ECG Necklace: Low-power Wireless Necklace for Continuous ECG monitoring

Research Background and Problem

• Identified Issues or Challenges: Current continuous electrocardiogram (ECG) monitoring tools, such as Holter monitors and smartwatches, face a trade-off between long-term wearability and electrode placement accuracy. While Holter monitors provide standardized electrode placement, their complex wiring and bulky equipment result in poor comfort. On the other hand, smartwatches can only record ECGs for short durations and do not support continuous monitoring.

• Significance: Cardiovascular diseases are the leading cause of death globally, with many symptoms being intermittent or "silent," such as asymptomatic heart attacks. These symptoms may go unnoticed without continuous monitoring, leading to late diagnoses. Continuous monitoring is critical for early intervention and disease detection.

• Research Motivation and Related Work: Current smart ECG monitoring devices, such as watches and chest straps, compromise between comfort and clinical diagnostic capability, failing to meet the demands of true daily continuous monitoring. Identifying a form factor that is both comfortable and accurate—such as a necklace, a natural accessory worn close to the chest—can provide standard Lead I ECG placement and address the aforementioned issues.

Proposed Solution

• Proposed Solution: The authors designed a low-power wireless necklace as a continuous ECG monitoring device. This necklace leverages the natural positioning of a necklace on the human body, placing two electrodes on the left and right sides of the chest to approximate the standard Lead I electrode configuration. Additionally, a novel adhesive-free silicone electrode based on skin moisture enhancement was developed to improve wearability and signal quality.

• Innovations:

  1. Electrode Design Innovation: Utilizing skin moisture as a "gel electrode" to mitigate the evaporation issues of traditional gel electrodes, while creating a moist microenvironment through a silicone barrier to prevent skin irritation.
  2. Device Form Factor Innovation: The necklace, as a widely accepted daily accessory, combines fashion with functionality, making it more suitable for everyday use.
  3. Miniaturization and Power Optimization: The main processing unit has a diameter of only 22mm and weighs 4 grams, offering up to 4 days of battery life.

• Implementation Steps and Key Technologies:

  1. Necklace Design: Optimizing electrode placement based on the natural shape of a necklace to enhance signal quality while maintaining aesthetic appeal.
  2. Hardware Selection: Using the MAX30003 chip and nRF52832 microcontroller to achieve high-quality ECG detection and data transmission.
  3. Experimental Evaluation: Evaluating the performance of the electrodes and signal quality of the necklace design through experiments, and comparing it with FDA-approved Holter devices.

Research Outcomes

• Specific Outcomes:

  1. Technical Performance: The ECG necklace provides signal quality comparable to FDA-certified Holter monitors, with key timing errors ranging from 3.2–15.7 milliseconds, well below the generally acceptable error range of 20 milliseconds.
  2. Wearability: In "all-day wear" experiments, participants strongly preferred the necklace over traditional chest strap devices, reporting higher comfort levels.
  3. Electrode Performance: The silicone electrodes of the ECG necklace, with a diameter of only 15mm, achieved signal quality comparable to standard gel electrodes.

• Advantages Compared to Existing Solutions:

  1. The necklace design significantly improves acceptability and comfort.
  2. The innovative electrode design avoids skin irritation issues associated with traditional gel electrodes while leveraging natural skin moisture to enhance signal quality.
  3. The device's size and weight are significantly smaller than existing ECG monitoring devices, supporting longer continuous usage.

• Experimental or Evaluation Results:

  1. During daily activities (e.g., using a phone, chatting), the effective ECG signal ratio of the necklace averaged 79.65%, with an SNR of 21.23dB, slightly higher than the 19.33dB of the Polar chest strap device.
  2. Signal synchronization with standardized devices showed that the timing errors for key P, R, and T waves were within acceptable ranges.

• Limitations and Future Directions:

  • Limitations:
    1. Performance has not been tested on areas with significant body hair or under specific skin conditions.
    2. Some users may experience signal quality degradation due to unstable electrode contact during activities.
  • Future Directions:
    1. Testing the clinical utility of the necklace for cardiac patients.
    2. Exploring additional sensor configurations to develop the necklace into a comprehensive health monitoring platform.
    3. Improving wear stability, such as adding weighted components to the electrodes.

Conclusion

This study proposes an innovative ECG necklace that integrates comfort, practicality, and technical performance to provide a solution for continuous ECG monitoring with extended battery life. A series of experiments validated the reliability of its signal quality and wearability, demonstrating its potential for use in daily scenarios. In the future, this necklace could be further developed into a multifunctional platform combining health monitoring and fashionable design.