Abstract
OBJECTIVES
Concomitant ablation is an established therapy in cardiac surgical patients with atrial fibrillation (AF). Post-discharge care seems to be an essential factor for clinical outcome. We analysed the influence of event recorder (ER) implantation and therapy guidance by the results of continuous rhythm monitoring of consecutive postoperative follow-up by our department of electrophysiology.
METHODS
Between July 2003 and August 2010, 401 cardiac surgical patients underwent concomitant surgical AF ablation therapy. Since August 2009, an ER (REVEAL XT, Medtronic, Inc., Minneapolis, MN, USA) was implanted in 98 patients intraoperatively. ER interrogation was performed by our department of electrophysiology 3, 6 and 12 months postoperatively. Results and outcomes were compared with a matched cohort of patients with ablation and no ER implantation. In those patients, rhythm follow-up was obtained by 24-h Holter ECG. Primary end-point of the study was sinus rhythm rate after 12 months.
RESULTS
Mean patient's age was 67.0 ± 9.7 years, and 68.4% were male. No major ablation-related complications occurred. The overall sinus rhythm rate was 65.3% after 1-year follow-up. The sinus rhythm rate off antiarrhythmic drugs was 60.3%. The conversion rate tended to be higher in patients with an implanted ER (69.3 vs 60.1%, respectively; P = 0.098). Also, the sinus rhythm rate of anti-arrhythmic drugs was higher in the ER group (64.3 vs 56.2). Patients with ER were seen more often by a cardiologist in the first postoperative year (3.1 ± 0.8 vs 1.5 ± 0.9; P < 0.05) and received significantly more additional procedures, like electrical cardioversion or additional catheter-based ablation (16.1 vs 4.3%; P < 0.001; 11.2 vs 3.1%; P < 0.001).
CONCLUSIONS
Implantation of an ER with link-up to a cardiology and/or electrophysiology provides optimized anti-arrhythmic drug management and higher rates of consecutive procedures like cardioversion or additional catheter-based ablation. As a result, a trend to higher sinus rhythm conversion rate was observed after 1-year follow-up.
Keywords: Event recorder, Atrial fibrillation, Surgical ablation
OBJECTIVES
Atrial fibrillation (AF) is the most common arrhythmia in patients undergoing cardiac surgery. Multiple studies have shown that AF leads to heart failure, thromboembolic events including stroke and reduction in the quality of life [1, 2]. Therefore, concomitant AF ablation is recommended in guidelines [3] for symptomatic patients, as well as asymptomatic patients with low risk of surgical ablation procedure [2, 3]. Cox first reported his technique of surgical AF ablation by the cut-and-sew principle in 1987, later revised to the Cox maze III procedure. Owing to success rates of >90%, it became the Gold standard for surgical ablation. However, due to the complexity of the procedure, the cut-and-sew principle has been replaced in recent years by the creation of transmural thermal lesions by the application of different energy sources like radiofrequency or cryotherapy, resulting in the so-called Cox maze IV procedure. There are few prospective randomized trials providing results between 44 and 80%, concerning freedom from AF in patients undergoing concomitant surgical AF ablation [4–7]. Apart from other reasons, such as inhomogeneous lesion sets and used energy sources, key issues for this diversity are incomplete, variable strategies and definitions to monitor the success rate of ablation. Several studies have shown that short-time rhythm monitoring with repeated 24-h Holter ECG underestimates the rate of AF recurrence after ablation therapy. [8] This is especially relevant in patients with paroxysmal AF due to the low sensitivity of discontinuous rhythm monitoring in those patients. Implantation of a leadless heart rhythm-monitoring device has been shown to be superior in the detection of AF episodes, compared with repeated 24-h Holter ECG. The XPECT trial [9] ascertained high sensitivity (96.1%) and negative predictive value (NPV) (97.4%) for the detection of AF episodes by Reveal XT event recorder (ER; Medtronic, Inc., Minneapolis, MN, USA). This device is inserted subcutaneously in the left pectoral area, programmed to detect arrhythmia episodes by analysis of irregularity and incoherence of R-R intervals. The Reveal XT is able to detect the duration of AF episodes, as well as AF burden, defined as percentage of time spent in AF. Furthermore, bradyarrhythmias and ventricular tachyarrhythmias are observed.
The purpose of our study was to analyse the influence of continuous rhythm monitoring and therapy guidance by ER on sinus rhythm rate after surgical AF ablation.
