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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