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Wednesday, 7 May 2014

Summer 1 - Wolf-Parkinson-White Syndrome

Welcome back all to a summer term of ECG diagnsotic fun! :)

If you are new to ECGclass - Welcome! 

Before we start you may like to read this to help explain what it's all about - #ECGclass and how it works



So here we go. 
Summer Term - Case 1

A 36 yrs old lady presents to you with a history of ‘blackouts’.
You assume these are some sort of vaso-vagal attack and ask about her menses, her alcohol habits and any other history but she shares no helpful relevations.


Examination is entirely normal, as are her FBC and electrolytes.


Does the explanation for her blackouts, lie in her abnormal ECG obtained below?


What are your thoughts?






Discussion:

The ECG shows the ‘delta wave’ of Wolf Parkinson White (WPW) Syndrome
This may not always be seen and can appear intermittently on different ECG’s on the same patient.  
It is often associated with a short PR interval (<3 small squares, <0.12sec). Thus, it is one of a group of conditions referred to as “pre-excitation” syndromes.
WPW is the commonest form of Atrio-Ventricular Re-entrant tachycardias (AVRT).

WPW Syndrome

Between 1.5 - 3 per 1000 population have the ECG signs of WPW. 
Two-thirds of these experience symptoms. (Include palpitations, dizzy spells or syncope)
In one-third the ECG finding may be detected incidentally. 

Although many remain symptom free throughout their lives, there is always a small risk of sudden cardiac death. (< 0.6%)

WPW in commoner in younger adults (age related fibrosis reduces its incidence).

The pre-excitation is caused by the presence of an abnormal accessory conduction pathway between the atria and ventricles. This pathway is called ‘The Bundle of Kent’.  Impulses which travel down this pathway, will cause the ventricles to contract prematurely. It is this premature contraction of the ventricles, which give rise to the short PR interval and the delta wave.  In turn this can give rise to a supraventricular tachycardia, or more specifically, an AVRT. 

ECG Features of WPW:
  • ·        Short PR interval
  • ·       Widened QRS due to presence of delta wave – Slurring of the upslope of the QRS complex:


HOWEVER, the ECG finding alone does not constitute the ‘syndrome’.  
To be truly diagnostic, there needs to be a history of syncope/palpitations as a result of episodes of Paroxysmal tachycardia.


So….What Now?
Given that this lady has been having symptoms, it would be safest to assume these are as a result of her WPW.  She should be referred urgently to an electrophysiologist cardiologist for risk stratification and further management.

Investigations:

  • ·       A 24hr ECG will be useful to look for runs of VT.
  • ·       An exercise ECG helps stratify risk – if the delta waves vanish at higher heart rates, the prognosis is better. (ie. There is reduced risk of fatal tachycardia if the aberrant pathway doesn’t conduct at higher rates).




Management Options:
  • ·       Radio frequency ablation
  • ·       Vagal stimulation
  • ·       Drugs –acutely (adenosine)
  • ·       Drugs – longer term (NOT AV nodal blockers)
  • ·       DC cardioversion (if WPW with Atrial fibrillation)
  • ·       Overdrive pacing (not common)




Well done if you recognized the delta waves – or the short PR interval!
(The degree of the delta wave, and the duration of the PR interval can vary widely from case to case – this can help identify the point to where the action potential may exist.)

Thanks to all who took part this evening. 
'Till next week! :)







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