Anatomical Representation of ECG Leads V1, V2, V3, and aVR
Leads V1, V2, and V3 represent the septal and anterior regions of the heart, while aVR represents a view from the right upper chamber looking toward the left ventricular apex.
Precordial Leads V1-V3
- V1: Positioned at the 4th intercostal space at the right sternal border, V1 primarily views the right ventricle, right atrium, and interventricular septum 1, 2
- V2: Located at the 4th intercostal space at the left sternal border, V2 views the interventricular septum and portions of both right and left ventricles 1, 2
- V3: Positioned midway between V2 and V4 (V4 being at the 5th intercostal space at the midclavicular line), V3 primarily views the anterior wall of the left ventricle 1, 2
Augmented Vector Right (aVR)
- aVR: This is a unipolar limb lead with the positive electrode on the right arm, effectively viewing the heart from the right shoulder 1, 3
- aVR faces the cavity of the heart from the right upper side, with its positive pole directed toward the right shoulder and away from the apex of the heart 4, 3
- In normal sinus rhythm, all waves (P, QRS, T) are typically negative in aVR as electrical forces move away from this lead 3
Clinical Significance
Anterior Wall Assessment
- V1-V3 are crucial for detecting anterior wall myocardial infarction, with ST elevation in these leads indicating potential occlusion of the left anterior descending (LAD) coronary artery 1
- The pattern of ST elevation across V1-V3 helps localize the site of occlusion within the LAD 1, 2:
- Proximal LAD occlusion: ST elevation in V1-V4, I, aVL, and often aVR
- Mid-LAD occlusion: No ST elevation in V1, but present in V2-V4
- Distal LAD occlusion: More prominent ST elevation in V3-V6, less in V2
Right Ventricular Assessment
- V1 can also reflect right ventricular pathology due to its position overlying the right ventricular free wall 5, 6
- However, the accuracy of using V1-V3 alone for diagnosing right ventricular infarction is limited, and right-sided chest leads (V3R, V4R) are more specific 1, 6
aVR in Coronary Disease
- ST elevation in aVR has significant diagnostic value 3:
- When accompanied by ST elevation in V1 and anterior leads, it suggests proximal LAD occlusion
- When accompanied by widespread ST depression, it suggests left main coronary artery disease
- aVR is particularly valuable in differentiating between proximal LAD and left main coronary artery occlusions 7, 3
Normal vs. Pathological Findings
- Age and gender affect normal ST elevation thresholds in V1-V3 8:
- Men >40 years: Up to 0.2 mV in V2-V3 is normal
- Men <40 years: Up to 0.25 mV in V2-V3 is normal
- Women: Up to 0.15 mV in V2-V3 is normal
Common Pitfalls
- ST depression in V1-V3 may represent posterior (now termed lateral) wall ischemia rather than primary septal involvement 1, 2
- Right ventricular infarction can cause ST elevation in V1 that might be misinterpreted as anterior wall infarction 5, 6
- ST elevation in aVR is often overlooked but provides valuable diagnostic information about coronary artery occlusion location 7, 3