Subcutaneous insertable cardiac monitor optimized for long term, low amplitude electrocardiographic data collection

• US 10,736,531 B2
• Filed: 11/01/2018
• Issued: 08/11/2020
• Est. Priority Date: 09/25/2013
• Status: Active Grant

• Current Assignee: Bardy Diagnostics, Inc. (Baxter International Inc.)
• Original Assignee: Bardy Diagnostics, Inc. (Baxter International Inc.)
• Inventors: Bardy, Gust H., Felix, Jason
• Primary Examiner(s): Getzow, Scott M.
• Application Number:
  US16/178,468
• Publication Number:
  US 20190069800A1
• Time in Patent Office: 649 Days
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/259 using conductive adhesive means, e.g. gels
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/287 Holders for multiple electrodes, e.g. electrode catheters for electrophysiological study [EPS]
• CPC Class Codes: A61B 5/332 Portable devices specially adapted therefor
• CPC Class Codes: A61B 5/335 using integrated circuit memory devices
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/6823 Trunk, e.g., chest, back, abdomen, hip
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7232 involving compression of the physiological signal, e.g. to extend the signal recording period
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

Long-term electrocardiographic and physiological monitoring over a period lasting up to several years in duration can be provided through a continuously-recording subcutaneous insertable cardiac monitor (ICM). The sensing circuitry and the physical layout of the electrodes are specifically optimized to capture electrical signals from the propagation of low amplitude, relatively low frequency content cardiac action potentials, particularly the P-waves that are generated during atrial activation. In general, the ICM is intended to be implanted centrally and positioned axially and slightly to either the left or right of the sternal midline in the parasternal region of the chest. Additionally, the ICM includes an ECG sensing circuit that measures raw cutaneous electrical signals and performs signal processing prior to outputting the processed signals for sampling and storage.

Claims

1. A subcutaneous insertable cardiac monitor (ICM) optimized for long term, low amplitude, electrocardiographic (ECG) data collection, comprising:

an implantable housing comprised of a biocompatible material that is suitable for implantation within a living body;

at least one pair of ECG sensing electrodes provided on a ventral surface and on opposite ends of the implantable housing operatively placed to facilitate sensing in closest proximity to the low amplitude, low frequency content cardiac action potentials that are generated during atrial activation; and

electronic circuitry provided within the implantable housing, the electronic circuitry comprising;

a low power microcontroller comprising firmware and operable to execute under modular micro program control as specified in the firmware;

an ECG front end circuit interfaced to the microcontroller and configured to capture the cardiac action potentials sensed by at least the pair of ECG sensing electrodes which are output as ECG signals, the ECG front end comprising;

a signal lead operable to sense the cardiac action potentials through one of the ECG sensing electrodes;

a reference lead operable to sense the cardiac action potentials through the other of the ECG sensing electrodes;

a termination resistor, a filter capacitor, and an operational amplifier through which a current of the sensed cardiac action potentials passes in a direct sequence prior to being output as the ECG signals; and

a reference generator comprising a pair of resistors configured to inject a driven reference containing power supply noise and system noise into the body; and

a non-volatile memory electrically interfaced with the microcontroller and operable to continuously store samples of the ECG signals.

2. A monitor according to claim 1, further comprising:

an analog-to-digital converter operable to convert the ECG signals into digital representations of the cardiac activation wave front amplitudes;

at least one low pass filter comprised in the firmware; and

at least one high pass filter comprised in the firmware,

wherein the cardiac activation wave front amplitudes are passed through the at least one low pass filter and the at least one high pass filter following conversion into the digital representations.

3. A monitor according to claim 2, further comprising:

a transceiver interfaced to the microcontroller and operable to wirelessly interface to a wireless network;

a download station comprising;

a data link operable to interface with the electronic circuitry via the wireless network; and

a download station controller configured to be removably connected to the electronic circuitry via the data link and operable to execute under programmable control as specified in software, the software comprising;

a data retrieval module configured to retrieve the samples of the ECG signals from the non-volatile memory; and

a data storage module configured to store the retrieved samples of the ECG signals into local storage.

4. A monitor according to claim 3, the software further comprising:

at least one software-implemented low pass filter that corresponds to the at least one low pass filter comprised in the firmware;

at least one software-implemented high pass filter that corresponds to the at least one high pass filter comprised in the firmware; and

a phase distortion correction module configured to run the retrieved samples of the ECG signals through each of the at least one software-implemented low pass filter and the at least one software-implemented high pass filter in a direction reversed respectively from the at least one low pass filter comprised in the firmware and the at least one high pass filter comprised in the firmware.

5. A monitor according to claim 3, the software further comprising:

a software-implemented bidirectional impulse infinite response (IIR) high pass filter; and

a phase distortion correction module configured to run the retrieved samples of the electrocardiographic signals through the IIR high pass filter first in a forward direction and then in a reverse direction.

