A guideline-changing clinical trial has been presented at the virtual American College of Cardiology (ACC) 2021 Scientific Session on 15th May. The Left Atrial Appendage Occlusion Study III (LAAOS III) proved that left atrial appendage occlusion performed at the time of heart surgery for another reason reduces the risk for stroke by about one third in high-risk patients with atrial fibrillation (AF).

The main risk of AF is ischaemic cardio-embolic stroke. Virchow triad - the risk factors for thrombosis - are haemostasis, hypercoagulable state and damage to the vessel wall. The slow blood flow in atria, particularly in the left atrial appendage (LAA), a sleeve-like structure attached to the left atrium, provides stasis in the triad. It is therefore no surprise that almost all blood clots in atrial fibrillation originate in LAA. The risk of stroke can be quantified with CHA2DS2-VASc score standing for Congestive heart failure, Hypertension, Age >75, Diabetes, Stroke or TIA, Vascular disease, Age >65 and female Sex category. Anticoagulation (‘blood thinning’) is usually recommended in patients with a CHA2DS2-VASc score of 1 in men or 2 in women. Anticoagulation tackles the coagulation part of the Virchow triad.

Many patients with AF need cardiac surgery, usually bypass grafting (CABG) or valve repair/replacement. Some surgeons remove LAA during the cardiac surgery - it adds only a few minutes to the operation - but not all, and up to now, there was no evidence to support this practice. That has now changed.

LAAOS III enrolled almost 5,000 pretty typical cardiac surgery patients with atrial fibrillation: mean age 71 years, 68% men, average CHA2DS2-VASc score 4.2 and approximately two-thirds of them underwent valve surgery. The patients remained on standard therapy, including anticoagulation, and were randomly assigned to either heart surgery alone or surgery with occlusion of the appendage. The allowed surgical techniques included amputation of the appendage, stapler and closure devices, but not percutaneous closure nor purse-string closure.

Follow-up lasted almost four years, and the - refreshingly simple - primary endpoint of ischemic stroke or systemic embolism occurred in 4.8% of patients in the occlusion group and 7.0% of those with no occlusion. This translated into a highly significant 33% relative risk reduction (hazard ratio 0.67; 95% CI, 0.53 - 0.85; P = 0.001). Absolute risk reduction in stroke was 2.2% which is far more than e.g. risk reduction achieved with apixaban vs warfarin in the ARISTOTLE trial. There were no safety concerns, and the LAA closure added only 6 minutes to bypass time (when the heart is stopped and its function taken over by a heart-lung machine).

LAAOS III means that for most patients with AF coming for their heart surgery, the LAA closure - a relatively cheap and easy procedure - will become a routine part of their procedure. They will still need anticoagulation, but their risk of stroke will be reduced by about a third, which is impressive.