Patients and methods
Study design
Between June 2005 and June 2015, a total of 61 patients underwent TVS at
the Prince of Wales Hospital, Hong Kong. Local paper and electronic
health records were retrospectively reviewed to collect perioperative
data. Database lock date was 1st March 2021. Paper and
electronic health records were reviewed to determine the occurrence of
postoperative complications and cardiac events. The Hong Kong Patient
Master Index provided data on vital status. The study was authorized by
the Joint Chinese University of Hong Kong – New Territories East
Cluster Clinical Research Ethics Committee and consent was waived in
view of its retrospective nature.
Operative technique
Median sternotomy and aorto-bicaval cannulation were the standard
surgical approach. Cardioplegic arrest was achieved by administering
cold crystalloid cardioplegia into the aortic root in antegrade fashion.
Coronary ostia were selectively cannulated and perfused with
cardioplegia in patients with aortic regurgitation. Tricuspid valve
repair was routinely performed with the heart arrested using a
remodeling annuloplasty ring and bicaval snares.
Definition of endpoints
The primary endpoint was operative mortality, which was defined as death
within any time interval after the operation if the patient had not been
discharged from the hospital or within 30 days of the operation. The
secondary endpoint was late cardiac events, which were defined as the
occurrence of recurrent congestive heart failure or cardiac death after
discharge.
Calculation of EuroSCORE and simplified
MELD-Na
Standard EuroSCORE definitions of preoperative risk factors and
postoperative adverse events were used. EuroSCORE was calculated by the
first author using the EuroSCORE web site
(www.euroscore.org).
Most patients had blood sampling multiple times in the months leading up
to surgery, usually due to prior hospitalizations for heart failure. In
addition, our unit routinely requests an organ function biochemistry
panel for all patients on the day prior to surgery. To ensure fair
comparison and account for day-to-day fluctuations in creatinine and
bilirubin measurements, it was the measurement taken the day prior to
surgery that was used in the final calculation.
The following formulas were used for calculation of MELD and MELD-Na:
\begin{equation}
Simplified\ MELD=\ 9.57\ x\ log\left(Creatinine\ in\ mg/dL\right)+\ 3.78\ x\ log(Bilirubin\ in\ mg/dL)\ +\ 6.43\nonumber \\
\end{equation}\begin{equation}
Simplified\ MELD\ including\ Na=\ MELD-Na\ in\ mEq/L-\left[\ 0.025\ x\ MELD\ x\ \left(140-Na\right)\ \right]+140\nonumber \\
\end{equation}International Normalized Ratio (INR) was omitted from the formula
because 85.2% of the cohort had atrial fibrillation and 82.0% were on
oral anticoagulants preoperatively.
Assessment of right ventricular systolic
function
Significant heterogeneity exists when comparing right ventricular
systolic function based on echocardiographic data alone. The most common
modalities used by referring institutions were tricuspid annular plane
systolic excursion (TAPSE) and fractional area change (FAC). Reporting
standards vary from one institution to another. Some institutions report
both while other institutions report just one parameter. For the purpose
of comparison, right ventricular systolic function was classified as
normal and abnormal using a TAPSE cut-off of 16mm and FAC cut-off of
35%, based on American Society of Echocardiography guidelines from
2016.8
Statistical analysis
Statistical analysis was performed with SPSS version 20.0. Descriptive
statistics were reported as mean with standard deviation for continuous
variables and as frequencies and percentages for categorical variables.
Univariate analysis was performed to determine risk factors for early
and late mortality. For categorical data, the χ2 test
was used to evaluate univariate categorical data when the minimum number
of observations in a category was over 5; otherwise, likelihood ratios
G-tests were used. For continuous data, simple logistic regression was
used. Variables with a p-value less than 0.05 on univariate analysis
were considered statistically significant.
Using logistic EuroSCORE as the base model, a hierarchical logistic
regression model incorporating MELD-Na was used to ascertain the
association between MELD-Na and operative mortality and major
morbidities.
Survival was estimated using the Kaplan–Meier method. Survival curves
were compared using Cox proportional-hazards model. The discriminatory
power of MELD-Na and EuroSCORE for in-hospital mortality evaluated using
area under the receiver operating characteristic (ROC) curve. The ROC
analysis results were interpreted as follows: AUC <0.70, low
diagnostic accuracy; AUC in the range of 0.70–0.90, moderate diagnostic
accuracy; and AUC ≥0.90, high diagnostic accuracy. Survival curves were
generated with MedCalc version 19.4.