SOKOLOW INDEX: MEASUREMENT, ELECTROCARDIOGRAM, AND CLINICAL SIGNIFICANCE - MEDICINE - 2025

The Sokolow index is a criterion that is used to diagnose the enlargement of the left ventricular chamber of the heart, based on the measurement of the waves that represent the left ventricle in the electrocardiogram.

The electrocardiogram is a non-invasive study that graphically represents the electrical activity of the heart. It is widely used as it is inexpensive, easy to use and provides important information on the patient's cardiac health status.

Electrocardiogram. By Andrewmeyerson - Own work, CC BY-SA 3.0, The electrocardiogram is printed on a millimeter sheet. From the sum of the small squares that the amplitude occupies a wave, the voltage of the same is obtained. The Sokolow index is the result of the sum of the amplitude of the S wave, in the precordial vectors V1 plus the R wave in V5 or V6. Thus: S V1 + RV 5 or 6 = Sokolow index.

A result greater than 35 mm indicates that the patient has left ventricular hypertrophy, meaning that his left ventricular heart chamber is thicker than normal.

This type of anomaly is a consequence of diseases such as arterial hypertension, which overloads the activity of the heart muscle due to the high pressures that it must overcome to pump blood.

Sokolow and Lyon

The North American cardiologists Maurice Sokolow and Thomas Lyon, based their professional careers on the study of arterial hypertension and its complications.

One of the most frequent morbidities associated with this disease is left ventricular hypertrophy, which is nothing more than the thickening of the muscular wall of the left ventricle of the heart.

Left ventricular hypertrophy. By Patrick J. Lynch, medical illustrator - Patrick J. Lynch, medical illustrator, CC BY 2.5, These specialists described a way to calculate the state of the heart muscle, through the measurement of the voltage of some waves in the electrocardiogram. The technique was published in 1949 in the scientific journal American heart journal and was entitled "The Ventricular Complex in Left Ventricular Hypertrophy Obtained by Limb and Precordial Unipolar Electrodes."

The method is called the Sokolow-Lyon index, and it is one of the criteria currently used to determine left ventricular hypertrophy in patients with heart disease, especially those with high blood pressure.

Electrocardiogram

The electrocardiogram is a non-invasive and painless study which gives an objective result of the cardiac electrical activity.

To do this, 10 devices called electrodes are placed. 6 of them go to specific points on the chest and the other 4 go to the wrists and ankles. The precordial electrodes (V) are arranged as follows:

Positioning of the precordial electrodes. By Mikael Häggström - Own work, CC0, 1: fourth intercostal space to the right of the sternum.

2: fourth intercostal space to the left of the sternum.

3: at the midpoint of the line connecting V2 to V4.

4: at the junction of the fifth intercostal space with the midclavicular line.

5: parallel to V4 but in the anterior axillary line.

6: parallel to the previous ones, but in the mid axillary line.

In this study, time, expressed in seconds, is measured in the horizontal plane. While the voltage, expressed in volts, in the vertical plane.

Printed electrocardiogram. From en: User: Nunh-huh - en: Image: EKG2.png, CC BY-SA 3.0, Therefore, on the graph paper where the electrocardiogram is printed, a 1 mm square on the horizontal plane represents 0.04 seconds and 0.1 millivolts on the vertical plane.

Waves and voltage

By international convention, the first wave that appears on the electrocardiogram is called the P wave and represents the state of atrial depolarization.

Ventricular depolarization, that is, the electrical activity of the ventricle, is represented by the so-called QRS complex where Q translates the depolarization of the ventricular septum; R is a positive wave that indicates the depolarization of the ventricular muscle and S is a negative wave that represents the late depolarization of the ventricle.

Waves and voltages. By The original uploader was Klox at English Wikipedia. Late versions were uploaded by Andrew pmk at en.wikipedia. - Transferred from en.wikipedia to Commons., CC BY-SA 3.0, After this complex, a positive wave of low amplitude is observed, the T wave, which indicates the repolarization of the ventricle.

Knowing these parameters and their normal values, any abnormality of the cardiac electrical system can be inferred just by studying the electrocardiogram in depth.

Sokolow index measurement

Doctors Sokolow and Lyon were pioneers in implementing measurements of the amplitude of the waves that reflect the state of the left heart, to diagnose anomalies in this region.

