What does V3R (right-sided precordial lead) in a 12-lead electrocardiogram (EKG) mean?

V3R in 12-Lead EKG: Right-Sided Precordial Lead for Right Ventricular Infarction Detection

V3R is a right-sided precordial lead placed on the right anterior chest wall (mirror image of V3 on the left side) that is specifically used to detect right ventricular involvement during acute inferior wall myocardial infarction. 1

Anatomical Placement

• V3R is positioned on the right anterior chest between V2R and V4R, mirroring the standard left precordial lead positions but on the opposite side 2
• Within the right-sided lead array, standard V1 is equivalent to V2R, and standard V2 is equivalent to V1R 1

Primary Clinical Indication

The American Heart Association and American College of Cardiology jointly recommend recording V3R (along with V4R) in ALL patients presenting with ECG evidence of acute inferior wall ischemia/infarction (ST elevation in leads II, III, and aVF). 1, 2

Why This Matters for Patient Outcomes:

• When the right coronary artery (RCA) is occluded proximally, right ventricular infarction occurs, directing the ST-segment vector rightward, anteriorly, and inferiorly 1
• This produces ST-segment elevation in V3R and V4R (and often V1), which indicates right ventricular involvement 1, 2
• Right ventricular involvement is associated with underlying right ventricular dysfunction and greater in-hospital complications, fundamentally changing management strategies 1

Diagnostic Criteria

• ST elevation ≥1 mm (0.1 mV) in V3R indicates right ventricular injury 2, 3
• ST elevation in V3R has high sensitivity and specificity for detecting right ventricular involvement when recorded early 4, 3
• The presence of QS or QR complexes in V3R (along with V4R) are specific markers of right ventricular necrosis with 100% specificity 5

Critical Timing Pitfall

The most important clinical caveat: ST elevation in right-sided chest leads (V3R, V4R) persists for a MUCH shorter duration than ST elevation in the inferior leads (II, III, aVF). 1, 2

• ST elevation in V3R disappears within 10 hours after chest pain onset in approximately 50% of patients with right ventricular involvement 3
• Therefore, V3R must be recorded as rapidly as possible after the onset of chest pain to avoid missing the diagnosis 1, 2
• This transient nature is why routine 12-lead ECGs often miss right ventricular infarction if right-sided leads are not obtained immediately 3

Clinical Utility Beyond Detection

V3R helps distinguish between:

• 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 2

Implementation Recommendations

• 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
• ECG machines should have mechanisms to properly label V3R 1
• Recording V3R in the absence of acute inferior infarction is not routinely recommended 1