THE LOW VOLTAGE Electrocardiogram (ECG/EKG)

The Low Voltage ECG 

A  “low voltage,” ECG is a  sign that something is getting in the way of the electrical conduction of the heart and the EKG leads on the patient’s chest. 

Low voltage is concerning for a condition where fluid collects between the heart’s muscle and the thin protective sac around it (the pericardium), called a pericardial effusion. 

Untreated severe pericardial effusion can eventually stop the heart from beating.

The QRS is said to be low voltage when:

The amplitudes of all the QRS complexes in the limb leads are < 5 mm; or

The amplitudes of all the QRS complexes in the precordial leads (V1-V6) are < 10 mm

Mechanisms

Low voltage is produced by:

  • The “damping” effect of increased layers of fluid, fat, or air between the heart and the recording electrode

  • Loss of viable myocardium

  • Diffuse infiltration or myxoedematous involvement of the heart

Causes

The most important cause is massive pericardial effusion, which produces a triad of:

  • Low voltage

  • Tachycardia

  • Electrical alternans

Patients with this triad need to be immediately assessed for clinical or echocardiographic evidence of tamponade.

Other causes of a low voltage ECG include:

  • Fluid: 

    • Pericardial effusion; Pleural effusion

  • Fat: 

    • Obesity

  • Air: 

    • Emphysema; Pneumothorax

  • Infiltrative / Connective Tissue Disorders

  • Myxoedema

  • Infiltrative myocardial diseases — 

    • i.e. restrictive cardiomyopathy due to amyloidosis, sarcoidosis, hemochromatosis

  • Constrictive pericarditis

  • Scleroderma

  • Loss of viable myocardium:

    • Previous massive MI

    • End-stage dilated cardiomyopathy

Cheryl