Pacing channel isolation in multi-site cardiac pacing systems

• US 20030023280A1
• Filed: 07/30/2001
• Published: 01/30/2003
• Est. Priority Date: 07/30/2001
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Thompson, David L.
• Granted Patent: US 6,711,437 B2
• Time in Patent Office: Days
• US Class Current: 607/9
• CPC Class Codes: A61N 1/368 comprising more than one electrode co-operating with different heart regions A61N1/3622, A61N1/3627 take precedence
• CPC Class Codes: A61N 1/3704 Circuits specially adapted therefor, e.g. for sensitivity control

Abstract

Cardiac pacing systems are disclosed for providing multi-site pacing in a single heart chamber or multi-chamber pacing in two or more heart chambers employing N pacing channels and miniaturized electrical isolation circuitry in up to N−1 pacing channels to minimize the effects of leakage currents generated during delivery of a pacing pulse in any one pacing channel from affecting sense amplifiers in the other pacing channels. Isolation of a the pace/sense electrodes from leakage currents is effected employing monolithic isolation circuit means. An isolated current replicator employing giant magnetoresistive (GMR) sense elements in conjunction with isolated planar cells fabricated in monolithic form is incorporated into conventional VLSI circuitry. Or, the monolithic isolation circuit means is formed of a micro-mechanical fabricated (MEMS) isolation transformer comprising low-loss input and output coils separated by an insulation layer that isolates the input coil from the output coil.

Claims

1. A pacing system for providing pacing and sensing in at least two sites in the heart comprising:

a first pacing channel comprising;

a first lead having first pace/sense electrodes located for sensing spontaneous cardiac depolarizations and applying pacing pulses to a first site in the heart to stimulate an evoked depolarization thereof;

first sensing means for sensing heart signals resulting from spontaneous cardiac depolarizations at the first site and providing a first sensed event signal; and

first pacing pulse output means responsive to a first pace trigger signal for supplying first site pacing pulses to said first lead to pace the heart at the first site through said first pace/sense electrodes;

a second pacing channel comprising;

a second lead having second pace/sense electrodes located for sensing spontaneous cardiac depolarizations and applying pacing pulses to a second site in the heart to stimulate an evoked depolarization thereof;

second sensing means for sensing heart signals resulting from spontaneous cardiac depolarizations at the second site and providing a second sensed event signal, and

second pacing pulse output means responsive to a second pace trigger signal for supplying second site pacing pulses to said second lead to pace the heart at the second site through the second pace/sense electrodes; and

timing and control means for enabling sensing by said first and second sensing means and operating said first and second pacing pulse output means to selectively apply provide pacing pulses to said first and second site,

wherein leakage current paths are present in the pacing circuitry between the first and second pacing channels, and at least one of said first and second pacing channels is an isolated pacing channel further comprising monolithic isolation circuit means comprising an output current loop coupled with the pace/sense electrodes of the pacing channel and an input current loop coupled to the sensing means of the pacing channel, the input and output current loops formed as integrated circuit conductors isolated from one another,

whereby cardiac depolarization signals are conducted to the output current loop from the pace/sense electrodes coupled therewith and replicated in the input current loop, and the output current loop coupled with the pace/sense electrodes is isolated from leakage current paths to inhibit transmission of leakage currents into the output current loop.

2. The pacing system of claim 1, wherein the timing and control means further comprises:

escape interval timing means for timing a pacing escape interval from a first pace trigger signal or a first sensed event signal;

means for generating the first pace trigger signal upon time-out of the pacing escape to thereby provide a basic pacing rate for pacing the first site in the absence of a first sensed event signal during time-out of the pacing escape interval;

delay timing means responsive to the time-out of the pacing escape interval or sensing of the first sensed event signal prior to time-out of the pacing escape interval for commencing timing of a delay window; and

means for generating said second heart pace trigger signal at the time-out of said delay window.

3. The pacing system of claim 1, wherein the isolated pacing channel further comprises blanking means interposed between the input current loop and the inputs of the sensing means adapted to uncouple the input current loop from the sensing means inputs during a blanking period comprising at least the duration of delivery of the first pacing pulse or the second pacing pulse.

4. The pacing system of claim 1, wherein the pacing pulse output means of the isolated pacing channel is coupled to said input current loop whereby a pacing pulse generated by the pacing pulse output means coupled therewith is replicated in the output current loop and applied to the pace/sense electrodes coupled with the output current loop.

5. The pacing system of claim 4, wherein:

the input current loop is formed of an input current carrying conductor on an integrated circuit substrate having a magnetic field inducing coil; and

the output current loop is formed of an output current carrying conductor on the integrated circuit substrate; and

further comprising;

at least one giant magneto-resistive resistor situated with respect to and electrically isolated from the input current carrying conductor that has a first resistance in the absence of an input current signal applied to the input current carrying conductor and a second resistance when an input current signal is applied to the input current carrying conductor; and

replicating circuit means coupled to the at least one giant magneto-resistive resistor and the output current carrying conductor for replicating the pacing pulse applied to the input current loop to form the pacing pulse in the output current loop when the magneto-resistive resistor is changed in resistance by the applied pacing pulse.

6. The pacing system of claim 5, wherein the replicating circuit means comprises an operational amplifier having an amplifier input coupled to said giant magneto-resistive resistor and an amplifier output coupled to said output current carrying loop.

