Impedance-Based Pacing Site Selection in Implantable Cardiac Devices
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Solution Overview
Problem
Current implantable medical devices (IMDs) face challenges in identifying optimal pacing sites for ventricular leads, particularly in patients with electromechanical dissociation, where the relationship between depolarization wave propagation and myocardial contraction is disrupted, leading to suboptimal pacing sites selection.
Innovation Solution
The use of impedance measurements at different ventricular sites to detect local myocardial contraction, selecting the site with the largest time difference between the start of contraction in another ventricle and local myocardial contraction as the optimal pacing site, thereby ensuring hemodynamically optimal stimulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If impedance measurements are used to detect local myocardial contraction, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical sensor systems (accelerometers, pressure sensors) with an electrical impedance-based detection system. The IMD measures impedance changes across ventricular sites to detect local myocardial contraction timing, substituting mechanical measurement with electrical measurement to achieve comparable or superior precision without mechanical sensor complexity
Solution Approach 2:
The patent utilizes the IMD's existing pacing electrodes and electrical signaling capabilities to perform dual functions: delivering pacing pulses and measuring impedance for contraction detection. The same electrodes used for stimulation serve as sensing elements, eliminating the need for separate dedicated sensors and reducing device complexity
2Measurement precision
If dedicated sensors are used for contraction detection, then measurement precision is improved, but ease of operation deteriorates
Solution Approach 1:
The patent makes the pacing electrodes multi-functional by using them for both stimulation and impedance-based contraction detection. This universal use of existing components eliminates the need for separate dedicated sensors, simplifying the implantation procedure and device operation while maintaining measurement precision
Solution Approach 2:
The patent extracts the contraction detection function from separate mechanical sensor systems and integrates it into the electrical pacing system. By taking out the dedicated sensor requirement and using impedance measurements through existing electrodes, the system achieves contraction detection without additional implantation complexity
3Measurement precision
If mechanical sensors are attached epicardially, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces epicardial mechanical sensor attachment with endocardial impedance-based detection using pacing electrodes. This substitution eliminates the need for separate mechanical sensor attachment procedures and integrates contraction detection into the existing electrical pacing infrastructure, reducing overall system complexity
Solution Approach 2:
The patent merges the contraction detection function with the electrical pacing system by using impedance measurements through the same electrodes used for stimulation. This combining of functions eliminates separate sensor systems and their associated complexity while maintaining measurement capability
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 allows for the selection of a hemodynamically optimal pacing site without relying on indirect contraction measurements, improving cardiac function and cardiac output, especially in patients with disrupted electromechanical relationships.
Implementation Method 1
an impedance detection unit, arranged for determining intracardiac impedance for the purpose of detecting local myocardial contraction at a ventricular site
Data Source
Figure 1~3
Figure 2
Figure 4~5
AI summary
An implantable medical device (100) applies an electric signal over two electrodes (216, 218) and measures the resulting electric signal over a candidate pair of neighboring electrodes (212, 214) on a lead (210) for a first heart ventricle (12) or over a candidate electrode (218) of the lead (210) and a case electrode (102). An impedance signal is determined for each candidate pair (212, 214) or electrode (218) based on the applied signal and the measured resulting signal. A time difference between start of contraction in a second ventricle (14) as caused by application of a pacing pulse to the second ventricle (14) and the timing of local myocardial contraction as identified from the impedance signal at the site of the candidate pair (212, 214) or electrode (218) is determined for each candidate pair (212, 214) or electrode (218). An optimal pacing electrode is selected to correspond to one of the electrodes of the candidate pair having the largest time difference or the candidate electrode having largest time difference.