Which three sites assist in electrode placement?

The sites that assist in electrode placement are primarily associated with the anatomical landmarks of the thoracic cavity where electrodes are positioned for optimal readings. Intercostal spaces are particularly significant because they provide specific anatomical guidance for electrode placement when performing procedures such as electrocardiograms (ECGs).

By placing electrodes in the intercostal spaces, you ensure that you capture the heart's electrical activity accurately from different angles. This positioning is critical for obtaining clear waveforms and interpreting the heart's rhythm effectively.

On the other hand, while the other options reference important concepts in cardiology, they are less directly related to the physical placement of electrodes. Einthoven's triangle pertains to the theoretical framework of how limb leads relate to each other, and the Angle of Waller is more about defining angles in relation to the heart's electrical axis rather than serving as a practical site for electrode placement. Intercostal lines can refer to divisions between rib spaces but lack the specificity of the intercostal spaces in terms of direct electrode application.