Cardiac Stimulator Sensing Unit with Adaptive Thresholds
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Solution Overview
Problem
Existing implantable cardiac stimulators face challenges in reliably detecting ventricular fibrillation while effectively suppressing T wave oversensing, especially with fluctuating amplitude signals, as current methods either fail to adequately sense fibrillation waves or risk misinterpreting T waves as R peaks.
Innovation Solution
An implantable cardiac stimulator with a sensing unit that employs automatic threshold adaptation, using two switchable sensing thresholds and a VF detection window, where a first lower threshold is applied for VF detection, followed by a T wave blanking window at an upper threshold, and then a second lower threshold for continued sensing, with the duration of the VF detection window adjusted based on heart rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single sensing threshold is used for detecting cardiac events, then the device complexity is reduced, but the reliability of ventricular fibrillation detection deteriorates due to T wave oversensing
Solution Approach 1:
The patent implements dynamic threshold switching between a first sensing threshold (for VF detection) and a second sensing threshold (for T wave blanking) based on the cardiac cycle phase. The control unit automatically transitions between thresholds: using the first threshold during the VF detection window and switching to the second threshold during the T wave blanking window, thereby adapting the sensing parameters to different physiological conditions without manual intervention
Solution Approach 2:
The patent divides the cardiac cycle into distinct detection windows with different threshold requirements: a VF detection window using a first sensing threshold and a T wave blanking window using a second sensing threshold. This segmentation allows independent optimization of each detection phase, enabling reliable VF detection while preventing T wave oversensing through tailored threshold settings for each temporal segment
2Measurement precision
If a lower sensing threshold is used to detect fluctuating amplitude fibrillation waves, then the measurement precision for VF detection is improved, but T wave oversensing increases as T waves exceed the threshold
Solution Approach 1:
The patent employs periodic switching between sensing thresholds synchronized with the cardiac cycle. A first lower sensing threshold is applied during the VF detection window to capture fluctuating fibrillation waves, then periodically switched to a second upper sensing threshold during the T wave blanking window to prevent T wave oversensing. This periodic threshold modulation aligns with the rhythmic nature of cardiac electrical activity
Solution Approach 2:
The patent establishes a predetermined VF detection window duration based on expected heart rate parameters before actual VF detection occurs. This preliminary configuration of the detection window timing and threshold sequence enables the system to be prepared for rapid VF detection while automatically preventing T wave oversensing, without requiring real-time manual adjustment of sensing parameters
3Measurement precision
If manual adjustment of sensing parameters is implemented to optimize VF detection, then the measurement precision is improved, but the ease of operation deteriorates due to requiring manual parameter tuning
Solution Approach 1:
The patent implements an automatic threshold selection system where the control unit autonomously determines and switches between sensing thresholds based on detected cardiac events and pre-programmed algorithms. The system self-adjusts by identifying the cardiac cycle phase and automatically selecting the appropriate threshold (first or second) without requiring external manual intervention, thereby maintaining high measurement precision while ensuring ease of operation
Solution Approach 2:
The patent incorporates feedback mechanisms where the sensing unit continuously monitors cardiac electrical signals and provides information to the control unit, which then adjusts the sensing threshold accordingly. The system uses feedback from detected R waves, T waves, and potential VF events to dynamically select appropriate thresholds, creating a closed-loop control system that optimizes detection precision automatically
Data Source
AI summary
An implantable cardiac stimulator includes a cardioversion/defibrillation unit connectable to at least one ventricular sensing electrode and one ventricular defibrillation electrode, and is designed to generate and deliver cardioversion or defibrillation shocks. A ventricular sensing unit having automatic threshold adaptation is connectable to the ventricular sensing electrode, and is designed to process the signals of the sensing electrode and detect a chamber contraction, and if a chamber contraction is detected, to output a ventricular sensing signal. The ventricular sensing unit processes the signals of the sensing electrode with at least two switchable sensing thresholds wherein after every sense, a VF detection window is started at a first lower sensing threshold; once the VF detection window has passed, a T wave blanking window is activated at an upper second sensing threshold; and once the T wave blanking window has passed, sensing at a second lower threshold is started.