Which term is defined as a positive or negative deflection from the baseline representing a single electrical event?

• A. Wave
• B. Interval
• C. Segment
• D. Complex

Answer: (A)

In ECG terminology, a wave is a positive or negative deflection from the baseline that marks a single electrical event in the heart. Each heartbeat creates distinct deflections: for example, the P wave reflects atrial depolarization, the QRS combination reflects ventricular depolarization, and the T wave reflects ventricular repolarization. These are individual, discrete events shown as changes above or below the isoelectric line.

Interpreting the other terms helps clarify why a wave fits the description here. An interval is the time span between two points on the tracing, such as from the start of the P wave to the start of the QRS, which is about timing, not a single deflection. A segment is a flat portion of the baseline between waves, indicating relatively little electrical activity. A complex is a grouping of waves that together represent a sequence of events, such as the QRS complex, which combines several deflections into one event cluster.

So the term that best matches a single deflection from baseline representing one electrical event is a wave.