In which leads is the axis of the heart most commonly evaluated?

The axis of the heart is primarily evaluated using Lead I and aVF because these leads provide essential information regarding the overall electrical activity of the heart in the frontal plane. When assessing the cardiac axis, Lead I measures the electrical activity from side to side (left to right), while aVF assesses the activity moving from the top to the bottom (superior to inferior). Together, these two leads enable a clear view of the vector direction of depolarization, allowing for precise determination of the heart's axis.

Using Lead I and aVF, clinicians can easily identify whether the heart is oriented normally or if there are deviations such as left axis deviation or right axis deviation. This assessment is crucial in diagnosing various cardiac conditions and in understanding the underlying cardiac function.

Other leads mentioned do not provide the same level of clarity regarding the axis. For instance, Lead II and V5 primarily focus on vertical and horizontal planes but are not standard for axis determination. Lead III and V1 offer different views that are less directly useful for this specific purpose. Lead aVR and V7 also do not contribute effectively to axis determination, as they do not give the necessary electrical orientation that aids in this analysis.