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.