WPW

 

Etiology:

    1. WPW is characterized by the presence of accessory pathway (AP). The
        activation of the ventricle during sinus rhythm occurs via both  AV node and
        AP.   During tachycardia, ventricular activation occurs  via  one of the following
        modes:

      - Orthodromic i.e. ventricle is activated via AV node and impulse returns to
        atria via AP or

      - Antidromic  in which the ventricle is activated via  AP and impulse returns
         to atria via AV node.

          2. WPW occurs in healthy  young  people. Occasionally myopathy or congenital
              heart disease may be present.

S & S:

    1. Pt may be completely asymptomatic or experience palpitations and/or
       hemodynamic instability.

DX:

    1. delta wave and short PR occurs in sinus rhythm. ST/T changes occur given
        abnormal repol-depol.

    2. In orthodromic tachycardia (most common), since activation occurs via AV
       node, wave is not evident and QRS is not wide. This presents  as one of  the
       causes of narrow complex SVT (reentrant SVT).

    3. In antidromic tachycardia , on the other hand,  AP is in charge of ventricular
       activation and  thus QRS is wide and  wave is visible. This can be one of the
       causes of  wide complex SVT.

    4. WPW can be further distinguished into type I and type II.  In type I, L ventricle
       is activated first and we'll see positive R wave in V1( one of  5 causes of positive
       R wave in V1). In     type II, R ventricle  is activated  first and  V1 has negative QS.

Treatment:

    1. Asymptomatic pt in sinus requires no treatment. If  this has to be instituted
       (pt is refusing EPS or  refuses admission), quinidine, Procainamide or B-blocker
       can be used.

    2. Pt in tachycardia is treated as any other narrow or wide complex  based  on
       pt's stability or instability.

    3. Not uncommonly  pt with WPW may suffer from A.flut or A.fib. These, in the
       presence of WPW and tachycardia must not be treated with CCB, Adenosine or  
       Dig since they can block AVN and promote acceleration via AP. Procainamide is
       the treatment of choice if A. fib and wide complex tachycardia have moderate
       ventricular response.  If ventricular response to A.fib is very rapid, Cardioversion
       with 100 -200 j is used. Procainamide dose is 10-15 mg/kg @ 50 mg/min till
       arrhythmia is controlled, QRS prolongs by 50%, hypotension develops or a max
       dose of 17 mg/kg were given.

      See also A.fib/Treatment/6.

 

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