aVR

aVR is one of the augmented limb leads used in the standard 12-lead electrocardiogram. It records the heart’s electrical activity from the right shoulder, with the positive electrode placed on the right arm and the left arm and left leg forming the reference. The lead is derived by augmenting the signal from the right arm while using the average of the other two limb electrodes as a reference point.

The lead’s orientation is toward the right shoulder, with an approximate frontal-plane axis around -150 degrees (about 210 degrees in some references). Because the heart’s main vector typically points away from this view, the QRS complex in aVR is usually negative.

In normal conditions, the aVR tracing often shows a small or negative QRS complex; the exact morphology of the P and T waves varies. Interpretation of aVR is best done in the context of the other leads, since abnormalities may be subtle or misleading if viewed in isolation. Changes in aVR can provide useful information when assessing ischemia or infarction patterns in acute settings.

Clinical significance: In acute coronary syndrome, ST-segment elevation in aVR with concurrent widespread ST-segment depression in other leads can indicate critical proximal coronary artery disease, such as left main or severe multivessel disease. The magnitude and pattern of aVR findings, like any single lead, must be integrated with the overall ECG and clinical presentation. aVR can also help identify technical issues such as dextrocardia or limb-lead misplacement.

Limitations: aVR has relatively small signal amplitude and can be more challenging to interpret; it is most informative when considered as part of the full 12-lead ECG.