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Monday, 4 February 2013

Pathological Q waves - or not?

When are the Q waves pathological?

How often do we see a computer generated report "Inferior infarct cannot be ruled out"  or "possible anterior infarct, aged undetermined".
This is a very common reason for otherwise well patients, or those with clearly non-cardiac chest pain, to be referred for a cardiology opinion. This can cause unnecessary alarm for the patient.

See previous #ECGclass - case 23,  for clinical details of the ECG below:
This 64yrs lady presented with mild exertional breathlessness:

Below are another couple of examples of patients who presented with non-cardiac sounding chest pain (prolonged at rest, with no exertional component) but were referred to RACPC because the ECG machine digital analysis reported 'possible infarct'. 

Unless of course, the clinical history or examination warranted referral (see post: The NICE Chest pain guidelines) , none of the three ECG's above show significant abnormality, which is alone worthy of a cardiology referral. 

Pathological Q waves

A pathological Q wave is a result of absence of electrical activity, following myocardial damage. They generally take several hours to develop after an MI, and usually persist indefinitely.
The exception to this is if seen during an acute MI, but the myocardial tissue is reperfused early by Primary PCI  (Percutaneous Coronary Intervention). The myocardial tissue can then recover, and the pathological Q waves disappear.

To be pathological there are a couple of simple rules of thumb:
  • The depth of the Q wave should be at least 25% of the depth of the associated R wave
  • The pathologically deep Q wave should appear in at least 2 contiguous leads (An isolated Q wave to lead III is a very common normal variant)
  • Any Q wave in leads V1- V3 with a duration of >0.02seconds is likely to be pathological. 
  • Many 'apparently' pathological Q-waves, often infact have a tiny R-deflection preceeding them - this can be so small it may need searching closely for. (seen in example 1 above).
  • A pathological Q wave may also be broad, in appearance, but again, must be seen in two contiguous leads. 
There are many more detailed criteria suggested for Pathological Q waves, if you are interested, search for either the ESC classification; the Minnesota Code Classification System; or the Novacode system.

The above rules, get me by!
Thank you, :)

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