METHODS
From January 2003 to October 2010, 401 patients underwent concomitant surgical ablation due to persistent (61, 15.2%), long-standing persistent (n = 169, 42.2%) or paroxysmal (171, 42.6%) AF. Since August 2009, an ER (REVEAL XT, Medtronic) was implanted intraoperatively in 98 patients for continuous rhythm monitoring. A retrospective single-centre data analysis was performed. Results and outcome of these patients were compared with a matched cohort of patients with surgical AF ablation without ER implantation. Patients were matched by baseline characteristics like age, left ventricular ejection fraction (LVEF), left atrial diameter, type of AF, type of ablation and cardiac pathology.
Surgical procedures were performed on mitral: n = 74 (ER: n = 38; no ER: n = 36), aortic: n = 86 (ER: n = 40; no ER: n = 46) or tricuspid valve: n = 22 (ER: n = 10; no ER: n = 12). MVR and TVR procedures were conducted in 7 patients of each group. Surgery of the thoracic aorta was performed in 7 cases in the ER group and in 4 without ER. CABG as surgical procedure was performed in 73 (ER: n = 36; no ER: n = 37) cases.
Left atrial ablation was conducted in 172 patients (ER: n = 84; no ER: n = 88) using the left atrial lesion set of the Cox maze IV procedure, including pulmonary vein ablation, box lesion, left atrial appendage and isthmus isolation. From 2008 in patients with persistent AF, bi-atrial ablation was conducted in 24 (ER: n = 14; no ER: n = 10) cases. In addition to the above-mentioned line set, right atrial ablation including intercaval lesion, isolation of the cavo-tricuspid isthmus, the right atrial appendage and terminal crest was performed. Applied energy sources included argon-based cryoablation (CryoICE Cryoablation Probe, Atricure, Inc., West Chester, OH, USA; Cardioblate CryoFlex Surgical Ablation Probe, Medtronic, Inc.) in 66 (ER: n = 14; no ER: n = 10) patients, unipolar radiofrequency ablation (Cardioblate unipolar RF pen, Medtronic Inc.) in 100 (ER: n = 49; no ER: n = 51) and bipolar radiofrequency ablation (Cardioblate BP2 device and Cardioblate Surgical Ablation System Generator, Medtronic, Inc.) in 30 patients (ER: n = 17; no ER: n = 13).
Statistical analysis
All statistical analyses were performed with SPSS statistical software version 18.0 (SPSS, Inc., Chicago, IL, USA). Continuous values are expressed as mean ± standard deviation and were compared with the Student t-test or Mann–Whitney U-test. Categorical variables are displayed as frequency and percentages and were compared using the chi-squared test or Fisher’s exact test as appropriate. A P-value of <0.05 was considered statistically significant. A logistic regression model was used to generate a control group without ER implantation matched for the variables detailed above. Uni- and multivariate logistic regression analysis was used to identify the predictors for sinus rhythm after 12 months.
Follow-up
In patients with ER, a follow-up visit with ER interrogation was accomplished in our department of electrophysiology 3, 6 and 12 months postoperatively. AF burden, as well as time and date of recurrent AF episodes were analysed. AF recurrence was defined as AF Burden >0.5% and duration of single AF episode >30s. ER-documented AF episodes were manually validated by two different examiners. In patients without ER, a 24-h Holter ECG was conducted 3, 6 and 12 months postoperatively. Anti-arrhythmic drugs and anticoagulation regimen were maintained for 3 months postoperatively in both groups and then adapted according to either ER- or 24-h ECG rhythm results. In patients without contraindications, amiodarone was used as first-line anti-arrhythmic drug therapy, otherwise beta-blocker therapy was used for at least 3 months postoperatively. In patients with persistent AF at the time of follow-up, an electrical cardioversion was initiated. In patients with persistent AF at 6-month follow-up visit, an additional catheter-based ablation was considered if reasonable.
RESULTS
Baseline patient characteristics are shown in Table 1. Owing to the matching process, there were no statistically significant differences between the two groups. Mean patient's age was 67.0 ± 9.7 years, 68.4% were male. Mean LVEF was 52.1% and left atrial diameter 50.8 mm. Surgical procedures and ablation methods are displayed in Tables 2 and 3, showing equal distribution in both groups.
