Discussion
Our data clearly show that in patients presenting to the ED with chest
pain and suspected ACS, GLS does not predict long term outcome, namely
cardiac death, ACS, revascularization, hospitalization for heart failure
or atrial fibrillation. The results were the same whether we defined
worse GLS as GLS > -18.7% (median GLS) or GLS
> -17% (abnormal GLS according to guidelines), or when we
analyzed only patients with optimal 2D echo image quality. To the best
of our knowledge, this is the first study to report the effect of GLS on
long-term outcome in patients with suspected ACS. We have previously
reported a significantly higher 6-month MACE in patients with ACS as
compared to patients in which ACS was excluded (5.8% vs. 0.6%,P =0.0002).15 The fact that 6-month MACE was
extremely rare in 2DSPER in patients in whom ACS was excluded, suggests
that the likelihood of missing significant CAD in these patients was
very low.
GLS has been shown to be a good predictor of outcome, better than LVEF,
in patients with heart failure, myocardial infarction and severe
valvular disease.7–11,25 In a meta-analysis of 16
published articles which included 5721 patients, Kalam et al concluded
that GLS predicts all-cause mortality and MACE (cardiac death,
hospitalization for heart failure and malignant
arrhythmia).10 Most of the patients included in the
meta-analysis had myocardial infarction, heart failure or severe
valvular or myocardial disease. In contrast to our study population,
these patients were sicker, had a wider range of GLS values and included
more patients with abnormal GLS values, thus explaining the discrepancy
between the other studies and ours. Even in patients with heart failure
and preserved LVEF, mean GLS was worse and standard deviation wider, as
compared to our group of patients with worse GLS (-15.2 ± 4.6% in the
study of Park et al, compared to -16.7±1.5% in our
study).9 Most of our patients had good LV function. In
2DSPER, patients without ACS had worse GLS as compared to control groups
in previous studies reporting high diagnostic accuracy of
2DLS.17,19 Worse GLS, however, was not associated with
poor outcome in our study.
In addition, most patients with ACS included in 2DSPER had unstable
angina pectoris and one vessel disease, and good outcome is expected in
such patients. In sicker patients with myocardial enzyme leak and severe
CAD, 2DLS is unnecessary for the diagnosis of ACS.26
Although 2DLS and GLS are accurate, reproducible and automated measures
of LV contraction, they are dependent on 2D echo image quality and
loading conditions which limit their accuracy, similar to
LVEF.4,27,28 Another measure of LV strain, global
circumferential strain, has been shown to be a better predictor of
outcome when compared to GLS.25 In 2DSPER we used a
new 2DLS parameter, the peak systolic strain value identifying the worst
20% LV segments (PSS20%), since this parameter was reported to
outperform GLS in diagnosing ACS, because of its ability to identify
minor wall motion abnormalities.17 Unfortunately, in
the 2DSPER study PSS20% was not superior to GLS in diagnosing
ACS.15 Similar to most other studies assessing the
utility of LV strain in predicting outcome, we used GLS, since GLS is a
simple and robust diagnostic tool, readily available in most commercial
echo machines.
In our study, independent predictors of long-term MACE were history of
CAD, ACS diagnosis, male gender and hypertension, but not GLS. Only 14%
of our study population had ACS, and recurrent ACS or revascularization
accounted for the majority of long-term events included in MACE, not
heart failure or cardiac death. In a study from Poland of 2731 patients
with unstable angina pectoris, the predictors of death or coronary
events during 3 years follow-up were age, kidney disease, hypertension,
diabetes, previous stroke and previous percutaneous coronary
interventions.29 In another study of 230 patients
discharged from the ED with a diagnosis of chest pain of undetermined
origin, 4.4% had MACE during 12 months of follow-up, and the predictors
of MACE were abnormal ECG, diabetes, or preexisting
CAD.30 As expected, in our study similar to the other
studies, markers of CAD at baseline predicted late coronary events. GLS,
contrary to previous reports, not only failed to accurately identify ACS
in the ED, but failed to predict future cardiac events as well, thus
extending our findings from the 2DSPER multicenter study, of a limited
value for GLS in low-risk patients presenting to the ED with suspected
ACS.