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Interact CardioVasc Thorac Surg 2008;7:990-995. doi:10.1510/icvts.2007.172668 © 2008 European Association of Cardio-Thoracic Surgery
Surgical treatment of atrial fibrillation using cryothermy in patients undergoing mitral valve surgeryDepartment of Cardiothoracic Surgery, Mount Sinai School of Medicine, Mount Sinai Hospital, 1190 Fifth Avenue, Box 1028, New York, NY 10029-1028, USA Received 6 December 2007; received in revised form 26 June 2008; accepted 30 June 2008
Corresponding author. Tel.: +1 212 659 6820; fax: +1 212 659 6818.
Surgical treatment of atrial fibrillation (AF) using a variety of energy sources and a mixture of lesion sets has become an important adjunct in patients undergoing cardiac surgery. We retrospectively analyzed prospectively collected data of 141 patients with a history of AF (mean duration of AF 35±39 months; intermittent AF: n=72; 51%; permanent AF: 69 (49%)) who underwent a left-sided Cryomaze procedure in conjunction with mitral valve (MV) surgery between January 2003 and September 2006. Freedom from AF was 77% at discharge and 87% at a mean follow-up of 305±195 days with a decreasing rate of AF during the first 3–9 months from 13% to 9% and an increase beyond the first year (29% at 2 years). Predictors of failed Cryomaze in multivariate analysis were left atrial size >50 mm (OR=5.7), AF at surgery (OR=5.0) and cardiac reoperation (OR=3.4), whereas preoperative beta-blocker treatment was a predictor of success (OR=0.2). Our data suggest that a left-sided Cryomaze procedure effectively restores sinus rhythm in patients with AF undergoing MV surgery. The success rate should not be evaluated immediately postoperatively because there is a steady increase in the rate of patients with freedom from AF in the first year. It appears, however, that there is a higher rate of recurrence during later follow-up.
Key Words: Atrial fibrillation; Maze procedure; Mitral valve surgery; Outcome
Atrial fibrillation (AF) is observed in 40–60% of patients referred for mitral valve (MV) surgery. Previous studies have shown that correction of MV disease alone does not effectively restore sinus rhythm, and that AF remains present in >90% of these patients [1]. During the last decade, several modifications of the classic cut-and-sew Cox maze III procedure have been developed to restore sinus rhythm in these patients. A variety of energy sources such as cryothermy or radiofrequency and lesion sets have been used to create lines of conduction block replacing the suture lines of the classic approach. Although several series have reported good early results, these studies have been limited by small sample size and short duration of follow-up [2, 3]. We report our experience with a left-sided maze procedure using argon-based cryothermy (Cryomaze) in a large series of patients with AF undergoing MV surgery.
2.1. Patient population and data collection A computer based prospective operative registry of patients who underwent MV surgery between January 2003 and September 2006 was used to identify those who underwent a concomitant left-sided Cryomaze procedure. Patient demographics, operative information, and postoperative outcome data were retrospectively analyzed (Appendix 1). Further information was obtained by a thorough medical chart review and questionnaires mailed to patients referring physicians. The protocol was approved by the Institutional Review Board. Preoperative AF was defined as intermittent (paroxysmal/persistent) or continuous (permanent) [4]. Additional rhythm related data collected included duration of AF, presence of AF at the time of surgery, and antiarrhythmic and anticoagulation medication. Left atrial (LA) size and left ventricular (LV) ejection fraction (EF) were assessed by transthoracic or transesophageal echocardiography. Our surgical approach to the MV has been previously described [5]. Cryomaze ablation was performed first using the flexible argon-based SurgiFrost® cryothermy ablation probe (CryoCath Technology, Pointe-Claire, Canada). Cryothermia was applied at a temperature of –150 °C for one minute for each lesion (Fig. 1). A left-sided lesion set was created with continuous endocardial lesions surrounding each group of right and left pulmonary veins (PV) with connecting lesions a) between the PV ostial lines and b) to the posterior segment of the MV. A right atrial lesion set which consisted of an isthmus lesion connecting the inferior vena cava with the tricuspid annulus was performed based on surgeon's preference. Left atrial appendage ligation was performed predominantly in patients with previous stroke and/or LA thrombus formation.
