Which term refers to the time interval between ventricular contraction and the beginning of ventricular relaxation?

• A. ST segment
• B. Stylus
• C. T wave
• D. Standardization mark

Answer: (A)

Focus here is the timing of ventricular electrical events that line up with mechanical moments. The end of ventricular contraction aligns with the end of the QRS complex, while the beginning of ventricular relaxation aligns with the start of the T wave. The stretch of the ECG between those two events—the flat interval between the end of depolarization and the start of repolarization—is called the ST segment. That’s the span representing the interval between contraction and the onset of relaxation. The T wave represents relaxation, and the QT interval covers the whole cycle from the start of contraction through the end of relaxation, so it isn’t the interval in question. The other terms listed (unrelated to ECG timing) don’t describe this segment.