Introduction Radiofrequency ablation (RFA) of typical atrial flutteru is the most successful method for treatment of atrial flutter. The acute (peri-procedural) efficacy is more than 95%. (1) Typical atrial flutter circuit uses the area between inferior caval vein and tricuspid anulus, so a RFA of typical flutter is performed by providing a linear lesion from inferior caval vein to tricuspid valve (this area is called as cavo-tricuspid isthmus). The recurrence of atrial flutter after ablation, which are caused by non-transmural RF lesion, are in less than 10% of cases. (2) During atrial flutter ablation, typically three electrophysiological catheters are used. Two catheters are diagnostic (one 10-pole inserted into coronary sinus and the other 20-pole inserted in the right atrium with the distal tip laterally from the cavo-ticuspid isthmus). The third is ablation catheter, inserted in the CT isthmus. The location of all three catheters is monitored by fluoroscopy and by the EP signals on catheters. Also the ablation catheter during the ablation is monitored by fluoroscopy and by the signals on the catheter.

Despite its high efficacy, the RFA of atrial flutter can be sometimes very difficult. The most difficulties are done by anatomical differences in patients. (3, 4) In the area of CTI, the rudimentary Eustachian valve can be present, which can hide the effective ablation of the CI tissue. Moreover, deep pouches can be present in the TI area, which, if unrecognized, can present the area of insufficient ablation. Both of them, Eustachian valve or pouches, are not visible by fluoroscopy. In rare cases, a complete block in the CTI are is not achieved, typically due to some anatomical difficulties. Furthermore, this anatomical obstacles can lead to prolonged fluoroscopy time (to find the location of conduction in CTI rea), more RF energy delivery and prolonged procedure time. Longer ablation time increases the risk of ablation (such as right atrial perforation). Next possible anatomical obstacle is the right coronary artery which can effective prevent sufficient ablation due to its cooling effect. (5) Intracardiac echocardiography (ICE) is done by using intracardiac echo probe. The probe is inserted in the right atrium, which allows the visualizing of the CTI area. (6, 7) ICE is used for AF ablation in some centers, but its effect has never been validated in the randomized study. The aim of our study is to assess whether routine use of ICE can lead to decrease fluoroscopy time, decrease need for RFA delivery (i.e. number of ablations) and a decrease procedure time. On the other hand, the safety endpoint will be to assess whether a routine use of ICE is not associated with higher rate of complications. We hypothesize, the use of ICE will shorten fluoroscopy, ablation and procedural time without increased number of complication

Patients and methods:

Consecutive patients indicated due to standard criteria (i.e. according to the guidelines of the European Society of Cardiology) for atrial flutter ablation will be enrolled. Exclusion criterion will be the absence of written informed content and a history of recent femoral vein thrombosis (\< 6 months).

Randomization: 1 to 1 for ICE vs. non ICE RF ablation will be done routinely, as it is done in the center. In the Ice group, ICE probe will be inserted through the left femoral vein in the right atrium TH ICE will be used for the visualization of the anatomy of CTI area and the visualization of the catheter during RF delivery. In case of the non-ICE group, RFA will be done without ICE catheter, as it is done routinely now. In both groups, the diagnostic catheters (10-pole CS and 20-po in the RA) and ablation catheter will be the same. In the non-ICE group, the location of the catheters will be assessed by fluoroscopy and by signals on catheters. At the end of ablation, total fluoroscopy time, the number and length of ablation and the duration of procedure will be calculated. On the day and two weeks after the procedure, the bleeding complication will be assessed.

End-points: the major end-points will be: 1) total procedure duration (min) 2) fluoroscopy time 3) the number of ablations 4) the total duration of RF energy delivery. Major safety end-point will be complication from left femoral ICE access.