What are anterolateral leads in an electrocardiogram (ECG)?

Anterolateral Leads in Electrocardiogram (ECG)

Anterolateral leads in an ECG refer to leads I, aVL, V5, and V6, which view the anterolateral region of the left ventricle. 1

Definition and Anatomical Representation

• Anterolateral leads (I, aVL, V5, V6) represent electrical activity from the anterolateral wall of the left ventricle 2, 1
• These leads are not truly "unipolar" but rather use derived electrode pairs to record electrical activity 2
• The term "anterolateral" refers to the anatomical region of the heart being viewed rather than the physical location of the electrodes on the body surface 2

Technical Aspects of Anterolateral Leads

• Lead I records the potential difference between the left arm (LA) and right arm (RA) electrodes 2
• Lead aVL represents the potential difference between the left arm and the modified terminal of Goldberger, which can be reduced to (lead I + lead III)/2 2
• Leads V5 and V6 are precordial leads that record potential differences between exploring electrodes on the left lateral chest wall and Wilson's central terminal 2
• Unlike the mathematical relationships between frontal plane limb leads, each precordial lead provides uniquely measured potential differences that cannot be calculated from other leads 2

Clinical Significance

• ST-segment elevation in anterolateral leads (I, aVL, V5, V6) may indicate myocardial ischemia or infarction in the anterolateral region of the left ventricle 2, 1
• When ST elevation appears in these leads, it often suggests occlusion of the left circumflex artery or diagonal branches of the left anterior descending artery 1
• The American Heart Association recommends avoiding labeling specific leads as "anterolateral," and instead using their original nomenclature (I, aVL, V5, V6) while still referring to the anatomical location of ischemia based on the pattern of ST-segment alterations 2, 1

Interpretation Considerations

• ST-segment changes in anterolateral leads should be interpreted in context with other leads to determine the location and extent of myocardial injury 2
• In some cases, ST elevation in anterolateral leads might be the reciprocal changes of myocardial strain in other regions of the heart 3
• The ratio of dominant QRS amplitude in lead II to lead III can help differentiate left anterolateral from left posterolateral accessory pathways in patients with Wolff-Parkinson-White syndrome 4

Common Pitfalls in Interpretation

• Assuming a one-to-one correspondence between lead location and myocardial region can lead to misdiagnosis 2, 1
• Other conditions besides ischemia can cause ST-segment changes in anterolateral leads, including pericarditis, electrolyte abnormalities, and normal variants 2
• The traditional ECG definition of "anteroseptal" AMI may actually represent anteroapical infarction, highlighting the importance of correlating ECG findings with other diagnostic modalities 5
• The standard ECG can be insensitive to changes in the lateral and posterolateral regions, potentially leading to "electrocardiographically silent" infarcts 6