Automated production of contour maps for electrophysiology III. Construction of contour maps

Abstract

Construction of contour maps of cardiac electrophysiological measurements is a complex problem because of wide variations of map geometry, because map geometry reflects highly irregular cardiac anatomy, because of the unpredictable absence of measurements from some electrodes, and because high program efficiency is essential for processing the large numbers of maps necessary to portray complete sequences of cardiac excitation and recovery. This report describes program modules for constructing such contour maps and for allowing wide variations in their style, e.g., the number and spacing of contour lines. The map construction method relies particularly on a carefully selected data structure, called an edge table, which describes the map's geometry in a form that results in highly efficient contour line construction and graceful treatment of the problem of missing measurements. Visually smooth contour lines are obtained using interval-by-interval bicubic interpolation. The problems that arise in contouring a region of constant voltage are resolved by systematically selecting the contour line voltage. The theoretical basis for constructing the map is shown to be mathematically sound; the resulting programs modules have proved highly successful in constructing thousands of maps rapidly, reliably, and accurately.