Final answer:
A wave of depolarization moving away from an ECG lead causes a negative deflection on the ECG trace. The P wave and QRS complex indicate atrial and ventricular depolarization with positive deflections, while atrial repolarization is masked by the QRS complex.
Step-by-step explanation:
A wave of depolarization traveling away from a lead in an electrocardiogram (ECG) results in a negative deflection or downward deflection on the ECG trace. This occurs because the ECG lead detects a decrease in voltage as the wave moves away from the positive pole of the lead. During atrial depolarization, represented by the P wave, and ventricular depolarization, represented by the QRS complex, the depolarization waves travel towards the leads, resulting in positive deflections for the corresponding waves. Conversely, waves traveling away from the leads would cause negative deflections, although in an actual ECG trace, this is masked because atrial repolarization occurs during the QRS complex. It's also important to note that the T wave represents ventricular repolarization and usually results in a positive deflection as well.