Left atrial appendage obliteration for stroke reduction

From the Sección de Cardiología No Invasiva, Servicio de Cardiología, Hospital General Universitario Gregorio Marañón, Madrid, Spain

In patients with atrial fibrillation, the left atrial appendage has been implicated in the formation of atrial thrombi and, as such, is involved in the origin of about 25% of all strokes.1,2 In previous studies, it has been suggested that greater risk of embolism may be indicated by markers such as the size of the left atrial appendage, reduction of left atrial appendage flow velocities,3,4 and detection of spontaneous echo contrast in either the left atrium or the left atrial appendage.5,6 Based on this decisive role of left atrial appendage, we assessed whether stroke risk correlated with surgical removal of the left atrial appendage.

Patients and methods

We retrospectively studied 242 patients who had previously had mitral valve replacement and who were referred for echocardiography at our institution. Patients with other possible causes of systemic embolism were not included in the study. A total of 205 patients took part in the study, of whom 130 were women (mean age, 62.4 years). Patients with biological valves received anticoagulation or antiplatelet therapy, and patients with mechanical valves were given warfarin (Coumadin). Occurrence of a stroke or embolic transient ischemic attack occurring 48 hours after the surgery were the outcome measures.

Transesophageal echocardiography (TEE) was used to carefully examine the left atrial appendage and the left atrium for the presence of thrombi and left atrial appendage spontaneous echo contrast. The lack of any anatomical structure between the mitral valve base and the upper left pulmonary artery7 indicated complete surgical ligation of the left atrial appendage. Color Doppler flow identified incomplete ligation, which was shown as a flow crossing the separation between the left atrial body and the left atrial appendage.7 The contribution of left atrial appendage surgical obliteration to the risk of future embolism was analyzed using multivariate analysis.

Results

Fifty-two patients received complete ligation of the left atrial appendage, and six patients received incomplete ligation. Twenty-seven patients had an embolic event during the time between valve replacement and echocardiographic study (mean, 69.4 ± 67 months), of which 19 were ischemic strokes, five were peripheral embolisms, and three were transient ischemic attacks. In patients who did not receive left atrial appendage removal, systemic embolism was markedly increased (17%), compared with patients who underwent left atrial appendage ligation (3.4%; P = .01). Systemic embolism was also more common in patients without left atrial appendage ligation compared with those who received left atrial appendage ligation if left atrium or left atrial appendage thrombus (14.8% compared with 3.4%;

P = .03) and left atrial appendage spontaneous echo contrast grade

3 or 4 (64% compared with 21.3%;

P < .001) were shown in the echocardiographic study (Table 1).

The absence of left atrial appendage removal (odds ratio [OR], 6.7; 95% confidence interval [CI], 1.5—31.0; P = .02) and the finding of

a left atrium or left atrial append-

age thrombus on TEE (OR, 5.8;

95% CI, 1.2—27.3; P = .03) were shown to be independent predictors of the occurrence of an embolic event after mitral valve replacement surgery on multivariate analysis (Table 2). The OR increased up to 11.9 (95% CI, 1.5–93.6; P = .02) when incomplete ligation shown by echocardiography was included in the model.

Discussion

It has been shown that the left atrial appendage is a cause of thromboembolic stroke. Stroke risk, therefore, would most likely be markedly diminished by removal of the left atrial appendage. Left atrial append-

age ligation has been performed since early surgical treatment for rheumatic mitral stenosis to diminish embolization risk. The benefits of obliteration of the left atrial appendage during mitral valve replacement surgery are still being debated, however. It has been suggested that removing the left atrial appendage during cardiac surgery can help to prevent strokes.8 But there are few studies proving the advantages of this procedure.9,10 Although the procedure is endorsed in the American College of Cardiology guidelines, its use depends on the preferences and skill of the individual surgical team.11

Incomplete surgical ligation of the left atrial appendage has been shown to have an important effect on the incidence of embolic events following surgery. In our study, 10.3% of patients had incomplete removal of the left atrial appendage and, of these, only one patient had an embolic event. It was shown in a recent study, however, that of 36%

of patients with incomplete ligation of the left atrial appendage, 22% had an embolic event.7 The effect of the surgical technique is clear, and it can result in a greater incidence of postoperative embolic events.

High-risk patients who received left atrial appendage removal during mitral valve replacement surgery were found to have a 6.7-fold reduced risk of embolism in our study. An additional decreased risk of embolism (11.9-fold) occurred when complete ligation was achieved and was shown on TEE. TEE may possibly be used to classify patients who are at greater risk for embolic events and therefore would receive greater advantage from ligation of the left atrial appendage. A greater risk of late embolism correlates with identification of the left atrial appendage or left atrium thrombus, higher left atrium size, and higher degrees of left atrial appendage spontaneous echo contrast on TEE.

Because high-risk patients receive anticoagulants for many years, some physicians might believe that left atrial appendage ligation is not necessary. But eradicating the cause of embolic events would be a reasonable approach because warfarin (Coumadin) is often not used correctly or not used at all. In our study, we did not collect data on patients’ levels of anticoagulant medications. It may be possible that reduced in-ternational normalized ratios affected the development of an embo-

lic event, despite the fact that all patients in our study who had a mechanical prosthesis received anticoagulant therapy. Regardless of the obvious clinical importance, we do not believe that the long-term anticoagulation profile is different for patients who undergo left atrial appendage ligation compared with those who do not receive left atrial appendage ligation. Therefore, in this setting, the amount of long-term anticoagulation therapy does not appear to be an important factor.

Conclusion

Our study provides clear evidence for the benefit of obliteration of the left atrial appendage during surgical procedures as a method of preventing a postoperative embolic event and supports surgical left atrial appendage removal during mitral valve replacement. Until results of a blind, randomized study are available,12 the current study provides new data on the effects of left atrial appendage ligation.