AVRT (atrioventricular reciprocating tachycardia) is a form of paroxysmal supraventricular tachycardia (SVT) caused by a re-entrant circuit that includes an accessory pathway, an abnormal electrical connection between the atria and ventricles that exists outside the normal AV node. This accessory pathway allows electrical impulses to bypass the AV node and travel directly between the atria and ventricles. The circuit loops between the normal conduction system travelling in one direction and the accessory pathway travelling in the opposite direction, sustaining a rapid tachycardia.
The most well-known condition involving an accessory pathway is Wolff-Parkinson-White (WPW) syndrome, in which the accessory pathway is detectable on a resting ECG as a characteristic delta wave (a slurring of the initial part of the QRS complex) and a short PR interval. Not all accessory pathways are visible on a resting ECG: concealed pathways conduct only in one direction (retrogradely, from ventricles to atria) and do not produce pre-excitation on the ECG. AVRT caused by a concealed pathway is the most common form.
AVRT is clinically important because certain accessory pathways, particularly those in WPW syndrome with a short refractory period, can conduct atrial fibrillation at very rapid rates directly to the ventricles, bypassing the normal rate-limiting function of the AV node. This can trigger ventricular fibrillation and sudden cardiac arrest. For this reason, WPW with a symptomatic accessory pathway is considered a significant risk and ablation is recommended.
Catheter ablation, which destroys the accessory pathway using radiofrequency energy or cryotherapy delivered via a catheter threaded to the heart, is the definitive treatment for AVRT and is highly effective, with success rates above 95 percent. It is recommended for symptomatic AVRT and for WPW patients with high-risk accessory pathway characteristics. Before ablation, an electrophysiology (EP) study maps the pathway to determine its location and properties. Medications such as beta-blockers, flecainide or verapamil may be used for rate control in some cases, but are not suitable for all patients with WPW.
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