A wave deflecting above the baseline on an ECG is described as which?

• A. Negative deflection
• B. Positive deflection
• C. Isoelectric
• D. Double deflection

Answer: (B)

In an ECG, deflections are determined by the direction of the heart’s electrical activity relative to the recording electrode. A wave that rises above the baseline is called a positive deflection because the electrical vector is moving toward the positive electrode, producing an upward spike on the trace. Conversely, activity moving away from the electrode makes a negative deflection (below the baseline), and a flat line indicates no net depolarization at that moment (isoelectric). A double deflection would imply a biphasic or two-peak pattern, not a single upward deflection. So the above-baseline deflection is best described as a positive deflection.