2.3. Postoperative management All patients received oral anticoagulation therapy with warfarin for two months regardless of postoperative rhythm. Patients with mechanical valves received life-long anticoagulation. Beta-blockers were used in all patients unless postoperative bradycardia or junctional rhythm was observed. These patients did not receive any anti-arrhythmic medication. Amiodarone was employed selectively in patients with postoperative AF at the cardiologist's discretion. 2.4. Outcome and cardiac rhythm assessment The main outcome parameter was freedom from AF at discharge and during follow-up. Further outcome measures included hospital mortality, major postoperative complications, and late survival (Appendix 1).Cardiac rhythm was recorded using 12-lead ECG at postoperative day one and three and after a follow-up of at least three months. Patients were classified as free from AF when they were in sinus rhythm, atrially paced without underlying AF, junctional rhythm or other regular rhythm. Patients who developed AF or atrial flutter, and those who were paced but had underlying AF were classified as AF patients. Failure of the Cryomaze procedure was defined as AF more than three months following the procedure. Patients who underwent a subsequent catheter-based ablation procedure were also classified as Cryomaze-failures. Normally distributed continuous variables are presented as mean±S.D. and otherwise as median and interquartile range (IQR). Categorical variables are shown as the percentage of the sample. A P<0.05 was considered significant for all used statistical methods. The 2-test, Fisher's exact test and the Linear-by-linear test were used to identify factors that were associated with a failed maze procedure one at a time. Stepwise multivariate logistic regression analysis was then performed to identify independent risk factors for cryomaze failures. Cardiac rhythm at follow-up was reported according to the STS guidelines plotting the rate of freedom from AF at the time of follow-up. Kaplan–Meier curves were used to determine patient's survival following discharge. Analysis was performed using SPSS 15.0 (SPSS Inc., Chicago, Illinois).
3.1. Patient demographics A total of 141 patients were included in the analysis. Detailed patient demographics and characteristics are summarized in Table 1.
The mean duration of AF was 35±39 months. Seventy-two (51%) patients had intermittent AF whereas 69 (49%) were in permanent AF. At the time of surgery AF was present in 90 (64%) patients. Etiologies of MV disease and echocardiography findings are shown in Table 2.
3.2. Operative procedure All patients underwent a left-sided Cryomaze procedure with a mean duration of 15±2 min. In 34 (24%) patients the LA appendage was ligated or excised. In 18 (13%) patients, additional RA lesion was performed. Most of these patients (n=12; 67%) underwent a concomitant tricuspid annuloplasty. Mitral valve reconstruction using Carpentier's techniques [6] was performed in 119 (84%) patients, whereas the MV was replaced in 22 (16%) patients (4 mechanical valves, 18 tissue valves) (Table 3).
3.3. Mortality and morbidity Hospital mortality was 2.8% (n=4). Postoperative complications included stroke (n=6; 4.3%), reoperation for bleeding (n=4; 2.8%), sepsis (n=5; 3.5%), gastrointestinal complications (n=2; 1.4%), dialysis (n=4; 2.8%), and respiratory failure (n=19; 13.5%). Following the procedure 72 (51%) patients were in sinus rhythm, 27 (19%) were in AF, and 4 (3%) had atrial flutter. Thirty-eight (27%) patients required temporary epicardial atrioventricular pacing for junctional rhythm (n=18) or intermittent atrio-ventricular blockage (n=20). Seventeen patients (12%) required a permanent pacemaker implantation for third degree atrioventricular block (n=12; 71%) or sick sinus syndrome (n=5; 29%). The remaining 21 patients recovered from their rhythm disorder. At the time of discharge, 28 out of 137 (21%) surviving patients were in AF and 3 (2%) were in atrial flutter. The remaining 106 (77%) patients had sinus rhythm (n=84; 61%), junctional rhythm (n=6; 4%) or were atrially paced without underlying AF (n=16; 12%). Patients with AF at the time of surgery had a significantly increased rate of AF at discharge compared to those with intermittent AF and sinus rhythm at the time of surgery (n=25/87, 28.7% vs. n=6/50, 12%, P=0.018). Similarly, AF was present at discharge in 29% (n=20/68) of patients with permanent AF compared to 16% (n=11/69) of patients with intermittent AF (P=0.046). Mean duration of follow-up among discharged patients was 304±195 days (range 3–27 months). Six (4%) patients died during follow-up and no information was available regarding their rhythm (Fig. 2). For the remaining 131 patients follow-up information was 100% complete. At follow-up 114 patients were free from AF (sinus rhythm: n=102; 78%; atrially paced: n=12; 9%) and 15 (11%) were in AF (Fig. 3). Two patients (2%) underwent subsequent percutaneous radiofrequency catheter ablation for refractory atrial flutter and were converted to sinus rhythm.
3.5. Predictors of a failed Cryomaze procedure Patients with AF were more likely to undergo reoperations, have a long-standing history of AF (>3 years), be in AF at the time of surgery, and have a LA diameter >50 mm in univariate analysis (Table 4). Type of AF, etiology of MV disease, an additional right-sided maze procedure, and postoperative administration of antiarrhythmic drugs (amiodarone) were not different between the two groups. Preoperative treatment with beta blockers was more likely in patients who had a successful Cryomaze procedure. Multivariate regression analysis revealed LA size (OR=5.7, CI=1.4–24.0, P=0.017), AF at surgery (OR=5.0, CI=1.0–24.7, P=0.047), and reoperation (OR=3.4, CI=1.1–11.1, P=0.042) as independent predictors of a failed Cryomaze procedure (Table 5). Preoperative beta-blocker treatment remained an independent predictor of a successful maze procedure (OR=0.2, CI=0.0–0.7, P=0.014).
