An atrial and ventricular (bifocal) demand pacer. A device is disclosed for providing electrical stimulation to the atrium after a first pre-determined time, and to the ventricle after a second pre-determined time, where both pre-determined times are measured from the last natural heart-beat. The pacer monitors the ventricular endocardial electrogram and programs both the atrial and the ventricular stimulation accordingly. In patients with atrial bradycardia but normal AV conduction, only the atria are stimulated. When the condition is complicated with AV block, both the atria and the ventricles are pacer-controlled. The interval between the atrial and ventricular stimulation is selected to facilitate the proper atrio-ventricular timing sequence. The pacer does not compete with spontaneous ventricular contractions. A free-running atrial and ventricular demand pacer is disclosed for treating patients suffering from sinus arrest (no spontaneous atrial activity) concurrent with intermittent AV block.
This patent application is a continuation in part of copending patent application, Ser. No. 810,519 filed on Mar. 26, 1969 and which was issued as U.S. Pat. No. 3,595,242 on July 27, 1971. The parent application is entitled Atrial and Ventricular Demand Pacer filed in the name of the applicant of the present invention.
A dual pace--dual sense cardiac pacemaker pulse generator having ventricular and atrial sensing and pulse generating means interconnected by circuit means to cause the atrium to be stimulated in the event that a natural atrial contraction is not sensed within a certain time from the last ventricular stimulus or natural contraction and the ventricle to be stimulated in the event that a naturally ventricular contraction is not sensed within a further time from the last atrial contraction or stimulus.
A programmable pacemaker pulse generator capable of operating in several atrial and ventricular pacing modes having atrial and ventricular sense amplifiers and output circuits and programmable memory and clock controlled digital timing circuits for selectively delivering stimulating pulses to the heart in an atrial synchronous mode of operation. The ventricular sense amplifier has a blanking and refractory period following the sensing of a ventricular heartbeat or the occurrence of a stimulation pulse. Delay means operatively connected to the atrial sense amplifier operate to trigger the generation of a ventricular stimulating pulse after an A-V delay interval following a sensed atrial depolarization. The A-V delay interval is lengthened by means responsive to the detection of two or more ventricular depolarizations without an intervening atrial depolarization, so as to avoid the application of a ventricular stimulating pulse into the vulnerable period (or T-wave) of the heart. In addition, the ventricular refractory period is prolonged by a like interval. In this way the time intervals are prolonged to alleviate the possibility of harmful pacing into the heart's vulnerable period while allowing the ventricular stimulating pulse to be delivered after the delay in synchrony with the detected P-wave.
A programmable pacemaker pulse generator capable of operating in several atrial and ventricular pacing modes, having atrial and ventricular sense amplifiers and output circuits and programmable memory and clock controlled digital timing circuits for selectively delivering stimulating pulses to the heart in an atrial synchronous mode of operation. The ventricular sense amplifier has a blanking and refractory period following the sensing of a ventricular heartbeat or the occurrence of a stimulation pulse. Delay means are operatively connected to the atrial sense amplifier operate to trigger the generation of a ventricular stimulating pulse after an A-V delay interval following a sensed atrial depolarization. An atrial blanking interval extends for the A-V delay interval and until after the expiration of the ventricular blanking interval. Programmable upper date intervals are also provided. The ventricular amplifier output is sampled after a test interval shorter than the above mentioned intervals, and if an output signal persists, then all of the aforementioned intervals are prolonged by the interval of the persisting signal.
Atrial refractory and ventricular inhibit functions are independently implemented in an atrial-synchronized pacer. Spontaneous signals on the ventricular lead inhibit ventricular stimulation for a predetermined interval independent of the atria, except when there is noise on the ventricular lead. The atrial-based pacing logic establishes the usual refractory period following spontaneous P-waves, and when noise is detected on the atrial lead, the pacing logic reverts to a fixed atrial rate. The ventricular-inhibited logic includes a retriggerable noise timing circuit and a non-retriggerable inhibit timing circuit both triggered by the output of the ventricular sense amplifier. The output of the inhibit circuit disables the ventricular stimulation output circuit. However, if the output of the noise circuit stays high for an interval indicative of electromagnetic interference, the trigger input to the inhibit timing circuit is disabled to permit ventricular stimulation. Meanwhile, the pacing logic institutes fixed rate pacing due to atrial noise. In AV synchronous and atrial-synchronized AV sequential pacer embodiments, the digital pacing logic uses existing circuitry while the ventricular-inhibited logic is implemented by an add-on RC-timed circuit. In the AV sequential pacer, the AV delay circuit is separate from the pacing logic, and its input is provided by the atrial sense amplifier normally and by the output of the pacing logic during ventricular noise.
