Molly Ayala
In the context of electrical axis, AVR stands for augmented voltage right arm. It is one of the leads in the multilead system used in electrocardiography (ECG) to determine the electrical axis of the heart. The electrical axis of the heart is the sum of all the depolarization vectors of the heart, and determining it can provide insight into underlying disease states and help diagnose certain arrhythmias. AVR is often ignored, even by experienced ECG readers, but careful attention to this lead can aid in the diagnosis of acute myocardial infarction.
| Characteristics | Values |
|---|---|
| Full Form | Augmented Voltage Right Arm |
| Lead System | Unipolar |
| Normal Range | +210° |
| Normal Axis | QRS axis between -30° and +90° |
| Abnormal Axis Deviation | Left Axis Deviation = QRS axis less than -30° |
| Abnormal Axis Deviation | Right Axis Deviation = QRS axis greater than +90° |
| Abnormal Axis Deviation | Extreme Axis Deviation = QRS axis between -90° and 180° |
| Normal Range in Dogs | +40 to +100 degrees |
| Normal Range in Cats | 0 to +160 degrees |
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What You'll Learn
- aVR is a unipolar lead with a single positive electrode at the right arm
- aVR is often ignored, even when considering complex ECGs
- aVR is used to determine the electrical axis of the heart
- aVR can be used to diagnose acute LMCA or proximal LAD occlusion
- aVRs adjust voltages to safe levels and provide surge protection
aVR is a unipolar lead with a single positive electrode at the right arm
Lead aVR is a unipolar lead with a single positive electrode at the right arm. It is oriented to 'look' at the right upper side of the heart, providing specific information about the right ventricle outflow tract and basal part of the septum. Lead aVR is often overlooked, even by experienced ECG readers, despite its multiple clinical applications and usefulness in interpreting ECGs.
The lead aVR is one of the augmented unipolar leads, which are of low electrical potential and are thus instrumentally augmented – hence the prefix ‘a’. The reference electrode is the mean of the potentials sensed by the left arm and left leg electrodes, with the right arm electrode being the exploring electrode. Lead aVR can be inverted into lead –aVR, which fills the gap between lead I and lead II in the coordinate system, facilitates the calculation of the heart’s electrical axis, and improves the diagnosis of acute ischemia/infarction.
In clinical practice, lead aVR is used to view the electrical activity of the heart from the frontal plane, at an angle of -150°. This means that lead aVR “views the lateral wall of the left ventricle”. The QRS axis must be at ± 90° from lead aVL at either +60° or -120°. Lead aVR is positive, with lead II negative. This puts the axis at -120°, an example of extreme axis deviation due to ventricular tachycardia.
Lead aVR is valuable in stress testing because it represents electrical forces oriented toward the cavity of the heart. It has been shown that exercise-induced ST depression in V5 and concomitant ST elevation in aVR may detect significant left anterior descending coronary artery stenosis in patients with single-vessel disease. Additionally, ST segment elevation in lead aVR during exercise testing was found to be more strongly correlated with positive tests such as nuclear imaging and coronary angiography, compared with right precordial lead changes.
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aVR is often ignored, even when considering complex ECGs
Lead aVR is a mostly ignored but valuable tool in clinical electrocardiography. It is oriented to 'look' at the right upper side of the heart and can provide specific information about the right ventricle outflow tract and basal part of the septum. However, due to its location and the reciprocal information it provides, which is also covered by leads aVL, II, V5, and V6, lead aVR is often overlooked, even by experienced ECG readers.
The lead aVR was introduced by Emanuel Goldberger in 1942, marking the beginning of the standard 12-lead ECG. It is a unipolar lead that looks at the right side of the heart, with the reference electrode constructed from the other limb electrodes. The purpose of lead aVR is to obtain specific information from the right upper side of the heart. However, in practice, most electrocardiographers consider lead aVR to give reciprocal information from the left lateral side, which can already be obtained from other leads. This perception has led to lead aVR being largely ignored.
Despite being often ignored, lead aVR has multiple clinical applications and is useful for interpreting ECGs. For example, it can be used to identify left main coronary artery (LMCA) obstruction, as demonstrated by Yamaji et al. They found that ST-segment elevation in lead aVR with less elevation in V1 is a significant predictor of acute LMCA obstruction and that the amount of ST-segment elevation is related to the patient's outcome. Additionally, the morphology of the P wave in lead aVR can differentiate atrial tachyarrhythmias. A positive P wave in aVR during tachycardia suggests atrioventricular nodal re-entry tachycardia.
There is an ongoing debate regarding the proposal to replace the frontal plane lead aVR with its inverse (-aVR). Proponents of this change argue that -aVR will retain the features of aVR while providing additional insights. However, others express reservations, noting that -aVR introduces a negative lead among the set of positive standard ECG leads, requiring interpreters to constantly keep in mind that -aVR registers a reversed image of what aVR 'sees'. This debate highlights the complex nature of ECG interpretation and the ongoing efforts to optimize the accuracy and effectiveness of ECG leads.