The measurement technique proposed by them consists of adding the S wave in V1 with the R wave in V5 or V6. This result should be less than 3.5 mV or 3.5 mm. A result greater than this value indicates an increase in the thickness of the left ventricle, which is pathological in a patient with arterial hypertension.

Electrocardiogram showing all leads to obtain the Sokolow-Lyon index. By Michael Rosengarten BEng, MD.McGill - EKG World Encyclopedia http://cme.med.mcgill.ca/php/index.php, courtesy of Michael Rosengarten BEng, MD.McGill, CC BY-SA 3.0, https: // commons.wikimedia.org/w/index.php?curid=24372709

The Sokolow-Lyon index very accurately diagnoses left ventricular hypertrophy, reaching up to 92% specificity. The problem is that its sensitivity reaches only 25%.

This means that it is very likely that it will interpret false negatives, identifying as healthy patients who actually have a hypertrophy of the ventricle in its initial stages.

The low sensitivity of the index is explained by the fact that when the study was conducted in 1949, the subjects evaluated were untreated hypertensive with very advanced disease. Therefore they had obvious hypertrophy.

Currently other criteria are used, together with the Sokolow index, to identify patients with left ventricular thickening. One of the most used is the Cornell index, in which measurements are adjusted for sex.

Importance and clinical value

The Sokolow index demonstrated that the electrocardiogram is a tool that can provide diagnostic data for serious morbidities of important diseases such as high blood pressure.

The gold standard for detecting ventricular hypertrophy is the echocardiogram. However, this study is expensive and requires trained personnel to conduct and analyze it.

The importance of the Sokolow index is that it is based on the measurement from the electrocardiogram, which is a basic study of the clinical examination, it is also inexpensive, easy to perform and can be analyzed by any general practitioner.

Based on the electrocardiogram, the doctor makes the diagnostic approach to ventricular hypertrophy and this patient will be referred to the cardiologist to be studied in depth.

References

1. Park, J. K; Shin, J. H; Kim, S. H; Lim, Y. H; Kim, K. S; Kim, S. G; Shin, J. (2012). A comparison of cornell and sokolow-lyon electrocardiographic criteria for left ventricular hypertrophy in korean patients. Korean circulation journal. Taken from: ncbi.nlm.nih.gov
2. Noble, R. J; Hillis, J. S; Rothbaum, DA (1990) Clinical Methods: The History, Physical, and Laboratory Examinations. Taken from: ncbi.nlm.nih.gov
3. Barrios, V; Calderón, A. (2004). Diagnosis of left ventricular hypertrophy by electrocardiography: Usefulness of the new criteria. Costa Rican Journal of Cardiology. Taken from: scielo.sa.cr
4. González, J; Cea, L; Bertomeu, V; Aznar, J. (2007). Electrocardiographic criteria for left ventricular hypertrophy and cardiovascular risk profile in hypertensive patients. VIIDA 2007 study. Taken from: revespcardiol.org
5. González, J; Martinez, B; Rivero, O; Salgado, A; Díaz, P. (2013). Electrocardiographic diagnosis of Left Ventricular Hypertrophy in hypertensive patients. Utility of the product duration by voltage of the QRS. Havana magazine of medical sciences. Taken from: scielo.sld.cu
6. Schröder, J; Nuding, S; Müller-Werdan, U; Werdan, K; Kluttig, A; Russ, M; Medenwald, D. (2015). Performance of Sokolow-Lyon index in detection of echocardiographically diagnosed left ventricular hypertrophy in a normal Eastern German population - results of the CARLA study. BMC cardiovascular disorders. Taken from: ncbi.nlm.nih.gov
7. Vijan, S. G; Manning, G; Millar-Craig, MW (1991). How reliable is the electrocardiogram in detecting left ventricular hypertrophy in hypertension? Postgraduate medical journal. Taken from: ncbi.nlm.nih.gov
8. Rodrigues, S; D'Angelo, L; Pereira, A; Krieger, J; Mill, J. (2008). Revision of the Sokolow-Lyon-Rappaport and cornell voltage criteria for left ventricular hypertrophy. Brazilian archives of cardiology. Taken from: scielo.br