Method and apparatus for reducing far-field interchamber interference in an implanted medical device
An implantable medical device comprises at least two sensing channels for receiving sensed first and second location electrical signals originating from two different locations of a heart. A control unit is connected to the sensing channels and is adapted to process sensed electrical signals originating from first and second locations of the heart. The control unit incorporates an adaptive filter compensator adapted to generate an estimate signal for compensating a far-field contribution of the second location signal to the first location signal, thereby generating an output signal representing a near field signal originating from the first location. A gate is connected to the second location sensing channel and is adapted to enable the adaptive filter compensator only if a predetermined signal is sensed via the second location sensing channel.
1. An implantable medical device comprising:
at least two sensing channels for receiving sensed first and second location electrical signals originating from two different locations of a heart;
a control unit connected to said sensing channels and being adapted to process the sensed electrical signals originating from the first and second locations of the heart, wherein the control unit incorporates an adaptive filter compensator adapted to generate an estimate signal for compensating a far-field contribution of the second location signal to the first location signal, and adapted to generate an output signal representing a near field signal originating from the first location using said estimate signal to reduce inter-chamber interference; and
a gate connected to the second location sensing channel and being adapted to enable the adaptive filter compensator only if a predetermined signal is sensed via the second location sensing channel;
wherein the device includes a morphology restoration block to restore an original morphology of the first location sensed after any said inter-chamber interference encountered in the implantable medical device is reduced by the adaptive-filter compensator; and
wherein the morphology restoration block includes an on/off switchable integrator, said integrator being adapted so that the integrator's output tracks the output signal while the adaptive filter compensator is not enabled, but sums the basic output signal values to the integrator's output whenever the adaptive filter compensator is enabled.
2. The implantable medical device according to claim 1 , wherein the gate is adapted to enable the adaptive filter compensator for a predetermined period of time.
3. The implantable medical device according to claim 1 , wherein the adaptive filter compensator comprises an L-stage least mean square adaptive filter.
4. The implantable medical device according to claim 1 , wherein the first location electrical signal is an atrial signal and the first sensing channel is an atrial sensing channel.
5. The implantable medical device according to claim 4 , wherein the first sensing channel is adapted to be connected to an intracardiac electrode lead having an atrial sensing electrode to be placed in an atrium of a heart.
6. The implantable medical device according to claim 1 , wherein the second location electrical signal is a ventricular signal and the second sensing channel is a ventricular sensing channel.
7. The implantable medical device according to claim 6 , wherein the second sensing channel is adapted to be connected to an intracardiac electrode lead having a ventricular sensing electrode to be placed in a ventricle of a heart.
8. The implantable medical device according to claim 4 , wherein the far-field contribution of the second location signal to the first location signal to be compensated is a far-field QRS signal originating from a ventricle and is sensed via the atrial channel and that the adaptive filter compensator is adapted to generate a compensation signal being approximately inverse to the far-field QRS signal sensed via the atrial channel.
9. The implantable medical device according to claim 1 , wherein the adaptive filter compensator has an input for an a noise reference input signal to be processed for generating the compensation signal, said noise reference input signal being a ventricular sensing signal.
10. The implantable medical device according to claim 1 , wherein the device comprises a preprocessor for preprocessing a noise reference input signal prior to processing by the adaptive filter compensator.
11. The implantable medical device according to claim 10 , wherein the preprocessor for preprocessing noise reference input signal comprises a fixed coefficient finite impulse response (FIR) filter.
12. The implantable medical device according to claim 1 further comprising a filter coefficient updater comprising a step size normalizer and, wherein the adaptive filter compensator comprises an L-stage least mean square filter which is connected to the filter coefficient updater.
13. The implantable medical device according to claim 1 , wherein the control unit is adapted to determine for each actual event in the second location sensed signal a new set of actual coefficients determining the operation of the adaptive filter compensator.
14. The implantable medical device according to claim 6 , wherein the far-field contribution of the second location signal to the first location signal to be compensated is a far-field QRS signal originating from a ventricle and is sensed via the atrial channel and that an adaptive filter compensation means is adapted to generate a compensation signal being approximately inverse to the far-field QRS signal sensed via the atrial channel.