Table 1:
Baseline patient characteristics
| ER (n = 98) | No ER (n = 98) | P | |
|---|---|---|---|
| Age (years) | 66.5 ± 8.0 | 67.5 ± 9.3 | 0.42 |
| Gender, male (%) | 69 | 67 | 0.87 |
| Paroxysmal AF, n (%) | 44 (45) | 44 (45) | 1.0 |
| Persistant AF, n (%) | 14 (14) | 16 (16) | 0.84 |
| Long-standing persistent AF, n (%) | 40 (41) | 38 (39) | 0.87 |
| LVEF (%) | 52.8 ± 8.9 | 51.3 ± 9.3 | 0.27 |
| LA diameter (mm) | 51.7 ± 9.4 | 49.8 ± 8.6 | 0.21 |
| Prior Stroke or TIA, n (%) | 3 (3) | 4 (4) | 0.99 |
| AF duration (years) | 3.2 ± 3.7 | 3.4 ± 3.9 | 0.71 |
| Renal insufficiency, n (%) | 12 (12) | 10 (10) | 0.82 |
| COPD, n (%) | 7 (7) | 9 (9) | 0.79 |
| Coronary artery disease | 41 (42) | 44 (45) | 0.77 |
Table 2:
Ablation procedures
| ER (n = 98) | No ER (n = 98) | P | |
|---|---|---|---|
| Bi-atrial, n (%) | 14 (14) | 10 (10) | 0.51 |
| Left atrial, n (%) | 84 (86) | 88 (90) | 0.51 |
| RF bipolar, n (%) | 17 (17) | 13 (13) | 0.55 |
| RF unipolar, n (%) | 49 (50) | 51 (52) | 0.88 |
| Cryoablation, n (%) | 32 (33) | 34 (35) | 0.87 |
Table 3:
Operative procedures
| ER (n = 98) | No ER (n = 98) | P | |
|---|---|---|---|
| CABG, n (%) | 36 (37) | 37 (38) | 0.88 |
| AVR, n (%) | 40 (41) | 46 (47) | 0.47 |
| MVR, n (%) | 38 (39) | 36 (37) | 0.88 |
| TVR, n (%) | 10 (10) | 12 (12) | 0.82 |
| Aortic surgery, n (%) | 7 (7) | 4 (4) | 0.53 |
| MVR + TVR, n (%) | 7 (7) | 7 (7) | 1.0 |
The number of patients with bi-atrial ablation was slightly higher in the group of patients with ER (n = 14) compared with those without ER (n = 10) showing no statistically significant difference. Also, the distribution of energy sources showed no significant difference between the two groups. Survival rate after 12-month follow-up was 97.9% in the ER group and 96.9% in the no ER group (P = 0.65). Survival rates did not statistically significantly differ, according to different types of AF (paroxysmal AF 97.9%, persistent AF 97.3%, long-standing persistent AF 96.9%). During the follow-up, no stroke occurred in any of the groups.
Rhythm results
The overall sinus rhythm conversion rate was 65.3% after 1-year follow-up. Patients with paroxysmal AF had statistically significant higher rate of sinus rhythm at 12-month follow-up (78.3%), compared with those with persistent (63.9%; P = 0.03) or long-standing persistent AF (54.2%; P = 0.002).
Intraoperatively, at discharge and at 3-month follow-up, there was no statistically relevant difference in the SR rate between the ER and no ER groups (55.2, 53.3, 58.2 vs 53.2, 50.1, 56.1%, respectively; P = ns). However, at 6-month follow-up, an increased difference between the two groups was found with sinus rhythm rate of 67.1% in the ER group compared with 58.3% in patients without ER. Limitation of the 6-month follow-up is that only 55% of the patients without ER had a 24-h Holter ECG at this point of time.
One-year follow-up showed a sinus rhythm rate of 69.3% in the ER group compared with 60.1% in group of patients without ER (Fig. 1). A statistically significant difference has not been found between the two groups (P = 0.098), but a trend towards considerably higher sinus rhythm rate in ER group was found. At 12-month follow-up, the sinus rhythm rate of anti-arrhythmic drugs was also higher in the ER group, compared with patients with 24-h Holter ECG monitoring showing no statistically significant difference (64.3 vs 56.2%; P = 0.21). In Table 4, the 1-year follow-up results, according to different types of AF are shown.
Figure 1:
Incidence of sinus rhythm (%).
