aVF

aVF, or augmented vector foot, is one of the limb leads in a standard twelve-lead electrocardiogram (ECG). It is a unipolar lead that records electrical activity from the heart with the positive electrode placed on the left leg. The reference for aVF is Wilson’s central terminal, which is formed by averaging the potentials of the three limb electrodes (right arm, left arm, and left leg). The ECG amplifier enhances this single positive electrode signal, producing the augmented lead tracing.

What it measures: aVF reflects electrical activity directed toward the inferior wall of the heart. The lead’s orientation is roughly toward the foot, corresponding to an anatomical inferior perspective of the heart. In a normal heart, the QRS complex in aVF is typically positive, and the overall QRS axis commonly falls within the range that yields a positive aVF tracing.

Clinical significance: aVF is used alongside other limb leads to assess cardiac axis, ischemia, and infarction patterns. Inferior myocardial infarction classically shows ST-segment elevation in leads II, III, and aVF, with reciprocal changes in lead aVL or lead I. Abnormalities in aVF can also arise from axis deviations, where a left-axis deviation may reduce or invert the aVF signal, while a vertical (rightward) axis may accentuate it. Lead changes may be influenced by electrode placement, patient anatomy, or pacing.

Limitations: Misplacement of limb electrodes, limb edema, or pathological conditions altering the heart’s electrical axis can affect aVF readings. Interpretation should consider the entire ECG, clinical context, and other leads to avoid misdiagnosis.