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]:

Table 3: 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.