Sokolow–Lyon Index (SV1 + tallest R in V5 or V6): Explanation and Clinical Context
The Sokolow–Lyon Index is a classic electrocardiographic voltage criterion for detecting left ventricular hypertrophy (LVH). It is calculated as the depth of the S wave in lead V1 plus the amplitude of the tallest R wave in lead V5 or V6 (measured in millimetres). A summed value > 35 mm (3.5 mV) is the conventional cut-off suggesting LVH in adults. The criterion has good specificity but modest sensitivity, meaning it is more reliable when positive than when negative; many patients with anatomically proven LVH will not meet ECG voltage criteria. ECG voltage is influenced by body habitus, age, chest configuration, and comorbidities (for example, obesity and chronic lung disease reduce surface voltages). Therefore, a positive Sokolow–Lyon Index should prompt clinical correlation and, where indicated, echocardiographic assessment of left ventricular mass and geometry for confirmation and risk stratification.
References:
Key primary and validation literature, and modern reviews that define the index and report performance characteristics (sensitivity/specificity) are listed below.