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.