The classic Cox-maze-procedure involves the creation of several scar lines in both atria and is associated with a success rate >90% at long-term [7]. We opted for a left-sided lesion set, based on the findings of Haissaguere et al. who have shown that the majority of ectopic foci triggering AF are located at the PV origins and have postulated that ablation of this foci will effectively treat AF in a greater number of patients, particularly those with intermittent AF [8]. In this study we achieved restoration of SR in 87% of patients at a mean follow-up of 304 days. Few series have analyzed the outcomes of a left-sided endocardial ablation of AF using cryothermy [9, 10]. Nakajima et al. and Manasse et al. reported freedom from AF rates of 84% and 82% at a mean follow-up of 18 and 35 months, respectively [9, 10]. These data are comparable with outcomes of modified maze procedures using other energy sources such as radiofrequency. Another interesting finding was that the maximum success rate was not obtained immediately postoperatively. During follow-up we noticed a steady increase in the success rate which achieved its maximum at 9 months (91%). The relatively higher rate of AF during the first three postoperative months is potentially explained by postoperative inflammatory mechanisms and is probably not reflecting long-term results [11]. Accordingly, the recent reporting guidelines for AF surgery recommend a ‘lock-out’ period related to AF during the first three months in the outcome analysis of ablation procedures [12]. Our data suggest that this period might be too short and probably needs to be extended beyond the first 6–9 months following surgery. In our study, we predominantly performed left-sided lesion sets. It has, however, been suggested that a compartmentalization of both atria as achieved with the classic Cox-maze procedure, may contribute in better results [13]. In the only study using Cryothermy to create biatrial lesion sets in 38 patients, Gammie et al. reported a success rate of 95% at 18 months [3]. Although the number of patients was small, it might be that the addition of a right-sided lesion has led to their better results. Despite the fact that the purpose of our study was not to determine if LA ablation alone or biatrial lesions are more efficient, our success rate of 87% in a large number of patients undergoing solely a left-sided Cryomaze procedure suggest that a left-sided lesion set alone may be a sufficient treatment modality in a majority of patients with AF undergoing MV surgery. Finally, we observed a steady decrease in the freedom from AF from 12 to 24 months from 89% to 71%. Although our study included a small number of patients at two-year follow-up, a major question which remains unanswered is the stability of the lesion sets created over time. Larger studies with longer follow-up are necessary to further confirm the initial increase in success rate over time that we have observed in our experience with an overall success rate of 87%. 4.1. Predictors of a successful maze procedure Patient characteristics such as duration and type of preoperative AF and LA size have been shown to be predictors of outcome following maze procedures [14]. In our study, patients with a LA size >50 mm were 5.7-times more likely to develop AF compared to those with smaller LA diameters. Gillinov et al. have confirmed our findings by showing that larger LA diameter was associated with a 2.6-fold increased risk of late occurrence of AF [14]. However, this finding was not confirmed by Mack et al. who did not find an association between LA size and recurrence of AF in Cryomaze patients [15]. Duration of AF has also been reported as a predictor of a failed maze procedure. Gaynor et al. reported that patients with a 20-year history of AF had a 20% higher failure rate compared to those with a AF history of 5 years [13]. In our analysis, duration of AF was correlated with an increased Cryomaze failure rate in univariate but not in multivariate analysis. One possible explanation for the association of left atrial size and/or duration of preoperative AF with recurrent AF following surgery is that long-lasting MV disease may lead to significant changes in tissue architecture reflected by an increased LA size [11]. In this case, the atrial size rather than the duration of AF reflects the degree of tissue remodeling, a process which might not be fully reversible even after correction of the MV pathology. It is possible that earlier referral of these patients may prevent irreversible remodeling of the atrium and increase the success rate of the maze procedure. However, this study has certain limitations which must be considered. This was a retrospective study and therefore, any conclusions are necessarily limited in their application. The majority of variables included were in accordance with the recent guidelines for reporting data and outcomes for the surgical treatment of AF [12]. However, data were collected before these guidelines were published and we are not able to provide all recommended variables. Furthermore, because a modified maze procedure is performed in all patients with AF who are referred for MV surgery, this study does not have a control group. Finally, follow-up rhythm assessment gives only a ‘snap-shot’ and we might not have identified all patients with asymptomatic intermittent AF.
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Abstract
1. Introduction
