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What are the prognostic implications and factors relating to exercise induced electrocardiographic ST segment changes in the setting of a non-ischaemic stress echocardiogram?

Background. Electrocardiographic (ECG) changes during stress testing are
a common and perplexing finding during non-ischaemic stress
echocardiography (SE). Research has provided conflicting results
regarding the implications. Methods. SE was performed after maximal
Bruce protocol treadmill exercise. Results. 3020 consecutive patients,
mean age 58±12 years, 36% female, were followed-up for up to 9 years
(mean 36±21 months) post SE. Time to first cardiac event (composite of
heart failure admission, worsening New York Heart Association class,
worsening ejection fraction, acute coronary syndrome, revascularization,
angina or cardiovascular death) was analyzed and adjusted using Cox
proportional hazards regression. Prognostic significance was found with
1.5mm of downsloping or horizontal ST depression. Adjusting for baseline
differences, increased risk of composite major adverse cardiac events
was shown with at least 1.5mm of exercise induced ST depression (Hazard
ratio [HR] of 2.47, 95% Confidence ratio [CI] 1.67-3.72,
p<0.0001). Patients achieving high level exercise capacity
(≥13 metabolic equivalents or METs) with ST depression lower risk of
cardiac events during follow-up Conclusion. Patients with ST segment
depression but non-ischaemic stress imaging have poorer prognosis
compared to patients with non-ischaemic stress echocardiograms with
normal stress ECGs. ST depression of 1.5mm or more was established as a
prognostically significance value. High exercise capacity improves
prognosis, and ECG changes in that setting can be regarded as false
positives. Overall, however, ST depression during non-ischaemic stress
imaging is not a benign finding.