Measuring ST Segments

In order to address these issues, there are three important questions which must be answered in order to accurately measure the ST segment.

1. Where is the baseline?

ST segment elevation is defined as deviation of the ST segment by greater than 0.1mV above a line joining two successive TP segments [3]; if the TP segment is not clearly identifiable then the PR segment can be used.

Fig 1: ST segment displayed with baseline (click on the ECG to enlarge)

2. Where is the J point?

This is defined as the junction between the QRS complex and the ST segment.

Fig 2: ST segment displayed with baseline and J point  (click on the ECG to enlarge)

3. Where exactly do we find that J point?

This can be easy when we have a flatter ST segment as in Fig 1.

It is more difficult with a sloping ST segment as in Fig 2. When the position of the J point is not clear cut it will make the measurement of the height of the ST segment also more variable. Possible sites (see variability points) which may be used to measure this ST segment can be seen [5].

Fig 3: ST segment displayed with variability points (click on the ECG to enlarge)