Table 4:
Sinus rhythm after 12 months according to different types of AF
| All (n = 196) | ER (n = 98) | No ER (n = 98) | P | |
|---|---|---|---|---|
| Paroxysmal AF, SR (%) | 78.3 | 81.2 | 75.4 | 0.25 |
| Persistent AF, SR (%) | 63.9 | 66.7 | 61.1 | 0.29 |
| Long-standing persistent AF, SR (%) | 54.2 | 57.0 | 51.4 | 0.39 |
Additional procedures
Patients in the ER group have been seen more often by a cardiologist in the first postoperative year (3.1 ± 0.8 vs 1.5 ± 0.9; P < 0.001). Also, more additional procedures have been performed in this group of patients. Sixteen (16.3%) patients with ER had an electrical cardioversion within the first postoperative year, compared with 4 (4.3%) in the group without ER (P = 0.004). Also statistically significantly more additional catheter-based ablations were performed in the ER group (ER: n = 11 (11.2%); no ER: n = 3 (3.1%); P = 0.027).
DISCUSSION
Former studies have shown that intermittent rhythm detection with standard surface ECG or 24-h Holter ECG underestimates the actual AF burden in patients with AF [10, 11]. This is, on the one hand, influenced by the short period of rhythm detection covered by those conventional rhythm-monitoring devices, and on the other hand, limited due to poor patient compliance to have repeated 12-lead surface ECG or 24-h Holter monitoring. Dagres et al. [11] demonstrated that the extension of monitoring time from 24-h Holter recording to external 7-day monitoring could significantly enhance the number of detected AF episodes. Similar results have been published by Botto et al. [12].
First experiences with the Medtronic Reveal XT, a leadless implantable subcutaneous ER with AF detection algorithm, have shown a high sensitivity, specificity and NPV for the detection of AF episodes. The XPECT trial showed a sensitivity of 96.1%, specificity of 85.4% and NPV of 97.4% for the detection of AF episodes in a prospective multicentre trial with 247 patients [9].
Hanke et al. investigated the accuracy of 24-h Holter ECG compared with continuous ER monitoring by Medtronic Reveal XT in patients after surgical AF ablation. In this study, ER monitoring identified statistically significantly more episodes of AF recurrence, compared with 24 h Holter ECG. Holter ECG (24 h) showed a sensitivity of 0.60 compared with ER monitoring when performed quarterly.
In our recent study, the overall sinus rhythm rate after surgical AF ablation at 1-year follow-up was 65.3%. Regarding the non-selected patient group with treatment by different ablation line sets, various energy sources and a high percentage of patients with persistent AF, these results are comparable to previous published studies [4–7].
However, there is an astonishing trend to higher sinus rhythm rate in patients with implanted ER after 1 year. This is contrary to the expected results, as we first would have expected a higher incidence of AF recurrence in patients with continuous rhythm monitoring due to the higher sensitivity of AF detection by ER. However, there was just a marginal difference in the sinus rhythm rate intraoperatively, at discharge and at 3-month follow-up. Therefore, we did not expect surgical procedure or type of ablation as reasons for the superior outcome in ER, particularly as the influence of those factors was minimized by the matching process. There was no difference concerning the anti-arrhythmic drug regimen in the two groups at time of discharge, 3- and 12-month follow-up. Patients with ER have been seen more often by a cardiologist in the first postoperative year, although patients in both groups were invited for 3-, 6- and 12-month follow-up. This can probably be explained by the closer link to the cardiologist/department of electrophysiology in those patients with implanted ER, and the need for device interrogation. Probably the implanted ER device was a factor that reminded patients to apprehend follow-up visits. A reason for missing follow-up visits, especially in patients with asymptomatic AF was that they did not see the necessity of consulting a doctor as they had no symptoms. Furthermore, recurrent 24-h Holter ECG recording was considered inconvenient by many patients.
Owing to more precise monitoring in patients with ER, including documentation of AF burden, time of AF recurrence and duration of AF episodes at 3-month follow-up, a more accurate therapy regimen could be created individually for each patient. On the one hand, a differentiated anti-arrhythmic drug regimen could be administered; on the other hand, additional procedures were initiated if reasonable. This resulted in a statistically significant higher number of electrical cardioversions and additional catheter-based ablations.
In our opinion, this adapted, patient-tailored therapy regimen led to a higher sinus rhythm rate in patients with ER, despite higher sensitivity in the detection of AF recurrence with the ER.
Conflict of interest: none declared.
APPENDIX. CONFERENCE DISCUSSION
Dr S. Benussi (Milan, Italy): This is a nice experience, and today many surgeons doing ablation surgery are looking with great interest at implantable event recorders. It strikes me as odd that you didn't actually mention what I think would be the major advantage in having an event recorder implanted, which is the possibility of stopping anticoagulant medication based on information about possible relapses. Why didn't you look into this? With an event recorder, probably mitral repair patients and those receiving a tissue valve could stop anticoagulant medication quite safely.