6. A monitor according to claim 3, the software further comprising:

a software-implemented P-wave base boost response filter adapted to restore missing frequency content in the retrieved samples of the ECG signals.

7. A monitor according to claim 3, the software further comprising:

an automatic gain adjustment module configured to apply a gain to the digital signals to the retrieved samples of the ECG signals.

8. A monitor according to claim 1, further comprising:

a compression algorithm comprised in the firmware,

wherein the cardiac activation wave front amplitudes are compressed with the compression algorithm into compressed digital representations prior to being stored in the non-volatile memory.

9. A monitor according to claim 1, further comprising:

an AC coupling capacitor through which the current passes directly before passing through the termination resistor.

10. A monitor according to claim 9, wherein the power supply noise and the system noise comprised within the driven reference are received from the power cell.

11. A subcutaneous implantable loop recorder for long term electrocardiographic (ECG) monitoring, comprising:

a hermetically sealed implantable housing and comprised of a biocompatible material that is suitable for implantation within a living body of a patient;

at least one pair of ECG sensing electrodes provided on a ventral surface and on opposite ends of the implantable housing operatively placed to facilitate sensing in closest proximity to the low amplitude, low frequency content cardiac action potentials that are generated during atrial activation;

a power source comprised within the implantable housing; and

electronic circuitry provided within the housing, the electronic circuitry comprising;

a low power microcontroller comprising firmware and operable to execute under modular micro program control as specified in firmware;

an ECG front end circuit interfaced to the microcontroller and configured to capture the cardiac action potentials sensed by at least the pair of ECG sensing electrodes which are output as ECG signals, the ECG front end comprising;

a signal lead operable to sense the cardiac action potentials through one of the ECG electrodes;

a reference lead operable to sense the cardiac action potentials through the other of the ECG electrodes;

a termination resistor, a filter capacitor, and an operational amplifier through which a current of the sensed cardiac action potentials passes in a direct sequence prior to being output as the ECG signals; and

a reference generator comprising a pair of resistors configured to inject a driven reference containing power supply noise and system noise into the body, the pair of resistance connected to the power source by a connection pair through which the pair of resistors receives the system noise and the power noise comprised in the driven reference signal; and

a non-volatile memory electrically interfaced with the microcontroller and operable to continuously store samples of the ECG signals.

12. A recorder according to claim 11, further comprising:

an analog-to-digital converter operable to convert the ECU signals into digital representations of the cardiac activation wave front amplitudes;

at least one low pass filter comprised in the firmware; and

at least one high pass filter comprised in the firmware,

wherein the cardiac activation wave front amplitudes are passed through the at least one low pass filter and the at least one high pass filter following conversion into the digital representations.

13. A recorder according to claim 12, further comprising:

a transceiver interfaced to the microcontroller and operable to wirelessly interface to a wireless network;

a download station comprising;

a data link operable to interface with the electronic circuitry via the wireless network; and

a download station controller configured to be removably connected to the electronic circuitry via the data link and operable to execute under programmable control as specified in software, the software comprising;

a data retrieval module configured to retrieve the samples of the ECG signals from the non-volatile memory; and

a data storage module configured to store the retrieved samples of the ECG signals into local storage.

14. A recorder according to claim 12, further comprising:

a compression algorithm comprised in the firmware,

wherein the cardiac activation wave front amplitudes are compressed with the compression algorithm into compressed digital representations prior to being stored in the non-volatile memory.

15. A monitor according to claim 13, the software further comprising:

at least one software-implemented low pass filter that corresponds to the at least one low pass filter comprised in the firmware;

at least one software-implemented high pass filter that corresponds to the at least one high pass filter comprised in the firmware; and

a phase distortion correction module configured to run the retrieved samples of the ECG signals through each of the at least one software-implemented low pass filter and the at least one software-implemented high pass filter in a direction reversed respectively from the at least one low pass filter comprised in the firmware and the at least one high pass filter comprised in the firmware.

16. A recorder according to claim 11, further comprising:

a power up sequence stored as part of the firmware, wherein the microcontroller is operable to execute the power up sequence upon the monitor being implanted into the body.

17. A recorder in accordance with claim 11, wherein the electrocardiographic signals are output as an analog signal and the microcontroller acquires the samples by sampling the analog signal, each of the samples comprising a disruption in the analog signal.

18. A recorder in accordance with claim 17, further comprising:

a hold capacitor comprised in the microcontroller that is charged to supply the analog signal for the acquisition.

19. A recorder in accordance with claim 11, further comprising:

an AC coupling capacitor through which the current passes directly before passing through the termination resistor.

20. A recorder in accordance with claim 11, the electronic circuitry further comprising:

a transceiver interfaced to the microcontroller and operable to wirelessly interface to a wireless network.