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 cases.
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.