Dr Pecha: Yes, this is one of the results. We looked at it, but not in this detailed analysis. In this analysis we just tried to evaluate the impact of continuous rhythm monitoring. There was a tailored anti-arrhythmic therapy for each patient and also the anticoagulation could be stopped earlier in the group of patients with the event recorder; if they had no AF burden, we stopped anticoagulation at six months postoperatively.
Dr Benussi: I suggest that you focus on such aspects in your next work, because this would be the only significant advantage of receiving an implantable event recorder in your experience; all the rest is not statistically significant.
Dr F. Wagner (Hamburg, Germany): I am from the same group. I just wanted to make a brief comment regarding your question. Indeed, it's a very important observation to note that the cardiologists, who mostly follow these patients, are very reluctant to take those patients of any kind of anticoagulation; this has not much to do with observed and documented rhythm, but more with elevated CHAD score or subjective reluctance to stop Coumadin in patients with a history of chronic AF. It's very disappointing that you have a patient in sinus rhythm, who seems to be cured (as documented by the event recorder), and still you find the patient, at one- and two-year follow-up, still on Coumadin or similar drugs.
Dr Benussi: I think this is possibly based on the fact that they are looking at their own ablation results. And based on those, they are probably very smart in not stopping anticoagulant medication, because the official guidelines state not to, but surgical results are very much different. And possibly with these implantable recorders, we will be able to prove it. So I think this is a very important experience.
Dr G. Marchetto (Turin, Italy): My question is, for what duration, and how frequently does the event have to happen to be considered recurrent AF after ablation requiring clinical action? Because quite often it's intermittent and lasts for very few seconds, and you may have many of these recordings with the loop recorder, so it's difficult to find a cut-off above which it is considered as recurrent AF, and also to decide to discontinue warfarin and medications.
Dr Pecha: We observed any episode that was of more than 30 sec' duration as recurrence of atrial fibrillation.
Dr Marchetto: But, I mean, even if you have a few minutes, you can discontinue warfarin, I believe. What are the views of the audience and the moderators?
Dr M. Castella (Barcelona, Spain): The international societies say that a recurrence of atrial fibrillation is more than 30 sec. These loop recorders record atrial fibrillation that exceeds two minutes, so they are difficult to use when you are going to do very precise studies within the international societies’ guidelines. Nevertheless, it's a wonderful tool because most of the episodes last for more than two minutes. So I think it's a great tool independent of what the guidelines are.
I was surprised, I thought we were going to see more cases with the recorder, so worse results than the people followed up just by 24-h Holter monitoring. But I see that the results are pretty much the same, or even better, so it was a nice surprise for me.
Dr Pecha: If I can reply, you end up considering the individual patient with his other risk factors in order to arrive at the final decision, so at the end of the day the loop recorder is only part of the decision.
Dr Castella: This is true.
Dr W. Wisser (Vienna, Austria): Just a short technical question. What's the maximum memory of an event recorder? In other words, for how many months can it record continuous rhythm? To my knowledge, it is a very limited time and, therefore, the time periods at which you read out the data may be crucial. In other words, if you implant an event recorder, you have the psychological feeling that you really record all the events. But if you don't read out the data, as far as I know, the memory is full and you won't record any events anymore. That might be the reason that the results in the event recorder group are much better because you don't read the data out. Can you comment on that?
Dr Pecha: We do event recorder interrogation every three months, and the storage is big enough. The episodes are not visualized by EGM, but it detects all AF episodes; you just have the information that the patient had an AF, period, but you cannot validate it manually.
Dr Benussi: It's less than one hour, as you know, the overall period allotted for the events.
Dr T. Hanke (Lübeck, Germany): Let me just answer this one question. You can see any AF episode there is, but you don't have the EGMs then anymore. They only give you EGMs for 30 minutes. So you kind of have to trust the Reveal, but you can see any AF episode there is. And then you can put them on call-in and they can send the data once a week or once a month.
I have a question. You were able to show that patients with the event recorder got better follow-up; I mean, they saw their cardiologists a lot more often, they got cardioverted a lot more often. So should every patient get an event recorder after an ablation therapy?
Dr Pecha: In my opinion, if there is no contraindication, the patient should get an event recorder. Although we had the same follow-up protocol for both groups of patients, the patients without an event recorder were not seen that often by a cardiologist. Even if they had an appointment, they didn't come to see the cardiologist. But if they have an event recorder, they are interested in their results and want to know if atrial fibrillation is still present, and so the compliance is much better, in my opinion.
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