ECG criteria
- Measure the depth of the S wave in lead V1 (in mm)
- Measure the height of the R wave in lead V5 or V6 — take the greater of the two values (in mm)
- Add S(V1) + R(V5 or V6)
- A sum of ≥35 mm (3.5 mV) corresponds to the voltage criterion for LVH in adults
- R in aVL ≥11 mm is a separate independent voltage criterion for LVH, not part of the Sokolow-Lyon index; the Gubner-Ungerleider criterion is another indicator: R(I) + S(III) >25 mm
- Check the recording calibration (1 mV = 10 mm at standard gain), otherwise the index is distorted
- Evaluate concomitant LVH signs: left axis deviation, QRS widening, secondary ST-T changes
What it looks like on ECG
The index is calculated from wave amplitudes in the chest leads. It takes the S depth in V1 (reflecting the posterior orientation of the depolarization vector with increased LV mass) and the R height in V5 or V6 (reflecting the predominant vector directed toward the left chest electrodes). Measured in millimeters at a known calibration, usually 10 mm/mV; recording speed does not affect the amplitude calculation.
| Lead | What is measured | Typical role |
|---|---|---|
| V1 | S depth | posterior/right vector |
| V5 or V6 | R height | left/lateral vector |
A sum of ≥35 mm (3.5 mV) corresponds to the voltage criterion for LVH in adults; this finding alone neither confirms nor excludes anatomical LVH and must be evaluated alongside other ECG signs and imaging data. Some sources also use a separate criterion of R(V5 or V6) >26 mm as an independent high-voltage sign. LVH is often accompanied by left axis deviation, moderate QRS widening (without complete block), and in advanced cases, ST depression and T-wave inversion in I, aVL, V5–V6 (signs of systolic overload, 'strain pattern').
Mechanism
In LV hypertrophy, muscle mass increases, as do the duration and amplitude of LV wall depolarization. The depolarization vector shifts to the left and posteriorly, enhancing the negative component in the right chest leads (deep S in V1) and the positive component in the left leads (tall R in V5–V6). The sum of these amplitudes approximately reflects the degree of muscle mass increase, although there is no linear correlation with true myocardial mass (by echocardiography).
Causes
- Arterial hypertension (most common cause)
- Aortic stenosis and other valvular diseases with LV pressure overload
- Hypertrophic cardiomyopathy
- Coarctation of the aorta
- Intensive physical training (physiological LVH in athletes)
- Obesity (may be associated with remodeling and LVH, but often decreases QRS amplitude and masks its ECG signs)
Differential diagnosis
- Normal high voltage in young, lean individuals and athletes — isolated index elevation without other signs of LVH (axis deviation, ST-T) should be interpreted with caution
- Left bundle branch block — wide QRS with a different morphology; voltage criteria for LVH are not applied in this case
- WPW syndrome with a delta wave — pseudohypertrophic voltages due to abnormal conduction
- Septal hypertrophy in HCM — voltage can be high without the typical overload configuration
Clinical significance and management
A high Sokolow-Lyon index is an independent marker of increased cardiovascular risk (myocardial infarction, stroke, heart failure, sudden death), especially in patients with arterial hypertension. The specificity of the criterion is high (about 85–100%), but sensitivity is low (20–30%): a normal index does not rule out LVH. The physician should indicate the presence of LVH voltage criteria in the report and, when clinically indicated (hypertension, murmur, dyspnea), refer the patient for echocardiography to confirm and assess the degree of hypertrophy, LV geometry, and systolic function. An isolated finding without clinical context requires no emergency action.
Common interpretation errors
- Failing to check recording calibration — with non-standard gain (5 mm/mV or 20 mm/mV), the index will be severely distorted
- Applying the criterion in wide QRS conditions (LBBB, WPW), where LVH voltage thresholds are not valid
- Assuming a normal index rules out LVH due to the low sensitivity of the method
- Disregarding age and sex — criteria were developed mainly for the adult population; different standards apply to children and adolescents
- Confusing V5 and V6 during measurement — the index uses the greater of the two R values, not an arbitrarily chosen lead
1. Which leads are used to calculate the Sokolow-Lyon index?
The index adds the depth of S in V1 and the height of R in V5 or V6 (the larger value).
2. What threshold level for the sum of S(V1)+R(V5/V6) is considered an LVH criterion in adults?
A sum of ≥35 mm (3.5 mV) is the classical threshold of the Sokolow-Lyon index for diagnosing LVH.
3. Why can the Sokolow-Lyon index not be reliably applied in left bundle branch block?
In LBBB, a wide aberrant QRS alters wave amplitudes due to conduction disturbance rather than hypertrophy, making LVH voltage criteria inapplicable.
Frequently asked questions
How to calculate the Sokolov–Lyon index?
The depth of the S wave in V1 and the height of the R wave in V5 or V6 are added together (taking the larger value). A sum of ≥35 mm (3.5 mV) corresponds to the LVH voltage criterion at standard recording calibration, but must be evaluated in conjunction with other signs and clinical data.
Is an elevated Sokolov–Lyon index dangerous?
This is not an acute condition on its own, but persistent elevation of the index is associated with an increased risk of cardiovascular events, especially in the setting of hypertension. It requires confirmation by echocardiography and risk factor assessment.
Why might the index be normal in the presence of true LVH?
The sensitivity of the criterion is low (about 20–30%), so normal voltage does not exclude hypertrophy. Echocardiography more accurately reflects true myocardial mass.
Can the Sokolov–Lyon index be used in left bundle branch block?
No, in wide QRS conditions (LBBB, WPW), LVH voltage criteria are not valid because the complex morphology is distorted by abnormal conduction.
How does the Sokolov–Lyon index differ from the Cornell criterion?
The Sokolow-Lyon index uses leads V1 and V5/V6, whereas the Cornell criterion uses R in aVL and S in V3, with different sex-specific thresholds. Both criteria are independent and are sometimes used together to increase diagnostic sensitivity.
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Related terms
More in the section «Hypertrophy and Chamber Enlargement»
Sources
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice, 6th ed.
- Hampton J. The ECG Made Easy
- Orlov V.N. Guide to Electrocardiography
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, 2009
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.