Implantable Device MRI Capture Threshold Adjustment
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Solution Overview
Problem
Magnetic resonance imaging (MRI) induces changes in the capture threshold of cardiac tissue, leading to potential loss of capture by implantable medical devices due to localized heating, compromising their effectiveness.
Innovation Solution
An implantable medical device with magnetic field detection circuitry that adjusts the energy delivery state during and after an MRI scan to maintain optimal stimulation of cardiac tissue, ensuring the capture threshold is met by switching to a higher energy state during MRI fields and adjusting post-scan based on measured thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the implantable medical device operates at normal energy levels, then energy consumption is minimized, but the capture threshold may not be met during MRI scans causing loss of capture
Solution Approach 1:
The device dynamically adjusts its energy delivery based on detected MRI conditions. The controller switches between normal operating mode and MRI mode energy levels based on detection of MRI scan fields, allowing the device to adapt its energy consumption to actual operational needs rather than maintaining fixed high energy levels
Solution Approach 2:
The device incorporates feedback mechanisms to detect MRI scan fields and adjust energy delivery accordingly. The controller continuously monitors for MRI conditions and modifies the energy state of pace pulses in response, creating a closed-loop system that maintains capture reliability while optimizing energy usage
2Reliability
If the device increases energy delivery during MRI scans, then capture threshold is met, but tissue heating increases due to RF field interaction
Solution Approach 1:
The device performs preliminary detection of MRI scan fields before delivering increased energy. By detecting the presence of MRI RF fields first, the device can proactively adjust energy levels appropriately rather than reacting after heating has already occurred
Solution Approach 2:
The device changes operational parameters (energy state of pace pulses) in response to detected MRI conditions. The controller modifies pulse amplitude, width, or other energy-delivery parameters to ensure capture threshold is met while monitoring tissue temperature effects
3Reliability
If the device continuously monitors capture threshold, then stimulation effectiveness is maintained, but device complexity increases
Solution Approach 1:
The device performs capture threshold monitoring at periodic intervals rather than continuously. This approach maintains stimulation effectiveness by regularly verifying capture while reducing the computational burden and device complexity associated with constant monitoring
Solution Approach 2:
The device uses its existing sensing and pacing capabilities to perform self-monitoring of capture threshold. By leveraging already-present hardware components for dual purposes (pacing and sensing), the device maintains reliability without adding significant complexity
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
The solution ensures continuous and effective stimulation of cardiac tissue by maintaining adequate energy delivery post-MRI scan, minimizing the risk of loss of capture and maintaining device performance.
Implementation Method 1
Magnetic field detection circuitry detects magnetic resonance imaging (MRI) scan fields
Implementation Method 2
During imaging, the electromagnetic radiation produced by the MRI system can be picked up by implantable device leads used in implantable medical devices such as pacemakers or cardiac defibrillators. This energy may be transferred through the lead to the electrode in contact with the tissue, which can cause elevated temperatures at the point of contact
Data Source
AI summary
Energy delivered from an implantable medical device to stimulate tissue within a patient's body is controlled. An electrical signal used to stimulate the tissue is changed from a first energy state to a second energy state during a magnetic resonance imaging (MRI) scan. The energy delivered is maintained at the second energy state after the MRI scan. A capture threshold of the tissue is then measured, and the energy delivered to the tissue is adjusted based on the measured capture threshold of the tissue.