Identification of the substrate of atrial vulnerability in patients with idiopathic atrial fibrillation

Background-Experimental studies have shown that atrial fibrillation (AF) ca uses remodeling, which facilitates AF perpetuation. AF may also, however, o ccur in patients without remodeling and underlying structural cardiac disea se. The substrate for enhanced vulnerability in these patients is unknown. Methods and Results-We studied 43 patients without structural heart disease : Is patients with documented sporadic paroxysmal AF and 25 control patient s without AF. In each patient, a decapolar catheter was positioned against the right atrial free wall, and a quadripolar catheter was positioned in th e right atrial appendage. Unipolar electrograms were recorded. Atrial vulne rability was assessed according to an increasingly aggressive stimulation p rotocol. Mean local fibrillatory interval (FI) was used as an index of loca l refractoriness. Spatial dispersion of refractoriness was assessed through the calculation of the coefficient of dispersion (CD), which was defined a s the SD of mean local Fl expressed as a percentage of the mean FI. In the AF group, AF was induced with a single extrastimulus in 16 of 18 patients; the CD was 5.4+/-2.6, and the mean FI was 164+/-29 ms. In the control group , AF could be induced only with more aggressive pacing in 23 of the 25 pati ents; the CD was 1.4+/-0.7 (P<0.0001), and the mean FT was 175+/-26 ms (NS) . Conclusions-Patients with idiopathic AF showed increased dispersion of refr actoriness, which may be the substrate for the observed enhanced inducibili ty and spontaneous occurrence of AF.