How do EKG lead placements differ between right ventricle (RV) infarcts and posterior infarcts?

EKG Lead Placement for RV vs Posterior Infarcts

For right ventricular infarction, place right-sided precordial leads V3R and V4R (mirror image of standard left precordial positions) when inferior MI is present; for posterior infarction, place posterior leads V7, V8, and V9 in the same horizontal plane as V6 along the posterior chest wall. 1, 2

Right Ventricular Infarction Lead Placement

Specific Lead Positions

• V4R is the most critical lead, positioned in the 5th intercostal space at the right midclavicular line (mirror image of V4 on the left side) 2
• V3R is positioned between V2R and V4R on the right anterior chest wall 2
• Standard V1 can be considered equivalent to V2R, and standard V2 equivalent to V1R within the right-sided electrode array 1, 3
• Additional leads V5R and V6R complete the right-sided array if comprehensive evaluation is needed 2

When to Record RV Leads

• Record V3R and V4R immediately in ALL patients with ST elevation in leads II, III, and aVF (inferior MI pattern) 2, 4
• ECG machines should be programmed to automatically suggest recording these leads when inferior ST elevation >0.1 mV is detected 2

Critical Timing Pitfall

• ST elevation in right-sided chest leads persists for a much shorter duration than ST elevation in inferior leads, so V3R and V4R must be recorded as rapidly as possible after chest pain onset 2
• This is the most important pitfall—delayed recording may miss RV involvement entirely 2

Diagnostic Criteria

• ST elevation ≥0.1 mV in V3R or V4R indicates right ventricular involvement with moderate sensitivity and specificity 2
• ST elevation >0.5 mm in V3R or V4R provides supportive criteria for right ventricular infarction 3

Posterior Infarction Lead Placement

Specific Lead Positions

• V7 is placed at the posterior axillary line 1
• V8 is placed below the scapula 1
• V9 is placed at the paravertebral border 1
• All three posterior leads must be in the same horizontal plane as V6 1

When to Record Posterior Leads

• Record V7-V9 when there is isolated ST depression ≥0.05 mV in leads V1-V3 with positive terminal T waves (reciprocal changes suggesting posterior MI) 4, 3
• Obtain posterior leads immediately when there is high clinical suspicion for acute circumflex occlusion, especially with initial non-diagnostic ECG 3
• Consider posterior leads when horizontal ST-segment depression in V1-V3 occurs with a dominant R-wave and upright T-waves in anterior leads 3

Diagnostic Criteria

• ST elevation ≥0.05 mV in at least one of V7-V9 confirms posterior MI 4, 3
• ST elevation ≥0.1 mV in posterior leads increases specificity, and this higher threshold should be used in men <40 years old 3
• ST elevation in posterior leads has moderate sensitivity and high specificity for posterior wall infarction 1

Key Clinical Distinctions

Anatomical Differences

• RV infarction directs the ST-segment vector rightward, anteriorly, and inferiorly, requiring right-sided chest leads to detect 2
• Posterior infarction directs the ST-segment vector posteriorly, away from standard anterior precordial leads, requiring posterior chest leads for direct visualization 1

Recognition Without Additional Leads

• RV infarction can sometimes be recognized from ST-segment elevation in V1 on standard 12-lead ECG, though this has limited sensitivity 1, 2
• Posterior MI can be suspected from reciprocal ST-segment depression in V1-V3 on standard ECG, which is electrocardiographically equivalent to posterior ST elevation 1, 4

Treatment Implications

• RV infarction requires specific management: avoid diuretics, administer fluids, as conventional heart failure treatment may be deleterious 5
• Posterior MI should be managed as STEMI requiring emergent reperfusion therapy 3
• Recent guidelines differ importantly for ST-elevation versus non-ST-elevation infarction, making documentation of ST elevation in posterior leads clinically significant for treatment algorithms 1

Practical Algorithm

1. For any inferior MI (ST elevation in II, III, aVF): Immediately record V3R and V4R 2, 4
2. For ST depression in V1-V3 with upright T-waves: Immediately record V7, V8, V9 4, 3
3. Time is critical for RV leads: Record within minutes of presentation, as ST elevation disappears quickly 2
4. Ensure proper labeling: ECG machines must properly label these additional leads to avoid confusion 2