Current flowing away from a positive electrode on an ECG trace creates which deflection?

• A. Downward deflection
• B. Upright deflection
• C. Isoelectric line
• D. Upward deflection

Answer: (A)

In ECG leads, deflection polarity reflects whether the heart’s depolarization vector is moving toward or away from the lead’s positive electrode. When the wave of depolarization moves toward the positive electrode, you get a positive (upright) deflection. When it moves away from the positive electrode, you get a negative deflection, which appears as a downward deflection on the trace. An isoelectric line occurs when there’s no net deflection relative to that lead (the activity is perpendicular or balanced), not when the current is moving away. So current flowing away from the positive electrode produces a downward deflection.