Minimally invasive clipping of the left atrial appendage: Reducing stroke risk in patients with atrial fibrillation

Ms Donna Eaton outlines how device closure of the left atrial appendage has emerged as a safe and effective alternative to anticoagulation for some patients

The most serious risk to patients with atrial fibrillation (AF) is thromboembolic stroke. There is a clear relationship between the left atrial appendage (LAA) and stroke in patients with non-valvular AF.  Device closure of the LAA has emerged as a safe and effective alternative to anticoagulation for some patients. Our own experience with surgical clipping/occlusion of the LAA has shown it to be a safe, simple, reliable and well-tolerated procedure with no serious complications and minimal morbidity.

The AtriClip device is placed epicardially over the base of the LAA under direct vision (and with transoesophageal echocardiography (TOE) guidance), effectively occluding the LAA. The device can be easily deployed via a minimally-invasive thoracoscopic surgical approach requiring only a short, 30-to-45 minute general anaesthetic. Epicardial clipping of the LAA using the AtriClip device achieves complete occlusion of the LAA in 98-to-100 per cent of patients. The clip, unlike alternative percutaneously-placed devices, does not require post-procedural anticoagulation, a huge advantage for those patients who have an absolute contraindication to anticoagulation. The clip is placed externally on the heart rather than internally, thus avoiding the risks of cardiac perforation, endocarditis or device migration. Additionally, the AtriClip produces complete electrical isolation of the LAA and thus in some patients, not only does the procedure reduce the patient’s risk of stroke, but it can also reduce their incidence of AF. 

We have found standalone thoracoscopic clipping of the LAA to be an ideal option in patients with contraindications to anticoagulation, patients who experience thromboembolic events despite anticoagulation, or indeed, patients in whom non-compliance with medication is felt to be an issue.

Background

Patients with non-valvular AF have a five-fold increase in lifetime major stroke risk compared to the general population. AF affects approximately 1.5-to-2 per cent of the population; it is a common cause of stroke worldwide and anticoagulation remains the standard strategy for stroke prevention and is recommended for patients with a CHA2DS2-VASc score of 2 or greater (ie, an adjusted stroke rate of 2.2 per cent or greater per year). Lifelong anticoagulation with either warfarin or novel oral anticoagulant (NOAC) medication is highly effective in preventing ischaemic stokes and improves survival in patients with AF. Anticoagulation, however, inevitably carries an increased risk of bleeding, increased associated costs, and significant lifestyle modifications. Additionally, some patients either do not tolerate oral anticoagulation or indeed have contraindications. Approximately 10 per cent of patients have a relative contraindication and 2 per cent have an absolute contraindication to anticoagulation. Among those patients who can initially tolerate warfarin or NOAC therapy, recurrent serious bleeding and/or intracranial bleeding may lead to cessation of therapy. Almost 50 per cent of patients who are initially started on warfarin will have their treatment stopped.  In practice, nearly 40 per cent of all patients at risk of stroke do not receive any form of oral anticoagulation; this is most prevalent in the elderly, who may be at the highest risk of stroke. Additionally, non-compliance generally, remains a substantial and fairly intractable issue, with estimates that around 30-to-50 per cent of patients on chronic medication fail to take their medications as directed. 

In essence, although effective pharmacological treatments exist, there is a clear need for alternative or adjunctive methods of stroke prevention.  Both interventional and surgical methods of reducing stroke risk have been explored, in particular targeting the LAA.

LAA occlusion devices

AF-related strokes are mostly embolic in nature, with the left atrium and the LAA being the main source. It is well recognised that blood pools in the LAA in patients with AF, and that the pooled/stagnant blood forms clots; if these clots break loose, they can travel to the smaller vessels in the brain, causing a stroke. The LAA is the source of over 90 per cent of emboli in patients with AF. Studies have shown 9.8 per cent of patients in AF will have thrombus in their LAA and 3.4 per cent of patients will have persistent thrombus, despite oral anticoagulation. LAA exclusion has therefore been explored as a means to manage the stroke risk of patients with AF. The ideal exclusion device is one that can provide safe, effective, complete and reproducible LAA exclusion. A handful of devices have now been used; these include devices placed using either a percutaneous approach, such as the WATCHMAN Left Atrial Appendage Closure Device, or surgical devices placed epicardially, such as the AtriClip LAA Occlusion System.

The WATCHMAN device is an umbrella-shaped plug that is percutaneously placed into the LAA through a trans-septal approach. The PROTECT-AF randomised clinical trial compared the WATCHMAN device versus warfarin therapy in stroke prevention. It was the first trial to demonstrate non-inferiority of LAA exclusion in stroke prevention, and follow-up publications (PREVAIL trials) have shown superiority of LAA exclusion over warfarin therapy. Despite this, concerns from the US Food and Drug Administration (FDA) about the percutaneous device’s safety profile and increased complication rates led to significant delays in both its approval and commercial availability. 

