Defibrillation Waveform Optimization via Membrane Time Constant
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Solution Overview
Problem
Current implantable cardiac defibrillators (ICDs) face challenges in determining the optimal defibrillation shock waveform for individual patients, as the membrane time constant of cardiac tissue cannot be precisely measured, leading to variable defibrillation thresholds and potential re-initiation of fibrillation due to inappropriate pulse widths.
Innovation Solution
Analyzing cardiac waveforms to determine optimal defibrillation shock waveform parameters, such as pulse widths and tilts, based on characteristics like membrane time constant and system impedance, allowing for personalized waveform optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If longer pulse widths are applied to ensure complete depolarization of cardiac tissue, then defibrillation effectiveness is improved, but re-initiation of fibrillation may occur and energy consumption increases
Solution Approach 1:
The patent applies parameter changes by adjusting the pulse width of the defibrillation waveform based on the measured membrane time constant. By changing the pulse width parameter to match the specific patient's cardiac tissue characteristics, the system achieves effective depolarization without excessive energy consumption, resolving the contradiction between reliability and energy use.
2Reliability
If pulse width is increased to depolarize all cardiac tissue cells simultaneously, then defibrillation success rate is improved, but the risk of re-initiation of fibrillation increases
Solution Approach 1:
The system changes the pulse width parameter based on the measured membrane time constant to achieve the minimum effective duration needed for simultaneous depolarization. This precise parameter adjustment ensures complete tissue depolarization while minimizing the risk of re-initiation, as the pulse is not excessively long.
3Device complexity
If fixed pulse width is used in defibrillation waveform, then device complexity is reduced, but defibrillation threshold becomes variable and effectiveness decreases
Solution Approach 1:
The patent implements feedback by measuring the membrane time constant from the patient's cardiac waveform and using this measurement to adjust the pulse width parameter. This closed-loop approach ensures consistent defibrillation threshold and effectiveness while adapting to individual patient characteristics, resolving the contradiction between simplicity and reliability.
4Measurement precision
If membrane time constant is measured accurately, then optimal waveform parameters can be determined, but measurement precision requirements increase system complexity
Solution Approach 1:
The system uses the patient's own cardiac waveform signals to measure the membrane time constant, requiring no external equipment or additional sensors. The defibrillation device itself performs the measurement and analysis, simplifying the overall system while achieving precise characterization of the patient's cardiac tissue.
Data Source
AI summary
Embodiments of the invention present methods and systems for determining an optimal defibrillation shock waveform for application to the heart of a patient to stop a rhythm abnormality such as ventricular fibrillation or ventricular tachycardia. Such methods and systems may include measuring and/or collecting information for a cardiac waveform of a patient, produced as a result of either an electrical stimulus applied to a heart of the patient, which may be a pacing shock/stimulus and/or a defibrillation shock waveform, or as the result of intrinsic cardiac activation, determining a characteristic of the cardiac waveform, comparing the determined characteristic of the cardiac waveform to a plurality of values for the characteristic with optional reference to the defibrillator system impedance, wherein each value of the characteristic is associated with a predetermined value for a parameter of an optimal defibrillation shock waveform, and selecting the predetermined value for the parameter of the optimal defibrillation shock waveform based on the comparison.