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Page 4 of 21 Carr et al. Vessel Plus 2020;4:12 I http://dx.doi.org/10.20517/2574-1209.2020.01

index surgical procedure. Twenty-three LT CABG mortality models were identified. The longest period
[15]
of follow-up was seven years, reported by Wu et al. When looking at those models considering only
preoperative (i.e., not intraoperative) risk factors, there were 75 ST models and 14 LT models (total = 89).
As a pre-planned sub-analysis, risk models considering on-pump vs. off-pump CABG and only preoperative
risk factors were also compared separately. This identified three ST and one LT models (total = 4). The
complete listing of variables for the ST vs. LT models with frequency counts is included in Table 1.

Overwhelmingly, age was the most common preoperative variable identified to be predictive of ST post-
CABG mortality, reported in 115 of 125 (86%) of those models. Of the articles summarized, 22/156 (14.1%)
did not report age as a risk factor. Across these 22 publications, the age-related variability in reporting
observed appears to be due in part to their study-specific populations’ inherent risk profile. For example,
articles focused upon higher risk patient sub-groups (e.g., emergent CABG patients or those experiencing
an acute myocardial infarction) commonly did not report age as a post-CABG mortality model finding.
Despite this observed pattern, however, there was not a single, simple explanation for the observed
inconsistency in age not being reported across all models.

Age was followed by left ventricular ejection fraction (included in 64% of ST mortality models), surgical
case priority or status (59%), patient gender (57%), and having undergone a prior cardiac surgical
procedure before the index procedure (55%); these represented the top five most common preoperative
variables for predicting ST post-CABG mortality. For LT models, the top five risk factors were age, ejection
fraction, diabetes mellitus, peripheral arterial disease, and renal failure. There appeared to be a trend
toward cerebrovascular disease and lung disease being more commonly reported by CABG risk models
focused upon mortality beyond one year (compared with other variables within that same subset of
models), perhaps suggesting debilitating chronic and complex comorbidities are more useful in prediction
of LT mortality.

When the results were grouped into early, mid, and late subgroups by year of publication [Tables 2-4], age
and ejection fraction remained among the most common risk factors for models throughout those time
periods. No definite trends over time were observed in risk factor prevalence for the overall group or the
ST or LT model subgroups, although sample size may have impacted the ability to detect such trends,
particularly within the subgroups. Results were also similar when considering models that included only
preoperative risk factors [Table 5] or those that considered on-pump vs. off-pump CABG [Table 6].

DISCUSSION
Across the post-CABG follow-up periods, different pre-CABG risk factors predictive of mortality were
documented. This literature search revealed dozens of logistic regression models, each reporting different
patient risk factors associated with time-varying post-CABG mortality endpoints. As documented by the
tables, the ST models found the patient’s risk variables related to their severity of coronary disease (e.g.,
more commonly reported be important predictors), whereas patient’s chronic comorbidities (e.g., diabetes,
cerebrovascular disease, or pulmonary disease) appeared to be more frequently associated with LT post-
CABG mortality. Following one-year post-CABG, life expectancy appears to be most strongly impacted
by non-cardiac comorbidities than cardiac factors or surgical processes of care. While optimizing CABG
patient selection and surgical techniques may be important ST, optimal management of non-cardiac
comorbidities may improve post-CABG patients’ LT survival. Moreover, across all follow-up time periods,
a patient’s age, ejection fraction, and renal function (e.g., creatinine or dialysis dependence) were important
predictors of post-CABG mortality; these were consistently reported for the ST and LT mortality time
periods.

A special sub-analysis was performed for the sub-group of models comprised of preoperative risk factors
along with a variable indicating the on-pump vs. off-pump surgical technique. Although there were