The WATCHMAN device requires a minimum of six weeks of warfarin anticoagulation post-procedure to allow for endothelialisation of the device and to avoid thrombus formation in the left atrium formation. This is obviously problematic in those patients where anticoagulation is truly contraindicated.

The surgical AtriClip has been FDA approved since 2009 and is currently the most widely-used LAA epicardial occlusion device. The AtriClip is a self-closing clip that is composed of two parallel titanium tubes with elastic nitinol springs covered by knit-braided polyester (see Figure 1). A number of studies have shown the excellent reliability and success of complete LAA closure with the AtriClip device (98-100 per cent). As the clip is placed epicardially, it can be used in patients with contraindications to anticoagulation. The AtriClip has been widely used during open cardiac surgery, providing safe and complete epicardial LAA exclusion — we have found it to be equally reliable when used via a minimally-invasive (thoracoscopic) approach. 

Thoracoscopic LAA occlusion

We have been using the AtriClip device to occlude the LAA via a minimally-invasive, video-assisted thoracoscopic surgical (VATS) approach.  The delivery system allows for controlled redeployment and repositioning of the device, ensuring optimal placement at the base of the LAA.  Studies have shown occlusion rates with the device to be between 98-and-100 per cent. In our experience, the AtriClip can be thoracoscopically deployed to occlude the base of the LAA via a short (30-to-45 minute) procedure. Deployment of the clip is done under direct vision and with intraoperative TOE confirmation of exclusion of the LAA. We have been performing thoracoscopic LAA appendage closures using the AtriClip, as a standalone procedure, as part of total thoracoscopic AF ablation, as an adjuvant during left-sided VATS procedures (such as lobectomy or lung biopsy), and as a hybrid procedure in combination with our cardiology colleagues (surgical LAA occlusion is combined with a catheter-based ablation, either as a combined or as staged procedures).

We have found thoracoscopic clipping to be safe, with no serious morbidity, minimal complications and with a median inpatient stay of three days. In all cases, the clip achieved complete LAA exclusion (confirmed by echocardiogram).

The device can be consistently deployed onto the base of the LAA, despite the large variations in LAA morphology, achieving complete occlusion of the appendage. It allows immediate cessation of anticoagulation medications – it does not require a period of anticoagulation post-deployment, which has proven to be a significant advantage in patients with contraindications to anticoagulation.

Discussion

LAA closure has emerged as a mechanical alternative (or adjuvant) to pharmacological stroke prevention.  It has been shown to be a safe alternative to anticoagulation, with less risk of intracranial bleeding and the same benefits as oral anticoagulation. The 2016 European Society of Cardiology guidelines recommend consideration of LAA occlusion in patients with high risk of stroke and contraindications to long-term anticoagulation (Class IIb). Additionally, there are some patients who experience TIAs or stokes despite oral anticoagulation, and these patients may well benefit from the addition of an LAA occlusion procedure to address their residual risk of stroke. 

Epicardially-placed devices such as the AtriClip are externally applied to the LAA, thus providing a mechanical force at the base of the LAA, and truly closing the neck of the LAA at its orifice. Over time, this leads to irreversible LAA. Surgical LAA occlusion performed using the AtriClip has been shown to produce complete occlusion rates of around 98-to-100 per cent. Epicardial LAA occlusion devices do not have a foreign body-blood interface, as they are placed externally onto the heart, thus reducing the potential risks of thrombosis, endocarditis, cardiac perforation, air embolism or device migration. The AtriClip does not require post-procedural anticoagulation, unlike the percutaneous WATCHMAN device. Exclusion of the LAA using the AtriClip has the additional benefit of interfering with the electrical activity of the LAA. Recent reports suggest that the LAA could be a source of re-entrant drivers in up to 30 per cent of patients who have undergone catheter-based pulmonary vein isolation (PVI) alone. The AtriClip electrically isolates the LAA and this can be particularly useful when performed in combination with an AF ablation procedure (either catheter based or thoracoscopic).

Summary

We have found thoracoscopic LAA closure using the AtriClip to be a safe, reproducible and reliable treatment for AF, particularly in:

Patients who cannot tolerate/have contraindications to anticoagulation.

Patients in whom compliance to oral anticoagulation may be an issue.

Patients who experience thromboembolic events despite anticoagulation.

It can be performed via a minimally–invasive approach as either:

A standalone procedure.

A hybrid procedure in combination with a catheter-based ablation (staged or combined procedures).

Part of a totally thoracoscopic AF ablation procedure.

An adjuvant in patients with AF undergoing left VATS procedures (lobectomy, lung biopsy, etc).