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aVR is used to determine the electrical axis of the heart
The lead aVR is used to determine the electrical axis of the heart. The lead aVR is oriented to 'look' at the right upper side of the heart, providing specific information about the right ventricle outflow tract and basal part of the septum. It is often ignored, even when considering complex ECGs, because it displays reciprocal information covered by leads aVL, II, V5, and V6.
Traditionally, the limb lead with the tallest R wave has been used to determine the electrical axis of the heart. Another method to determine the electrical axis of the heart involves finding the lead with the deepest negative deflection or S wave. If aVR is noted to have the deepest S wave, it follows that the electrical axis should be directly opposite the hexiaxial reference system, i.e. +30°.
The electrical axis of the heart can be visualised on a Cartesian coordinate system in the frontal plane. A horizontal line from the centre towards the left arm is defined as 0˚, and any rotation clockwise represents a positive angle, while a counter-clockwise rotation represents a negative angle. The bipolar (I, II, III) and augmented unipolar (aVF, aVR, aVL) limb leads are shown as position vectors with a well-defined angle to the x-axis.
The mean electrical axis of the heart, θ, can be determined graphically using the “circle of axes”. The cardiac vector, E, is reconstructed from the net QRS voltage in two bipolar limb leads, here leads I and II. The length of the projection of the cardiac vector onto leads I and II equals the net QRS voltage. The “circle of axes” is typically used to graphically derive the mean electrical axis of the heart by plotting the net voltage of the QRS complex in two bipolar limb leads.
Interpreting the electrocardiogram (ECG) is a key step in determining the heart's electrical axis. The cardiac axis is the sum of all depolarization vectors of the heart, and vector analysis determines the direction of the net flow of current through the heart. Adequate knowledge and appropriate application of vector analysis are important for all clinicians because defining the electrical axis can provide insight into underlying disease states and help steer the differential diagnosis towards or away from certain diagnoses.
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aVR can be used to diagnose acute LMCA or proximal LAD occlusion
AVR stands for 'augmented voltage right'. The lead aVR is oriented to 'look' at the right upper side of the heart and can provide specific information about the right ventricle outflow tract and basal part of the septum.
Several studies have examined the utility of ST elevation in aVR for predicting severe coronary artery disease (proximal LAD/LMCA) and mortality in patients with acute coronary syndromes. Gorgels et al. (1993) found that patients with LMCA frequently demonstrated ST segment depression in multiple leads (typically I, II, and V4-V6) plus ST-segment elevation in lead aVR during attacks of angina. Engelen et al. (1999) found that STE in aVR of any magnitude was 43% sensitive and 95% specific for LAD occlusion proximal to the first septal branch. Kosuge et al. (2005) found that STE in aVR ≥ 0.5 mm was the strongest predictor of LMCA or 3VD and was superior to the presence of ST depression in other leads for predicting LMCA/3VD. Aygul et al. (2008) found that STE in aVR ≥ 0.5 mm predicted proximal LAD occlusion with 50% sensitivity and 91% specificity.
In summary, aVR can be a useful tool for interpreting ECGs and diagnosing acute LMCA or proximal LAD occlusion. However, it is often overlooked, even by experienced ECG readers. Careful attention to this lead during evaluation of the ECG can aid in the diagnosis of acute LMCA or proximal LAD occlusion, affecting the timing and type of therapy, and predicting prognosis in patients with acute myocardial infarction.
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aVRs adjust voltages to safe levels and provide surge protection
In the context of electrical axis, AVR stands for "augmented voltage right arm". It is a unipolar lead with a single positive electrode attached to the right arm.
AVRs, or automatic voltage regulators, are essential devices used in generators to automatically regulate voltage levels. They adjust voltages to safe levels, providing protection against electrical surges, spikes, and generator overload. This is achieved by stabilising the output voltage of generators at variable loads, ensuring a constant output at a fixed voltage. AVRs are designed to maintain a steady voltage level, delivering a consistent voltage to electrical devices and protecting them from voltage spikes and drops.
Voltage spikes can create excess heat, potentially overloading and damaging devices. AVRs reduce the risk of spike and drop-related damage by providing a consistent voltage, which also enhances the performance of electrical devices. They achieve this by continuously monitoring incoming voltage and detecting changes in voltage levels, ensuring that devices consistently receive the necessary voltage.
Regular AVR maintenance is critical to ensure proper function and protect connected devices. Maintenance includes visual checks for wear and tear, airbrushing to remove dirt and dust buildup, and voltage testing to ensure the AVR can handle different voltages while delivering consistent voltage outputs.
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Frequently asked questions
AVR stands for Augmented Voltage Right Arm.
The mean electrical axis is the principal vector of ventricular depolarization. It represents the sum of all the waves of depolarization that are occurring simultaneously.
In dogs, the normal range is +40 to +100 degrees, and in cats, it is 0 to +160 degrees.
To determine the mean electrical axis, you must obtain a six-lead ECG from a patient positioned in right lateral recumbency with the limbs perpendicular to the long axis of the patient's body.
Determining the electrical axis provides insight into underlying disease states and helps steer the differential diagnosis toward or away from certain diagnoses. It is also important for correctly identifying certain life-threatening arrhythmias.
