Ø It is a
condition characterized by abnormal pathway between atria and ventricles(
Bundle of Kent).
Ø The
accessory pathway comprises fibers that are similar to that of the Purkinje
tissue( conducts rapidly and is rich in sodium channels).
Ø Mostly
these pathways conduct the impulse in the retrograde direction( concealed
accessory pathway).
Ø If it
conducts the impulse in antegrade direction then it causes distortion of the QRS
complex( Delta wave). Known as manifest accessory pathway.
As the AV node and the accessory
pathway have different conduction speed and the refractory periods, re-entry
circuits develop causing tachycardia.
ECG in this condition is
indistinguishable from AV Nodal Re-entry Tachycardia.
Carotid sinus pressure and IV
adenosine can control the tachycardia.
If atrial fibrillation occurs
it may produce dangerous rapid ventricular rate ( as accessory pathway
does not have rate limiting properties as AV node). This is known as
Pre-excited atrial fibrillation leading to collapse, syncope and even death and
should be treated as an emergency condition by DC cardioversion.
Management:
v Catheter
ablation is the first-line treatment (almost always curative).
v Prophylactic
anti-arrhythmic drugs( flecainide or propafenone) used to slow conduction and
prolong the refractory period of the accessory pathway.
v Long
term therapy - not preferred
What should not be given?
v Amiodarone
should not be used as its side effect profile cannot be justified.
v Digoxin
and verapamil shorten the refractory period and hence should not be used.
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