Limitations
Our study has several limitations. Firstly, the ANZSCTS Database
collects different data points to major international registries such as
the STS and the European database utilised for creating the EuroSCORE
II. In contrast to the STS database, procedure type is categorised
differently, and ethnicity data, previous mediastinal radiation, cancer
and chronic liver disease are not captured [15]. Unlike EuroSCORE
II, ANZSCTS does not capture pulmonary hypertension as a risk factor
[16]. Consequently, we could not correctly calculate the EuroSCORE
II nor STS score for our patients, limiting direct comparability of risk
profiles to international data.
Secondly, by focussing on the most recent decade of procedures to fit
contemporaneous standards of best practice, we have limited our
follow-up period to 30 days. This limits the capacity to assess any
longer-term outcome difference between patients who underwent repair
versus replacement. Nonetheless, this study is founded on the a
priori assumption that repair is preferable to replacement with respect
to long-term mortality. Additionally, a 30-day follow-up does not allow
for assessment of reoperation rate or repair durability, relevant to
both the quality of repair and the durability of replacement prostheses.
As directed by the European guidelines for management of chronic primary
MR, “achieving a durable valve repair is essential [2]l;” a
competent valve intraoperatively or at 30 days does not necessarily
equate with durability.
Finally, the presence of only 83 30-day mortalities limited the capacity
to assess contributing variables, and in particular to assess for the
effect of procedural volume. In comparison, Vassileva et al’s similar
study using Medicare Provider Analysis and Review data from the US
analysed a cohort of 125,079 patients aged 65 and over; a hospital
mortality rate of 10.7% equated to more than 12,000 patients [8].
This much larger cohort and much higher mortality rate facilitated
assessment of impact of procedural volume on mortality, which we were
unable to achieve to statistical significance.