What is inside the electrocardiograph?

Gregg, Richard E.; Zhou, Sophia H.; Lindauer, James M.; Helfenbein, Eric; Giuliano, Karen K.

doi:10.1016/j.jelectrocard.2007.08.059

Cited by 35 publications

(22 citation statements)

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“…A malfunctional limb electrode (eg, microfractures, interrupted cable, poor electrode contact) may cause sharp changes in electric impedance, thus impairing the filtering processes of the ECG machines and distorting electric signals. 2 These distorted signals may manifest as phase shifts that become more apparent after high-amplitude signals (such as ST deviation after QRS complexes). [1][2][3] Because the Wilson central terminal is used to generate the signals of all unipolar leads, the artefacts would be reflected in all leads except the bipolar lead that does not use the malfunctional electrode (in this case, lead II does not use the presumably malfunctional left-arm electrode).…”

Section: Response To Ecg Challengementioning

confidence: 99%

Inferior ST-Elevation on the ECG

Mărgulescu¹

2017

Circulation

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A 62-year-old woman presented to another hospital with a 36-hour history of uninterrupted, nonspecific chest pain. Her medical history included long-standing hypertension and diabetes mellitus for which she took metoprolol, perindopril, felodipine, metformin, and glimepiride. She had stopped smoking 10 years earlier, and did not drink alcohol or use illicit drugs. The ECG on the admission to the other hospital is shown in Figure 1. Laboratory results at the other hospital were all normal, with the exception of mild hyperglycemia; cardiac troponin I was also normal. Based on the ECG in Figure 1, the patient was transferred to our unit for emergency coronary angiography. Clinical examination on admission to our hospital was unremarkable. A repeated ECG on admission in our hospital is disclosed in Figure 2. Based on the history of uninterrupted chest pain in a patient with cardiovascular risk factors and the aspect of the ECG in Figure 1, the on-call cardiology team in our unit agreed with the indication for emergency coronary angiography. This, however, disclosed no significant coronary artery disease. Over the next 48 hours, serial ECGs remained unchanged (Figure 2), and repeated blood tests (including serial troponin I levels) remained unremarkable. Echocardiography disclosed mild left ventricular hypertrophy with preserved ejection fraction and no wall motion abnormality.What is the most likely explanation of the ECG in Figure 1?

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Section: Response To Ecg Challengementioning

confidence: 99%

Inferior ST-Elevation on the ECG

Mărgulescu¹

2017

Circulation

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“…They often occur in intervals and such fractionation may be misleading, because it is not cardiac in origin. 16 Such artifacts may especially arise when unipolar recordings are applied.…”

Section: What Makes Electrograms Complex? Artifactsmentioning

confidence: 99%

The Pathophysiologic Basis of Fractionated and Complex Electrograms and the Impact of Recording Techniques on Their Detection and Interpretation

Bakker

Wittkampf

2010

Circ: Arrhythmia and Electrophysiology

166

139

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E xtracellular electrograms, recorded directly from the heart, are the hallmarks of invasive cardiac electrophysiology and provide information about the electric status of the underlying myocardium. These electrograms are generated by depolarization of cardiomyocytes that generates transmembrane currents in extracellular space and potential differences due to electric resistance of the extracellular medium. In healthy myocardium, the basic configuration of the extracellular electrogram is simple. Under pathological conditions, however, electrograms may consist of multiple components and long duration, which have been attributed to abnormal conduction and arrhythmogenicity. Although complex and fractionated electrograms are presently considered to be a real phenomenon, this was not the case some 20 years ago. Debates about the "fact or artifact" of complex and fractionated electrograms were common. 1 At that time, electrograms consisting of multiple "high frequency" components with low amplitudes and long duration, termed "fractionated," were recorded in patients with healed myocardial infarction during endocardial mapping. Several investigators presumed that fractionated electrograms were artifacts, resulting from movements between electrode and myocardium, filter characteristics of amplifiers, or represented far field effects. A classic example to support the "artifact theory" was the recording of continuous activity from the jello brain. 2 In those days, much attention had been paid to fractionated electrograms in healed myocardial infarction to guide catheter ablation or antiarrhythmic surgery. [3][4][5] Although artifacts indeed may cause complex electrograms, most of the complex and fractionated electrograms are a "fact" and caused by the peculiar behavior of activation fronts, due to structural and electric complexity of the underlying myocardium. This article delineates the origin of the unipolar extracellular electrogram, reviews the circumstances that cause fractionated and complex electrograms, and discusses the impact of the recording technique on detection and interpretation of multifaceted electrograms.

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“…Consequently, according to Fourier's theorem, the signal can be expressed as the sum of infinite sine waves. Each of them exhibits certain amplitude and a frequency and constitutes an integral multiple of a fundamental frequency [4]. It may be shown that the value of this fundamental frequency equals the inverse of the period of repetition ( T ) of the original signal.…”

Section: Discussionmentioning

confidence: 99%

“…High-pass filters with low cut-off frequencies exhibit phase distortion (phase nonlinearities) which describes the fact that a filter delays components of different frequencies by different amounts so that a distortion results when the signal components are summed together again [4, 8, 9]. …”

Section: Discussionmentioning

confidence: 99%

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High-Bandpass Filters in Electrocardiography: Source of Error in the Interpretation of the ST Segment

Buendía-Fuentes

Arnau-Vives

et al. 2012

ISRN Cardiology

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Introduction. Artifactual variations in the ST segment may lead to confusion with acute coronary syndromes. Objective. To evaluate how the technical characteristics of the recording mode may distort the ST segment. Material and Method. We made a series of electrocardiograms using different filter configurations in 45 asymptomatic patients. A spectral analysis of the electrocardiograms was made by discrete Fourier transforms, and an accurate recomposition of the ECG signal was obtained from the addition of successive harmonics. Digital high-pass filters of 0.05 and 0.5 Hz were used, and the resulting shapes were compared with the originals. Results. In 42 patients (93%) clinically significant alterations in ST segment level were detected. These changes were only seen in “real time mode” with high-pass filter of 0.5 Hz. Conclusions. Interpretation of the ST segment in “real time mode” should only be carried out using high-pass filters of 0.05 Hz.

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What is inside the electrocardiograph?

Cited by 35 publications

References 1 publication

Inferior ST-Elevation on the ECG

Inferior ST-Elevation on the ECG

The Pathophysiologic Basis of Fractionated and Complex Electrograms and the Impact of Recording Techniques on Their Detection and Interpretation

High-Bandpass Filters in Electrocardiography: Source of Error in the Interpretation of the ST Segment

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