Cardiac Impedance Artifact Reduction in Implantable Devices
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Solution Overview
Problem
Implantable medical devices (IMDs) face challenges in collecting high-quality cardiac impedance data due to interference from pacing pulses, which can result in crosstalk and loss of measurement, especially given the small dynamic range of intracardiac impedance variations.
Innovation Solution
An IMD system with a cardiac impedance sensor circuitry and an artifact reduction module that manages therapy timing and active impedance collection windows to avoid pacing pulses during data collection, and reconstructs impedance data using polynomial fits, interpolation, or sinusoidal curve fitting to remove artifacts, applying high and low pass filters as needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pacing pulses are delivered during impedance data collection, then cardiac therapy is provided, but artifacts are introduced into the impedance data stream
Solution Approach 1:
The patent segments the impedance data collection process into multiple windows, with the first window excluding the pacing pulse artifact period. By dividing the measurement timeline into segments (pre-pace, during-pace, post-pace) and selectively using only the clean segments for measurement, the system achieves high-quality impedance data without compromising therapy delivery.
Solution Approach 2:
The patent performs preliminary identification of the artifact period duration based on pacing pulse characteristics before actual impedance measurement. By pre-calculating the artifact window and establishing exclusion criteria in advance, the system prepares the measurement protocol to automatically avoid contaminated data points, ensuring reliable impedance measurements from the outset.
2Measurement precision
If impedance measurement occurs during pacing pulse delivery, then continuous monitoring is maintained, but measurement precision deteriorates due to crosstalk and disconnection
Solution Approach 1:
The patent implements periodic impedance measurement windows that are synchronized with the cardiac cycle and pacing rhythm. By establishing regular measurement intervals that occur during artifact-free periods (such as during the T-wave or between paced beats), the system maintains continuous monitoring capability while ensuring each measurement occurs under optimal conditions for precision.
Solution Approach 2:
The system pre-identifies optimal measurement windows by analyzing the pacing regimen and cardiac rhythm in advance. By determining ahead of time which time intervals will be artifact-free based on expected pacing events, the system can confidently schedule high-precision measurements during these pre-approved windows without compromising overall monitoring continuity.
3Measurement precision
If artifact reduction through reconstruction is applied, then signal fidelity is improved, but device complexity increases
Solution Approach 1:
The patent extracts and removes the identified artifact portions from the impedance data stream by simply excluding the time periods containing pacing pulse artifacts. Rather than applying complex reconstruction algorithms, the system takes out the contaminated segments and relies on the clean segments for measurement, significantly reducing computational complexity while maintaining signal fidelity.
Solution Approach 2:
The system uses the inherent structure of the cardiac cycle and pacing rhythm to automatically identify and exclude artifact periods without external intervention. By leveraging the known timing relationships between pacing pulses and cardiac events, the device self-manages the artifact reduction process through simple temporal exclusion logic, avoiding the need for complex external processing or advanced reconstruction techniques.
Data Source
AI summary
An implantable medical device, comprised of at least one lead configured to be located proximate to a heart, the at least one lead including electrodes, at least a portion of the electrodes configured to sense cardiac activity. A therapy module configured to control delivery of pacing pulses in accordance with a therapy timing and based on the cardiac sensed activity sensed. Cardiac impedance (CI) sensor circuitry configured to be coupled to at least a first combination of the electrodes to sense cardiac impedance (CI), the CI sensor circuitry generating an impedance data stream associated with a corresponding CI sensing vector.