By Andre d’Avila and Arash Aryana
Cardioembolic stroke is the most devastating complication of atrial fibrillation (AF). It accounts for ~20% of all ischaemic strokes. Failure of the fibrillating atrium to contract is believed to result in atrial stretch and dilatation, promoting stasis and thrombosis within the left atrial appendage (LAA), which is the only trabeculated portion of the left atrium. Nearly 90% of atrial thrombi in patients with non-valvular atrial fibrillation originate from the LAA (compared with less than half in those with valvular atrial fibrillation), thus making this structure an attractive target for therapeutic intervention for stroke prevention in patients with non-valvular atrial fibrillation.
Three general strategies have been devised for exclusion of the LAA: 1) a surgical approach aimed at amputation or ligation, 2) a percutaneous endovascular strategy allowing deployment of an occluding device within the LAA, and 3) a closed-chest, epicardial technique directed at percutaneous ligation of this structure. The long term safety and efficacy of these strategies have not yet been completely elucidated.
1. Surgical left atrial appendage exclusion
Surgical left atrial appendage exclusion by either amputation or ligation is considered standard of care in patients undergoing mitral valve surgery or as an adjunct to a surgical maze procedure for treatment of AF. However, this strategy has met with mixed results and has not shown a clear clinical benefit. This may be in part because the studied cohorts often include patients with valvular atrial fibrillation possibly attenuating the clinical benefit of left atrial appendage exclusion. In addition, this procedure can frequently yield incomplete surgical left atrial appendage ligation (ISLL) in as many as 11 to 83% of patients. ISLL may in turn lead to a further decrease in blood flow into the ‘stenotic’ LAA (Figure 1), thereby predisposing to thrombus formation in up to 50% of patients and subsequent thromboembolic sequelae in as many as eight per cent. Consistent with this, we have observed an inverse correlation between the size of ISLL neck diameter and risk of embolic stroke (unpublished data) (1); unless treated with long term oral anticoagulation or subsequent ISLL occlusion.
2. Percutaneous endovascular left atrial appendage occlusion
To date, three devices specifically designed for endocardial LAA occlusion have been studied (2). These include the Percutaneous LAA Transcatheter Occlusion (Plaato, eV3), the Watchman LAA system (Boston Scientific) and the Amplatzer Cardiac Plug (ACP, St Jude Medical). None of these devices have yet been approved by the FDA. Each system has unique features but the implant methods are similar. Short-term results using all three devices have been promising with successful implantation rates in > 90%. Both Plaato and the ACP device were shown to reduce the annual stroke risk by ~ 65% (based on cohorts’ predicted stroke risks calculated through CHADS2 risk stratification method). The Watchman is the only device which has been prospectively evaluated against warfarin in a randomised controlled fashion, and found to be non-inferior to the latter with regards to freedom from stroke, cardiovascular death and systemic embolism. Interestingly, despite the presence of a peri-device leak in as many as one-third of Watchman recipients, this did not predict an increased thromboembolic risk during long term follow-up (Vilez-Gonzalez et al; J Am Coll Cardiol, 2012; 59:923–9). Nevertheless, these findings require further investigation. A randomised controlled-trial is presently under way to evaluate the safety and efficacy of the ACP device against oral anticoagulation in a similar manner.
3. Percutaneous epicardial left atrial appendage ligation
Recently, the safety and feasibility of a percutaneous, epicardial left atrial appendage ligation technique using the Lariat snare device (SentreHeart), was also reported (Bartus et al; J Am Coll Cardiol 2012; S0735-1097(12)03035–5). While complete closure could be achieved in 95% of patients, more than half of the cohort was maintained on long term oral anticoagulation therapy. Therefore, no definite conclusions with regards to stroke reduction may be derived with respect to this strategy.
To conclude, exclusion by either surgical or percutaneous epicardial ligation or through percutaneous endocardial occlusion seems safe and feasible in AF patients. However, surgical ligation is limited by a high incidence of incomplete surgical left atrial appendage ligation and insufficient data on its long term efficacy in stroke prevention. To date, the Watchman is the only device studied head-to-head against oral anticoagulation, which proved non-inferior compared to the latter despite presence of peri-device leak in as many as one third of patients. These results and observations warrant further investigation.
André d’Avila is from the Helmsley Cardiac Arrhythmia Service, Mount Sinai School of Medicine, New York, USA.
Arash Aryana is from the Regional Cardiology Associates and Mercy Heart & Vascular Institute, Sacramento, California, USA.
- Aryana A, Cavaco, D, Arthur, A, et al. Percutaneous endocardial occlusion of incompletely surgically ligated left atrial appendage. Submitted for publication.
- Aryana A, Saad EB, d’Avila A. Left atrial appendage occlusion and ligation devices: What is available, how to implement them, and how to manage and avoid complications. Curr Treat Options Cardiovasc Med. 2012 Oct; 14(5):503-19.