What is an atrial clip made of and how does it work, and can it migrate after placement?

Atrial Clip Composition, Mechanism, and Migration Risk

Device Composition and Structure

The left atrial appendage (LAA) clip is constructed from two parallel rigid titanium tubes connected by two nitinol springs, with a knit-braided polyester fabric covering the device. 1, 2 This third-generation design was specifically engineered to provide uniform pressure distribution at the appendage base during occlusion. 1

The device differs fundamentally from percutaneous LAA occluders:

• Percutaneous devices (WATCHMAN, Amplatzer) use a self-expanding nitinol cage with barbs for anchoring and a polyethylene or polyester membrane for occlusion 3
• Surgical epicardial clips (AtriClip, Gillinov-Cosgrove) use external compression with titanium and nitinol components 3, 4

Mechanism of Action

The clip works through mechanical compression and exclusion of the LAA from the left atrial cavity. 1, 2 The device is applied epicardially at the base of the LAA via a specially designed delivery tool, creating complete occlusion through:

• Uniform pressure application across the appendage base without causing tissue damage 1
• Acute electrical isolation of the LAA, which occurs within 18 minutes of clip placement and may reduce AF recurrence 5
• Endothelialization of the occluded orifice by 90 days post-implantation, creating a new tissue layer that seals the exclusion site 1

The clip achieves occlusion without requiring entry into the left atrium, avoiding risks associated with endocardial approaches. 2

Migration Risk Assessment

Device migration following proper placement is exceptionally rare to non-existent with modern epicardial LAA clips. The evidence demonstrates:

• Zero migration events in a prospective study of 97 patients with mean follow-up of 685 days (1.87 years) 4
• No secondary dislocation observed in 36 patients followed for mean duration of 3.5 years on serial CT imaging 6
• Complete stability confirmed at 7,30, and 90-day intervals in animal models 1

This contrasts sharply with surgical suture or stapling techniques, which show incomplete occlusion rates of 77% and 100% respectively, though these represent inadequate closure rather than migration. 3

Detection of Device Position and Complications

Transesophageal echocardiography (TEE) is the primary modality for assessing clip position and efficacy, with the following surveillance protocol:

Imaging Modalities

• TEE provides real-time assessment of device position, LAA occlusion completeness, and detection of device-related thrombus 3, 4
• Cardiac CT offers superior visualization of clip stability, residual LAA neck size, and long-term device positioning 6
• 3D imaging techniques enhance visualization of LAA anatomy and device-tissue interface 4

Surveillance Timing

• Intraoperative TEE immediately after placement to confirm adequate positioning and exclude LAA perfusion 6
• Follow-up imaging at 3,12,24, and 36 months using CT to assess for migration, residual LAA neck, and thrombus formation 6

Failure Criteria to Assess

• Residual LAA pouch ≥10 mm indicates incomplete occlusion 4
• Persistent flow into the LAA on color Doppler 3, 4
• Device-related thrombus formation on the clip surface 4
• Peri-device leaks (though these apply more to percutaneous devices) 7

Key Imaging Findings

Complete occlusion success rates with epicardial clips reach 96-100%, far superior to surgical suture (23%) or stapling (0%) techniques. 3, 4, 6 The AtriClip specifically demonstrated 96% successful closure at follow-up with no clip migration or device-related thrombus on 3D imaging. 4

Critical Clinical Considerations

The clip does NOT eliminate the need for anticoagulation in all patients. 8, 7 Important caveats include:

• Incomplete occlusion occurs in approximately 50% of surgical LAA closures overall (though modern clips perform far better) 3
• Thrombus formation can occur in approximately 25% of patients with unsuccessful LAA occlusion 3
• Alternative thrombus sources exist within the left atrium beyond the LAA 7
• Continued anticoagulation is required if atrial fibrillation persists, as LAA occlusion is an adjunct to, not replacement for, anticoagulation 8, 7

The circumflex coronary artery lies in close proximity to the LAA base, requiring careful placement technique, though no coronary damage has been reported with proper clip application. 3, 1, 2