar lead adapter has a proximal connector that is connected to the pacemaker's bipolar female input/output connector. The adapter couples the anode electrode of the pacemaker's bipolar input/output connector to a first female distal connector, and couples the cathode electrode of such bipolar input/output connector to a second female distal connector.

Abstract: An implantable cardioverter-defibrillator (ICD) provides a tiered therapy designed to automatically terminate tachyarrhythmias using the least aggressive therapy possible while reducing the "time-to-therapy." The tiered therapy first applies a first tier of therapy (e.g., antitachycardia). If unsuccessful, the tiered therapy next applies a second tier of therapy (e.g., cardioversion pulse with a pulse of moderate energy). If unsuccessful, the tiered therapy finally applies a third tier of therapy (e.g., a high energy pulse). So that more aggressive (higher energy) tiered therapies may be applied as early as possible following the failure of a less aggressive (lower energy) therapy, the ICD begins charging one or more high voltage capacitors of the ICD in parallel with the application of the less aggressive therapy, and/or in parallel with the verification interval immediately following a prior therapy attempt during which the ICD attempts to verify the successful termination of the tachyarrhythmia.

Abstract: A sense amplifier adapted for use with a cardiac pacer or the like includes a constant gain filter, a window comparator circuit and a programmable threshold reference generator circuit. The reference generator circuit generates a programmable window (reference) voltage used by the window comparator circuit to determine whether an input signal, amplified by the constant gain filter, exceeds the window voltage. The reference generator circuit is based on a bipolar junction device having an adjustable emitter area through which a constant current flows. The emitter area is adjusted in response to a control signal. As the emitter area changes as controlled by the control signal, the voltage across the device changes. In a preferred embodiment, a parallel combination or network of switched bipolar junction devices is used to realize the adjustable emitter area.

Abstract: A method and system for monitoring the behavior of an implanted pacemaker counts (records) the number of times that a given internal event or state change of the pacemaker occurs, and also determines the rate at which each event or state change thus counted occurs. The event counts and their associated rate are stored (recorded) in appropriate memory circuits housed within the pacemaker device. At an appropriate time, the stored event count and rate data are downloaded to an external programming device. The external programming device processes the event count and rate data, and displays a distribution of the event count data as a function of its rate of occurrence, as well as other statistical information derived therefrom. The displayed information, and its associated statistical information, allows a baseline recording to be made that establishes the implanted pacemaker's behavior for a given patient under known conditions.

Abstract: A system and method for preventing atrial competition during sensor-driven operation of a dual-chamber pacemaker includes means for sensing atrial activity during an atrial refractory period. Atrial competition is avoided by either: (1) generating an atrial competition prevention (ACP) interval upon the detection of any atrial activity during the relative refractory portion of an atrial refractory period, and preventing any atrial stimulation pulses from being generated for the duration of such ACP interval; or (2) shortening the atrial refractory period in the event that the sensor-driven rate of the pacemaker begins to approach a rate that might place atrial stimulation pulses near the end of the unshortened atrial refractory period.

Abstract: A rate-responsive pacing system and method allows the inter-related sensor operating parameters associated with the physiological sensor of a rate-responsive pacemaker to be automatically and/or optimally set for a particular patient. The system includes both a pacemaker and an external programming device. The pacemaker includes appropriate memory circuits for recording a sensor indicated rate (SIR) signal in a histogram. The external programming device retrieves the SIR histogram data, as well as other data associated with the operation of the pacemaker, and selectively processes and displays such data in a prescribed manner. An Auto-Set sequence or routine, carried out by the external programming device, sets all of the rate-responsive operating parameters to a known initial value and places the pacemaker in a passive mode. In the passive mode the SIR signal does not control the pacing rate. The Auto-Set routine then displays instructions for the physician that cause diagnostic data to be collected.

