AV nodal reentrant tachycardia (AVNRT) occurs in the presence of a reentrant circuit (an abnormal or extra electrical pathway in the heart, a kind of "short circuit.") involving two anatomically and physiologically distinct pathways (fast and slow pathways) linking the right atrium to the AV node. AVNRT is the most common paroxysmal supraventricular tachycardia (PSVT).
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).
ECG readings
In typical (slow-fast) AVNRT, activation spreads from the atrium to the AV node via the slow pathway and returns to the atrium via the fast pathway. The ECG reveals a rate usually between l50-250 bpm-with a P wave obscured by the nearly synchronous atrial and ventricular depolarization-and a QRS complex that is either normal (base-line) or broadened, owing to rate-related aberrancy In atypical (fast-slow) AVNRT, the activation pathway is reversed, the rate is similar to that for typical AVNRT but an inverted P wave usually is readily apparent in the T wave, resulting in a normal or minimally prolonged PR interval.
Treatment
Initial therapy of acute episodes of narrow-complex tachycardias, particularly AVNRT 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.
