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Heart, Lung, and Vascular Surgical Centre, Mt Elizabeth Hospital, 3 Mount Elizabeth, #16-06 Mt. Elizabeth Medical Centre, Singapore, Singapore 269316
(Email: javas{at}magix.com.sg).
Among patients undergoing mitral valve surgery, atrial fibrillation (AF) commonly occurs in approximately 40% to 60% of them [1]. Generally, the presence of this dysrhythmia is associated with adverse cardiovascular outcomes, such as stroke events. Although the benefit of rhythm control has not been shown to be superior to rate control among those with lone atrial fibrillation [2], the favorable effects of restoration to sinus rhythm among patients undergoing mitral valve surgery has been shown in several surgical trials [3]. In this issue, Fukunaga and colleagues [4] demonstrated a reduction in thromboembolic events, notably stroke, and a trend in improved long-term survival among patients whose rhythm has been successfully converted to sinus rhythm after undergoing mitral valve surgery. In this retrospective analysis, patients received different procedures for rhythm surgery, with the standard Cox maze performed in only 10 patients with the majority (ie, 104 patients) being treated with the Kosakai maze. The left atrial procedure was performed in 33 patients, and this procedure has not been consistently considered as maze surgery. The variety of procedures performed in this study may contribute to the interpretation of the results of this study.
Earlier surgical trials for AF with concomitant mitral valve surgery compared a strategy with the maze and without the maze procedure (2 groups). Patients who did not undergo the maze procedure were used as the control group and were matched with those who have undergone the maze procedure. Of note, most of these trials conclude concomitant maze surgery resulted in a significant reduction of thromboembolic events, notably stroke, but with similar long-term survival [3]. On the other hand, the authors used another approach in their analysis. Those with untreated AF were considered as the control group, and patients who have received the maze procedure were considered the other group; these patients were divided into two groups of those with sinus rhythm that has been restored (sinus group) and those that remained in AF (intractable AF). This strategy allowed simultaneous comparison of the effect of cardiac rhythm and the effect of AF surgery on the outcomes. Importantly, the sinus rhythm group showed significant improvement in the freedom from thromboembolic and all complications compared with the other two groups (sinus group, 80%; intractable AF, 56%; and control, 53%; p = 0.002). In addition, there is a trend toward improvement in long-term survival for the sinus group. This trend strengthens the argument for restoration of sinus rhythm among patients undergoing mitral valve surgery.
Surprisingly, the intractable AF group has more thromboembolic complications than the untreated AF group (78% vs 89%; p = 0.01). Intuitively, one would have expected similar event rates. The authors explained this discrepancy by the fact that multiple incision lines used in the procedure resulted in scarring and tethering of the posterior wall of the left atrium, causing decreased atrial mobility, thus favoring thromboembolism. However, echocardiogram or dynamic magnetic resonance imaging was not used to evaluate the contractility of the left atrial posterior wall to support this hypothesis. Instead, another plausible explanation may be related to the proportion of patients converting to sinus rhythm spontaneously. Spontaneous conversion to sinus rhythm after mitral valve surgery has been reported before. In fact, some earlier matched control studies have shown a higher than 25% sinus conversion in the untreated AF group [3]. Among patients in Fukunaga and colleagues' [4] study, in the untreated AF group, it was 8.2% compared with only 2.6% in the intractable AF group. This difference may account, in part, for the 11% gap in thromboembolic complications in favor of the untreated AF group. Therefore, it appears that failure to restore sinus rhythm after maze surgery among patients undergoing mitral valve procedure portends a poorer prognosis.
Anticoagulation has been extensively used to prevent thromboembolic complications, particularly among those with AF and organic cardiac lesions. However, the adequacy of anticoagulation was unclear in this article. Patients who remained in AF or who had a mechanical valve, or both, were put on long-term anticoagulation. However, the target international normalized ratio of 1.8 to 2.8 seems a bit low, which could influence outcomes. Moreover the international normalized ratio between the three groups was not compared. Certainly, the degree and care in administration of anticoagulant is critical in the management of these groups of patients.
Today, the general consensus in our surgical community is that treatment of AF during mitral valve surgery is worthwhile. Despite the several limitations in Fukunaga and colleagues' [4] article, restoration of sinus rhythm is likely to prevent catastrophe embolic events. It is timely to definitively determine the impact of concomitant maze in mitral valve surgery on clinical outcomes by conducting randomized controlled trials or propensity-matched studies with adequate follow-up period.
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