ICD Quiet Timer for EMI Detection in Cardiac Signals
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Solution Overview
Problem
Implantable cardiac devices face challenges in accurately detecting cardiac electrical signals due to electromagnetic interference (EMI), leading to potential false detection of tachyarrhythmias and inappropriate therapy delivery.
Innovation Solution
An implantable cardioverter defibrillator (ICD) system with a therapy delivery circuit, sensing circuit, and control circuit that uses a quiet timer to differentiate between cardiac events and EMI, withholding tachyarrhythmia therapy when EMI is detected by identifying EMI events based on timer behavior parameters and updating an EMI event count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensing circuit detects cardiac electrical signals using a fixed threshold, then the detection process is simple and fast, but electromagnetic interference causes false detection of tachyarrhythmias
Solution Approach 1:
The patent implements dynamic threshold adjustment by continuously monitoring signal characteristics and adapting the detection threshold based on the calculated noise level. The threshold is no longer fixed but dynamically modified according to environmental conditions, allowing the device to maintain high detection accuracy while rejecting electromagnetic interference.
Solution Approach 2:
The patent introduces an intermediary noise analysis process that sits between the raw signal and the tachyarrhythmia detection algorithm. This intermediary layer calculates noise metrics from the cardiac electrical signal and uses these metrics to adjust detection parameters, effectively mediating the impact of EMI on detection accuracy.
2Reliability
If the device withholds therapy when EMI is detected, then inappropriate therapy delivery is prevented, but genuine tachyarrhythmias may be missed during EMI periods
Solution Approach 1:
The patent changes detection parameters dynamically based on noise levels. When EMI is detected, the device adjusts the tachyarrhythmia detection criteria by modifying rate thresholds, morphology requirements, or detection windows. This parameter adaptation allows the device to maintain reliability by withholding therapy during clear EMI while still detecting genuine arrhythmias that meet adjusted criteria.
Solution Approach 2:
The patent implements a feedback mechanism where the noise analysis results continuously inform the tachyarrhythmia detection algorithm. The system monitors detection outcomes and adjusts its behavior based on the relationship between noise levels and detected events, providing feedback that helps distinguish genuine arrhythmias from EMI artifacts.
Data Source
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AI summary
A medical device, such as an implantable cardioverter defibrillator (ICD), starts a timer set to a time interval in response to a cardiac electrical signal crossing a noise threshold amplitude and resets the timer to the time interval in response to each crossing of the noise threshold amplitude by the cardiac electrical signal that occurs prior to the time interval expiring. A control circuit of the medical device determines a parameter of the behavior of the timer and identifies a sensed cardiac event as an electromagnetic interference (EMI) event based on the parameter. The medical device may detect EMI in response to the EMI event and withhold a tachyarrhythmia detection or therapy in response to EMI detection.