DISCUSSION
A substantial increase in arrhythmia surgery has occurred in recent years owing to both the increase in AF frequency in our ageing population and the introduction of ablative technologies that have made AF correction procedures easier to perform. The Cox-Maze IV remains the most effective surgical treatment for AF and is the only surgical procedure to receive an indication from the Food and Drug Administration for the treatment of AF [16,17]. Since its introduction in 2002, the Cox-Maze IV has shown excellent success rates with low morbidity and mortality rates. However, the efficacy of the Cox-Maze IV at late follow-up in elderly patients has remained poorly defined. This study evaluated the efficacy and safety of the Cox-Maze IV in high risk cardiac surgery in those patients aged above 70 years.
This study showed that surgical ablation was highly effective in the treatment of AF with 84.9% at annual follow-up and 80.0% at long-term follow-up. As expected, these results were far superior to the No-surgical AF treatment procedure groups. Our results confirm previous studies assessing long-term outcomes in elderly patients. Macgregor et al showed the freedom from atrial tachyarrhythmia on or off anti-arrhythmic drugs was 80% and 61% at 1 and 5 year follow-up respectively in elderly cohort aged >75 years who had had Cox Maze IV [17]. In another study, Ad and Colleagues showed freedom from atrial tachyarrhythmia after Cox-Maze IV in patients > 75 years was 90%, 85% and 60% at 6 months, 1 and 2 years respectively [18]. Our results were also favorable compared to catheter ablation studies in elderly patients. Bunch et al showed that 46 patients aged >80 years reported freedom from AF on or off anti-arrythmic drugs of 75% and under 30% at 1 and 5 year follow-up after catheter ablation [19].
It is clear that surgical ablation is under-utilized in current practice. One of the reasons is the perception that a concomitant procedure will increase the complexity and operating times of the procedure and thereby lead to higher peri-operative complications. This concern is likely to be accentuated in the elderly patients undergoing high risk surgery with multiple cardiac procedures. Our study clearly demonstrates that surgical ablation can be performed safely with low peri-operative complications in elderly patients undergoing 2 or more procedures. Operating times as reflected in CPB and X-Clamp times were not significantly increased by concomitant surgical ablation. No patient who had Cox-Maze IV or PVI had a post-operative stroke which is an important finding given the known morbidity and mortality associated with this complication.
Additionally, elderly patients in our study did not experience an increase in renal failure requiring dialysis, reoperation for bleeding, respiratory complications or longer ICU/hospital stay. These findings are similar to those previously published by Ad et al [18], as well as complication rates documented in other studies examining catheter-based ablation of AF in elderly patients [19]. On the basis of their findings, Ad et al, advocated that age should not be the only discriminatory factor in deciding whether to perform a concurrent Cox Maze procedure [18].
There were 3 patients requiring a PPM post-operatively after Cox Maze procedure (4.3%) which is comparable to the other groups in our study. These rates are acceptable as elderly patients experience a greater rate of post-operative PPM compared with younger patients as demonstrated by a recent study by Macgregor et al [17]. Electrophysiological changes in atrial tissue due to increasing age may impair sinus node function and increase the risk of failed sinus node recovery. Despite this, our long-term need for PPM in the entire cohort was relatively low (7.9%) and as a result, we were unable to capture any significant difference between the groups during long-term follow-up.
The rate of death within the normal population for patients >70 years old carries significance when trying to interpret survival over time. Despite this, our study showed survival advantages of the Cox-Maze IV compared to the group that had no intervention. Of course, the patients receiving surgical ablation were selected and the survival difference may merely reflect the preoperative condition. Nonetheless, the sustained maintenance of SR following ablation may confer survival benefits in the Cox-Maze group. This is clearly demonstrated in previous studies that have shown patients who have surgery without concomitant AF ablation have poorer short and long-term outcomes than patients that come to surgery and are in SR [20,21]. In addition, AF was found to be an independent significant predictor of long-term mortality [22]. Ngaage et al demonstrated that pre-operative AF on patients undergoing cardiac surgery was associated with increased morbidity and decreased survival if not corrected [23-25]. Despite the inherent selection bias, our study adds to the evidence that even elderly patients undergoing high risk surgery will achieve mortality benefits with concomitant Cox-Maze IV procedures.
The performance of the Cox Maze procedure, the high rate and maintanence of SR and exclusion of the left atrial appendage may have an important effect on risk reduction of thromboembolic and bleeding events. Although the Kaplan-Meyer curve does not show a significantly lower rate of stroke in the Cox Maze group, the number of patients in the study was relatively small and most of our patients in all groups continued to remain on long-term anticoagulation. There are recent evidence suggesting that anticoagulation can be safely minimized 3-6 months after successful Cox-Maze procedure without increasing the risk of stroke or associated mortality [26], and this would be another advantage of successful ablation.
We are pleased with the finding that suggests reduced symptoms following the Cox-Maze procedure. This is demonstrated by a significantly higher number of patients who were in NYHA 1 status in the Cox-Maze group compared to the other group. The assessment of symptoms and quality of life is challenging, especially in this subgroup of elderly patients who underwent a concomitant surgical procedure due to valvular or coronary disease. As a result, part of their symptom benefits can be related to the functional improvement as a result of their main cardiac procedure. However, several studies have shown that the return and maintenance of SR for patients with pre-operative AF conveyed a significant increase in quality of life [18,27,28]. Ad et al also demonstrated improved quality of life through SF-12 and AF-specific questionnaire in the elderly cohort > 75 years who had concomitant Cox-Maze IV [18]. Gu et al showed patients who were restored to SR post-operatively had significantly better NYHA status compared to those in AF [29]. They also demonstrated significantly improved LVF and decreased size of LA and RA [29]. Our study did not show that the LVF was significantly improved in the Cox-Maze group but it decreased in the other group. However, we feel the reverse remodelling effect and prevention of heart failure could contribute to the improvement in symptoms in these patients in SR.
LIMITATIONS
This study is a retrospective and non-randomized study. This means there is interval censoring as well as selection bias of the Cox-Maze group leading to better symptomatic and prognostic benefits in this selected group. Another potential limitation is that the cause of death was not available for all patients. Knowing if the cause of death was cardiac in origin would be of interest as many of these elderly patients carry several cormorbid diagnoses as highlighted by the very high Euroscore in the study cohort. Finally, incomplete follow-up for some of the patients may lead to the study suffering attrition and cause reporting biases.