Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-06-07
2001-12-25
Jastrzab, Jeffrey R. (Department: 3262)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06334071
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to implantable devices providing cardiac therapy to a patient, and more particularly to pacemakers adapted to provide pacing on demand in single- or dual-chamber modes for patients suffering from bradycardia (pacing rates lower than the sinus rhythm). Frequently, such devices are also incorporated into implantable cardioversion devices (ICDs) used to treat tachyarrhythmias. More particularly, the present invention pertains to pacemakers which provide pacing on demand using a metabolic demand parameter such as minute volume to determine the optimal pacing rate.
Minute volume (MV, sometimes referred to as minute ventilation) has become accepted in the industry as a metabolic demand parameter because it is indicative of the respiration rate and tidal volume of the patient.
BACKGROUND OF THE INVENTION
Prior to the present invention, minute volume has been typically measured using three electrodes, with two of the electrodes being in the same cardiac chamber (i.e., either the atrium or the ventricle), and the third electrode being at the end of a lead or comprising the pacemaker case. A current was passed between one of the electrodes in the cardiac chamber and the third electrode. The resulting voltage between the other electrode in the cardiac chamber and the third electrode was measured. The current and the voltage values were then used to determine the transthoracic impedance dynamically. (See, for instance, U.S. Pat. No. 4,702,253.) A problem with this approach is that it requires at least two electrodes disposed within the heart. As a result, MV type pacemakers could not be implanted to replace old pacemakers using a unipolar lead (with only one electrode), or a bipolar lead one of whose wires is broken (thus also having only one effective electrode).
U.S. Pat. No. 4,901,725 shows how to determine minute volume using standard bipolar leads, each bipolar lead consisting of a ring and a tip electrode. In this patent, current is injected between the ring electrode and the pacemaker case. The voltage between the tip electrode and the case is used to determine the transthoracic impedance.
U.S. Pat. No. 5,562,712 teaches how to measure MV using two unipolar leads, the two leads terminating at electrodes in different cardiac chambers. This configuration is useful when an MV pacemaker replaces a standard pacemaker coupled to two unipolar leads, rather than a bipolar lead.
Of course, a major disadvantage of all these arrangements is that they still require at least two electrodes in the heart of the patient. In the prior art, an MV pacemaker could not be used to replace a pacemaker used with a unipolar lead, or used with a multi-wire lead in which only one wire is still intact.
SUMMARY OF THE INVENTION
In general terms, the subject application pertains to a rate-responsive pacemaker using MV as the metabolic indicating parameter, and which requires only a single distal electrode, such as the electrode of a unipolar lead, to measure the MV parameter. Preferably, the pacemaker measures the MV parameter by providing two electrodes on the case of the pacemaker, and using the distal electrode of the lead as the common return. In this manner, current can be injected between one of the case electrodes and the distal electrode, and what is sensed is the resulting voltage between the second case electrode and the distal electrode. In one configuration, the case is provided with two dot electrodes. In another configuration, all or most of the surface of the pacemaker case is used as one of the case electrodes, and a dot electrode (insulated electrically from the rest of the case) is used as the other case electrode.
A pacemaker constructed in accordance with this invention includes a case having two electrodes, with a lead coupled to (but insulted from) the case having a distal electrode in a cardiac chamber. The case and the distal electrode are arranged so that they span the pleural cavity of the patient.
The pacemaker includes a sensing amplifier for sensing intrinsic cardiac activity, a timing and control circuit coupled to the sensing amplifier which generates trigger signals, and a pace generator that generates pacing pulses in response to the trigger signals.
Importantly, the pacemaker further includes a metabolic demand sensor circuit for sensing the metabolic demand of the patient. The timing and control circuit, which is based on a microprocessor, is coupled to the metabolic demand sensor circuit so that it can operate in a rate-responsive mode.
The metabolic demand sensor circuit includes a current source arranged to inject a current between one of the case electrodes and the distal electrode. The metabolic demand sensor circuit further includes a voltage monitor circuit that monitors the resulting voltage between the second case electrode and the distal electrode. This voltage is used as a measure of the transthoracic impedance.
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Jastrzab Jeffrey R.
Pacesetter Inc.
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