Automated ULV Determination Using Variable T-Wave Shocks
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Solution Overview
Problem
Current methods for determining the upper limit of vulnerability (ULV) for T-wave shock delivery in implantable cardioverter defibrillators (ICDs) are time-consuming and require significant skill, as they rely on manual measurement of T-wave timing using 12-lead ECG signals, leading to potential inaccuracies in determining the defibrillation threshold (DFT).
Innovation Solution
An automated system within the ICD that uses a ULV subsystem to deliver a series of T-wave shocks at varying offsets relative to a computed T-wave shock interval, based on signal quality analysis, to ensure accurate timing and reduce the number of fibrillation inductions needed for reliable DFT estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual measurement of T-wave timing using 12-lead ECG signals is used, then timing accuracy for T-shock delivery can be achieved, but the process becomes time-consuming and requires considerable skill
Solution Approach 1:
The ICD device automatically performs T-wave timing measurement and ULV determination using its own electrograms and shock delivery capabilities, eliminating the need for external 12-lead ECG equipment and manual measurement by clinicians. The device self-calibrates by delivering test shocks and measuring the resulting electrograms to identify T-wave timing autonomously
Solution Approach 2:
The manual mechanical process of 12-lead ECG measurement and calculation is replaced by an automated electronic system within the ICD that uses signal processing algorithms to automatically detect T-wave timing from intracardiac electrograms, eliminating the need for manual intervention and external equipment
2Reliability
If T-shocks are delivered outside the vulnerable period, then fibrillation induction may fail, but this leads to incorrect ULV determination
Solution Approach 1:
The system delivers a series of T-shocks at varying offsets relative to the computed T-wave shock interval and uses the results of each shock (whether fibrillation was induced or not) as feedback to refine the timing and identify the true ULV. This iterative feedback process ensures accurate ULV determination while maintaining reliable fibrillation induction when needed
Solution Approach 2:
Instead of delivering a single T-shock at the precisely calculated optimal time, the system delivers multiple T-shocks at varying offsets around the computed timing. This excessive action approach ensures that at least some shocks will fall within the vulnerable period, allowing reliable ULV determination even with timing uncertainties
3Measurement precision
If multiple T-wave shocks are delivered at varying offsets, then accurate ULV determination is achieved, but the number of fibrillation inductions increases
Solution Approach 1:
The system delivers a limited series of T-shocks at varying offsets (a controlled form of excessive action) to ensure sufficient sampling of the vulnerable period without unnecessarily increasing the number of fibrillation inductions. This optimized approach achieves accurate ULV determination with the minimum necessary number of shocks
Solution Approach 2:
The system first computes an optimal T-wave shock interval based on preliminary analysis of the T-wave electrogram morphology and timing characteristics. This preliminary calculation guides the subsequent delivery of T-shocks at varying offsets, ensuring that the shocks are strategically positioned to maximize ULV determination accuracy while minimizing the total number of shocks required
Data Source
Figure 1
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Figure 3A~3B
AI summary
An apparatus senses a cardiac electrical signal and determines a signal quality parameter of the cardiac electrical signal. A number of shock pulses to be delivered to a patient's heart is determined in response to the signal quality parameter. Each of the shock pulses are scheduled to be delivered at a unique offset from a T-wave shock interval in one embodiment of the disclosure.