Patients and methods: Between August 2012 and August 2017, a total of 55 patients (27 males, 28 females; mean age 51.6±11.2 years; range, 44 to 71 years) with atrial fibrillation who underwent isolated left atrial ablation during mitral valve surgery in our clinic were included. Radiofrequency was applied to 41 patients and cryoablation to 14 patients. In both procedure, ablation was performed to isolate all pulmonary veins. Radiofrequency ablation utilized a RF current that was applied in a point-by-point mode, heating the tissue and leading to cellular necrosis. Cryogenic ablation induced necrosis by pumping refrigerant (nitrous oxide) through a balloon in a single-step mode, thereby freezing the tissue. The success of both techniques was evaluated through control echocardiography and electrocardiography.

Results: There was no statistically significant difference in the success rates of both techniques in terms of returning to the sinus rhythm. Two patients in the radiofrequency ablation group developed third-degree atrioventricular block with the need of permanent pacemaker implantation. In contrast no patient in the cryoablation group developed the same block. In patients who underwent radiofrequency ablation, the need for inotropic support in the postoperative period was higher with prolonged length of stay in the intensive care unit.

Conclusion: Our study results show that the success rate of both techniques is similar in patients with atrial fibrillation undergoing mitral valve surgery.

The incidence of AF ranges between 30 and 90% in patients with mitral valve disease.[3,4] The risk of stroke in patients with AF is almost five to seven-times higher.[4] This rate increases up to 17% annually in cases with mitral valve diseases. Atrial fibrillation is also responsible for 15% of all strokes.[5]

Mitral valve diseases have been implicated as one of the main causes of AF due to the high incidence of AF in these patients. However, the rate of return to sinus rhythm was found to be 23%, if no additional treatment is given in addition to the surgical treatment. Some authors have shown that treatment of valvular disease alone remains insufficient.[6] On the other hand, the rate of return to the sinus rhythm has been reported as 68 to 70% with ablation therapy in mitral valve disease. Based on these results, the treatment of AF has been also improved.[6]

In the present study, we aimed to evaluate early results and possible complications of cryoablation and radiofrequency ablation in patients with AF undergoing mitral valve surgery.

Radiofrequency ablation was performed in 41 of 55 patients and cryoablation was performed in 11 patients. All patients had permanent AF for more than three months. All patients were using beta-blocker, calcium channel blocker, and digitalis for heart rate control in addition to vitamin K antagonist for preoperative persistent AF.

Echocardiography (ECHO) and electrocardiography (ECG) measurements were recorded before and immediately after the operation and on the day of discharge and at one month postoperatively. All patients underwent isolated left atrial ablation with a radiofrequency catheter or cryoablation catheter. The left atrial appendix ostium was treated with box lesions which were created in such a way that the right and left pulmonary vein pair was separated and the boxes applied to the orifice of the pulmonary veins were combined with lesions to form a line lesion. The right line lesion was created to the P2-P3 leaflet of the mitral valve. The ablation period was approximately five to seven minutes with both methods. Ablation was performed in all patients prior to other surgical procedures. Left atrial appendage was closed in all patients. Epicardial temporary pacing was placed into the right ventricle and right atrium in all patients. Both ablation procedures were performed in the same region.

After the removal of the cross-clamp, all patients were treated with amiodarone 900 mg/day. Amiodarone 200 mg tablets t.i.d. once daily for the maintenance therapy were continued for seven days, and then b.i.d once daily for one week, and one tablet for two weeks. Additionally, metoprolol was started at a dose of 25 to 100 mg in all patients.

Statistical analysis
Statistical analysis was performed with PASW version 17.0 program (SPSS Inc., Chicago, IL, USA). The normal distribution of the variables was examined by histogram graphs and the Kolmogorov- Smirnov test. Mean, standard deviation, median and minimum-maximum values were used to present descriptive analyzes. Pearson chi-square and Fisher?s exact tests were compared with 2¥2 Tables. While normally distributed (parametric) variables were evaluated among the groups, Student t-test was used. Mann-Whitney U test was used to evaluate nonparametric variables. P-values <0.05 were evaluated as statistically significant results.