7. The pacing system of claim 4, wherein:

the input current loop is formed of an input current carrying conductor on an integrated circuit substrate including first and second magnetic field inducing coils that generate first and second magnetic fields when a current is induced in or applied to the input current carrying conductor; and

the output current loop is formed of a second current carrying conductor on the integrated circuit substrate including third and fourth magnetic field inducing coils that generate third and fourth magnetic fields when a current is induced in or applied to the output current carrying conductor; and

further comprising a bridge circuit comprising;

an operational amplifier formed on the integrated circuit having first and second amplifier inputs and an amplifier output coupled to said output current loop;

first, second, third and fourth giant magneto-resistive resistors situated with respect to and electrically isolated from the first, second, third, and fourth magnetic field inducing coils, respectively, each giant magneto-resistive resistor having a first resistance in the absence of an applied magnetic field and a second resistance when exposed to a magnetic field generated by a current applied through a magnetic field inducing coil; and

means for coupling the first, second, third and fourth giant magneto-resistive resistors to a current source and across the inputs of the operational amplifier in a bridge circuit such that the operational amplifier responds to a pacing pulse applied to the input current carrying conductor to replicate the pacing pulse in the output current carrying conductor when the first and second magneto-resistive resistors coupled with the first and second operational amplifier inputs are changed in resistance by the pacing pulse current and the operational amplifier responds to a cardiac depolarization signal on the output current carrying conductor to replicate the cardiac depolarization signal in the input current loop when the third and fourth magneto-resistive resistors coupled with the first and second operational amplifier inputs are changed in resistance by the cardiac depolarization current.

8. The pacing system of claim 4, wherein the isolated pacing channel further comprises blanking means interposed between the input current loop and the inputs of the sensing means adapted to uncouple the input current loop from the sensing means inputs during a blanking period comprising at least the duration of delivery of the first pacing pulse or the second pacing pulse.

9. The pacing system of claim 1, wherein:

the input current loop is formed of an input current carrying conductor on an integrated circuit substrate including first and second magnetic field inducing coils that generate first and second magnetic fields when a current is induced in or applied to the input current carrying conductor; and

the output current loop is formed of a second current carrying conductor on the integrated circuit substrate including third and fourth magnetic field inducing coils that generate third and fourth magnetic fields when a current is induced in or applied to the output current carrying conductor; and

further comprising a bridge circuit comprising;

an operational amplifier formed on the integrated circuit having first and second amplifier inputs and an amplifier output coupled to said output current loop;

first, second, third and fourth giant magneto-resistive resistors situated with respect to and electrically isolated from the first, second, third, and fourth magnetic field inducing coils, respectively, each giant magneto-resistive resistor having a first resistance in the absence of an applied magnetic field and a second resistance when exposed to a magnetic field generated by a current applied through a magnetic field inducing coil;

means for coupling the first, second, third and fourth giant magneto-resistive resistors to a current source and across the inputs of the operational amplifier in a bridge circuit such that the operational amplifier responds to a cardiac depolarization signal on the output current carrying conductor to replicate the cardiac depolarization signal in the input current loop when the third and fourth magneto-resistive resistors coupled with the first and second operational amplifier inputs are changed in resistance by the cardiac depolarization current.

10. The pacing system of claim 9, wherein the isolated pacing channel further comprises blanking means interposed between the input current loop and the inputs of the sensing means adapted to uncouple the input current loop from the sensing means inputs during a blanking period comprising at least the duration of delivery of the first pacing pulse or the second pacing pulse.

11. The pacing system of claim 1, wherein:

the input current loop is formed of an input current carrying conductor on an integrated circuit substrate having a magnetic field inducing coil;

at least one giant magneto-resistive resistor is situated with respect to and electrically isolated from the input current carrying conductor that has a first resistance in the absence of an input current signal and a second resistance when an input current signal is applied to the input current carrying conductor;

the output current loop is formed of an output current carrying conductor on the integrated circuit substrate; and

further comprising replicating circuit means coupled to the at least one giant magneto-resistive resistor and the input and output current carrying conductors for replicating a cardiac depolarization signal appearing in the output current loop upon the input current loop when the magneto-resistive resistor is changed in resistance by the input current signal.

12. The pacing system of claim 11, wherein the isolated pacing channel further comprises blanking means interposed between the input current loop and the inputs of the sensing means adapted to uncouple the input current loop from the sensing means inputs during a blanking period comprising at least the duration of delivery of the first pacing pulse or the second pacing pulse.

13. The pacing system of claim 11, wherein the replicating circuit means comprises an operational amplifier having an amplifier input coupled to said giant magneto-resistive resistor and an amplifier output coupled to said output current carrying loop.

14. The pacing system of claim 1, wherein the first site is one of a first heart chamber and a second heart chamber and the second site is the other of the first and second heart chamber.

15. The pacing system of claim 1, wherein the first site is one of the right atrium and the left atrium and the second site is the other the right atrium and the left atrium.

16. The pacing system of claim 1, wherein the first site is one of the right ventricle and the left ventricle and the second site is the other the right ventricle and the left ventricle.

17. The pacing system of claim 1, wherein the first site is one of an atrial heart chamber and a ventricular heart chamber and the second site is the other of the atrial heart chamber and the ventricular heart chamber.

18. The pacing system of claim 1, wherein the monolithic isolation circuit means is formed of a micro-mechanical fabricated (MEMS) isolation transformer comprising low-loss input and output coils separated by an insulation layer that isolates the input coil from the output coil.

19. The pacing system of claim 18, wherein the isolated pacing channel further comprises blanking means interposed between the low-loss output coil and the inputs of the sensing means adapted to uncouple the output current loop from the sensing means inputs during a blanking period comprising at least the duration of delivery of the first pacing pulse or the second pacing pulse.