Association between device-related thrombus and the neo-appendage with left-atrial appendage occlusion devices

This commentary refers to ‘Left atrial appendage occlusion with the Amplatzer™ Amulet™ device: full results of the prospective global observational study’, by D. Hildick-Smith et al., doi:10.1093/eurheartj/ehaa169. We read the findings of the Amulet Observational Study by Hildick-Smith and colleagues with great interest.1 The authors demonstrated the second-generation Amplatzer Amulet (Abbott Laboratories, USA) was associated with excellent implant success (99.1%) and occlusion (98.4%) rates. We were particularly intrigued by the low rate of device-related thrombus (DRT) with the Amulet device (1.6%). A pooled analysis of 1739 patients with another left atrial appendage occlusion (LAAO) device, the WATCHMAN (Boston Scientific, USA), demonstrated a DRT prevalence of 3.7% whilst another large registry with 1020 patients had a prevalence of 4.1%.2,3Device-related thrombus is an important finding, as it has been associated with a three-fold increase in post-procedural thrombo-embolic events.2 Concerningly, the thrombo-embolic event rate increases over time in patients that develop DRT.2 We believe the dissimilarities in appendageal sealing may play a crucial role in the different DRT rates between these devices (1.7% vs. 3.7–4.1%). The Amulet seals the appendage at its orifice, effectively excluding the whole length of the appendage. The WATCHMAN is implanted slightly deeper into the appendage, leaving a volume of uncovered appendage, which we classify as the neo-appendage. The neo-appendage is a potential space for the formation of thrombus, which may partly explain the higher rates of DRT with WATCHMAN devices (Figure 1). Left atrial size has been shown to strongly predict DRT with WATCHMAN devices, which would imply larger pre-implant appendage and residual neo-appendage post-implant. There are other non-procedural factors associated with DRT including previous stroke, permanent atrial fibrillation (AF), and reduced left-ventricular function.2 The figure demonstrates a plausible explanation behind the lower rate of device-related thrombus with the Amplatzer Amulet when compared to the WATCHMAN device. The WATCHMAN is associated with a larger neo-appendage than the Amulet, theoretically contributing to the higher risk of thrombus formation. A recent randomized trial demonstrated the non-inferiority of WATCHMAN when compared to direct oral anticoagulants with regards to the composite endpoint of death, thrombo-embolic events, and clinically relevant bleeding in high-risk patients with AF.4 There was a trend to reduced rates of non-procedural bleeding in the LAAO arm (hazards ratio = 0.53; P = 0.07), which may be clinically significant at longer follow-up. Further data on the long-term safety and efficacy of the Amulet device are essential, though the results from this registry are reassuring. We believe future randomized studies investigating clinical and DRT outcomes between these two LAAO devices are warranted. Dr Hashrul N. Rashid is supported by the Postgraduate Scholarship (Reference No. APP 1191131) from the National Health and Medical Research Council (NHMRC), Health Professional Scholarship (Reference No. 102452) from the National Heart Foundation of Australia and the Kincaid-Smith Scholarship from the Royal Australasian College of Physicians (RACP). Conflict of interest: none declared.