1 Introduction
When choosing the most optimal interventional treatment for patients with atrial fibrillation (AF), not only the success rate in eliminating AF, but also the potential risks for complications, such as adverse effects on adjacent structures, should be considered. It is already confirmed that the Cox maze III procedure results in a sustained decrease in atrial contractility [
1,
2] but the effect of transvenous catheter-based pulmonary vein (PV) isolation on left atrial (LA) function is unclear and study results are conflicting [
3‐
8]. Preserved atrial function may have several important implications, an essential contribution to the ventricular myocardial performance and a lower rate of AF recurrences and thromboembolic events.
Epicardial PV isolation off-pump combined with ganglionated plexi (GP) ablation has been used for the treatment of AF [
9‐
14]. Although several studies have reported high success rates ranging between 74 and 90% in eliminating AF [
10‐
14], the information about the performance of the left atrium after this type of surgery is still limited. The purpose of the present study was therefore to assess the effects on size and mechanical function of the left atrium of combined epicardial PV isolation and GP ablation, and its relation to the extensiveness of the ablation applications.
4 Discussion
In the past decade, several new surgical AF ablation procedures have been developed, all of which may result in a reduced atrial mechanical function related to extensive scarring of the left atrium, but the effect on LA function has not been systematically studied. Apart from the fact that atrial contractility is an essential contribution to ventricular myocardial performance, that may have important implications for the well-being of the patient, a reduced contractility may also promote thromboembolic events even if AF is successfully eliminated. It is therefore important to assess the LA function when introducing new non-pharmacological procedures for patients with AF.
To the best of our knowledge, the present study is the first to investigate the LA function after epicardial PV isolation combined with GP ablation as a stand-alone procedure.
After the more complex and extensive Cox maze III procedure, a sustained reduction of the atrial mechanical function, by echocardiographic measures of atrial area fractional change and E/A ratios, was reported for patients with paroxysmal lone AF [
2,
1]. The clinical impact of studies showing severely compromised LA function may warrant a more restrictive attitude to refer patients with paroxysmal AF for such surgical procedures. Catheter-based RF ablation of AF has also resulted in a reduction in LA function [
3‐
5] although the reports are conflicting, as several studies have demonstrated no change or even an improvement in LA function [
6‐
8].
Among the three studies that have reported a reduction in LA function following catheter-based PV isolation, two were combined with linear lesions. One of these studies including linear lesions observed a reduction in LA ejection fraction (EF) as measured by ECG-gated computed tomography (CT) [
3] while the other reported a reduction in LA EF as measured by magnetic resonance (MR) imaging already 48 days after the procedure which was limited to PV isolation and right atrial linear lesion [
4]. The sensitivity of detecting a reduction in LA contractility may be higher with CT than with echocardiography and the additional lesion sets along the mitral isthmus and LA roof may have more extensive impact on LA function. Results are also difficult to interpret in small series of patients (
n = 10) included [
3] as compared with our study with 27 patients. Studies of atrial function made early after surgery may, however, reflect incomplete atrial remodeling, although the reduced atrial systolic function seemed strongly correlated with the volume of LA scar [
4]. The third study reporting an impairment of LA function was an echocardiographic evaluation of left atrial emptying fraction mean 8 ± 2 months after a catheter-based PV isolation procedure in patients with paroxysmal AF [
5].
Two other studies evaluating the same type of procedure in patients with paroxysmal AF [
6] or paroxysmal and non-paroxysmal AF [
8] reported no change in LA function as indicated by preserved LA active emptying fraction as measured by echocardiography [
6] and by stable LA EF according to cardiac MR 12 months after PV isolation [
8]. Others have reported an improved LA EF and a decrease in LA area (end systolic and end diastolic) in patients with symptomatic paroxysmal or persistent AF at 6 months after an AF ablation as assessed by cine electron beam computed tomography (EBCT) [
7]. A significant decrease in LA size was also seen in patients with the largest LA at baseline in the present study and may either be related to the effect of remodeling after maintenance of sinus rhythm or as a result of the scar tissue shrinkage, the latter of which is contradicted by lack of effect on atrial contractility. Although, normal values for LA area [
16] were recently presented, comparisons are not recommended as the literature is scarce [
17]. We therefore preferred to refer to the standard LA diameter.
These diverse results observed in the literature may be related to the patient’s age, type of AF, the duration of follow-up, the type and the extent of ablation lesions, and also the methods used for evaluation. The previous studies have used diverse techniques for the evaluation of LA size and function, including echocardiography, EBCT, CT, or MR; comparisons of studies are difficult. Most of these imaging techniques are associated with limitations, for example, an asymmetric dilatation of the left atrium may under- or overestimate the LA area or volume. Echocardiographic calculations of LA volume rely on geometrical assumptions, which per se is an inherent limitation. CT may be more sensitive to detect small reductions in LA function but is associated with a burden of X-ray, and therefore not widely applied. A meta-analysis recently concluded that successful RF catheter ablation in patients with AF significantly decreases LA size and volumes but does not seem to adversely affect LA function [
18]. Theoretically, the epicardial AF ablation approach might result in a more extensive scar since the RF clamp is applied well outside the PV pairs in the LA antrum. There are some studies examining the LA function after epicardial PV isolation and limited LA surgical ablation concomitant to cardiac surgery, a procedure that is difficult to compare with the results in our study since the cardiac surgery itself most likely affect the LA function [
19‐
21].
Compier et al. [
19] concluded that even limited LA ablation decreased LA volume, contraction, transport function, and compliance, indicating both reverse remodeling combined with significant functional deterioration. In contrast, surgical PV isolation alone decreased LA volume while function remained unchanged. They made limited LA ablation as a concomitant procedure for patients scheduled for valve surgery and/or coronary revascularization and had a control group consisting of patients undergoing concomitant epicardial PV isolation only. Signs of atrial dysfunction were also reported after combined mitral valve surgery and left atrial cryoablation for AF as opposed to with mitral valve surgery alone [
21], although in that procedure extra linear lesions were also included.
Others, Buber J et al. [
20], concluded that absence of LA contraction resulted in a fivefold increase and a LA volume index ≥ 33 ml/m
2 in a threefold increase in the risk for thromboembolic stroke after the concomitant RF and cryoablation maze procedure, even when accounting for CHADS-VASc, in patients in sinus rhythm at 2 years follow-up.
According to our study, the mEPVI-GPabl does not seem to affect LA mechanical function or LA size, as assessed 6 months after the procedure. Neither were there signs of LA function deterioration with the extent of surgical ablation applications. The relatively small number of patients and the missing data may have affected the result.
As described previously [
9], 76% had no symptomatic AF recurrences or AF episodes on 24-h Holter recordings at 12 months follow-up. The success rate is important since AF may cause significant structural remodeling and decreased contractility of the left atrium [
22] promoting thromboembolism [
23]. In our study, there were no thromboembolic events during 12 months follow-up except for in the one patient in whom an adequate anticoagulation medication had not been followed which emphasizes the importance of adequate anticoagulation throughout the procedure.