Introduction:
Despite low mortality, cardiac surgery patients may experience serious life-threatening post-operative complications, often due to extracorporeal circulation and reperfusion. Miniaturised cardiopulmonary bypass (minimally invasive extracorporeal circulation) has been developed aiming to reduce the risk of post-operative complications arising with conventional extracorporeal circulation.

Methods:
The COMICS trial is a multi-centre, international, two-group parallel randomised controlled trial testing whether type II, III or IV minimally invasive extracorporeal circulation is effective and cost-effective compared to conventional extracorporeal circulation in patients undergoing elective or urgent coronary artery bypass grafting, aortic valve replacement or coronary artery bypass grafting + aortic valve replacement. Randomisation (1:1 ratio) is concealed and stratified by centre and surgical procedure. The primary outcome is a composite of 12 serious complications, objectively defined or adjudicated, 30 days after surgery. Secondary outcomes (at 30 days) include other serious adverse events (primary safety outcome), use of blood products, length of intensive care and hospital stay and generic health status (also at 90 days).

Status of the trial:
Two centres started recruiting on 08 May 2018; 10 are currently recruiting and 603 patients have been randomised (11 May 2020). The recruitment rate from 01 April 2019 to 31 March 2020 was 40-50 patients/month. About 80% have had coronary artery bypass grafting only. Adherence to allocation is good.

Conclusions:
The trial is feasible but criteria for progressing to a full trial were not met on time. The Trial Steering and Data Monitoring Committees have recommended that the trial should currently continue.