Discussion
By focussing on degenerative MR for which repair is the gold-standard, excluding operations for mitral stenosis and non-degenerative MR, the cohort size was reduced. To increase the cohort size, we chose to analyse all procedures for degenerative MR rather than only isolated procedures. This is in contrast to the four previously reported comparable US studies which structured their analyses differently, each of which varied both in inclusion of different aetiologies of mitral valve disease and of concomitant procedures [6-9].
Our study identified that only two surgeons in Australia in the evaluated time period performed close to 40 procedures annually, whereas the top four North American surgeons by volume were performing more than 100 isolated mitral valve surgeries annually [7], albeit “only a handful” of North American surgeons perform more than 50 annually [12]. Despite this difference in volume, Australian surgeons have achieved reasonable results. The overall repair rate was 68.5%, or 73.4% for isolated mitral valve procedures (± atrial arrhythmia surgery). The comparable STS data revealed an 82.5% repair rate for isolated mitral valve surgery for “degenerative leaflet prolapse,” though no repair rate for mitral valve surgeries with concomitant procedures was available [13]. The Australian 30-day mortality outcomes were excellent, with an overall 1.67% 30-day mortality rate (unadjusted) for mitral valve procedures including concomitant CABG or other major cardiac surgery, and 0.9% for isolated mitral valve procedures (± atrial arrhythmia surgery). The comparable STS mortality rate for isolated mitral valve procedures for degenerative MR was 1.2%, albeit risk profile could not be compared [13], and no US mortality rate was available for surgery for degenerative MR with concomitant procedures.
Of note, almost 50% (2,471 of 4,965) of operations were performed by surgeons only performing up to 10 procedures per year. This is similar to North America, where STS data suggests that the average surgeon performs fewer than 10 mitral valve surgeries per year [12]. This is problematic, as it may indicate that there is a proportion of patients undergoing replacement for potentially reparable pathology. Whereas Bridgewater et al’s United Kingdom group attempted to establish “best practice standards” for mitral surgery, recommending an individual surgeon threshold of more than 25 annual procedures and hospital threshold of 50 [14], Bonow et al acknowledge that these volumes would be “difficult to meet at many centers [sic] [12].” However, a threshold of 10 procedures per surgeon or hospital, at a minimum, is likely more achievable.