VAGAL-MEDIATED ATRIAL PREMATURE BEATS - A COMPUTER-MODEL

A computer algorithm is described that used experimental data to model the arrhythmogenic interaction of phasic vagal stimuli and atrial ect opic pacemakers. The model consisted of a dominant sinus node and a si ngle ectopic pacemaker center separated by conducting atrial tissue. I ts primary operation was to predict the timing and incidence of atrial premature beats resulting from transient escape of ectopic automatic impulses when vagal-induced entrance block of the sinus impulse was si mulated near the ectopic focus. These predictions were based on a seri es of experimentally derived phase-response and corrected recovery tim e curves, describing the modulation of ectopic pacemaker periodicity b y vagal input and overdrive suppression, respectively. Depending on th e combination of curves tested, the model predicted premature beats to develop only with critically timed vagal stimuli. The coupling interv als of vagal-induced premature beats were >300 ms and varied as a func tion of vagal timing and sinus cycle length. The model suggests theref ore that phasic vagal stimuli within the atrium may transiently protec t ectopic pacemaker foci from conducted sinus impulses and mediate the genesis of atrial extrasystoles with long coupling intervals.