Electrophysiology and endocardial mapping of induced atrial fibrillation in patients with spontaneous atrial fibrillation

We analyzed the patterns of atrial activation and characterized the electro physiologic properties of regional atrial sites in the right atrium and lef t atrium at the onset of atrial fibrillation (AF) induced with programmed r ight atrial (RA) stimulation. Intraatrial conduction, atrial electrogram re turn cycle lengths for the first AF cycle, RA and left atrial (LA) activati on maps during AF, and the stability and reproducibility of atrial activati on sequences at AF onset and maintenance were analyzed in 23 patients with AF. Correlation of intracardiac electrograms with surface electrocardiograp hic morphology was attempted. Maximum intraatrial conduction delay for high RA premature beats was observed at the coronary sinus ostium (n = 15), His bundle region (n = 13) or interatrial septum (n = 15). The return cycle le ngths for the first AF cycle showed increasing conduction delay with increa sing prematurity of the last extrastimulus in most patients. Surprisingly, discrete atrial electrograms with regular or irregular cycle lengths were p resent at the onset of electrocardiographic documented coarse AF in 13 of 1 5 patients (87%). Fragmented or chaotic atrial activity were present in 2 o f 15 patients (13%) in coarse AF but observed at greater than or equal to 1 atrial sites in 7 of 8 patients (88%) with fine AF (p = 0.001). The atrial activation sequence at the onset of the induced AF elicited by high RA ext rastimuli usually showed the earliest activation site at the crista termina lis (9 patients) or interatrial septum (9 patients) In contrast, induced BF elicited from other RA sites usually showed earliest atrial activation at the septum (3 patients) or coronary sinus ostium (3 patients). Atrial activ ation sequences for the first induced AF cycle were usually reproducible in most patients. Atrial activation patterns during the first 10 cycles for A F were stable in RA and LA regions in 6 of 23 patients (26%) but demonstrat ed significant change(s) at greater than or equal to 1 region in 17 of 23 p atients (74%) (p < 0.05). We conclude that pacing induced AF elicited by RA premature beats commences as a regular or irregular rapid atrial tachycard ia consistent with a transitional, but often organized, arrhythmia. The act ivation sequence and electrophysiologic behavior of the first induced AF cy cle is consistent with intraatrial reentry and reproducible in mast patient s. More than 1 atrial activation sequence can sometimes be observed, emphas izing the dynamic nature of the initial RA reentrant circuits. (C) 1999 by Excerpta Medico, Inc.