Abstract:

Cardiac arrhythmias are a serious concern to both the individual patient’s health and society as a whole. Treatment and diagnosis of cardiac arrhythmias and fibrosis rely heavily on voltage mapping procedures. Even though voltage mapping is widely used, the factors influencing mapping of the atria are vast and not fully understood. Multiple studies have stressed the importance of revising a universal voltage threshold for classification of diseased heart tissue. In this thesis two in silico studies are conducted by the means of bidomain simulations with a model of atrial tissue. For the first part, a pair of variably sized electrodes is placed on the tissue and the resulting signals are compared in order to investigate the effects electrode size and shape have on the recorded unipolar and bipolar electrograms. Other influence factors like inter-electrode distance (IED) distance, wavefront angle and conduction velocity are kept constant. It is assessed, how accurately the measurements represent the extracellular potential for two different electrode conductivities. In addition, two models of fibrotic tissue (epicardial and transmural) are simulated with the same setups. The two main characteristics investigated were bipolar peak-to-peak voltage and local activation time. We have found various averaging effects in the electrodes affected bipolar signals differently dependent on electrode shape. The highest amplitudes were 8.6 mV recorded with the smallest electrode (0.2 mm × 0.2 mm × 0.2 mm). Electrodes that increased in length showed a linear decrease in voltage of ca. 1 mV/mm. If the electrodes increased in length and width simultaneously, the drop was quadratic and steeper. Bipolar amplitude decreased exponentially with respect to size when cubic electrodes were used. Our study suggests voltage averaging effects in wavefront direction and in the normal direction to the tissue are responsible for a decrease in unipolar amplitudes and thus change the bipolar amplitude as well. For the second study, a lasso catheter model is placed on a patch of atrial tissue. In multiple simulations, positions of a pair of 1 mm cylindrical electrodes are shifted along the lasso. The resulting changes in wavefront angle and interelectrode distance led to changes in bipolar peak-to-peak voltage. When the angle between the electrode pair and the wavefront approached 0◦, the bipolar peak-to-peak voltage decreased towards 0 mV. The conducted studies improved our understanding of electrogram (EGM) behaviour when electrode sizes, shapes and configurations are varied. We’ve shown these variations to be significant to EGM interpretation. Because the variety of catheters in clinical use, the specific nature of the EGM-geometry relationship needs to be investigated further.