Introduction 1 5 1 13 14 15 The purpose of this study was to evaluate the long term outcome of CTI cryoablation in a large patient population with common type AFL in a single center. Methods One hundred and eighty patients with sustained symptomatic common type AFL referred for CTI ablation were enrolled prospectively from July 2001 to July 2006 in our institution. Signed written consent, approved by the local ethics committee, was obtained from all participants. Before CTI cryoablation, anticoagulation with warfarin aiming a therapeutic international normalized ratio of 2 to 3 was kept for at least 3 weeks. Antiarrhythmic drugs were not discontinued before ablation. Electrophysiologic study and ablation We focused our study on the clinical aspects and long term follow-up of patients with AFL who were submitted to CTI cryoablation. 15 15 19 2 10 15 16 20 21 22 All patients were studied in the fasting state without sedation. Those presenting in AF while on the catheterization table were converted to sinus rhythm by internal or external cardioversion. During the procedure intravenous heparin was given as a 100-IU/kg bolus dose after the venous sheaths were inserted. The 12-lead ECG and intracardiac electrograms were recorded and stored by the BARD Labsystem PRO. Post ablation management All patients were monitored in hospital for 24 h and oral anticoagulation was started the day of ablation. Antiarrhythmic drugs (AAD) were stopped after the procedure in patients without a history of AF; in those with AF/AFL the same AAD were continued. All patients had anticoagulation for at least 1 month. Subsequently, the need for chronic anticoagulation was assessed by the amount of recurrences of AFL/AF and the presence of risk factors for thromboembolic events. All patients had a 12-lead ECG and a 24 h Holter recording at discharge and during each clinic visit (1 month, 3, 6, 9, 12 months and yearly thereafter) or earlier if they had symptoms. Due to the logistics of the Maastricht area—and also the presence of a dedicated research nurse (S. P.) who was available to address patients’ concerns and questions at any time—we were able to follow every patient on an individual basis. Statistical analysis Continuous variables are presented as mean ± SD, where appropriate. In cases of a non-Gaussian distribution, medians and quartiles are given. Categorical variables are expressed as numbers and percentages of patients. t P The authors had full access to the data and take responsibility for its integrity. Results Of the 180 enrolled patients, 39 patients (22%) were women with a mean age of 58 (from 18 to 80) years. More than half of the patients (92 patients, 52%) had structural heart disease: arterial hypertension: 57 patients, coronary artery disease: 22 patients, valvular heart disease: 13 patients, congenital heart disease: 11 patients, idiopathic cardiomyopathy: 18 patients. Counterclockwise AFL was documented in 91% (164) of the patients and clockwise AFL in 9% (16 patients). 1 Table 1 Characteristics of the 180 patients with atrial flutter referred for CTI cryoablation related to the presence or absence of atrial fibrillation AF before ablation   AF/AFL patients (123 patients), 69% AFL only (57 patients), 31% p Age (year) 57 ± 13 58 ± 13 ns Women 19% (23 patients) 28% (16 patients) ns No SHD 55% (68 patients) 32% (18 patients) < 0.05 LAd (cm) 4.4 4.5 ns LVEF (%) 58 55 ns a 5% (6 patients) 5% (3 patients) ns AF in long term follow up 69% (85 patients) 35% (20 patients) < 0.05 a AF AFL CTI Lad LVEF SHD . The acute success rate for cryoablation of the CTI was 95% (171 patients). There were no complications. Of the nine patients in whom bidirectional CTI block was not achieved, three underwent a successful reablation. The other six patients had much improvement of their symptoms (despite an incomplete line) and preferred not to have another procedure. 1 Fig. 1 Percentage of patients (171 successfully ablated) free of common type atrial flutter over time  Despite the success as far as AFL was concerned, AF was still present in 85 patients (69%) with a prior history of this arrhythmia. Those patients were treated by AAD (69 patients, 81%), PVI (14 patients, 16%) or AV nodal ablation with pacemaker implantation (two patients, 3%). New episodes of AF developed in 20 (35%) of those 57 patients without documented AF prior to CTI cryoablation and were all controlled by AAD. Discussion Main findings Our current study showed a 91% chronic success rate of CTI cryoablation in a large population (180 patients) with AFL followed for a long period of time (1 to 5 years, mean of 27 months). 2 14 23 24 25 26 1 4 7 11 12 27 28 The relation of AF with AFL 1 5 14 21 29 39 40 11 14 21 31 32 37 39 Study limitations 1 4 6 8 12 Conclusions In this prospectively studied large population of patients with common type AFL, cryoablation of the CTI has a 91% chronic success rate during long term follow-up (range 1 to 5 years, mean of 27 months). These results are similar to those obtained with RF, validating cryothermy as an efficient alternative energy source. We also were able to ratify the frequent association of AF with AFL.