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Atrioventricular Reentry Tachycardia (AVRT)

Atrioventricular Reentry Tachycardia (AVRT) is a form of paroxysmal supraventricular tachycardia that occurs in patients with accessory pathways, usually due to formation of a reentry circuit between the AV node and accessory pathway. ECG features depend on the direction of conduction, which can be orthodromic or antidromic.

In orthodromic AVRT, anterograde conduction is via the AV node, producing a regular narrow complex rhythm (in the absence of preexisting bundle branch block)
In antidromic AVRT, anterograde conduction is via the accessory pathway (AP), producing a regular wide complex rhythm. This can be difficult to distinguish from ventricular tachycardia (VT)
Often triggered by premature atrial or premature ventricular beats
In both forms, the features of preexcitation are lost

What is AVNRT?

Atrioventricular Nodal Reentrant Tachycardia is a type of supraventricular tachycardia (ie it originates above the level of the Bundle of His) and is the commonest cause of palpitations in patients with hearts exhibiting no structurally abnormality.

Clinical Features of AVNRT

AVNRT is typically paroxysmal and may occur spontaneously in patients or upon provocation with exertion, coffee, tea or alcohol. It is more common in women than men (~75% of cases occurring in women) and may occur in young and healthy patients as well as those suffering chronic heart disease.
Patients will typically complain of the sudden onset of rapid, regular palpitations. The patient may experience a brief fall in blood pressure causing presyncope or occasionally syncope.
If the patient has underlying coronary artery disease the patient may experience chest pain similar to angina (tight band around the chest radiating to left arm or left jaw).
The patient may complain of shortness of breath, anxiety and occasionally polyuria due to elevated atrial pressure releasing atrial natriuretic peptide.
The tachycardia typically ranges between 140280 bpm and is regular in nature. It may cease spontaneously (and abruptly) or continue indefinitely until medical treatment is sought.
The condition is generally well tolerated and is rarely life threatening in patients with preexisting heart disease.

Pathophysiology and types of AVNRT

AVNRT is caused by a reentry circuit in or around the AV node.
The circuit is formed by the creation of two pathways forming the reentrant circuit, namely the slow and fast pathways.
The fast pathway is usually anteriorly situated along septal portion of tricuspid annulus with the slow pathway situated posteriorly, close to the coronary sinus ostium.
Sustained reentry occurs over a circuit comprising the AV node, His Bundle, ventricle, accessory pathway and atrium.
The various forms of AVNRT can be described in terms of ECG appearance such as RP intervals or Slow/Fast pathway dominance.

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