Low Voltage

The traditional definition of low voltage is QRS amplitudes less than 5 mm in all limb leads or less than 10 mm in all precordial leads. The differential for low voltage can be conceptualized by considering two categories: cardiac abnormalities resulting in diminished impulse generation and increased impedance related to attenuating substances between the heart and surface leads (fluid, air, or adipose). Cardiac causes include prior infarcts, infiltrative cardiomyopathies like amyloidosis, and hypothyroidism. Extracardiac causes include pericardial processes like pericardial effusion or constrictive calcific pericarditis, chronic obstructive pulmonary disease, pleural effusion, subcutaneous or mediastinal emphysema, and obesity. The combination of low voltage and bradycardia should raise the concern for hypothyroidism/myxedema.



  1. Danzi S, Klein I. Thyroid disease and the cardiovascular system. Endocrinology and Metabolism Clinics of North America. 2014;43(2):517-528.
  2. Madias JE. Low QRS voltage and its causes. Journal of Electrocardiology. 2008;41(6):498-500.
  3. Ingram D, Strecker-McGraw MK. Electrical Alternans. StatPearls. Published online on August 11, 2021. Accessed January 3, 2022.