Abstract: A system and method for preventing atrial competition during sensor-driven operation of a dual-chamber pacemaker includes means for sensing atrial activity during an atrial refractory period. Atrial competition is avoided by either: (1) generating an atrial competition prevention (ACP) interval upon the detection of any atrial activity during the relative refractory portion of an atrial refractory period, and preventing any atrial stimulation pulses from being generated for the duration of such ACP interval; or (2) shortening the atrial refractory period in the event that the sensor-driven rate of the pacemaker begins to approach a rate that might place atrial stimulation pulses near the end of the unshortened atrial refractory period.

Abstract: An implantable pacemaker provides three types of hysteresis for use in dual chamber and/or atrial tracking modes, such as VDI, VDD, DDI, DDD, VDIR, VDDR, DDIR or DDDR. The pacemaker defines a basic atrial escape interval (AEI) that defines the maximum time between a ventricular event and a subsequent atrial event, as well as an AV delay (AVD) that defines the maximum time between an atrial event and the next ventricular event. The sum of AEI plus AVD thus sets the rate at which stimulation pulses are generated in the absence of sensed natural cardiac activity. A first type of hysteresis, atrial escape rate hysteresis, causes the AEI to be extended upon sensing natural atrial beats (P-waves). The increased AEI remains in force so long as natural P-waves continue to be sensed during the AEI. Should a P-wave not be sensed during the AEI, a stimulation pulse is generated and the AEI reverts to its initial value.

Abstract: An implantable programmable pacemaker includes a sensor for measuring SO.sub.2 levels in blood on a periodic basis, e.g., every 15 seconds, while the pacemaker is operating in its programmed mode of operation. The energy of stimulation pulses generated by the pacemaker is automatically adjusted, as required, in order to maintain a prescribed level of SO.sub.2 in the blood. At least a minimum level of SO.sub.2 is presumed when the stimulation pulses are of sufficient energy to effectuate capture. Hence, the SO.sub.2 level is monitored to provide an indication of whether capture has been lost, and if so, to increase the stimulation energy. In one embodiment, the stimulation energy is increased by first increasing the pulse width of the stimulation pulse a prescribed amount. After the pulse width has been increased a maximum amount, and if capture is still lost, the stimulation energy is further increased by increasing the pulse amplitude a prescribed amount.

Abstract: A system within an implantable stimulation device and a method for limiting the extent to which any high power consumption modes, such as a rate response mode, can be utilized during low battery periods. A battery threshold detector is utilized to detect when the battery is below a predetermined threshold. The implantable stimulation device then switches from a high current drain mode of operation to progressively lower current drain modes of operation. This configuration allows a significant reduction in current drain at RRT and further prevents the output amplitude from dropping below the capture level and prevents the remaining battery capacity from being rapidly used up.

Abstract: A system and method for terminating a cardiac arrhythmia includes pacing means for stimulating the heart with at least one stimulation pulse during a narrow region of susceptibility (termination window) of the arrhythmia cycle. The location of the region of susceptibility is initially found by delivering the stimulation pulse(s) to the heart in accordance with a prescribed scan pattern. The scan pattern delivers the stimulation pulse(s) at a time during the cardiac cycle such that each successive stimulation pulse is presented to the heart at a slightly different time than was a prior stimulation pulse, thereby assuring that the region of susceptibility or termination window is eventually located. When the arrhythmia is successfully terminated, the location of the successful stimulation pulse within the prescribed scan pattern is stored.

Abstract: An implantable pacemaker having means for detecting and responding to a premature ventricular contraction (PVC), also includes circuit means for minimizing the likelihood of sensing a PVC when in fact a PVC has not occurred. The circuit means latches the occurrence of any atrial events sensed during the relative atrial refractory period of the pacemaker, whether such atrial events are noise or an early P-wave; and, in response to such latching, disables the PVC detection circuit until certain prescribed events occur, whereupon the PVC detection circuit is re-enabled. The prescribed events that re-enable the PVC detection circuit after it has been disabled include, e.g., the occurrence of a ventricular pulse or sensed R-wave. Further, in the event a PVC is detected and a desired PVC response is invoked, an additional circuit means automatically terminates the PVC response in the event the PVC response becomes stuck.

