V3R and V4R Correspond to the Right Ventricle
Leads V3R and V4R are right-sided precordial leads that correspond to the right ventricle of the heart. 1
Anatomical Location and Clinical Significance
These leads are positioned on the right anterior chest wall, mirroring the standard left precordial lead positions but on the opposite side. 1 Specifically:
- V4R is the most commonly used right-sided chest lead and is positioned in the 5th intercostal space at the right midclavicular line 1
- V3R is positioned between V2R and V4R on the right anterior chest 1
Primary Clinical Application: Right Ventricular Infarction
The critical value of V3R and V4R lies in detecting right ventricular involvement during inferior wall myocardial infarction. 1, 2
When proximal right coronary artery (RCA) occlusion occurs:
- Ischemia/infarction of the right ventricle directs the ST-segment vector rightward, anteriorly, and inferiorly 1, 3
- This produces ST-segment elevation in V3R and V4R, and often in V1 1, 2
- V4R has the greatest diagnostic value for right ventricular involvement in the setting of inferior wall infarction 1
Critical Timing Consideration
A major pitfall is that ST elevation in right-sided chest leads persists for a much shorter duration than ST elevation in the inferior leads (II, III, aVF). 1, 2, 3 Therefore:
- V3R and V4R must be recorded as rapidly as possible after chest pain onset 1, 2, 3
- Delayed recording may miss transient right ventricular involvement entirely 1
Guideline Recommendations
The American Heart Association and American College of Cardiology jointly recommend:
- Right-sided chest leads V3R and V4R should be recorded in ALL patients presenting with ECG evidence of acute inferior wall ischemia/infarction (ST elevation in leads II, III, and aVF) 1, 2
- ECG machines should be programmed to automatically suggest recording V3R and V4R when ST elevation >0.1 mV occurs in leads II, III, and aVF 1, 2, 3
- ECG machines should have mechanisms to properly label these leads 1
Diagnostic Utility
V4R is particularly valuable for distinguishing:
- RCA versus left circumflex artery (LCx) occlusion in inferior MI 1
- Proximal versus distal RCA occlusion 1
- Presence or absence of right ventricular involvement, which has significant prognostic and therapeutic implications 1, 2
The specificity and positive predictive value of ST elevation in V3R for right ventricular infarction is 81% and 77% respectively, which increases to 100% when combined with ST elevation in V4R-V7R. 4