Impedance Phase Angle Classifier for Cardiac Catheter Contact
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Solution Overview
Problem
Existing methods for verifying electrode contact with cardiac tissue during ablation procedures are unreliable, particularly due to binary impedance-based contact indications that are sensitive to changes in impedance between the body-surface electrode and skin.
Innovation Solution
A method involving the determination of impedance phase angles between an electrode and the heart wall, with a binary classifier set between the minimum and maximum phase angles, and hysteresis factors to accurately assess and report contact states, ensuring reliable contact verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If binary impedance-based contact indication is used, then the device complexity is reduced, but the measurement precision and reliability of contact detection deteriorates
Solution Approach 1:
The patent transitions from binary impedance magnitude thresholds to multi-parameter impedance phase angle analysis. By measuring phase angles at multiple frequencies (e.g., 40 Hz, 80 Hz, 120 Hz) and comparing them against predetermined ranges, the system achieves more precise contact detection. This parameter-based approach distinguishes between true contact and false positives caused by impedance variations, resolving the contradiction between simplicity and accuracy.
2Ease of operation
If binary impedance threshold method is used, then the ease of operation is improved, but the reliability of contact indication deteriorates due to sensitivity to impedance changes
Solution Approach 1:
The system implements feedback by continuously monitoring impedance phase angles and comparing them against predetermined ranges that represent contact and non-contact states. The controller provides real-time feedback about contact status based on whether measured phase angles fall within the contact range or non-contact range. This feedback mechanism maintains reliability while preserving ease of operation through automated classification.
Solution Approach 2:
The patent introduces impedance phase angle as an intermediary parameter between the raw impedance measurement and the final contact decision. Instead of directly using impedance magnitude thresholds that are sensitive to variations, the phase angle serves as a more stable mediator that reliably indicates contact status. This intermediary approach filters out false signals while maintaining system simplicity.
3Measurement precision
If impedance phase angle analysis with binary classifier is implemented, then the measurement precision of contact detection is improved, but the device complexity increases
Solution Approach 1:
The patent segments the impedance analysis into distinct frequency components by measuring phase angles at multiple frequencies (e.g., 40 Hz, 80 Hz, 120 Hz). Each frequency provides independent information about contact status. The controller evaluates each frequency's phase angle separately against predetermined ranges, then integrates these segmented measurements to make the final contact determination. This segmentation improves precision while keeping processing manageable through modular analysis.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a more reliable and adaptive method for determining contact states, reducing the risk of delivering ablation energy while the electrode is out of contact with the endocardium and improving the accuracy of ablation procedures.
Implementation Method 1
A measurement circuit adapted to measure impedance may be implemented between the electrode and ground as the electrode approaches a target tissue. A processor or processing units may be implemented to determine a contact condition for the target tissue based at least in part on reactance of the impedance measured by the measurement circuit. In another embodiment, the contact condition may be based on the phase angle of the impedance.
Data Source
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AI summary
Cardiac catheterization is carried out by memorizing a designation of a contact state between an electrode of the probe and the heart wall as one of an in-contact state and an out-of-contact state, and making a series of determinations of an impedance phase angle of an electrical current passing through the electrode and another electrode, identifying maximum and minimum phase angles in the series, and defining a binary classifier adaptively as midway between the extremes. A test value is compared to the classifier as adjusted by a hysteresis factor, and a change in the contact state is reported when the test value exceeds or falls below the adjusted classifier.