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AV reciprocating tachycardia (AVRT)
AVRT belongs to a group of conditions known as
paroxysmal supraventricular tachycardia. These are characterized by
an abrupt onset and abrupt termination. AVRT is caused by an
accessory pathway in the conduction system between atria and
ventricles (e.g. Wolf-Parkinson-White syndrome).
In AVRT the accessory pathway bypasses the AV node
into the ventricle (orthodromic - retrograde "narrow complex" /
antidromic - antegrade "wide complex").
In orthodromic AV reciprocating tachycardia (AVRT) there is conduction down the AV node and His-Purkinje system (orthodromic), then
retrograde conduction up the accessory bypass tract (a reentrant circuit
or an abnormal or extra electrical pathway in the heart, a kind of "short
circuit.") to re-excite the atria. The accessory AV connection bypass
tract represents a congenital defect, with an incidence of 3 in 1000 in
the general population.
Symptoms and signs
These includes attacks of palpitations, dizziness and syncope,
dyspnea, chest pain as well as anxiety. These attacks start and
terminate abruptly (i.e. paroxysmal).
Orthodromic tachycardias typically occur at rates of l50-250 beats
per minute. A retrograde P wave may be seen at the end of the QRS complex
or in the early part of the ST segment. Typically, the onset of orthodromic
tachycardia is abrupt, initiated by a premature atrial or ventricular
complex. Concealed accessory bypass tracts account for up to 30% of clinical
Initial therapy of acute episodes of narrow-complex
tachycardias, particularly AVRT includes vagal maneuvers (e.g. carotid
massage, Valsalva maneuver) and, if unsuccessful, bolus administration
of short-acting agents that slow or block AV nodal conduction, such as
adenosine, verapamil, or diltiazem.
Chronic drug therapy may include calcium
channel antagonists, beta-adrenergic antagonists, or digoxin. Radiofrequency
catheter ablation now can obviate the need for such therapy in most patients.
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