Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-07-22
2001-02-13
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06188928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for tissue stimulation, and in particular a heart pacemaker, for detection of a response to a stimulation pulse when the measured signal is corrupted by an electrode polarisation artefact.
2. Description of the Prior Art
It is desirable that pacemakers have a low energy consumption such that the battery lasts longer. To enable the reduction of the energy consumption it must be clear whether there has been a capture (=a heart contraction/evoked response) or not at the prevailing stimulation voltage. For a proper detection of capture, it is important that the artefact at stimulation, i.e. the polarization voltage, is not so large that it is detected as capture. If the polarization voltage could be eliminated the detection of capture would be easier and more reliable.
U.S. Pat. No. 4,543,956 discloses a system for detecting the evoked response in which the polarization is neutralized using a biphasic waveform technique whereby a compensating current pulse is transmitted in the opposite direction from the stimulating current pulse. However, the compensating current pulse is often emitted very close in time to the stimulation pulse, the recharge pulse thus tending to mask the electrical response from the heart and in particular in the case where a unipolar electrode is used.
U.S. Pat. No. 5,431,693 discloses a pacemaker for detecting capture based on the observation that the non-capture potential is exponential in form and the evoked response potential, while generally exponential in form, has one or more small-amplitude perturbations superimposed on the exponential waveform and whereby the perturbations are enhanced for ease of detection. The perturbations involve relatively abrupt slope changes, which are enhanced by processing the waveform signal differentiation. Abrupt slope changes in the second derivative are used to detect morphological features indicative of capture which are otherwise difficult to discriminate.
U.S. Pat. No. 5,165,405 relates to a pacemaker comprising means for acquiring the curve of the polarisation phenomenon by stimulating the tissue with a stimulation energy lying below the stimulation threshold, so that the electrical potential signal in the tissue subsequently acquired by the detector means corresponds to the polarization phenomena produced by the stimulation attempt without these having an evoked response of the tissue superimposed thereon. By regularly updating the polarisation signal, an optimal compensation of the polarisation components contained in the acquired electrical potential signal is achieved for the purpose of detecting an evoked response.
U.S. Pat. No. 5,417,718 defines a pacemaker that includes a so called Autocapture™ system for automatically maintaining the energy of the stimulation pulses generated by the pacemaker at a predetermined level safely above that needed to effectuate capture. The Autocapture™ system performs its function by comparing the electrical evoked response of the heart following the generation of a stimulation pulse to a polarization template determined by a capture verification test. During the capture verification test, the Autocapture™ system causes the pacemaker to first generate a series of pacing pulse pairs. The first pulse of the pair has a high energy to ensure capture. The second pulse of the pair is of the prescribed stimulation energy. The signal corresponding to the second pulse (which signal is dominated by polarization information) is sensed through a sensing circuit having a specified sensitivity setting. Such signal is stored as the polarization template corresponding to that particular energy and sensitivity setting. In view of the lead polarization signal not being easily characterised, due to it being a complex function of e.g. the lead materials, lead geometry, tissue impedance, stimulation energy, most of which are continuously changing over time, the capture verification test creates a table of polarization templates as a function of sensitivity settings for a particular stimulation energy.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus for tissue stimulation wherein the reaction of the tissue to the stimulation is reliably detected independently of the presence of a polarization voltage.
The invention is embodied in an apparatus for tissue stimulation achieving a reliable capture detection which would make it possible to use different pacemakers with one and the same electrode, and in particular a unipolar electrode. This would be highly favorable for patients who have an already implanted and well functioning unipolar electrode, but who are in need of a new pulse generator due to e.g. battery end of life (EOL) and/or in need of a more modern pacemaker e.g. comprising the Autocapture™ function.
Due to a faster detector unit response, another advantage would be the possibility of more reliably reducing the stimulation voltage needed for capture (Autocapture™ function).
These advantages are achieved in accordance with the invention, which is based on the observation that a detected heart signal and any signal disturbing the detected heart signal, e.g. a polarisation signal, can be approximated by mathematical functions. These functions comprise parameters. These parameters are different for each of these mathematical functions depending on if the stimulation pulse has caused capture or not. By letting the pacemaker during a predetermined time interval register the electrode signal for determining the parameters for one or more different mathematical functions, one or several parameters can be used to determine the activity of the heart, i.e. if the registered electrode signal corresponds to capture or non capture.
In a preferred embodiment the mathematical functions may be more or less direct or indirect and hence, an autocorrelation calculation may be needed before the determination of the parameters. A regression analysis may also be appropriate. Moreover, by using a recursive autoregression model the parameters for the detected signal with respect to the corresponding stimulation pulse may be used as a means for detecting the evoked response. Furthermore, a Kalman filter may be used to determine the parameters, especially if the signals have properties known beforehand.
In a preferred embodiment the parameters are continuously determined during a time interval of 10 ms to 120 ms after a stimulation pulse and evaluated in a window from 15 ms to 120 ms or 50 to 100 ms. In another preferred embodiment the parameters are determined and evaluated only once at a point between 50 and 100 ms and preferably at 60 ms after the stimulation pulse.
REFERENCES:
patent: 4245643 (1981-01-01), Benzing, III et al.
patent: 4305395 (1981-12-01), Wittkampf et al.
patent: 4543956 (1985-10-01), Herscovici
patent: 5165405 (1992-11-01), Eckwall
patent: 5330512 (1994-07-01), Hauck et al.
patent: 5417718 (1995-05-01), Kleks et al.
patent: 5431693 (1995-07-01), Schroeppel
patent: 5443485 (1995-08-01), Housworth et al.
patent: 5549643 (1996-08-01), Kroll et al.
patent: 5571144 (1996-11-01), Schroeppel
patent: 5735883 (1998-04-01), Paul et al.
Hirschberg Jakub
Noren Kjell
Strandberg Hans
Kamm William E.
Pacesetter AB
Schiff & Hardin & Waite
LandOfFree
Apparatus for tissue stimulation does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for tissue stimulation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for tissue stimulation will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2609428