Table 1: Baseline demographic and clinical characteristics of patients

In the early postoperative period, 27 (65.9%) of radiofrequency patients returned to sinus rhythm, whereas 12 (85.7%) of cryoablation patients returned to sinus rhythm, indicating no statistically significant difference. On the day of discharge, 31 (77.5%) of radiofrequency patients and nine (81.8%) of cryoablation patients were in sinus rhythm, indicating no statistically significant difference. Thirty three (82.5%) versus nine patients (81.8%) were still in sinus rhythm at one month (Table 2).

Table 2: Returning to sinus rhythm at different time points following radiofrequency ablation versus cryoablation

A total of 38 patients (92.7%) who underwent radiofrequency ablation needed inotropic support, while nine (64.3%) of the patients who underwent cryoablation needed inotropic support. The need for inotropic support was higher in patients who underwent radiofrequency (Table 3).

Table 3: Postoperative inotropic support requirement following radiofrequency ablation versus cryoablation

Sixteen (39.0%) of the patients who underwent radiofrequency ablation and four (28.6%) of the patients who underwent cryoablation required postoperative permanent pacemaker implantation. There was no statistically significant difference in the need for permanent pacemaker between the two ablation techniques (Table 4).

Table 4: Pacemaker requirement following radiofrequency ablation versus cryoablation

In addition, the length of hospital and intensive care unit stay was higher in the patients who were treated with radiofrequency ablation compared to those treated with cryoablation (Table 5).

Table 5: Length of intensive care unit and hospital stay following radiofrequency ablation versus cryoablation

In our study, no significant difference was found between the two techniques. In similar studies in the literature, the rate of establishing the sinus rhythm was about 63 to 92% with radiofrequency ablation and 59 to 82% with cryoablation,[6,13] consistent with our study results. However, delayed return to sinus rhythm was observed in long-term follow-up patients who were ablated for AF.[14,15]

Although there are many studies using energy sources and procedures, no consensus has been established, yet. Previous studies using similar methods demonstrated similar rates of sinus node dysfunction, nodal rhythm, and complete atrioventricular block (AV) block rates in the early postoperative period. In our study, no atrial flutter was seen, compared to the other studies, which was found to be 4 to 6% of occurrence.[16-18] Meta-analyses showed that the rate of permanent pacemaker requirement in patients undergoing radiofrequency ablation procedure ranged from 0 to 10% and the rate of patients who required permanent pacemakers in patients undergoing cryoablation procedure was 0 to 21%.[7,13] In our study, two patients who underwent radiofrequency ablation required permanent pacemaker implantation due to complete AV block; however, none of the cryoablation patients required permanent pacemaker.

In the literature, isolated left atrial ablation-related complications such as esophageal injury, trachea injury, circumflex artery injury, and pulmonary vein stenosis have been reported.[19-22] It was also shown that patients undergoing maze procedure had longer hospitalizations, but there were no differences between the ablation methods.[23] In our study, these complications were not encountered, although the need for inotropic support was found to be higher with longer intensive care unit and hospital stay in the patients who underwent radiofrequency ablation than cryoablation. In another study, the risk of thromboembolism was found to be higher in the radiofrequency ablation group than cryoablation,[24] although thromboembolism complications were not seen in both methods in our study.

In conclusion, our study results suggest that radiofrequency ablation and cryoablation can be used in patients with atrial fibrillation scheduled for open heart surgery. The success rate of both techniques is also similar in our study. However, further, large-scale and long-term studies are needed to fully elucidate the effects of both energy sources.

Declaration of conflicting interests
The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

Funding
The authors received no financial support for the research and/or authorship of this article.

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