Noise in ECG and how to deal with - University of Southern ...

1 1 Noise in ECG and how Noise in ECG and how to deal with itto deal with itDjordjeDjordjePopovic, MDPopovic, MDOutlineOutline Frequency characteristics of ECGF requency characteristics of ECG Most common sources of Noise , Most common sources of Noise , characteristics and examplescharacteristics and examples How to deal with some of them (filtering How to deal with some of them (filtering techniques)techniques)2 Frequency characteristics of Frequency characteristics of normal ECGnormal ECGS ources of noiseSources of Noise Power line interferencePower line interference Electrode contact Noise , baseline drift and Electrode contact Noise , baseline drift and motion artifactsmotion artifacts EMG from the chest wallEMG from the chest wall Instrumentation noiseInstrumentation Noise Electrosurgical noiseElectrosurgical noise3 Power line interferencePower line interference 60 Hz & multiples60 Hz & multiples Up to 50% of QRS amplitudeUp to 50% of QRS amplitudeSolutionsSolutions Notch filter at 60 HzNotch filter at 60 Hz Comb filterComb x 60 Hz=n x 60 HzY(iY(i)=)=X(i)X(i)--X(iX(i--nn)) (kHz)Magnitude (dB)Magnitude Response (dB) (kHz)Magnitude (dB)Magnitude Response (dB)

2 4 Adaptive filtering of power humAdaptive filtering of power humElectrode contact noiseElectrode contact Noise Loose contactLoose contact Motion artifactMotion artifact Baseline driftBaseline driftdue to respirationdue to respiration5 SolutionsSolutions Typically < Hz signals (except for the Typically < Hz signals (except for the abrupt shifts due to motion)abrupt shifts due to motion) HighHigh--pass filtering with cutpass filtering with cut--off frequency at off frequency at ~ , realized in hardware or software~ , realized in hardware or softwareAbrupt motion artifact cancellationAbrupt motion artifact cancellation Adaptive recurrentAdaptive recurrentfilteringfiltering6 EMGEMG Amplitude Amplitude ~ 10% ECG~ 10% ECG Broadband Broadband (20 (20 1000 Hz1000 HzSolutionsSolutions LowLow--pass filter with cutpass filter with cut--off frequency off frequency >40Hz>40Hz Adaptive filter with Adaptive filter with aVfaVfas primary and as primary and aVraVr--aVlaVlas referenceas reference7 SummarySummary Many different sources of Noise , frequency Many different sources of Noise .))

3 Frequency content of some of them overlaps with content of some of them overlaps with ECGECG Limited capabilities of linear filteringLimited capabilities of linear filtering Final solution dependent on each Final solution dependent on each particular case, and our goalsparticular case, and our goalsQuestions?Questions?8 Use of adaptive filters in Use of adaptive filters in ECG processingECG processingDjordjeDjordjePopovic, MDPopovic, MDStructure of an AFStructure of an AF S1/S2 or n1/n2 need not be the same, only correlated in some wayS1/S2 or n1/n2 need not be the same, only correlated in some way!!!!9 Noise cancellationNoise cancellation Power line interferencePower line interference Baseline driftBaseline driftEMG cancellationEMG cancellation10 Arrhythmia detection Arrhythmia detection Goal: to cancel normal QRS complexes, Goal: to cancel normal QRS complexes, and to analyze the signal that remains and to analyze the signal that remains after the cancellationafter the cancellationDetection of Detection of ectopicectopicbeatsbeats11PP--wave analysiswave analysisAtrialAtrialfibrillation and/or flatterfibrillation and/or flatter