CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 3, April 2012
160
AFRICA
Review Articles
Cardiac surgery risk-stratification models
CARLA PRINS, I DE VILLIERS JONKER, LEZELLE BOTES, FRANCIS E SMIT
Abstract
Risk models are widely used to predict outcomes after
cardiac surgery. Not only is risk modelling applied in the
assessment of the relative impact of specific risk factors
on surgical outcomes, but also in patient counselling, the
selection of treatment options, comparison of postoperative
results, and quality-improvement programmes. At least 19
risk-stratification models exist for open-heart surgery. The
focus of risk models was originally on pre-operative predic-
tion of mortality. However, major morbidity is in general
more common than mortality and the ability to predict only
operative mortality is not an adequate method of determin-
ing surgical outcome. Multiple intra- and postoperative
variables have been excluded in the majority of models and
the possible effect of their future inclusion remains to be
seen. The unique patient population of sub-Saharan Africa
requires a unique risk model that reflects the patient popula-
tion and levels of care.
Keywords:
risk-stratification models, open-heart surgery, intra-
and postoperative variables, surgical outcomes
Submitted 15/9/10, accepted 6/9/11
Cardiovasc J Afr
2012;
23
: 160–164
DOI: 10.5830/CVJA-2011-047
Risk models are widely applied in the assessment of the relative
impact of specific risk factors on surgical outcomes. These
models enable surgeons to select the ideal treatment option for a
specific patient and to counsel patients accordingly. They allow
for comparison of postoperative results and assist in assessment
of quality-improvement programmes.
1,2
One of the original aims for the development of cardiac
risk models was risk adjustment, allowing fair comparison of
treatment outcomes among different institutions or surgeons.
2
Risk models were then also applied in clinical decision making,
advising individual patients of their peri-operative risk, quality-
improvement programmes comparing year-to-year outcomes, as
well as allocation of healthcare resources through the prediction
of length of stay and postoperative complication rates.
1,3
The first widely used risk model, the Parsonnet score, was
based on a retrospective analysis of data collected during the
1980s.
1,4
Risk modelling since then has been significantly
influenced by advances made in diagnostic and interventional
technology. The advances in interventional cardiology are
believed to have adversely changed the risk profile of patients
presenting for cardiac surgery. A greater number of elderly
patients, those with associated illnesses, and patients presenting
for re-operation are now seen.
3,5
At least 19 risk-stratification models exist for open-heart
surgery.
4
These models are summarised in Table 1.
The focus of risk models was originally on pre-operative
prediction of mortality. However, major morbidity is in general
more common than mortality, and the ability to predict only
operative mortality is not an adequate method of determining
surgical outcome.
6
Risk modelling has therefore now in some
instances, for example the STS score, been expanded to also
allow for the calculation of postoperative morbidity.
1
The assessment of variables that may affect patient outcome,
which are not necessarily related to pre-operative patient
characteristics, are also often not taken into account. These
variables include factors related to the skill and experience
of the surgical and postoperative care teams, which in turn
influence various aspects of the intra-operative and immediate
postoperative period.
1
Knowledge of adverse intra-operative
events has been shown to enhance pre-operative risk prediction,
and it is reasonable and necessary to include these variables in
risk models.
7
Cardiac risk models are generally comparable with regard
to the pre-operative risk factors included. The most widely
used models (e.g. EuroSCORE) were usually designed for
various cardiac surgical procedures and cannot necessarily
account for co-morbid diseases and aspects of the underlying
pathophysiology/disease progression not included in the
calculation of risk.
1
However, over-complication of models
has also received a lot of criticism from strong supporters of
the concept that ‘simple models will sometimes outperform
more complex models...’.
8
Nevertheless, when the problem is
complex, deliberate limitation of the complexity of a model may
be unproductive.
8
The objective of this article is to provide a review of the most
common currently used risk-stratification models in cardiac
surgery, with critique in general that relates to practice in
sub-Saharan Africa.
Currently used models
There are a number of risk-stratification models in cardiac
surgery. Three of the most widely used models, applicable to
Department of Cardiothoracic Surgery, University of the
Free State, Bloemfontein, South Africa
CARLA PRINS, BMed Sc (Hons),
I DE VILLIERS JONKER, MD,
FRANCIS E SMIT, MB ChB, MMed
School of Health Technology, Central University of
Technology, Bloemfontein, South Africa
LIZELLE BOTES, DTech
