ECG Case 063

Overview

The most striking abnormality on this ECG is extremely low QRS voltage, in this case due to severe myxoedema.

Definition

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 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

Specific causes of low voltage 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, haemochromatosis; constrictive pericarditis; and scleroderma.
  
• Loss of viable myocardium: Previous massive MI; end-stage dilated cardiomyopathy
  

Most important cause:

Massive pericardial effusion with triad of:

• Low voltage
• Tachycardia
• Electrical alternans

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

Further Reading

• Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
• Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
• Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
• Rawshani A. Clinical ECG Interpretation ECG Waves
• Smith SW. Dr Smith’s ECG blog.
• Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF