Fail-Safe Implantable Lead Conductor Configuration
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Solution Overview
Problem
Implantable cardiac defibrillator leads are susceptible to fractures due to repetitive stresses, leading to intermittent contact and erroneous detection of cardiac fibrillation, resulting in unnecessary high voltage shock therapy.
Innovation Solution
A robust and fail-safe configuration of conductors in the medical electrical lead, featuring a tri-lumen insulative lead body with distinct conductor configurations for low and high voltage electrodes, where the high voltage conductor is more likely to fracture first, thereby preventing multiple inappropriate shocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional conductor configurations are used in implantable medical electrical leads, then the lead can be manufactured with standard designs, but the conductors become susceptible to fracture after many years of chronic implantation due to repetitive stresses
Solution Approach 1:
The conductor is divided into multiple independent wire filars (typically 7-19 filars) instead of using a single solid wire. This segmentation allows the conductor to better withstand repetitive bending stresses by distributing the mechanical stress across multiple smaller elements, thereby improving fracture resistance while maintaining manufacturability with standard multi-filar construction processes
Solution Approach 2:
The conductor uses a composite structure combining multiple wire filars of different materials (e.g., iridium alloy, platinum, or other biocompatible conductive materials) with different mechanical properties. This composite construction provides both the electrical conductivity needed and enhanced fracture resistance through the synergistic properties of the different filar materials, resolving the contradiction between standard manufacturing and improved reliability
2Device complexity
If a single conductor connects the low voltage electrode to the connector, then the lead structure is simpler, but fracture of this conductor may produce intermittent contact that mimics cardiac fibrillation signals and leads to erroneous detection
Solution Approach 1:
The lead incorporates redundant conductors specifically for the low voltage sensing circuit (at least two separate conductors connecting the low voltage electrode to the connector) while the high voltage circuit may use a single conductor. This local redundancy in the sensing circuit ensures that if one conductor fractures, the other can still provide accurate cardiac signal detection, preventing erroneous fibrillation detection while maintaining overall structural simplicity
Solution Approach 2:
The redundant conductor configuration acts as a pre-established backup system that cushions against the harmful effect of conductor fracture. Before any fracture can occur, the system is designed with spare conductors in place, so that if one conductor fails, the redundant conductor immediately takes over to maintain accurate signal detection and prevent inappropriate shock delivery
3Reliability
If the lead uses robust conductor configurations to prevent fracture, then fracture resistance is improved, but the lead body requires multiple lumens and more complex conductor routing
Solution Approach 1:
The lead body integrates multiple lumens (typically three lumens) that are constructed as a unified structure from a single piece of insulative material or tightly bonded layers. The lumens are arranged to efficiently route the redundant low voltage conductors and high voltage conductors without requiring excessive complexity in the overall lead body design, merging the insulation and structural support functions into a consolidated configuration
Data Source
AI summary
An integrated bipolar implantable medical electrical lead, which may be employed by a cardiac defibrillator, has a single low voltage electrode and a single high voltage electrode and employs a relatively robust and fail-safe configuration of three conductors. Each of the three conductors extends within an individual lumen of a tri-lumen insulative body of the lead. First and second conductors of the three connect, in parallel, the low voltage electrode to a first contact of a connector terminal assembly of the lead, and a third conductor of the three connects the high voltage electrode to a second and a third contact of the connector terminal assembly. A configuration of the third conductor differs from that of the first and second conductors in order to make the third conductor more susceptible to fracture, relative to the first and second conductors, after many years of chronic implant under extreme loading conditions.