Biomedical subjects

J Nenonen

Publications and source records attributed to J Nenonen.

28 records · Page 2Linked to original sources

PubMed1993

Magnetocardiography: supraventricular arrhythmias and preexcitation syndromes.

Magnetocardiography is an elegant non-invasive method with which to study the electrical activity of the heart. The localization of cardiac electric sources, such as arrhythmia foci, would, in particular, be an interesting clinical application. In addition the detection of different abnormalities that could lead to cardiac depolarization and repolarization gives insight into how cardiac arrhythmias and arrhythmia mechanisms are generated. We have studied patients with supraventricular arrhythmias, especially those suffering from the Wolff-Parkinson-White (WPW) syndrome. Magnetocardiographic localization of the preexcitation site was performed in 26 WPW patients, with an average accuracy of 2 +/- 1 cm in comparison to the results obtained by invasive catheter mapping. By inspection of spatial isofield maps during atrial depolarization, the risk of atrial fibrillation was classified correctly in 11/20 (55%) patients with documented atrial fibrillation, and in 4/6 (67%) patients without atrial fibrillation. In a case of focal atrial tachycardia, magnetocardiographic localization of the origin of the arrhythmia was performed during tachycardia. In addition, the level of conduction block was successfully determined in six patients with third-degree congenital atrioventricular block.

Adult↗

PubMed1992

Localization of accessory pathways in Wolff-Parkinson-White syndrome by high-resolution magnetocardiographic mapping.

Fifteen patients with Wolff-Parkinson-White syndrome were studied with standard 12-lead electrocardiogram, invasive electrophysiologic study, and high-resolution magnetocardiographic (MCG) mapping. In addition, intraoperative epicardial mapping was performed in seven surgically treated patients. The MCG characteristics of ventricular preexcitation for different locations of the atrioventricular accessory pathways were described in terms of morphology and field patterns. Three mathematical source models in semi-infinite conducting space were used for localization computations: the current dipole model, the truncated current multipole model and the magnetic dipole model. Finally, the localization results of MCG and invasive mappings and electrocardiograms were compared. The mean three-dimensional distance between the localization results obtained from MCG maps and electrophysiologic study was 3.9 cm for the magnetic dipole model, 4.8 cm for the truncated current multipole model, and 7.3 cm for the current dipole model. The corresponding distances in the seven intraoperatively mapped cases were 2.3 cm for the magnetic dipole model, 5.2 cm for the truncated current multipole model, and 6.3 cm for the current dipole model. In conclusion, noninvasive MCG mapping may significantly contribute to the invasive catheter mapping for optimal preoperative localization of preexcitation site and atrioventricular accessory pathways in Wolff-Parkinson-White syndrome.

Adult↗

PubMed1991

Mathematical modelling for biomagnetic localization.

Non-invasive biomagnetic measurements are feasible for obtaining functional information concerning the electrical activity of the human heart and brain. These methods have turned out to be promising in localizing various bioelectric sources in the body. For example, in magnetocardiographic studies of localizing arrhythmogenic tissue and both normal and abnormal conduction pathways between the atrial and the ventricles, the best accuracies reported are comparable to the results obtained by the invasive methods. We consider here basic principles of biomagnetic source localization methods, focusing on the magnetocardiographic mapping.

Action Potentials↗

PubMed1991

Magnetocardiographic localisation and modelling.

In our magnetocardiographic (MCG) localisation studies, two modelling approaches have been applied: (a) modelling the sources with dipole and quadrupole moments in a general multipole expansion and using a homogeneous, semi-infinite volume conductor, and (b) using a single current dipole source in a homogeneous, realistically shaped torso. Both approaches have been successfully applied in localising the premature ventricular excitation site in patients suffering from the Wolff-Parkinson-White syndrome. In addition, we have participated in developing a model of propagation of electrical activation in the ventricles. Anisotropic conductivity properties and spiral arrangement of myocardial fibres are included in the model.

Heart Function Tests↗

PubMed1991

Magnetocardiographic functional localization using current multipole models.

High-resolution magnetocardiographic mapping was applied to localize the ventricular preexcitation site in ten patients suffering form Wolff-Parkinson-White syndrome. Three different source models were tested, consisting of the dipole and quadrupole moments in a general multipole expansion. Noninvasive localizations were performed by computations based on measured magnetic maps without a priori assumptions of the source location and without imposing any constraints. In all cases, the computed results were compared with invasive localization results obtained by catheter mapping technique. Preoperative catheterization localizes the atrial end of the accessory pathway, while our method localizes the ventricular preexcitation site. Of the models used, the average three-dimensional difference between the invasive localization results and the HR-MCG results was smallest 2.9 cm for the source model consisting of the magnetic dipole. The preexcitation site was very deep in all cases. The current dipole alone was inaccurate in estimating the source depth, but inclusion of the quadrupole moments improved the results. Two of the patients underwent surgery to interrupt the accessory pathway, which provided further validation for the noninvasive localizations.

