Atrial Activation as Seen on the Esophageal Electrogram and Its Importance in Diagnosis of Complex Arrhythmias.

The interpretation of cardiac arrhythmias is based on the reliable observation of atrial and ventricular events (P waves and QRS complexes) over a period of time. However, in conventional clinical electrocardiography, the timing of cardiac electrical events cannot always be reliably determined. The detection of atrial activity has been the most important limiting factor of many arrhythmia analysis systems. The development of an easily swallowed esophageal electrode has provided a means to acquire precise timing of atrial events and recently has found value in computerized arrhythmia recognition. This thesis examines the importance of the esophageal P wave in the diagnosis of complex arrhythmias. We have applied the solid angle method quantitatively to the interpretation of esophageal electrograms. The calculation of the solid angle subtended by an object with a regular boundary is presented and an analytical expression, based on volume conductor theory, for the potential generated by a uniform double layer, is given. The solid angle subtended by an object with an irregular boundary is treated by using the spherical triangle method. An atrial model based on atrial electrical activity was developed. Numerical (X, Y, Z) coordinates of the free walls of the atria at thirteen levels (cross-sections) were determined and activation wavefronts were superimposed on the model. The solid angle subtended by the activation boundary at a point P in the esophagus was calculated at successive time intervals and a simulated electrogram derived. The potential at the esophagus was analytically determined for three cases: normal conduction originating in the sinus node, abnormal conduction originating in an ectopic focus, and retrograde activation from the atrio-ventricular node. Experimental data from four normal subjects and five patients were recorded and compared with computed data. Results were found to be in close agreement. Esophageal waveform analysis has been incorporated into a special-purpose microcomputer system for automated arrhythmia diagnosis. The system contains dual microprocessors which execute in parallel for simultaneous data acquisition and concurrent analysis of underlying arrhythmias.PhDBiomedical engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159962/1/8412173.pd