How should ECG (electrocardiogram) leads V1-V4 be interpreted in a patient with an unknown medical history and symptoms?

ECG Leads V1-V4: Interpretation Guide

Leads V1-V4 are the anterior precordial leads that primarily assess the anterior wall of the left ventricle and interventricular septum, with V1 also providing critical information about right ventricular activity. 1

Anatomical Territory and Coronary Correlation

Lead-Specific Anatomy

• V1: Positioned closest to the right ventricle anatomically; reflects right ventricular activity and basal interventricular septum 1, 2
• V1-V4: Collectively represent the anterior wall and interventricular septum of the left ventricle 1
• V2-V4: Specifically reflect the mid-anterior left ventricular wall when V1 is not involved 1

Coronary Artery Territories

• Proximal LAD occlusion (above first septal and diagonal branches): Produces ST elevation in V1-V4, plus leads I and aVL, with reciprocal ST depression in II, III, aVF 1
• Mid-LAD occlusion (between first septal and diagonal): ST elevation in V2-V4 but NOT V1; V1 is spared because basal septum is not involved 1
• Distal LAD occlusion (below septal and diagonal branches): ST elevation more prominent in V3-V6, less prominent in V2, with possible inferior ST elevation rather than depression 1

Critical Diagnostic Patterns in V1-V4

ST-Segment Elevation Patterns

Extensive Anterior/Anterobasal MI:

• ST elevation in V1-V4 PLUS I and aVL, WITH reciprocal ST depression in II, III, aVF indicates proximal LAD occlusion involving basal left ventricle, anterior/lateral walls, and septum 1
• More ST elevation in aVL than aVR, and more ST depression in lead III than lead II confirms leftward vector orientation 1

Anterior Wall MI (mid/distal LAD):

• ST elevation in V3-V6 WITHOUT ST depression in II, III, aVF suggests more distal LAD occlusion 1
• Absence of V1 involvement indicates sparing of basal septum 1

Right Ventricular Involvement:

• ST elevation in V1 (along with inferior leads) suggests proximal RCA occlusion with right ventricular infarction 1, 2, 3
• Critical caveat: When inferior MI is present, immediately record right-sided leads V3R and V4R, as ST elevation in these leads persists for much shorter duration than inferior ST elevation 2, 4, 3

ST-Segment Depression Patterns

Posterior/Posterolateral Ischemia:

• ST depression isolated to V1-V3 (with or without V2) may represent posterior wall involvement, typically from RCA or LCx occlusion 1
• This pattern requires recording posterior leads (V7-V9) for confirmation 4
• The American College of Cardiology recommends retaining the term "posterior" despite some controversy about anatomical terminology 1

Subendocardial Ischemia:

• ST depression in V1-V4 without elevation elsewhere suggests subendocardial ischemia from supply-demand mismatch, distal embolization, or subocclusion 5

T-Wave Abnormalities

Deep T-Wave Inversion (Wellens' Pattern):

• Deeply inverted T waves (>0.5 mV) in V2-V4, often with QT prolongation, after chest pain episode indicates severe proximal LAD stenosis with high risk of anterior MI 1
• This is a medical emergency requiring urgent angiography even without ongoing ST elevation 1

Juvenile Pattern (Age <16 years):

• T-wave inversion in V1-V3 is normal in adolescents under 16 years who have not completed puberty (present in 10-15% of white adolescent athletes) 1
• Does not require further evaluation unless symptoms, signs, or family history of cardiac disease are present 1

Athletic Variants:

• Early repolarization with J-point elevation and peaked T waves in V1-V4 occurs in up to 45% of Caucasian athletes and 63-91% of black athletes 1
• In black athletes specifically, convex ST elevation with T-wave inversion in V1-V4 is a normal variant and does not require investigation absent other pathological features 1

Conduction Abnormalities in V1-V4

Right Bundle Branch Block (RBBB)

• Complete RBBB: RSR' pattern in V1 with QRS ≥120 ms in adults; terminal rightward deflection ≥40 ms 1
• Incomplete RBBB: Same pattern but QRS 110-119 ms in adults 1
• Important: An rSR' pattern in V1-V2 with normal QRS duration is a normal variant in children 1

Left Bundle Branch Block (LBBB)

• Broad notched/slurred R waves in V5-V6, with absent q waves and R-peak time >60 ms 1
• Critical for MI diagnosis: LBBB obscures typical ST-segment criteria for acute MI; requires specialized criteria 1

Left Ventricular Hypertrophy (LVH)

• Isolated QRS voltage criteria for LVH in V1-V4 is part of normal spectrum in athletes and does not require evaluation 1

Systematic Interpretation Algorithm for V1-V4

1. Assess QRS morphology and duration:

   • Look for bundle branch blocks, hypertrophy patterns, or pathologic Q waves 1
   • Measure QRS duration (normal <120 ms in adults) 1

2. Evaluate ST segments:

   • Measure J-point elevation/depression relative to baseline 1, 5
   • Determine if elevation is concave (benign) vs. convex or horizontal (concerning) 1, 5
   • Check for reciprocal changes in other leads 1

3. Analyze T waves:

   • Measure amplitude and assess for inversion depth 1
   • Consider age, ethnicity, and athletic status for normal variants 1

4. Correlate with clinical context:

   • The ECG must always be interpreted with clinical symptoms and prior ECGs 6, 5
   • Dynamic changes over time are critical, especially in acute coronary syndrome 6, 5

5. If ST elevation in V1-V4 is present:

   • Check leads I, aVL for additional elevation (proximal LAD) 1
   • Check II, III, aVF for reciprocal depression (extensive anterior) or elevation (distal LAD) 1
   • If inferior leads also show ST elevation, immediately record V3R and V4R to assess for RV involvement 2, 4, 3

Common Pitfalls and Caveats

• Do not miss right ventricular infarction: ST elevation in V1 with inferior MI requires immediate right-sided lead recording, as this finding disappears rapidly 2, 4, 3
• Distinguish AMI from LVA: In patients with ST elevation and unknown history, calculate T-wave/QRS amplitude ratios in V1-V4 (if sum of ratios >0.22 or any single lead ratio ≥0.36, AMI is more likely than left ventricular aneurysm) 7
• Recognize Wellens' pattern: Deep T-wave inversion in V2-V4 after chest pain is a high-risk marker requiring urgent intervention, not reassurance 1
• Consider age and ethnicity: T-wave inversion in V1-V3 may be normal in adolescents <16 years and in black athletes with J-point elevation 1
• Lead placement matters: Abnormal findings in V1 may result from high or rightward lead placement rather than pathology 1
• LBBB obscures MI diagnosis: Standard ST-segment criteria do not apply; use specialized concordance criteria 1