Abstract
Abstract The electrocardiogram (ECG) is a well-known technique used to diagnose cardiac diseases. To acquire the spatial signal characteristics from the thorax, multiple electrodes are commonly used. Displacements of electrodes affect the signal morphologies and can lead to incorrect diagnoses. For quantitative analysis of these effects we propose the usage of a numerical computer simulation. In order to create a realistic representation of the human thorax including the heart and lung a three-dimensional model with a simplified geometry is used. The electrical excitation of the heart is modelled on a cellular level via the bidomain approach. To numerically solve the differential equations, describing the signal propagation within the body, we use the finite element method in COMSOL Multiphysics®. The spatial gradients of the simulated body potentials are calculated to determine placement sensitivity maps. The simulated results show that the sensitivity is different for each considered point in time of each ECG wave. In general, the impact of displacement is increased as an electrode is more closely located to the signal source. However, in some specific regions associated with differential ECG leads the placement sensitivity distribution deviates from this simple circular pattern. The results provide useful information to enhance the understanding of placed specific effects on classical ECG features. By additional consideration of patient-specific characteristics in the future, the used model has the ability to investigate additional body-related aspects such as geometrical body shape or composition of various tissue types.
Highlights
The electrocardiogram (ECG) is a well-known non-invasive technique used to diagnose cardiac diseases
A quantitative sensitivity analysis of the whole thorax to electrode displacement is often associated with high effort due to the large number of electrode measurements and is not comprehensively investigated in the literature. For this reason and in order to investigate patient-specific aspects in perspective, we propose the usage of heart modelling combined with numerical computer simulation to obtain placement sensitivity maps for the P, R and T wave of the ECG which visualize the influence of electrode displacements
In certain areas where differential ECG electrodes are typically placed, such as the chest wall electrodes, the regional sensitivity differs from this simple circular pattern
Summary
The electrocardiogram (ECG) is a well-known non-invasive technique used to diagnose cardiac diseases. To acquire the spatial signal characteristics from the human thorax, the potentials can be detected with multiple electrodes on the skin surface. A 12-lead ECG is recorded, whereby the electrodes are aligned in a standardised manner to the limbs and thorax. A challenge in signal acquisition is electrode displacements deviating from the ideally used positions. The ECG signals change and incorrect diagnoses can be made. In a study by Bond et al [2] it was shown that electrode displacements have a probability of 17 - 24 % to influence the signal interpretation. The incorrect placements are caused by variability of physicians in identifying standardised electrode positions [3]. The individual patient anatomy further influences this as the localisation of the heart in the human body is not exactly known [4]. Electrode shifts relatively to the heart induced by body deformation such as lying on one side of the body can be challenging [5]
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