Discussion
Mitral
valve disease is one of the major pathophysiological causes of AF. Up to
50% of patients undergoing mitral valve surgery had atrial
fibrillation10. On the other hand, AF is also a common
complication after mitral valve surgery, with an incidence as high as
25%11. Concomitant valvular surgery at the time of
maze procedure is usually recommended for patients with AF and mitral
valve disease. However, previous studies have suggested that the
proportion of surgical AF ablation in complex mitral valve surgery was
only about 64.6%10.
Catheter
ablation may be considered for patients without surgical ablation in
mitral valve replacement surgery or with new-onset AF after mitral valve
surgery. Several studies have investigated the efficacy and safety of
catheter ablation of AF with mitral mechanical valve replacement or
mitral valvuloplasty12-14. There is no evidence for
the safety and efficacy of catheter ablation of AF with mitral
bioprosthetic valve replacement. Considering the problems such as
structural valve deterioration, patients under 50 years old were
recommended to use mechanical valves, patients over 65 years of age were
recommended to use bioprosthetic valves, and either type was optional
for patients in the intermediate age range according to
guidelines15,16. The median age of this study
population was 59 years with mechanical valve replacement and 61 years
with bioprosthetic valve replacement. Considering the interval between
valve replacement surgery and catheter ablation for AF, which was from
10 months to 29 years, this study population followed the
recommendations by guidelines in the choice of valve type. During the
follow-up period, no procedure-related adverse events were observed
after catheter ablation in the patients after bioprosthetic MVR. The
recurrence rate of AF after catheter ablation did not differ between
mechanical and bioprosthetic MVR. Catheter ablation may be safe and
effective in patients with AF with bioprosthetic MVR.
The STAR AF II study reported that linear ablation performed in addition
to pulmonary vein isolation in patients with non-valvular persistent AF
did not change the outcomes of AF recurrence17.
However, it is unclear whether additional linear ablation is required in
patients with rheumatic heart disease. In addition, atrial flutter was
also frequent in patients after mitral valve surgery18,19. In this study, 67.6% of patients had rheumatic
heart disease and 82% of patients with paroxysmal AF had atrial flutter
at the time of the ablation procedure. Therefore, PVI plus linear
ablation was performed in these patients. At the time of MI line
ablation, the physician will cautiously approach the mechanical mitral
ring to avoid mitral valve entrapment. Sometimes, it is difficult to
reach the anatomical boundary of the ablation line to achieve MI block.
In the patients with bioprosthetic MVR, the ablation line anatomical
boundary can be more easily reached without worrying about valve
entrapment. Therefore, we assumed that the MI linear block rate in the
patients with bioprosthetic MVR might be higher than the patients with
mechanical valve replacement. However, there was no statistical
difference in the success rate of bidirectional MI linear block between
the two groups in this study, even though a large proportion of patients
with bioprosthetic MVR underwent Marshall ligament alcohol ablation.
This result is different from our hypothesis. Possible reasons: (1) The
pouch structure existed in the isthmus of the mitral valve after valve
replacement, which was the main reason affecting the MI linear block.
Long et al. and Deng et al.20,21 both reported that
the isthmus of the mitral valve in patients with mechanical MVR may have
pouched MI, which might result in significantly increasing the
difficulty in the achievement of block across MI line. (2) Statistical
Class II errors might be caused by the small sample size of this study.
Lang
et al.14 observed that sinus rhythm was maintained in
73% of patients with AF and mechanical MVR 1 year after catheter
ablation. The study by Liu et al.22 indicated that the
recurrence-free survival rate of AF in patients with persistent AF 6
months after rheumatic valve surgery who underwent catheter ablation was
55.2%. Almorad et al. (2022) reported a recurrence-free survival rate
of 31.7% after the first catheter ablation of AF after mitral valve
surgery23. In this study, the overall sinus rhythm was
maintained at 69.1% after catheter ablation, which may be related to
the correction of hemodynamic abnormalities after mitral valve surgery.
Similarly, Kim et al.12 also demonstrated that there
was no significant difference in recurrence rate after catheter ablation
of valvular AF after hemodynamic correction compared with non-valvular
AF (38.7% vs. 30.6%, p=0.366).
Compared with the mechanical MVR group, the incidence of bleeding events
after AF catheter ablation was reduced in the bioprosthetic MVR group.
Non-vitamin K antagonist oral anticoagulations were used for
anticoagulation after catheter ablation in the bioprosthetic MVR group,
while warfarin was used in the mechanical MVR group. The INRs of
patients in the mechanical MVR group ranged from 2.37 to 4.0 when
bleeding events occurred. Previous studies have shown that NOACs were
associated with lower rates of intracranial hemorrhage, major
hemorrhage, fatal bleeding events, and cardiovascular death than
warfarin, and were noninferior to warfarin in preventing stroke or
systemic embolism 24,25.
Some studies have shown that left atrial size was a predictor of the
recurrence of AF after catheter ablation for non-valvular AF and
valvular AF12,26. However, Kim et al. (2018) did not
report a correlation between left atrial size and recurrence after
catheter ablation of valvular AF12. Meanwhile, no
relationship between left atrial size and AF recurrence after catheter
ablation was observed in this study, which may be related to the
generally large atria in the patients included in the study. In
addition, Cox regression models showed no predictors of outcome.
Study limitations
The small sample size in single center was the main limitation of this
study. However, we screened the study population from 17,496 patients,
and the incidence of valvular disease combined with AF in China was
higher than that in developed countries. To the best of our knowledge,
this study was still the first and the largest study to explore catheter
ablation of AF in the patients with bioprosthetic MVR. Due to the
retrospective study, the study did not clearly distinguish the order
between receiving valve surgery and diagnosis of AF. It may be related
to the differences in the mechanism of postoperative AF recurrence in
patients who underwent MVR, and future studies will improve on this
problem.
Conclusion
In conclusion, this study demonstrated the rate of AF recurrence after
catheter ablation was not significantly different between the patients
with bioprosthetic MVR and mechanical MVR. Compared to the patients with
mechanical mitral valves, bleeding events occurred non-significantly
less frequently in the patients with bioprosthetic MVR replacement
during the follow-up.
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