Multi-Pole LV Lead Hybrid Impedance Stroke Volume Tracking
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Solution Overview
Problem
Current implantable cardiac rhythm management devices face challenges in accurately estimating stroke volume and cardiac output from impedance signals due to variability in intra-cardiac impedance, which complicates the detection and tracking of heart failure progression.
Innovation Solution
A hybrid impedance detection configuration using a multi-pole left ventricular lead and a stable reference electrode, such as an SVC coil, to measure impedance differences and apply a pre-calibrated scaling factor for estimating absolute stroke volume, enabling more precise tracking of heart failure and optimization of pacing delays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional impedance detection methods are used with standard leads, then the device structure remains simple, but the measurement precision of stroke volume is insufficient due to variability in intra-cardiac impedance
Solution Approach 1:
The LV lead is divided into multiple poles (at least four electrodes: distal tip, proximal ring, and at least one intermediate ring electrode), allowing segmentation of the measurement function across multiple sensing points. This enables more precise local impedance measurements that can be combined to overcome variability issues.
Solution Approach 2:
A stable reference electrode (such as an SVC coil or can electrode) is introduced as an intermediary to provide a consistent reference point for all LV lead measurements. This mediator stabilizes the impedance measurements by providing a common reference that reduces variability caused by lead positioning and tissue properties.
2Reliability
If a stable reference electrode is used with multi-pole LV lead, then absolute stroke volume values can be obtained, but the device and lead configuration becomes more complex
Solution Approach 1:
The stable reference electrode serves multiple functions: it provides a reference for stroke volume measurement, a reference for cardiac output calculation, and a stable point for detecting various cardiac parameters. The multi-pole LV lead also serves dual purposes for both pacing and impedance sensing, reducing the need for separate dedicated components.
Solution Approach 2:
The reference electrode and multi-pole LV lead configuration is established during the initial implantation procedure, preparing the system in advance for accurate stroke volume measurement. Pre-calibration procedures are performed to establish baseline impedance values and scaling factors before clinical use, ensuring reliability from the start.
3Measurement precision
If multiple impedance vectors are measured using multi-pole lead, then measurement precision improves, but the complexity of processing and analyzing the data increases
Solution Approach 1:
Impedance measurements from multiple LV lead poles are combined and summed to generate a single composite impedance value that represents overall LV function. This merging approach consolidates multiple measurements into one integrated parameter, simplifying the data processing while maintaining the precision benefits of multi-point sensing.
Solution Approach 2:
The device continuously monitors impedance changes and uses feedback algorithms to track stroke volume and cardiac output over time. The system compares current measurements with historical data to detect trends and changes in cardiac function, automatically adjusting for variations and providing reliable heart failure detection without requiring complex manual 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 method provides clinicians with reliable, absolute values of stroke volume, facilitating better diagnosis and therapy decisions, and enabling the detection and tracking of heart failure progression, thereby improving patient management.
Implementation Method 1
A hybrid impedance detection configuration using a multi-pole left ventricular lead and a stable reference electrode, such as an SVC coil, to measure impedance differences
Data Source
AI summary
Techniques are provided for use with an implantable medical device for assessing stroke volume or related cardiac function parameters such as cardiac output based on impedance signals obtained using hybrid impedance configurations that exploit a multi-pole cardiac pacing/sensing lead implanted near the left ventricle. In one example, current is injected between a large and stable reference electrode and a ring electrode in the RV. The reference electrode may be, e.g., a coil electrode implanted within the superior vena cava (SVC). Impedance values are measured along a set of different sensing vectors between the reference electrode and each of the electrodes of the multi-pole LV lead. Stroke volume is then estimated and tracked within the patient using the impedance values. In this manner, a hybrid impedance detection configuration is exploited whereby one vector is used to inject current and other vectors are used to measure impedance.