An electrocardiogram (ECG or EKG) is a non-invasive test that measures the electrical activity of the heart over a period of time. This recording reflects the electrical changes that occur as the heart muscle depolarizes and repolarizes during each heartbeat. A standard ECG uses a 12-lead system, viewing the heart’s electrical potential from twelve different angles. These twelve leads are derived from just ten electrodes placed on the patient’s limbs and chest. The aVR lead is one of these standard leads, providing a unique vantage point for a complete assessment of cardiac health.
The Unique Role of the aVR Lead
The designation aVR stands for “Augmented Voltage Right.” This lead is an augmented unipolar limb lead, viewing the heart’s electrical activity from the perspective of the right arm. The “augmented” term refers to a technical modification in signal recording.
The aVR lead is mathematically calculated using a reference point that combines the electrical signals from the left arm and the left leg. This technique, called Goldberger’s modification, increases the amplitude of the electrical signal recorded at the right arm electrode, making the tracing easier to analyze. Using the right arm as its positive electrode, aVR looks into the heart cavity from the upper right side. This unique viewing angle is electrically opposite to the main direction of the heart’s overall electrical flow.
Identifying a Normal aVR Waveform
A normal aVR tracing appears distinct from most other ECG leads, which typically show positive deflections. In a healthy heart, the P wave, QRS complex, and T wave are all inverted, showing a downward or negative deflection below the baseline. This characteristic inverted pattern is the physiological norm for aVR.
This negative deflection occurs because of the cardiac vector, which represents the overall direction of the heart’s electrical impulse. The electrical impulse generally moves away from the right shoulder and toward the lower-left side of the body. Since aVR is positioned at the right arm, the electrical activity moves away from the lead’s positive electrode, resulting in the characteristic inverted waveform.
Clinical Implications of an Abnormal aVR
When the aVR lead displays an upright or positive waveform, it is a significant finding that points to either a technical error or a serious medical condition. The most common reason for a positive aVR is a simple lead reversal, specifically the switching of the right and left arm electrodes. In this scenario, the electrodes measure activity from the wrong direction, causing the lead I tracing to be inverted and aVR to appear positive, though the chest leads remain normal.
Beyond technical issues, an abnormal aVR can signal heart disease. ST-segment elevation in aVR, especially when accompanied by widespread ST-segment depression in multiple other leads, is a concerning finding. This pattern suggests subendocardial ischemia, often caused by stenosis in the left main coronary artery or proximal left anterior descending artery.
The magnitude of the ST elevation in aVR correlates with disease severity and can predict mortality in patients experiencing acute coronary syndrome. The aVR lead is also instrumental in diagnosing Dextrocardia, a condition where the heart is positioned on the right side of the chest. In mirror-image Dextrocardia, the aVR lead appears positive, similar to lead reversal, but the precordial (chest) leads show a distinct, abnormal R-wave progression, which helps distinguish it from a simple electrode error.