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Landmark Study Delivers Major Stroke Prevention Breakthrough In The Treatment Of A Common Heart Condition

A simple procedure, taking six minutes on average, and performed at the same time as other heart surgery, reduces the risk of stroke by about one third in high-risk patients with atrial fibrillation, according to results of the recently published ‘Left Atrial Appendage Occlusion Study III’ (LAAOS III).

New Zealand trial lead Dr Shay McGuinness, Medical Research Institute of New Zealand (MRINZ) Senior Clinical Research Fellow, was the principal investigator for the Auckland District Health Board LAAOS III trial site, co-authoring the study alongside international contemporaries. 

Atrial fibrillation (AF) is a common medical condition where the upper chambers of the heart do not always beat in a coordinated way with the lower chambers. People can experience palpitations when this happens, and in a certain part of the heart — the left atrial appendage — this can lead to blood becoming stagnant and forming clots. These clots are at risk of dislodging and being pumped into the brain, where they can block blood vessels to cause a stroke. The clots also risk being pumped into other parts of the body, where they can cause trouble by cutting off blood supply.

The left atrial appendage can be surgically 'blocked off', known as occlusion, in several ways to prevent clot formation, theoretically preventing this kind of stroke in patients with AF. However, until now, there has been no definitive evidence to prove whether this is effective.

129 patients from Auckland, Waikato and Wellington Hospitals contributed to this large international study, which included 4770 participants, across 105 centres, in 27 countries.

Dr Shay McGuinness, MRINZ Senior Clinical Research Fellow says “In my view this is the most important recent study conducted in cardiac surgery. Quite simply it's a game-changer for patients who have a history of atrial fibrillation who need open heart surgery. At the time of their main surgery, they can have their left atrial appendix closed with no additional risk of bleeding or other complications. Our study showed that this dramatically reduced the risk of stroke for many years after the procedure."

2379 trial participants worldwide were randomly selected to have their left atrial appendage closed during cardiac surgery, while a control group of 2391 did not. Both were followed up for an average of almost 4 years, and it was found that stroke or other embolism occurred 33% less commonly in those in the occlusion group compared to the control group. There were no differences in the rates of bleeding during the operation, complications after, or death. This means the study showed that the occlusion procedure helped to prevent stroke in patients with AF and did not increase the rates of complications.

The finding opens a new approach for stroke prevention in atrial fibrillation and will undoubtedly be incorporated into local and international guidelines.

MRINZ’s established Cardiothoracic Research Programme IOACS Net (the Improving Outcomes After Cardiothoracic Surgery Network), has been exploring the care of patients undergoing cardiac surgery at public hospitals across New Zealand since 2015. MRINZ also has a long history of stroke research, with a particular focus on ethnic disparities in post-stroke outcomes, and self-rehabilitation.

Professor Richard Beasley, Director of MRINZ says, “the findings from this trial have the power to change clinical practice both in Aotearoa New Zealand and globally, due to the marked reduction in risk of stroke with this surgical procedure. The LAAOS III study highlights the impact that the dedicated work of our IOACS Net cardiac surgeons, anaesthetists, intensivists, clinical perfusionists and researchers can have both locally and internationally.”


The 'Left Atrial Appendage Occlusion during Cardiac Surgery to Prevent Stroke (LAAOS III) study has shown that appendage closure reduces atrial fibrillation stroke risk by one third. The study has opened a new treatment option for stroke prevention in atrial fibrillation. 

129 patients from three sites in Aotearoa New Zealand, Auckland, Waikato and Wellington, contributed to this large international study, which included 4770 participants, across 105 centres, in 27 countries. 

Medical Research Institute of New Zealand (MRINZ) Senior Clinical Research Fellow, Dr Shay McGuinness co-authored the LAAOS III study, alongside international contemporaries. 

The LAAOS III study highlights the impact that MRINZ-Led IOACS Net (the Improving Outcomes After Cardiothoracic Surgery Network) has on changing clinical practice, both here in Aotearoa and internationally.

The results of the 'Left Atrial Appendage Occlusion during Cardiac Surgery to Prevent Stroke (LAAOS III) clinical trial were recently published in the prestigious New England Journal of Medicine.



Surgical occlusion of the left atrial appendage has been hypothesized to prevent ischemic stroke in patients with atrial fibrillation, but until this LAAOS Trial this has not been proved. The procedure can be performed during cardiac surgery undertaken for other reasons. 

An international team conducted a multicenter, randomized trial involving participants with atrial fibrillation and a CHA2DS2-VASc score of at least 2 (on a scale from 0 to 9, with higher scores indicating greater risk of stroke) who were scheduled to undergo cardiac surgery for another indication. The participants were randomly assigned to undergo or not undergo occlusion of the left atrial appendage during surgery; all the participants were expected to receive usual care, including oral anticoagulation, during follow-up. The primary outcome was the occurrence of ischemic stroke (including transient ischemic attack with positive neuroimaging) or systemic embolism. The participants, research personnel, and primary care physicians (other than the surgeons) were unaware of the trial-group assignments. 

The primary analysis population included 2379 participants from 27 countries in the occlusion group and 2391 in the no-occlusion group, with a mean age of 71 years and a mean CHA2DS2-VASc score of 4.2. 

The participants were followed for a mean of 3.8 years. A total of 92.1% of the participants received the assigned procedure, and at 3 years, 76.8% of the participants continued to receive oral anticoagulation. Stroke or systemic embolism occurred in 114 participants (4.8%) in the occlusion group and in 168 (7.0%) in the no-occlusion group (hazard ratio, 0.67; 95% confidence interval, 0.53 to 0.85; P=0.001). The incidence of perioperative bleeding, heart failure, or death did not differ significantly between the trial groups. 

Among participants with atrial fibrillation who had undergone cardiac surgery, most of whom continued to receive ongoing antithrombotic therapy, the risk of ischemic stroke or systemic embolism was lower with concomitant left atrial appendage occlusion performed during the surgery than without it.



Medical Research Institute of New Zealand 
The Medical Research Institute of New Zealand (MRINZ) is Aotearoa New Zealand’s leading independent medical research institute, committed to research that changes clinical practice for the better.

The MRINZ is an internationally recognised academic institution and operates under a charitable trust pursuing advances in clinical practice. MRINZ’s medical scientists are dedicated to investigating the causes of important public health problems, to delivering high quality evidence on which to improve the management of diseases and patient care across a wide range of fields, and providing a base for specialist training in medical research.

The Improving Outcomes after Cardiac Surgery Network (IOACSNet) is a Cardiac Surgical research programme based at the MRINZ, in Wellington. IOACSNet aims to improve patient outcomes through the generation of high-quality clinical evidence, particularly through the involvement of New Zealand cardiac surgical centres in high quality international clinical trials and by having a structured programme for the translation of such evidence into clinical practice.

Dr Shay McGuinness 
Shay is a Specialist in Cardiac Anaesthesia and Intensive care in Tāmaki Makaurau, and a Senior Clinical Research Fellow at the MRINZ.

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