Monday, 13 September 2010

MRCP revision battle 10.7: Causes of low-voltage complexes on ECG

'Low voltage complex' on ECG is defined as:
  • QRS amplitude <5mm in all limb leads and/or
  • QRS amplitude <10mm in all chest leads

The causes of low voltage complexes can be split into 2 main groups: increased distance from leads to heart or infiltrative disease of heart.

Using these divisions:
  1. increased distance from leads to heart:
    • emphysema/COPD
    • pericardial effusion
    • severe obesity
    • pleural effusion
  2. infiltrative disease of heart/problems with heart itself: 
    • amyloid
    • haemochromatosis
    • cardiomyopathies
    • global ischaemia

Myxoedema can also cause low complex ECGs but my search for why this is (?caused by myxoedema or ?caused by effects of myxoedema) proved fruitless... please let me know if you have the answer!

If you see an ECG with alternating normal complexes and low-voltage complexes, you are looking at electrical alternans which tends to be a sign of pericardial effusion/cardiac tamponade.  Click here to see an image of it.

So today's battles are over.  If you want to undertake the war to see how much of yesterday's battles you recall, please click here