Implantable Cardiac Sensing During MRI Noise and Therapy Conflicts
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Solution Overview
Problem
Magnetic resonance imaging (MRI) strong magnetic fields interfere with the operation of implantable medical devices (IMDs), causing parasitic currents that can trigger unwanted pacing pulses or defibrillation shocks, inhibit necessary therapy delivery, and mask true arrhythmias, leading to unreliable sensing during MRI procedures.
Innovation Solution
An implantable medical device (IMD) with sensing circuitry and processing capabilities to differentiate MRI-induced noise from physiological signals, manage sensing operations during active field intervals, and communicate with an external device to adjust MRI scanning sequences to ensure reliable signal reception and therapy delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If MRI scanning is performed with strong magnetic fields, then imaging quality is improved, but parasitic currents are induced in IMD leads causing unreliable sensing and potential harmful therapy delivery
Solution Approach 1:
The IMD detects MRI gradient fields and proactively switches to a safe sensing mode before parasitic currents can cause harmful effects. The device preemptively adjusts its operation in response to detected gradient fields, preventing rather than reacting to the harmful interference
Solution Approach 2:
The patent introduces an intermediary detection and response mechanism between the MRI gradient fields and the IMD sensing circuitry. The IMD detects the presence of gradient fields and uses this information to mediate its sensing operation, switching modes to filter or reject contaminated signals while accepting clean signals during safe intervals
2Object-affected harmful factors
If the IMD switches to MRI-safe mode during scanning, then patient safety is improved, but therapy delivery capability is reduced
Solution Approach 1:
The IMD periodically switches between safe sensing mode and normal therapy mode based on the periodic nature of MRI gradient fields. The device exploits the intermittent presence of gradient fields to deliver therapy during safe intervals while maintaining safety during gradient-active periods, creating a periodic pattern of mode switching
Solution Approach 2:
The IMD dynamically adjusts its sensing and therapy delivery capabilities based on real-time detection of gradient field presence. Rather than remaining statically in a safe mode throughout the MRI procedure, the device transitions between operational states to optimize both safety and therapeutic effectiveness
3Measurement precision
If the IMD filters out MRI-induced noise, then sensing accuracy is improved, but true arrhythmias may be missed
Solution Approach 1:
The IMD applies different processing qualities to different time intervals based on gradient field presence. During gradient-active intervals, the device applies aggressive noise filtering to achieve local signal cleanliness, while during gradient-absent intervals, it uses minimal filtering to preserve all signal information including potential arrhythmias
4Productivity
If the IMD continues normal operation during MRI, then therapy delivery is maintained, but parasitic currents can trigger unwanted pacing or defibrillation
Solution Approach 1:
The IMD converts the harmful presence of gradient fields into a beneficial trigger for mode switching. The detection of gradient fields, which initially causes harmful interference, becomes the signal that prompts the device to switch to a protective sensing mode, thereby preventing the harmful effects while maintaining therapeutic capability during safe intervals
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
Enables IMDs to continue normal pacing and sensing modes during MRI, preventing life-threatening fibrillation and ensuring accurate detection of arrhythmias by filtering out MRI-induced noise, allowing necessary therapy to be delivered when needed.
Implementation Method 1
The sensors are typically connected to the implantable device via electrical signal conduction paths within the various leads
Implementation Method 2
RF fields of the MRI can induce currents along the conduction paths
Implementation Method 3
pulsed gradient magnetic fields are then applied to cause the protons within selected locations of the body to emit RF signals
Data Source
AI summary
An implantable medical device (IMD) is provided and includes sensing circuitry coupled to electrodes. The sensing circuitry is configured to sense electrical biological signals indicative of a non-physiologic condition of interest experienced by a patient during a magnetic resonance imaging (MRI) procedure, and in the presence of an MRI scanning sequence, the MRI scanning sequence includes at least one of radio frequency (RF) or gradient fields that are in an active state for active field intervals. The device includes memory to store the biological signals and to store program instructions and includes a processor that, when executing the program instructions, is configured to: determine start times for the active field intervals when the at least one of RF or gradient fields switch to the active state and manage generation of MRI-induced-noise corrected (MRI-INC) biological signals, based on the start times for the active field intervals, by at least one of: 1) applying a blanking interval to the sensing circuitry to blank a sensing operation during at least portions of the active field interval or 2) modifying segments of the biological signal sensed during at least the portions of the active field interval, and 3) comparing biologic signal sensed during at least the portions of the active field interval to a template. The device analyzes the biological signals for an indication that the patient is experiencing the non-physiologic condition.