Owczarek I, Banasiak W, Metner E, Fuglewicz A, Telichowski A, Lacheta W, Klaniewski T. Pol Arch Med Wewn 1997;98(9):197-205. Paroxysmal palpitation is a frequent non-specific symptom observed in clinical practice. It is not always possible to identify the arrhythmogenic cause of this complaint. The induction of paroxysmal atrial fibrillation (PAF) during transoesophageal pacing (TEP) was found to be particularly useful when arrhythmia paroxysms were not evidenced by standard electrocardiography or by 24-hour Holter monitoring. The objective of the present study was a comparative assessment of the electrophysiological parameters obtained from a patient group with PAF induced during TEP and from a patient group with no arrhythmia, in order to determine the hazard of spontaneous PAF occurrence. The study included 116 patients complaining of palpitations who underwent TEP. Of these, 53 were selected (34 males and 19 females; mean age, 47.6 +/- 13.1) in whom a sustained PAF episode (> 30 sec) had been induced during TEP. These patients are referred to Group I. Group II (control) comprised the remaining 63 patients (38 males and 25 females; mean age 45.5 +/- 8.5) in whom no PAF episode had been induced during TEP. All patients (Group I and Group II) underwent echocardiography, 24-hour Holter monitoring, exercise test and TEP. During TEP the following parameters were evaluated: left atrial effective refractory period (AERP), sinoatrial conduction time (SACT), maximal and corrected sinus node recovery time (SNRT and CNRT), Wenckebach periodicity (WP) and mean cycle duration (CD). Thus, the AERP value amounted to 299.8 +/- 42.4 msec and 259.5 +/- 54.9 msec (p < 0.001) for Group I and Group II, respectively. The SACT and SNRT values totalled 132.3 +/- 45.1 msec and 1011.1 +/- 165.6 msec in Group I, and 103.2 +/- 29.9 msec and 838.3 +/- 172.7 msec in Group II, respectively (p < 0.001). Compared to the control (235 +/- 95.7 msec; 200.3 +/- 64.9 msec, respectively), the group of patients with electrically-induced PAF (Group I) showed significantly longer CNRT (383.4 +/- 172.5 msec, p < 0.001) and WP (350.8 +/- 59.3 msec, p < 0.001). The study had led to the following finding: patients with electrically-induced PAF had significantly longer left effective refractory periods, sinoatrial conduction times, maximal and corrected sinus node recovery times and Wenckebach periodicities.