In evaluating ST-segment changes for ischemia, the displacement threshold is measured at what time after the J point?

In evaluating ST-segment changes for ischemia, the displacement threshold is measured at what time after the J point?

• A. 60-80 ms
• B. 0-20 ms
• C. 100-120 ms
• D. 200-260 ms

Answer: (B)

The key idea is to quantify ST-segment displacement as early as possible after the J point. Measuring within 0–20 milliseconds after the J point captures the onset of the ST segment before the T wave and other later repolarization changes can alter the waveform. This early window provides the most reliable indication of ischemic deviation, whereas waiting longer (60–80 ms, 100–120 ms, or 200–260 ms) risks contamination from evolving repolarization and T-wave morphology, making the threshold less specific. That’s why the correct window is the first 20 milliseconds after the J point.

The key idea is to quantify ST-segment displacement as early as possible after the J point. Measuring within 0–20 milliseconds after the J point captures the onset of the ST segment before the T wave and other later repolarization changes can alter the waveform. This early window provides the most reliable indication of ischemic deviation, whereas waiting longer (60–80 ms, 100–120 ms, or 200–260 ms) risks contamination from evolving repolarization and T-wave morphology, making the threshold less specific. That’s why the correct window is the first 20 milliseconds after the J point.