Atrial fibrillation has been found to be present in almost one third of patients with heart disease requiring cardiac surgery in the three years prior to surgery (1). Surgical treatment of atrial fibrillation during concomitant cardiac surgery is today a class I recommendation for symptomatic patients with atrial fibrillation of both short and long standing (6). Cardiologists and cardiac surgeons should therefore decide whether concomitant ablation is to be performed during cardiac surgery.
Our study supports radiofrequency ablation for atrial fibrillation according to the CMIV protocol as a safe procedure with few complications. In the short term, and with follow-up according to a standard monitoring regime, the procedure can be expected to restore sinus rhythm in more than 2/3 of patients. These findings are consistent with the results of the CURE-AF trial published by Damiano et al. (5). They found that the number of patients with sinus rhythm (without supraventricular tachycardia) on Holter monitoring after 6–9 months (our figures in parentheses) was 66 % (74 %) for the whole group, 63 % (67 %) for the group with long-standing persistent atrial fibrillation and 82 % (86 %) for the group with persistent atrial fibrillation. The patient population that was studied and followed up in this trial is small, and we had no control group to verify the benefit of the procedure. However, the patients were closely followed up for a long time after the procedure. Although the execution of the study and the follow-up survey took place a while back, neither indications, interventional method nor follow-up of patients who have undergone surgical ablation have changed substantially. The results are therefore still regarded as relevant.
Increased left atrial diameter, short ablation time and number of additional procedures have all been found to increase the risk of recurrence of atrial fibrillation (5). We were unable to confirm these relationships, probably because of the selection criteria for the study and the small population size. A complete ablation pattern with transmural lesions is a prerequisite for a good result in all ablation for atrial fibrillation (7). Pulmonary vein ablation was conducted with bipolar equipment, and transmurality was confirmed by blocked impulse conduction between pulmonary veins and left atrium (exit block). We found that repeated ablation procedures were necessary in some patients to achieve exit block. Even where this was documented, one patient was found to experience recurrence after six months in the form of atrial flutter from an ablated pulmonary vein. Short ablation time (< 360 seconds) has proved to be a risk factor for recurrence (5). The median ablation time in our study (379 seconds) was higher than this, but varied substantially across patients. Incomplete ablation can probably explain some of the recurrences in this study.
Long duration of preoperative atrial fibrillation is a risk factor for recurrence of atrial fibrillation (8), which is confirmed in our study by significantly different recurrence rates between the groups with long-standing persistent atrial fibrillation and persistent atrial fibrillation. Long-term results after a CMIV procedure for atrial fibrillation show considerable variation. The CURE-AF trial in the United States was stopped after nine months, and to the best of our knowledge follow-up data have not been published. We investigated heart rhythm five years after the procedure and found a high rate of atrial fibrillation recurrence, particularly in the group with long-standing persistent atrial fibrillation. The recurrences often generated limited symptoms, and were not always picked up early enough by the primary health service (data not shown).
At the end of the study, after 5–6 years, 44 % of our patients had sinus rhythm. This is considerably lower than reported in two recent studies from the United States, where 66 % and 64 % had sinus rhythm five years after a similar procedure (8, 9). In both these studies, the patients were closely followed up and appropriately treated for recurrence of atrial fibrillation in the years following the procedure. Since early results in our study were in line with those of other centres, we suspect that one important cause of the high recurrence rate is deficiencies in follow-up and electroconversion, particularly in the group with long-standing persistent atrial fibrillation. This is supported by findings in a Danish study, where follow-up was also left to the primary health service, and where only 33 % and 25 % of the patients were without supraventricular tachycardia after five and seven years, respectively (10).
The recurrence rate has proved to be substantial after 18–36 months (9), which again underscores the importance of long-term follow-up and prompt intervention at a specialist centre in the event of recurrence of atrial fibrillation (9, 10). This emerged clearly during the follow-up survey in our study, as over a third of the patients (7/18) proved to need further arrhythmia diagnostics. In addition, some patients with long-standing persistent atrial fibrillation had already developed permanent atrial fibrillation during the first few years after the operation.
In order to improve the long-term results after ablation for atrial fibrillation concomitant with heart surgery, it seems reasonable to recommend a regular follow-up programme, for example with an annual ECG and sometimes 24-hour ECG monitoring, allowing recurrences to be revealed earlier and adequate treatment initiated.