Ville Mäntynen

Non-invasive detection of conduction pathways to left atrium using magnetocardiography: validation by intra-cardiac electroanatomic mapping

AIMS Alteration in conduction from right to left atrium (LA) is linked to susceptibility to atrial fibrillation (AF). We examined whether different inter-atrial conduction pathways can be identified non-invasively by magnetocardiographic mapping (MCG). METHODS AND RESULTS In 27 patients undergoing catheter ablation of paroxysmal AF, LA activation sequence was determined during sinus rhythm using invasive electroanatomic mapping. Before this, 99-channel magnetocardiography was recorded over anterior chest. The orientation of the magnetic fields during the early (40-70 ms from P onset) and later part (last 50%) of LA depolarization was determined using pseudocurrent conversion. Breakthrough of electrical activation to LA occurred through Bachmann bundle (BB) in 14, margin of fossa ovalis (FO) in 3, coronary sinus ostial region (CS) in 2, and their combinations in 10 cases by invasive reference in total of 29 different P-waves. Based on the combination of pseudocurrent angles over early and late parts of LA activation, the MCG maps were divided to three types. These types correctly identified the LA breakthrough sites to BB, CS, FO, or their combinations in 27 of 29 (93%) cases. CONCLUSION Magnetocardiographic mapping seems capable of distinguishing inter-atrial conduction pathways. Recognizing the inter-atrial conduction pattern may assist in understanding the pathogenesis of AF and identifying the subgroups for patient-tailored therapy.

Reversal of Atrial Remodeling after Cardioversion of Persistent Atrial Fibrillation Measured with Magnetocardiography

Background: Atrial fibrillation (AF) causes electrical, functional, and structural changes in the atria. We examined electrophysiologic remodeling caused by AF and its reversal noninvasively by applying a new atrial signal analysis based on magnetocardiography (MCG).

Investigations of sensitivity and resolution of ECG and MCG in a realistically shaped thorax model

Solving the inverse problem of electrocardiography (ECG) and magnetocardiography (MCG) is often referred to as cardiac source imaging. Spatial properties of ECG and MCG as imaging systems are, however, not well known. In this modelling study, we investigate the sensitivity and point-spread function (PSF) of ECG, MCG, and combined ECG+MCG as a function of source position and orientation, globally around the ventricles: signal topographies are modelled using a realistically-shaped volume conductor model, and the inverse problem is solved using a distributed source model and linear source estimation with minimal use of prior information. The results show that the sensitivity depends not only on the modality but also on the location and orientation of the source and that the sensitivity distribution is clearly reflected in the PSF. MCG can better characterize tangential anterior sources (with respect to the heart surface), while ECG excels with normally-oriented and posterior sources. Compared to either modality used alone, the sensitivity of combined ECG+MCG is less dependent on source orientation per source location, leading to better source estimates. Thus, for maximal sensitivity and optimal source estimation, the electric and magnetic measurements should be combined.

Comparison of minimum-norm estimation and beamforming in electrocardiography with acute ischemia

In the electrocardiographic (ECG) inverse problem, the electrical activity of the heart is estimated from measured electrocardiogram. A model of thorax conductivities and a model of the cardiac generator is required for the ECG inverse problem. Limitations and errors in methods, models, and data will lead to errors in the estimates. However, in experimental applications, the use of limited or erroneous models is often inevitable due to necessary model simplifications and the difficulty of obtaining accurate 3D anatomical imaging data. In this work, we focus on two methods for solving the inverse problem of ECG in the case of acute ischemia: minimum-norm (MN) estimation and linearly constrained minimum-variance beamforming. We study how these methods perform with different sizes of ischemia and with erroneous conductivity models. The results indicate that the beamformer can localize small ischemia given an accurate model, but it cannot be used for estimating the size of ischemia. The MN estimator is tolerant to geometry errors and excels in estimating the size of ischemia, although the beamformer performs better with accurate model and small ischemia.

Noninvasive mapping reveals recurrent and suddenly changing patterns in atrial fibrillation—a magnetocardiographic study

OBJECTIVE To study noninvasive magnetocardiographic (MCG) mapping of ongoing atrial fibrillation (AF) and, for the possible mapping patterns observed, to develop simplified but meaningful descriptors or parameters, providing a possible basis for future research and clinical use of the mappings. APPROACH MCG mapping with simultaneous ECG was recorded during arrhythmia in patients representing a range of typical, clinically classical atrial arrhythmias. The recordings were assessed using MCG map animations, and a method to compute magnetic field map orientation (MFO) and its time course was created to facilitate presentation of the findings. All the data were segmented into four categories of ECG waveform regularity. MAIN RESULTS In visual observation of the MCG animations, an abundance of clear spatial and temporal patterns with regularity were found, often perceived as rotations of the map. This rotation and its sudden reversals of direction were distinctly present in the time course of the MFO. The shortest segments with consistent rotation lasted for some hundreds of milliseconds, i.e. a couple of cycles, but segments lasting for tens of seconds were observed as well. In the ECG, all four categories of regularity were present. The rotation of the MFO was observed in all patients under study and regardless of the ECG categories. Further, a change in ECG category during a measurement was frequently, but not always, found to be simultaneous with a change in the rotation pattern of the MFO. Utilization of spatial information of MCG mapping could enable detection of both regularities and instantaneous phenomena during AF. SIGNIFICANCE Cardiac mapping may offer a useful noninvasive means to study the mechanisms of AF, including superior temporal resolution.