ST Segment Elevation
The presence of ST segment elevation, new Q wave formation or a new conduction deficit (e.g. left bundle branch block), in the context of acute ischaemic chest pain, is associated with such significantly positive likelihood ratios for AMI (see Table 1) that the diagnosis can usually be made with confidence and appropriate therapy commenced.
Table 4
| 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.
However, the ECG by itself cannot define AMI, which also requires the demonstration of a cardiac marker rise. There are situations where this ‘injury’ pattern (i.e. ST segment elevation) does not necessarily indicate that myocardial necrosis has or will occur, such as:
- ‘Aborted’ myocardial infarction where early reperfusion has occurred [11]
- Coronary artery vasospasm with spontaneous resolution
Pitfall: There are occasional situations where ST elevation in the setting of ischaemic chest pain does not indicate that necrosis has or will occur.
ST segment elevation will typically be found in a ‘territorial’ distribution on the ECG that reflects, and is determined by, coronary artery anatomy
Click on the links below to view the ECGs.
Fig 1
Fig 2
