Prevalence of typical atrial flutter with reentry circuit posterior to the superior vena cava: Use of entrainment at the atrial roof

AIMS: Upper turn-around of the reentry circuit in typical atrial flutter (AF) is classically described to be located in front of the superior vena cava (SVC), but circuits posterior to the SVC as well as lower loop reentry (LLR) involving only the lower part of the right atrium have been described. However, true prevalence of such AF circuits remains unknown. METHODS AND RESULTS: Fifty consecutive patients (46 men, 68 +/- 9 years old) undergoing radiofrequency (RF) ablation of typical counter-clockwise AF were prospectively investigated. Prior to RF deliverance, AF was entrained by pacing 10 ms shorter than the AF cycle length (AFCL). Post-pacing interval (PPI) at the cavotricuspid isthmus (CTI) and at the atrial roof (AR)-between SVC and the high tricuspid annulus-were determined. AR was considered to be part of the AF circuit when local PPI-AFCL was < or =20 or 30 ms or, in case of long PPI at the CTI isthmus, if difference between AR-PPI and CT-PPI was < or =10 ms. In 47 patients, CTI-PPI-AFCL was < or =30 ms (94%). Among them, AR-PPI-AFCL was >30 ms in 12 cases (25%). In the remaining three patients, AR-PPI-AFCL did not exceed CTI-PPI-AFCL by more than 10 ms. In 42 patients, CTI-PPI-AFCL was < or =20 ms (84%). Among them, AR-PPI-AFCL was >20 ms in 16 cases (39%). In the remaining eight patients, AR-PPI-AFCL was more than 10 ms longer than CTI-PPI-AFCL in only one instance. Taken together, AR PPI was >20 or >30 ms longer than AFCL or >10 ms longer than CTI PPI when prolonged in 17 (34%) and 12 patients (24%), respectively. CONCLUSION: In around a quarter to one-third of patients referred for RF ablation of typical AF, the atrial roof is not part of the circuit, thus they may present a 'posterior' variant of the typical counter-clockwise AF reentry circuit.