Electrophysiological properties of the left atrium evaluated by coronary sinus pacing in patients with atrial fibrillation

Repetitive atrial firing (RAF), marked fragmentation of atrial activity (FA A), and interatrial conduction delay (CD) have been shown to be electrophys iological features of the atrium in patients with atrial fibrillation (AF). Moreover, it has been observed that atrial extrastimuli are more likely to induce AF when delivered from the right atrial appendage (RAA) than from t he distal coronary sinus (CSd). We examined the electrophysiological proper ties of the atrial muscle by CS and RAA stimulation in patients with paroxy smal AF. Patients were divided into two groups: group I, consisting of 18 p atients with clinical paroxysmal AF; and group II, consisting of 22 patient s with various cardiac arrhythmias in which the substrate does not exist in the atrium. In group I, the following values of electrophysiological param eters of the atrium indicated that AF was more likely to be induced during RAA pacing than CSd pacing: atrial effective refractory period (RAA vs CSd: 201 +/- 28 ms vs 240 +/- 35 ms, P < 0.001), RAF zone (16 +/- 25 ms vs 0 +/ - 0 ms, P < 0.03), FAA zone (38 +/- 37 ms vs 5 +/- 19 ms, P < 0.01), maximu m interatrial conduction time (144 +/- 19 ms vs 93 +/- 19 ms, P < 0.0001) a nd CD zone 153 +/- 21 ms vs 9 +/- 18 ms, P < 0.0001). The values of the ele ctrophysiological parameters of the atrium evaluated by CSd pacing in group I patients were not significantly different from those in group II patient s. In conclusion, when coronary sinus stimulation is performed, electrophys iological properties of the atrium in patients with AF show a significant d ecrease in atrial vulnerability compared to stimulation from RAA and also s how similar values to those in patients without AF. It might be suggested t hat the left posterior or posterolateral atrium is electrophysiologically s table even in patients with paroxysmal AF.