Abstract: An implantable pacemaker provides a paced AV delay that is automatically adjusted to include patient variations in latency conduction, that is, the time interval between a stimulus to the heart and an evoked potential, time due to lead position and specific patient latency. An AV timer, designed to provide a programmed AV interval, starts its timing operation at the generation of an atrial pulse, and restarts the timing operation again at the occurrence of the evoked atrial potential. The evoked atrial potential is typically monitored from a ring electrode of a bipolar lead relative to the pacemaker can (case), although other monitoring configurations are also possible. The length of the AV intrval is programmed to a desired value using conventional programming techniques.

Abstract: A rate-responsive pacing method and system senses the minimum blood oxygen saturation in the right atrium of a patient's heart and uses such minimum blood oxygen saturation as a control parameter for indicating the muscular activity of a patient. Because the oxygen content of the venous blood in the right atrium varies significantly as venous blood from all parts of the body is introduced therein, evidencing differing levels of oxygen demand throughout the patient's body, the minimum oxygen content of the venous blood provides an accurate and reliable measure of those portions of the patient's body experiencing the greatest oxygen demand, i.e., experiencing muscular activity. A rate-responsive pacing system includes means for sensing the minimum oxygen content in the right atrium over a prescribed time interval, and using such minimum oxygen content as a control parameter for adjusting the rate of the pacemaker.

Abstract: A self-adjusting rate-responsive pacemaker includes a conventional programmable pulse generator, a physiological sensor, and a processor, all packaged within an implantable case. The pulse generator generates heart stimulation pulses on demand, or as otherwise programmed, as controlled by a sensor-indicated rate signal. The sensor-indicated rate signal is derived from a raw signal obtained from the physiological sensor, and provides some indication of whether the heart rate should increase or decrease. The processor converts the raw signal to the sensor-indicated rate signal in accordance with a desired relationship (FIGS. 2, 3, 7A, 8). A minimum sensor signal value sets the minimum rate at which the pacemaker generates stimulation pulses, and a maximum sensor signal value sets the maximum rate at which the pacemaker generates stimulation pulses.

Abstract: A pacemaker mediated tachycardia (PMT) is detected by circuitry within an implantable pacemaker. The PMT is detected by first detecting a tachycardia condition that includes a prescribed number of consecutive cardiac cycles having a rate faster than a prescribed rate. Each cardiac cycle of the tachycardia condition includes a natural atrial event, i.e., a P-wave, and a paced ventricular event, i.e., a V-pulse generated by a pacemaker. After the prescribed number of such cardiac cycles, e.g., two to ten, a P-V delay in a single cardiac cycle is modified by a first prescribed amount, e.g., 50 milliseconds. The time interval of a V-P interval associated with at least one cardiac cycle preceding the modified P-V delay is then compared to a V-P interval immediately following the modified P-V delay. Only if the difference between the V-P intervals thus measured is less than a second prescribed amount, e.g., 25 milliseconds, is a PMT indicated. If a PMT is indicated, a PMT termination regimen, e.g.

Abstract: A switched-capacitor, band-pass, programmable amplifier is used as a sense amplifier in an implantable cardiac pacemaker. Switching means are used to switchably connect various capacitors to the same amplifier circuits. Clock generator means are used to generate clock signals that are used to control the rate at which the switching means operates. By programmably selecting the switching rate to be a desired value, the band-pass characteristics and gain of the sense amplifier may be varied. When a pacemaker stimulation pulse occurs, the band-pass characteristics and/or gain of the sense amplifier, may also be automatically varied to improve amplifier recovery time. The rate at which the capacitors are switchably connected to the amplifier circuits, may be selected remotely, thereby allowing the band-pass characteristics to be programmable.