Electrocardiography
Broadly speaking, the ECG will directly determine whether a patient’s further management follows:
- An immediate fibrinoytic or mechanical reperfusion strategy, i.e. ST segment elevation and left bundle branch block
- An anti-thrombotic and anti-platelet strategy (ST segment depression or T-wave inversion)
- A ‘rule out’ strategy (normal ECG)
The image shows partial and complete coronary occlusion.
What ECG changes are indicative of myocardial ischaemia that may progress to AMI [2]?
ST segment changes, new conduction defects, Q waves and T wave changes may indicate AMI [2].
Example of a Non-STE ACS ECG:
Example of a STEMI ECG showing myocardial infarction:
Table 3 below shows the likelihood ratios for the association of various ECG changes with AMI [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.