What does a biphasic lead imply in an ECG?

A biphasic lead in an ECG refers to a lead that displays both positive and negative deflections within a single waveform. This occurs when the electrical activity of the heart generates a complex signal that varies in polarity as it travels through the heart muscle. In a biphasic waveform, you will see an initial positive deflection followed by a negative deflection or vice versa, indicating changes in the heart's electrical activity during depolarization and repolarization.

This feature is significant because it reflects the direction of electrical impulse in relation to the lead's placement. Specifically, the presence of both deflections in a biphasic lead suggests that the lead is positioned in a manner that captures the electrical activity from multiple angles, providing a more comprehensive view of the heart's electrical function. It also aids in diagnosing different cardiac conditions by displaying a complete picture of how the heart's electrical activity is propagating through the myocardial tissue.

The other options—only positive deflections, only negative deflections, and no deflections—do not describe the character of a biphasic lead, as they indicate signals that would lack the combination of both phases that is characteristic of biphasic recordings.