Browsing by Author "Montonen, Juha, Dr., Helsinki University and Helsinki University Hospital, Finland"

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The cardiomagnetic field: Non-invasive mapping of atrial fibrillation and model-based characterization of sensitivity and resolution
(2017) Mäntynen, Ville
School of Science | Doctoral dissertation (article-based)
Atrial fibrillation (AF) is the most common arrhythmia of the heart and a major burden to health care. The prevalence of AF (2%) is increasing with ageing population. Different physiological mechanisms underlying AF as well as increasing options for its treatment call for advancement in diagnostics. One approach is through measurement of the electromagnetic field that the electrochemical activity of the heart gives rise to. In magnetocardiography (MCG), the cardiomagnetic field is measured outside the thorax and analyzed. In this Thesis, I have studied and developed multichannel MCG mapping in order to characterize the cardiac function and AF. The cardiomagnetic field was studied using non-invasive MCG mappings of healthy subjects and AF patients as well as with computer simulations. To identify and characterize MCG signal features related to AF, the atrial activity was assessed using MCG recorded during both the sinus rhythm and arrhythmia. During the sinus rhythm, the MCG map pattern was shown to depend on the interatrial conduction pathway (CP) as determined by invasive electrophysiological study; an MCG method was developed to assess the CP non-invasively. In another study, MCG map types associated with different CPs were found to occur in different proportions in patients and in healthy subjects. In addition, a technique for assessing the temporal evolution of the MCG map during ongoing arrhythmia was introduced. The technique brought up recurrent spatiotemporal MCG map patterns with abrupt changes and substantial interpatient differences. The techniques developed provide new means for non-invasive characterization of atrial activity and may also be clinically useful. In the modelling part of this work, spatial properties of MCG, electrocardiography (ECG), and combined MCG+ECG were studied in terms of signal generation characteristics and source-estimation performance. These were assessed by amplitudes of simulated signal topographies and characteristics of point-spread functions for sources all around the heart. The results showed that the relative signal amplitude depends not only on the location and orientation of the source but also on the measurement modality, and that this amplitude profile is also reflected to the source estimates. The simulations illustrate the complementary information pro-vided by electro- and magnetocardiography. For optimal sensitivity and resolution, MCG and ECG should be combined.