Adult↗

PubMed1991

Magnetocardiographic functional localization using a current dipole in a realistic torso.

We describe a fast and numerically effective biomagnetic inverse solution using a moving dipole in a realistic homogeneous torso. We applied the localization model and high-resolution magnetocardiographic mapping to localize noninvasively the ventricular preexcitation site in ten patients suffering from Wolff-Parkinson-White syndrome. In all cases, the computed localization results were compared to the results obtained by invasive catheter technique. Using a standard-size torso model in all cases, the average 3-D distance between the computed noninvasive locations and the invasively obtained results was 2.8 +/- 1.4 cm. When the torso was rescaled to better match the true shape of the subject in five cases, the 3-D average was improved to 2.2 +/- 1.0 cm. This accuracy is very satisfactory, suggesting that the method would be clinically useful.

Adult↗

PubMed1991

Sensitivity limits in biomagnetic measurements.

It is important to understand the character and the contribution of thermal magnetic noise in designing the measurement site and the instrumentation for biomagnetic measurements. The ultimate limit of the sensitivity is the thermal noise due to the object under study. In the case of the human body, it has been estimated to be about 0.1/square root of Hz. Magnetically shielded rooms are necessary for ultrasensitive biomagnetic measurements of human subject, but they also generate external noise which in some cases may become detectable. This noise problem can be avoided if the innermost walls are constructed of magnetically soft ferromagnetic material. Close to the conducting walls the thermal noise is higher than at the centre. Thus, the shielded room should be relatively large in size. The gantry and other things inside the room may contain metal parts, which can cause excess noise. The intensity depends on the conductivity, geometry, location and movement of these parts. In comparison to bioelectric studies, this inductive noise coupling demands extra attention. In most biomagnetic measurements performed inside a magnetically shielded room, the limiting factor of the sensitivity is the thermal noise caused by electrically conducting thermal shielding used inside the cryogenic measurement dewar. Fortunately, it is possible to reduce the noise contribution arising from the superinsulation in the dewar by careful design. The properties and dynamics of the SQUIDs are well understood nowadays. Studies of the nonlinear character in the coupling between the SQUID and external detection coil have made it possible to reduce the noise contribution of the sensor itself.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioelectric Energy Sources↗

PubMed1987

On the accuracy of source localisation in cardiac measurements.

This paper describes a localisation study of the sources of bioelectrical activity in the human heart. In particular, the atrial activation (P wave) and the activation of an extra pre-excitation area in the WPW syndrome are investigated. Different models based on the current multipole expansion are used to calculate the inverse solution. A comparison between calculated results, invasive electrophysiological studies and known physiological data is performed. The best results were obtained by the current multipole model with dipole and quadrupole terms. Non-invasive localisation of cardiac electric sources can be useful in studies of arrhythmia patients in the future.

Atrial Function↗

PubMedDate not supplied

Magnetocardiographic localization of ventricular pre-excitation in a child with a congenital heart defect.

Magnetocardiographic mapping was performed on a 2-year-old boy who suffered from the Wolff-Parkinson-White syndrome in association with a complex congenital heart defect. The pre-excitation site was determined noninvasively from the measured cardiac magnetic fields. The location was in the same anatomic region as found by intraoperative epicardial mapping. This result shows that magnetocardiography can be helpful for determining an accessory pathway also in patients with grossly abnormal cardiac anatomy.

Child, Preschool↗

PubMedDate not supplied

Simulated epicardial potential maps during paced activation reflect myocardial fibrous structure.

Using a three-dimensional propagation model of the human ventricular myocardium, we studied the role of fibrous structure in generating epicardial potential maps. This model represents the myocardium as an anisotropic bidomain with an equal anisotropy ratio, and it incorporates a realistic representation of anatomical features, including epi-endocardial fiber rotation in the compact portion of the wall (compacta) and a distinct fiber arrangement of the trabeculated portion (trabeculata). Activation sequences were elicited at various intramural depths, and maps were calculated throughout a 60 ms sequence. The simulated maps closely resembled those measured by others in the canine heart. During the early stages of activation, a typical map featuring a central minimum flanked by two maxima emerged, with the axis joining these extrema approximately parallel to the fibers near the pacing site, and the axis joining the maxima rotated in the same direction as the fibers for different pacing depths; for endocardial and subendocardial pacing this map changed into one with an oblong positive area. During the later stages of activation, the positive areas of the maps expanded and rotated with the transmural fiber rotation. In concurrence with experiments, we saw a fragmentation and asymmetry of expanding and rotating positive areas. The latter features-apparently caused by the interface between the compacta and trabeculata, variable local thickness of the wall, or local undulations of the vetricular surface-could not be reproduced by more idealized, slab models.

Animals↗