Biomedical subjects

Uwe Steinhoff

Publications and source records attributed to Uwe Steinhoff.

4 recordsLinked to original sources

PubMed2004

MCG to ECG source differences: measurements and a two-dimensional computer model study.

In this work we combine body surface potential map (BSPM) and magnetocardiogram (MCG) measurements with computer simulations in order to elucidate a recent thesis that claims the orthogonality of the main sources of MCG and ECG. Body surface currents and MCG pseudo currents are calculated from measured BSPM and MCG data, respectively. In contrast to the MCG-ECG source orthogonality thesis, we observe the main orientation of the BSPM currents and MCG pseudo currents to have similar axis during most of the depolarization R wave. In an attempt to explain such measurements we simulate a 2D transmural slice of the left ventricle in contact to a volume conductor. The main magnetic source currents along the wave front are indeed orthogonal to the extracellular electric current. However, fiber orientation inhomogeneity through the ventricular wall, volume conductor interface, wave front shape and extra- and intracellular potential distributions, all distort the symmetry of the current loops that contain the wave front currents. The resulting asymmetry rotates the main axis of the pseudo MCG currents away from the orthogonal axis of the body surface currents. Thus, the simulation results could solve the apparent contradiction between the orthogonal source theory and the observed similar ECG and MCG main current axis.

Body Surface Potential Mapping↗

PubMed2004

Magnetocardiography for pharmacology safety studies requiring high patient throughput and reliability.

Recent guideline drafts of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) underline the necessity to test nonantiarrhythmic drugs for their potential to prolong the QT or the corrected QT (QTc) interval. The implementation of these guidelines requires a large amount of ECG measurements on animals and humans in preclinical and clinical phases of the drug development process. We propose the use of magnetocardiography (MCG) as a complementary method with particular advantages in high-throughput studies, where signal quality and reliability are key factors. Our proposal is based on a review of recent MCG studies investigating the repolarization phase and results of methodological work assessing QT interval parameters from the MCG. The applicability of MCG for pre-clinical in-vivo studies is demonstrated by the ease of measurement in unrestrained non-anesthetized rabbits, guinea pigs, and hamsters..

Animals↗

PubMed2003

Comparison of automatic repolarization measurement techniques in the normal magnetocardiogram.

Multichannel MCG noninvasively measures cardiac magnetic field strength from many sites at the body surface, potentially providing useful regional information about ventricular repolarization. Previous work on ECGs has shown that automatic techniques for repolarization measurement are better than manual measurement at discriminating patients with cardiac conditions from normal subjects. Although automatic repolarization measurement techniques have been quantified for ECGs, no comparative data exists for the MCG. In this study four different automatic repolarization (QT) interval techniques for detecting T wave end in the MCG were compared. The influence of MCG filtering on the automatic algorithms was also quantified. MCGs were obtained at 49 sites over the heart from 23 normal subjects. Automatic measurements of the repolarization (QT) interval were made following the addition of different high pass (0.25, 0.5, 1 Hz) and low pass (100, 60, 40, 30 Hz) filters. There were consistent differences between automatic techniques in the unfiltered data amounting to greatest mean difference of 52.3 ms. Low pass filtering significantly increased the automatic repolarization (QT) interval relative to unfiltered measurement by 6.5 (3.2) ms (mean SD) for 100 Hz, 6.0 (3.0) ms for 60 Hz, 8.1 (3.2) ms for 40 Hz, and 8.8 (3.1) ms for 30 Hz across all techniques. High pass filtering significantly decreased the value by -2.6 (6.0) ms for 0.25 Hz, -5.5 (5.3) ms for 0.5 Hz, and -17.1 (7.8) ms for 1 Hz. Automatic measurements of repolarization (QT) in the MCG differ between techniques and are influenced by filtering. These effects should be considered when comparing results.

Analysis of Variance↗

PubMed2002

Errors in repolarization measurement using magnetocardiography.

Multichannel magnetocardiography (MCG) noninvasively measures variations in magnetic field strength from many sites at the body surface, potentially providing useful regional information about ventricular repolarization. MCGs contain features similar to ECGs, and although errors associated with repolarization measurement have been quantified for ECGs, no comparative data exists for MCGs. In this study, errors in manual measurement of repolarization interval in the MCG were determined. Sixteen MCG channels and three ECG leads were recorded simultaneously in eight healthy subjects. Each recording was displayed in a random order on a computer screen, in presentations with different noise levels, time display widths, and amplitude display heights. In total, manual measurement of repolarization intervals in 2,048 (eight subjects x 16 channels x eight presentations x two repeats) MCGs were made by each of four analysts. Measured repolarization intervals were reduced by 3 ms when noise was added and by a further 3 ms when this noise was doubled. Intervals were shortened by 9 ms when the time display width was doubled and by a further 10 ms when the display width was doubled again. Measurements increased by 7 ms for a doubling of amplitude display height, equivalent to a doubling of T wave height. There were also consistent differences between analysts; amounting to a greatest mean difference of 24 ms. Display characteristics, added noise, and different analysts thus affect manual repolarization interval measurements in MCG. The errors detected demonstrate the importance of a standard presentation for repolarization measurement in the MCG.

Electrocardiography↗