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Page 4 of 11 Conway et al. Vessel Plus 2020;4:25 I http://dx.doi.org/10.20517/2574-1209.2020.19

Statistical methods
We generated descriptive statistics for background demographic data, using mean and standard deviation,
median and inter-quartile range (IQR), or percentage where appropriate. We used chi-square tests for
comparisons between categorical variables and 30-day in-hospital mortality. Over our prolonged 8 year
study period, many patients were admitted more than once; 62%, 42% and 30.4% were admitted more
than once, twice, or three times respectively, with 7.9% admitted > 10 times. There will be a difference in
mortality rate if calculated by admission or by patient (only last admission considered if > 1); in this study
calculated mortality is therefore explicitly stated as per admission or as per patient. In order to allow for
[29]
clustering we utilized a logistic regression model with robust estimate . This logistic regression analysis
was used to identify potential predictors of mortality in our dataset. Identified significant univariate
predictors, as defined by P < 0.1 by Wald test, were then examined in the multivariate model to achieve
optimized prediction. We adjusted 30-day in-hospital mortality for other known predictor variables
[31]
including AISS [29,38] , Comorbidity Score [39,40] and Sepsis status . We used computations of average marginal
effects to estimate and interpret adjusted predictions for sub-groups while controlling for other variables.
The model parameters were stored; post-estimation intra-model and cross-model hypotheses could thereby
be tested. We calculated adjusted OR and 95%CI for significant predictors. Statistical significance at P < 0.05
was assumed throughout. Stata v.15 (Stata Corporation, College Station, Texas) statistical software was used
for analysis.

RESULTS
Patient demographics
There were a total of 52,214 emergency medical admissions in 28,982 patients over the 8 year study period
(2011-2018). 48.6% of admissions were male. The median (IQR) length of stay (LOS) was 5.0 (2.1, 9.5) days.
The median (IQR) age was 64.7 (45.2, 78.9) years, with the upper 10% boundary at 86.2 years. Between 2011
and 2018, there was a linear decline in 30-day in-hospital mortality. Calculated per admission episode, the
30-day in-hospital mortality averaged 3.9% (95%CI: 3.8%-4.1%) with no statistical change over time (P =
0.07). Calculated on a per patient basis (last admission if > 1), the 30-day in-hospital mortality averaged 7.1%
(95%CI: 6.8%-7.4%) with a relative risk reduction of 39.7% from 8.1 % to 4.9% (P = 0.001) and calculated
NNT of 31.1.

The baseline characteristic of admissions stratified by hscTnT level are outlined in Table 1. Admissions with
a positive hscTnT result were older at median (IQR) 75 years (60.2, 83.6) vs. 61 years (42.4, 76.4). Gender
balance appeared similar at 49.8% vs. 50.2%. Admissions with a positive hscTnT had a longer median (IQR)
LOS at 6.6 days (3.1, 12.3) vs. 4.6 days (2.0, 8.7). Admissions with a positive hscTnT were much more
likely to have high AISS (Group 5/6 81.6% vs. 54.5%), Sepsis status (Culture positive 3.7% vs. 2.8%) and
Comorbidity Score (> 10 points - 65% vs. 41.3%). They had more Major Disease Categories of respiratory
(MDC 4) and cardiac (MDC 5), but less neurology (MDC 1) in primary diagnoses.

HscTnT level and 30-day in-hospital mortality
HscTnT was a univariate linear predictor of 30-day in-hospital mortality [OR 1.67 (95%CI: 1.60-1.73)].
In the multivariable model adjusted for other significant risk predictors of AISS [OR 2.59 (95%CI: 2.25-
2.98)], Comorbidity Score [OR 1.28 (95%CI: 1.25-1.30)] and Sepsis Status [OR 1.19 (95%CI: 1.06-1.33)],
the OR was 1.23 (95%CI: 1.16-1.29). Irrespective of whether 30-day in-hospital mortality was calculated
either by patient or by all admissions, mortality increased as a linear function of hscTnT result [Figure 1].
Per admission 30-day in-hospital mortality with no troponin performed was 3.6 % (95%CI: 3.4-3.9), but
for hscTnT ≥ 25 ng/L this rose to 5.3 % (95%CI: 4.9-5.6); and there were further mortality elevations at
troponin levels ≥ 100 ng/L and 1000 ng/L to 7.4 % (95%CI: 6.6-8.3) and 8.8 % (95%CI: 7.5-10.0) respectively.