On the atrial response to focal discharges in man

INTRODUCTION: Triggers and vulnerability are key factors for the occurrence of atrial fibrillation (AF). The aim of this study was to assess spatial dispersion of atrial refractoriness and vulnerability in response to both focal discharges as well as programmed electrical stimulation in patients undergoing ablation of atrial arrhythmogenic foci. METHODS AND RESULTS: Twenty-nine patients were studied, and 12 right atrial unipolar electrograms were recorded. Inducibility of AF was assessed by a pacing protocol that started with one extrastimulus, followed by more aggressive pacing until AF was obtained. Mean fibrillatory intervals were used to assess the local refractoriness of each recording site. Spatial dispersion of refractoriness was calculated as the coefficient of dispersion (CD value: standard deviation of the mean of all local mean fibrillatory intervals as a percentage of the overall mean fibrillatory interval). Based on our previous study, a CD value 3.0 was considered enhanced spatial dispersion of refractoriness. Fifteen of 29 patients had normal dispersion of refractoriness (mean CD value 1.65 +/- 0.43), and AF was inducible with burst pacing only. These patients had focal discharges causing rapid atrial tachycardia with a focal activation pattern. Activation mapping of focal activity was possible in 14 of 15 patients. Focal triggering of AF occurred in only 1 of 15 patients. Fourteen of 29 patients had enhanced dispersion (mean CD value 4.2 +/- 0.72). AF was inducible with a single extrastimulus in 11 of 14 patients (P < 0.001). Focal triggering of AF occurred in all 14 patients. CONCLUSION: Spatial dispersion of atrial refractoriness determines whether focal atrial discharges trigger AF with disorganized activity or, alternatively, only rapid atrial tachycardia.