Statistical analysis
Categorical variables were presented as number and percentage.
Univariable comparisons of preoperative, operative and postoperative
variables were performed between patients who underwent re-sternotomy
and isolated AVR (group 1) and re-sternotomy and AVR with a concomitant
cardiac procedure(s) (group 2) using the chi-square test (categorical
variables) or Mann-Whitney U test (continuous variables).
A multivariable logistic regression analysis, using a backward stepwise
variables selection with p<0.15, was performed to identify
predictors of in-hospital mortality and a postoperative (predischarge)
composite outcome of in-hospital death, TIA/stroke, renal failure
requiring new hemofiltration, deep sternal wound infection,
re-exploration for bleeding/tamponade and length of stay
>30 days. Variables included were: gender; age; previous
myocardial infarction; NYHA class; diabetes mellitus; hypertension;
COPD; creatinine>200 µmol/l; extracardiac arteriopathy;
LVEF<30%; use of IABP; previous left internal thoracic artery
(LIMA); patent LIMA; injury at re-sternotomy (involving LIMA, vein
graft(s), right atrium, right ventricle, aorta, pulmonary artery); LIMA
injury; CPB established before re-sternotomy; isolated AVR, period
(2000-2009 or 2010-2019). A p value of < 0.05 was considered
statistically significant.
Long term survival statistics were collected from a combination of
Patient Administration System (e-CAMIS) and the NHS Spine Portal Summary
Care Records (SCR) which is an electronic database of GP medical
records. Kaplan-Meier survival curves were plotted and compared using
the log rank test.
Cox proportional hazards model with backward elimination with
p<0.15 was used to determine predictors for long term survival
(calculated from the date of discharge to death or last follow up).
Proportionality assumption was checked using Schoenfeld residuals.
Subgroup survival analysis was performed for group 1 versus group 2, for
those with and without the composite of perioperative complications and
for those with and without cardiovascular injury at re-sternotomy.
Cardiovascular injury was defined as injury to a graft/any mediastinal
cardiac or vascular structure.
Survival data for the cohorts was compared with age matched survival
data for first time AVR at our unit for the period and age-matched UK
population data from the Office of National Statistics, UK.