Atrioventricular nodal reentry tachycardia (AVNRT) is the most common type of reentrant supraventricular tachycardia (SVT). Because it begins quickly and it’s termination is equally abrupt, a very nonspecific term, paroxysmal supraventricular tachycardia, has been coined to help describe this phenomenon. AVNRT may be functional rather than anatomic, as many young patients exhibit symptoms of this arrhythmia.
It can, however, be seen in patients with structural heart disease also.
Physiologically, the AV node is divided into two pathways that form the reentrant circuit. Most patients, during AVNRT, antegrade conduction occurs to the ventricle over the slow (alpha) pathway and retrograde conduction occurs over the fast (beta) pathway. (7) In most instances of AVNRT, a premature atrial contraction (PAC) is blocked in the fast pathway with a longer refractory period, thus conduction flows down the slow pathway with a shorter refractory period. As the impulse conducts to the ventricle in the alpha pathway (antegrade conduction), the beta pathway recovers. This allows the impulse to conduct retrograde up the beta pathway to the atrium and the atrial end of the slow pathway (retrograde conduction). AVNRT can also be induced by a premature ventricular contraction (PVC) (about 1/3 of documented cases).
Atypical AV nodal reentry can occur in the opposite direction, with antegrade conduction in the beta (fast) pathway and retrograde conduction in the (alpha) slow pathway. Approximately 60% of all patients with SVT have AVNRT. The true prevalence of the dysrhythmia is unknown, but it is common.
AVNRT is usually well tolerated, though it can be dangerous to those with structural heart disease or a history of congestive heart failure (CHF). In this popluation, it can cause angina, worsen CHF, and even lead to an acute myocardial infarction (AMI). It can also cause syncope and lead to falls in the elderly.
This is due to due to poor ventricular filling, decreased cardiac output, hypotension, and reduced cerebral perfusion.
Symptoms of AVNRT include, but are not limited to:
Palpitations, nervousness, anxiety, lightheadedness, neck pounding, neck and chest discomfort, and/or shortness of breath.
Heart rates range from 140-250 beats per minute with typical AVNRT.
Signs of left heart failure may develop or worsen in patients with poor left ventricular function.
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