What are the implications of an increased AVL (augmented limb lead) on an electrocardiogram (ECG)?

Implications of Increased AVL on ECG

ST-segment elevation or depression in lead aVL on an ECG is a significant finding that can indicate myocardial ischemia or infarction, particularly involving the high lateral wall of the left ventricle or reciprocal changes from other territories.

Understanding Lead aVL

Lead aVL is an augmented limb lead that represents the potential difference between the left arm and the modified Goldberger terminal. It provides a unique vectorial perspective within the frontal plane 1:

• Located at -30° in the hexaxial frontal plane
• Reflects electrical activity from the high lateral wall of the left ventricle
• Can be mathematically derived as (lead I + lead III)/2

Clinical Significance of Changes in Lead aVL

ST-Segment Elevation in aVL

ST-segment elevation ≥0.1 mV (1 mm) in lead aVL may indicate:

1. High lateral wall myocardial infarction - Particularly when accompanied by ST elevation in lead I 2
2. Left anterior descending (LAD) coronary artery lesion - When accompanied by ST elevation in V2-V5, strongly suggests LAD occlusion proximal to the first diagonal branch (PPV 95%, NPV 94%) 3
3. First diagonal branch occlusion - When accompanied by ST elevation in V2 only, without ST elevation in V3-V5 (PPV 89%, NPV 100%) 3

ST-Segment Depression in aVL

ST-segment depression ≥0.1 mV (1 mm) in lead aVL may indicate:

1. Reciprocal changes from inferior wall infarction - ST depression in aVL is reciprocal to ST elevation in lead III 1, 2
2. Ischemia in other territories - The AHA/ACC notes that ST depression in aVL (with its positive pole to the left and superiorly placed) is similar in meaning to ST elevation in lead III (with its positive pole located to the right and inferiorly placed) 1

T-Wave Inversion in aVL

T-wave inversion in lead aVL may indicate:

1. Mid-segment LAD lesion - Isolated T-wave inversion in aVL has shown sensitivity of 76.7% and specificity of 71.4% for predicting a mid-LAD lesion >50% 4
2. Early warning sign - May precede more obvious ECG changes of acute coronary syndrome 4

Diagnostic Value in Acute Coronary Syndrome

Lead aVL has been identified as one of the most valuable leads for detecting acute coronary syndrome:

• In a neural network analysis, aVL was the best individual lead for detecting ACS, with an area under the ROC curve of 75.5% 5
• The best 3-lead combination for detecting ACS was III, aVL, and V2 (ROC area 82.0%) 5

Potential Confounding Factors

Several conditions can cause ST-segment changes that mimic ischemia 1, 2:

• Left ventricular hypertrophy
• Electrolyte abnormalities (hypo/hyperkalemia)
• Cardioactive drugs
• Pericarditis
• Myocarditis
• Early repolarization (normal variant)

Clinical Approach to Interpreting aVL Changes

1. Evaluate in context of other leads:

   • Check for reciprocal changes (especially in inferior leads)
   • Assess for ST changes in contiguous leads
   • Consider the pattern across all leads

2. Consider patient's clinical presentation:

   • Chest pain characteristics
   • Risk factors for coronary artery disease
   • Vital signs and hemodynamic stability

3. Correlate with cardiac biomarkers:

   • Elevated troponin levels would support myocardial injury

4. Consider further cardiac testing:

   • Echocardiography to assess wall motion abnormalities
   • Coronary angiography if ACS is suspected

Key Pitfalls to Avoid

1. Interpreting lead aVL in isolation - Always consider the entire 12-lead ECG pattern
2. Overlooking reciprocal changes - ST depression in aVL may be a reciprocal change from inferior MI
3. Failing to recognize non-ischemic causes of ST changes
4. Ignoring subtle changes in aVL - Even minor ST depression or T-wave inversion can be significant

Summary

Changes in lead aVL on ECG can provide valuable diagnostic information about myocardial ischemia and infarction. ST elevation in aVL typically indicates high lateral wall involvement, while ST depression often represents reciprocal changes from inferior wall ischemia. T-wave inversion in aVL may be an early sign of mid-LAD lesion. These findings should always be interpreted in the context of the entire ECG, clinical presentation, and cardiac biomarkers.