🔎 Where to measure ST Elevation:
- At the J-point
- According to the Fourth Universal Definition of Myocardial Infarction (2018) the magnitude of ST elevation should be determined using the J-point (junction between QRS termination and ST-segment onset)
🔎 Where to measure ST Baseline:
- At the QRS onset
- According to the Fourth Universal Definition of Myocardial Infarction (2018) the QRS onset should be used as the reference point.
- They note that in patients with a stable baseline, the TP segment (isoelectric interval) is a more accurate method to assess the magnitude of ST-segment shift.
- Tachycardia and baseline shift are common in the acute setting and can make this determination difficult. Therefore, QRS onset is recommended as the reference point for J-point determination
- No clinical trial of reperfusion therapy has designated a method of measurement of ST elevation.
- Because the PR segment may be normally depressed as part of the atrial repolarization wave, and that wave extends to the J-point, then if measured at the J-point, the ST segment should be measured relative to the PR segment.
- If the ST segment is measured at 60 to 80 ms after the J-point (a point used in prior trials), it should be measured relative to the TP segment.
- Measuring at 60-80 ms after the J-point, results in dramatically higher values (Source: PMID 16531592)
