Study design
This study was approved by the Monash Health Human Resource Ethics Committee (reference number HREC/43701/MonH-2018-67577). This was a retrospective cohort study, limited to adults (aged ≥18) who underwent either mitral valve repair or replacement for degenerative mitral valve disease, as identified in the ANZSCTS Database from January 1 2008 to December 31 2017. The data identifier for mitral procedure type was Item #91.0, codes 3 ‘replacement’, 4 ‘repair or reconstruction with annuloplasty’ and 5 ‘repair or reconstruction without annuloplasty’. The aetiology of mitral disease, Item #91.10, was narrowed by code 5 ‘myxomatous degeneration’, encompassing the spectrum of fibroelastic deficiency through to Barlow’s disease. There were no exclusions. Concomitant coronary artery bypass grafting (CABG), non-CABG major cardiac surgery and surgery for atrial arrhythmias were included as binary variables (see ‘Variables’ below).