ST Segment Depression and T Wave Changes

The presence of ST segment depression and/or T wave changes (see Fig 1), in the context of acute ischaemic chest pain, normally indicates myocardial ischaemia (i.e. unstable angina) but is also associated with a positive likelihood ratio for AMI (i.e. NSTEMI see Table 1).

Fig 1

Table 5

Table 5: Value of specific components of the ECG for the diagnosis of acute myocardial infarction [9,10]
ECG finding Likelihood ratio
Ref 9 Ref 10
Increased likelihood of AMI:
New ST segment elevation 5.7 – 53.9* 13.1
New Q wave formation 5.3 – 24.8* 5.0
New conduction deficit 6.3
New ST segment depression 3.0 5.2* 3.13
T wave peaking and/or inversion 3.1 1.9
Decreased likelihood of AMI:
Normal ECG 0.1 – 0.3 0.1

* In heterogenous studies, likelihood ratios are expressed as a range.

Approximately 50% of patients with ST depression and 33% of patients with T wave inversion will subsequently be shown to have myocardial infarction [2,12]. This group of patients are presenting with an ACS (i.e. UA or NSTEMI).