Thermal Switch for Implantable Leads

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Solution Overview

Problem

Implantable medical device leads can cause tissue heating when exposed to RF electromagnetic fields, leading to potential tissue damage, especially in MRI environments, as they act as antennas and dissipate energy, causing water molecules near electrodes to oscillate and heat.

Innovation Solution

Incorporating a thermally activated switch adjacent to or inside the electrodes, which disconnects the conductor from the electrode during MRI exposure, preventing RF energy dissipation and overheating by using a bimetallic strip or shape memory alloy that deflects at elevated temperatures to break the circuit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If leads are exposed to RF electromagnetic fields during MRI procedures, then diagnostic imaging capability is improved, but tissue heating occurs leading to potential tissue damage

Engineering Contradiction:

Improvediagnostic imaging capabilityVSAvoidtissue heating

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The thermal switch is pre-positioned in the lead to detect temperature increases before they cause tissue damage. When the switch detects elevated temperatures during MRI procedures, it automatically opens the circuit to prevent further RF energy dissipation and tissue heating, thereby providing preliminary protection against harmful thermal effects.

Inventive Principle:

Principle #9Preliminary anti-action

Solution Approach 2:

The thermal switch acts as an intermediary component between the RF electromagnetic field and the tissue. It monitors temperature conditions and intervenes by opening the circuit when necessary, mediating the interaction between the lead and tissue to prevent harmful heating while allowing diagnostic imaging to proceed.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a thermal switch is added to disconnect the circuit during overheating, then tissue safety is improved, but device complexity increases

Engineering Contradiction:

Improvetissue safetyVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The thermal switch is designed to automatically detect temperature increases and open the circuit without requiring external control or additional sensors. This self-service mechanism provides tissue safety protection through a simple, passive thermal response that minimizes added complexity while maximizing reliability.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The thermal switch utilizes changes in thermal parameters (temperature) to trigger circuit interruption. By relying on fundamental thermal expansion or phase change properties of materials, the device achieves automatic protection based on physical parameter changes rather than complex electronic sensing and control systems.

Inventive Principle:

Principle #35Parameter changes

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

Effectively prevents tissue overheating by disconnecting the circuit before significant temperature increases occur, ensuring safe operation of implantable medical devices during MRI procedures.

Implementation Method 1

which disconnects the conductor from the electrode during MRI exposure, preventing RF energy dissipation and overheating by using a bimetallic strip or shape memory alloy that deflects at elevated temperatures to break the circuit

Methodology Applied

Scientific EffectBimetallic strip: Bi-Metallic Strip

Implementation Method 2

Methodology Applied

Scientific EffectShape memory alloy: Shape Memory Alloy

Implementation Method 3

a bimetallic strip or shape memory alloy that deflects at elevated temperatures to break the circuit

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8219207B2Thermal switch for implantable medical devices

Publication Date: 2012.07.10 MEDTRONIC INC

AI summary

An implantable medical device includes an electrode having a thermal switch. The thermal switch is configured to electrically decouple components of the implantable medical device when in contact with tissue at temperatures above normal body temperature.