Cardiac pacemaker and method for detecting cardiac signals

• US 5,228,437 A
• Filed: 05/06/1991
• Issued: 07/20/1993
• Est. Priority Date: 05/06/1991
• Status: Expired due to Term

• Current Assignee: Intermedics Incorporated
• Original Assignee: Intermedics Orthopedics, Inc.
• Inventors: Schroeppel, Edward A.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US07/696,160
• Time in Patent Office: 806 Days
• Field of Search: 128/419 PG
• US Class Current: 607/18
• CPC Class Codes: A61N 1/365 controlled by a physiological parameter, e.g. heart potential evoked response A61N1/371

Abstract

An apparatus for detecting an electrical potential in a human body to control the delivery of a therapy. The electrical potential comprises a principal signal and a baseline signal. The apparatus samples the potential through an electrode during a selected interval and stores the value of that potential at the end of the interval. The stored value of the potential will be restored as an initial condition on the electrode at the end of a second interval after delivery of the therapy. In a heart pacemaker, the baseline signal is useful for controlling the output pulses of the pacemaker. The apparatus permits sensing of the baseline signal despite stimulating pulses and charge canceling.

Claims

1. An apparatus for delivering a controlled therapy to a human body in response to a detected electrical potential comprising a principal signal and a baseline signal, said apparatus comprising

an electrode adapted to be connected to said human body to detect said electrical potential;

timing means for timing a series of first and second intervals;

means for sensing said electrical potential during said first intervals;

means for storing the magnitude of said baseline potential at the end of said first intervals;

means responsive to said principal signal and said baseline signal for delivering said therapy to said human body during selected second intervals;

means for canceling an electrical after-effect of said therapy during said selected second intervals; and

means for recreating the stored magnitude of said baseline signal at said electrode at the end of said second intervals.

2. The apparatus according to claim 1 further comprising means for compensating for expected losses in recreating the stored value of said baseline signal.

3. The apparatus according to claim 1 further comprising a ground potential and wherein said canceling means comprise means for connecting the electrode to said ground potential prior to recreating the stored value of the electrical potential.

4. The apparatus according to claim 1 further comprising a plurality of switches, at least one switch selectively connecting and disconnecting each of the storing means, the recreating means, and the canceling means to said electrode and wherein said timing means further comprises means for controlling said switches to connect said storing means to said electrode at the end of said first intervals, said recreating means at the end of said second intervals, and said canceling means during said second intervals.

5. A heart pacemaker comprising

means for generating stimulating pulses of electrical charge for application to the heart of a patient;

a lead adapted to connect said pacemaker to the heart;

at least one electrode on said lead;

means for sensing an electrical potential in the heart, said electrical potential comprising a baseline potential and periodic QRS signals, said sensing means comprising

means for canceling the charge of said stimulating pulses,

means for sensing said QRS signals,

timing means for timing a series of first and second intervals;

means for sensing said baseline potential during said first intervals;

means remote from said electrode for storing the magnitude of said baseline potential at the end of said first intervals; and

means for recreating at said electrode the stored magnitude of said baseline potential at the end of said second intervals; and

means responsive to said electrical potential sensing means for pacing the heart as a function of said sensed QRS signals and said sensed baseline potential.

6. The heart pacemaker according to claim 5 further comprising means for compensating for expected losses in recreating the stored magnitude of said baseline potential.

7. The heart pacemaker according to claim 5 wherein said pacemaker further comprises a ground potential and wherein said means for canceling the charge of said stimulating pulses further comprise means for connecting the sensing means to said ground potential prior to recreating the stored magnitude of the baseline potential at said electrode.

8. The heart pacemaker according to claim 5 further comprising a plurality of switches, at least one switch selectively connecting and disconnecting each of the storing means, the recreating means, and the charge canceling means to said electrode and wherein said timing means further comprises means for controlling said switches to connect said storing means to said electrode at the end of said first intervals, said recreating means at the end of said second intervals, and said charge canceling means during said second intervals.

9. A method for pacing a human heart comprising the steps of

timing a series of first and second intervals;

detecting said electrical potential through an electrode during said first intervals said electrical potential comprising a series of QRS signals and a baseline potential;

storing the magnitude of said baseline potential at the end of said first intervals;

selectively pacing the heart during said second interval;

canceling a charge created at said electrode by said pacing;

recreating the stored value of said baseline potential at the end of said second intervals.

10. The method for pacing a human heart according to claim 9 further comprising compensating for expected losses in recreating the stored value of said baseline potential.

11. The method for pacing a human heart according to claim 10 wherein the charge canceling step comprises connecting said electrode to a ground potential prior to recreating the stored value of the electrical potential.

12. The method for pacing a human heart according to claim 11 further comprising selectively connecting and disconnecting storing means, recreating means, and ground connecting means to said electrode.