Abstract:

Ablation strategies to prevent episodes of paroxysmal atrial fibrillation (AF) have been subject to many clinical studies. The issues mainly concern pattern and transmurality of the lesions. This paper investigates ten different ablation strategies on a multilayered 3-D anatomical model of the atria with respect to 23 different setups of AF initiation in a biophysical computer model. There were 495 simulations carried out showing that circumferential lesions around the pulmonary veins (PVs) yield the highest success rate if at least two additional linear lesions are carried out. The findings compare with clinical studies as well as with other computer simulations. The anatomy and the setup of ectopic beats play an important role in the initiation and maintenance of AF as well as the resulting therapy. The computer model presented in this paper is a suitable tool to investigate different ablation strategies. By including individual patient anatomy and electrophysiological measurement, the model could be parameterized to yield an effective tool for future investigation of tailored ablation strategies and their effects on atrial fibrillation.

Abstract:

Numerous studies about the effects in human body of high frequency magnetic fields on the one hand and extremely low frequency fields on the other hand have been carried out. This is not the case for the mid frequency range around 100 kHz. When applying external magnetic fields to the human body in this frequency range both electric stimulation and thermal heating effects have to be considered. Magnetic Particle Imaging (MPI), a new imaging technique, and Hyperthermia, a tumor treatment therapy, both apply magnetic fields in a frequency range around 100 kHz. In MPI thermal heating of the body has to be prevented, whereas in Hyperthermia a temperature increase of about 4 K in the target region is desirable. Induced currents may lead to muscle stimulation which is not acceptable above a certain threshold. This paper presents the results of induced current densities and SAR in a numeric field calculation simulation. For the model of the human body the torso of the Visible Man Dataset has been employed, along with the dielectric properties of biological tissues investigated by Gabriel & Gabriel. The model has been exposed to a sinusoidal magnetic field with an amplitude of 10 mT. The results of the induced current densities and SAR values have been compared with the currently valid official guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). It turns out that limits of induced current densities are reached by applying a magnetic flux density of 10 mT and the SAR limit even is exceeded.