Discussion
The CMP-IV remains the most effective treatment for AF, and has been
shown to be effective for both paroxysmal and non-paroxysmal
AF.[13–15,18]
There have been few published reports on the late results of the CMP-IV
in patients with longstanding persistent AF, who composed the most
common subgroup of patients referred for surgical
ablation.[12]
Our results showed excellent and durable success with the CMP-IV for
longstanding persistent AF from early through late follow-up amongst 174
consecutive patients. Freedom from ATAs and freedom from both ATAs and
AADs was 88% and 68% respectively at 7 years postoperatively. This is
particularly impressive in this group of difficult-to-treat patients,
with a median preoperative duration of AF of 7.8 years and a mean LA
diameter of 4.8cm, the majority of whom (71%, 124/174) had failed one
or more catheter ablations. Our findings support the use of surgical
ablation as a treatment of symptomatic AF refractory to AADs in patients
who have failed or are poor candidates for catheter-based interventions,
as recommended by the HRS, STS, and European Cardiac Arrhythmia
Society.[2,10,30]
The late results of the CMP-IV in our population were superior to
previous studies published on catheter ablation in longstanding
persistent
AF.[7,8] Within
our cohort, ATA-free survival at 5 and 7 years was 83% and 88%,
compared with 24% AF-free survival at 10 years in persistent AF
patients in one study
[7], and just 17% ATAs
recurrence-free survival at 5 years after a single catheter ablation in
persistent AF patients in
another[8]. This
suggests that the CMP-IV should be considered in lieu of catheter
ablation in selected patients at high risk for failure (i.e. large left
atrial volume, long duration of preoperative AF).
The late results of the CMP-IV in our population were also superior to
other surgical ablation
techniques.[31,32]
At 5 years follow-up, our cohort had a 76% ATA-free survival, compared
to one study’s 29% AF-free survival in longstanding persistent AF
patients after LAA exclusion, pulmonary vein isolation, and ganglionated
plexi ablation [32] at
the same time point. This supports the use of the full CMP-IV lesion set
for surgical ablation in patients with long-standing persistent AF who
have failed catheter ablation, especially in light of our low
complication rates. There was no significant relationship between the
type of ablation device used and freedom from ATA recurrence, though
there was a trend toward better late outcomes with dry bipolar
radiofrequency clamps.
The stand-alone CMP-IV was performed with minimal morbidity and no
30-day mortality, regardless of surgical approach. There was only one
late CVA (0.6%). Postoperative pacemaker placement (7.5%, 13/174) was
comparable to previously published studies, with 85% of those
pacemakers (11/13) placed for sick sinus syndrome, and 15% (2/13)
placed for complete heart
block.[12,22]
Patients with ATA recurrence had significantly longer median
postoperative hospital length of stay, ICU length of stay, and
mechanical ventilation time, compared to those without recurrence. This
may have been secondary to differences in patients’ underlying baseline
health, but could also indicate that greater stress in the postoperative
period contributed to eventual recurrence.
On Fine-Gray multivariable regression, the only two factors predictive
of late ATAs recurrence were preoperative length of time in AF and early
postoperative ATAs. This is similar to previously published results from
both our group and
others.[15,33,34]
Although this study is one of the largest in the literature to report
late rhythm outcomes for stand-alone surgical ablation in patients with
longstanding persistent AF, it is not without limitations. This study
was retrospective and nonrandomized, thus subject to inherent selection
bias. All operations were performed at a single institution, with most
completed by a single, highly-experienced surgeon (n=164). This may
limit generalizability to other centers. Referral patterns and patient
selection may have had an impact on our results. Moreover, sample size
may have contributed to the variability of these results and increased
risk of type II error. An inherent limitation in the study design was
the lack of continuous monitoring on all patients, which can lead to
interval censoring and underestimation of ATAs recurrence. However, the
majority of patients underwent prolonged monitoring during follow-up,
and Fine-Gray regression does not assume non-informative censoring.
Moreover, the number of patients both followed longer than 5 years and
who had prolonged monitoring is higher than most previously published
studies. While the majority of patients underwent prolonged monitoring,
AF burden was not recorded in the available medical record for most of
these patients, precluding a burden-based analysis. Burden calculations
are only possible in patients with pacemakers or implantable loop
recorders (ILRs), which were present in only a small minority of our
patients. We have previously studied the utility of ILR use following
CMP-IV, and found that ILR use did not increase ATA detection compared
to Holter monitoring or
ECG.[35] Given this, it
is unlikely that increasing available burden data via more liberal use
of ILRs would significantly alter our findings.