Protection circuit and method for implanted ECG telemetry circuits

• US 4,741,341 A
• Filed: 03/12/1986
• Issued: 05/03/1988
• Est. Priority Date: 03/12/1986
• Status: Expired due to Term

• Current Assignee: Pacesetter Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Siemens Pacesetter, Inc. (Abbott Laboratories Incorporated)
• Inventors: Marach, Ronald R.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US06/839,233
• Time in Patent Office: 783 Days
• Field of Search: 128/419 PG, 128/696, 128/697, 128/903
• US Class Current: 607/32
• CPC Class Codes: A61N 1/37 Monitoring; Protecting
• CPC Class Codes: A61N 1/3718 Monitoring of or protection against external electromagnetic fields or currents
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

A protection circuit for an implanted telemetry circuit used to telemeter ECG or other low level signals sensed on the same lead whereon high level stimulation or other signals may also appear. The protection circuit includes a first FET switch that selectively connects a buffered monitoring point of the lead to the input of the telemetry circuit whenever a telemetry mode of operation is desired. A second FET switch switchably connects the buffered monitoring point to ground in the presence of any high level signals appearing on the lead, thereby preventing such high level signals from being applied to the telemetry circuit.

Claims

1. In a cardiac pacemaker system comprised of a pacemaker having a pulse generator that generates high level stimulation pulses, a lead connected to said pacemaker through which said pacemaker may deliver high level stimulation pulses to a desired cardiac location and through which low level cardiac signals may be sensed, a receiver remote from said pacemaker, and telemetry means within said pacemaker for transmitting signals applied thereto to said receiver, a means for preserving the integrity of the low level signals comprising:

first switch means for selectively connecting said lead to an input signal line of said telemetry means whenever said high level stimulation pulses are not being delivered over said lead and whenever a telemetry mode is enabled, and for disconnecting said lead from said input signal line whenever said high level stimulation pulses are being delivered over said lead,

buffer means interposed between said first switch means and said lead for buffering said telemetry means from signals and stimulation pulses appearing on said lead; and

second switch means for selectively connecting the first switch means side of said passive buffer means to a fixed voltage potential within said pacemaker when a high-level signal appears on said lead.

2. The pacemaker of claim 1 further including control circuit means coupled to said pulse generator for generating control signals that control when the pulse generator generates said high level stimulation pulses, and wherein said first and second switch means comprise FET switches that are turned on and off with control signals generated by said control circuit means.

3. The pacemaker of claim 2 wherein said FET switches comprise P-channel FET switches.

4. In an implantable circuit having a pulse generator for generating high level stimulation pulses, a lead connected to said pulse generator for delivering said high level stimulation pulses to a desired tissue location, and a telemetry modulation circuit connected to said lead, said telemetry modulation circuit including means for transmitting to a location remote from said implantable circuit low level signals appearing on said lead, said telemetry modulation circuit having an input signal range limited to low level analog signals, a protection circuit for preventing the high level stimulation signals from appearing at an input terminal of the telemetry modulation circuit, said protection circuit comprising

a first semiconductor switch that couples the low level analog signals appearing on said lead to the input terminal of said modulation circuit during selected intervals when said pulse generator is not generating said high level stimulation pulses;

buffer means connected between said lead and said input terminal of said first semiconductor switch; and

a second semiconductor switch that connects the first semiconductor switch side of said buffer means to a fixed voltage potential within said implantable circuit whenever said pulse generator is generating said high level stimulation pulses.

5. The protection circuit of claim 4 wherein said first semiconductor switch and said second semiconductor switch comprises P-channel enhancement mode FET transistors.

6. A method for preventing undesirable high level stimulation signals from being applied to an input terminal of a telemetry circuit included within an implantable device, said implantable device having means for generating high level stimulating signals, a lead connected to said generating means and said telemetry circuit through which said high level stimulation signals are selectively delivered and through which low level signals are sensed, said implantable device further having a means for providing power thereto that includes a fixed reference potential, said method comprising the steps of:

(a) buffering a monitoring point connected to said lead with a passive buffer element, both said high level stimulation signals and said low level signals appearing on said lead being detectable at said monitoring point;

(b) switchably connecting the monitoring point of step (a) to said fixed reference potential during the same time that high level stimulation signals appear on said lead; and

(c) switchably connecting the monitoring point of step (a) to the input terminal of the telemetry circuit whenever it is desired to telemeter low level signals and whenever said high level stimulation signals are not present on said lead.