Design and performance of lead systems for the analysis of atrial signal components in the ECG

For over a century, electrocardiology has been observing human cardiac activity through recordings of electrocardiograms (ECG). The potential differences derived from the nine electrodes of the standard 12-lead ECG, placed at their designated positions, are the expression of electric dynamics of which the heart is the source. According to well-defined protocols and established criteria of diagnosis, the signals of the electrocardiogram are used as indicators of cardiac pathology. However, of the four chambers of the human heart, each of which has a specific function, most attention in cardiology has been traditionally placed on the ventricles. This has meant that the conventional ECG system is focused on the observation of ventricular activity, and might not be optimal in studying the activity of the atria. The increasing prevalence of atrial fibrillation in the general population, with its inherent severe complications as well as the known social and economic impacts of the disease, has elicited studies investigating body surface potentials of atrial arrhythmias, invariably pivoted on the standard ECG. The aim of this thesis is to investigate the conception and validation of a lead system targeted at the analysis of atrial fibrillation. This new lead system should be dedicated and optimized to capturing a maximal amount of information about the atrial electric activity taking place during fibrillation, but at the same time be well anchored to the standard ECG configuration, in view of its application in clinical practice. This constraint has led to the use of the same number of electrodes, nine, while leaving at least half of these, five, in their initial positions. In the first part of this thesis, observations of body surface potential maps during normal atrial activity are discussed. The objective was to study the involvement of atrial repolarization in body surface potentials. While studying ECG signals recorded with 64-lead systems from 73 patients, special attention was devoted to the processing of low-amplitude signals. The local potential extremes were found at positions not sampled by the standard leads. Moreover, the PQ segment was found to be not electrically silent, the time course of the potential distribution being very similar to that during the P wave but for a reversed polarity and about 3-fold lower magnitudes. The results demonstrate a significant involvement of atrial repolarization during the PQ interval, and a small dispersion of atrial action potential durations. In the second part, the design and evaluation of a new optimized lead system (OACG) dedicated to atrial fibrillation is presented, based on a biophysical-model study. Considering the material constraint mentioned above, the locations of four of the six precordial electrodes were optimized while leaving the remaining five electrodes of the standard ECG system in place. The analysis was based on episodes of eleven different variants of AF simulated by a biophysical