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
| 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).