The impulse transmitted down the fast pathway enters the distal end of the slow pathway and the two impulses cancel each other out During normal sinus rhythm, electrical impulses travel down both pathways simultaneously.Mechanism of re-entry in “slow-fast” AVNRT:ġ) A premature atrial contraction (PAC) arrives while the fast pathway is still refractory, and is directed down the slow pathwayĢ) The ERP in the fast pathway ends, and the PAC impulse travels retrogradely up the fast pathwayģ) The impulse continually cycles around the two pathways Initiation of re-entry In comparison to AVRT, which involves an anatomical re-entry circuit (Bundle of Kent), in AVNRT there is a functional re-entry circuit within the AV node. The condition is generally well tolerated and is rarely life threatening in patients with pre-existing heart disease.It may self-resolve or continue indefinitely until medical treatment is sought The tachycardia typically ranges between 140-280 bpm and is regular in nature.Rarely, polyuria due to elevated atrial pressures causing release of atrial natriuretic peptide.Chest pain, especially in the context of underlying coronary artery disease.Presyncope or syncope due to a transient fall in blood pressure.Patients will typically complain of the sudden onset of rapid, regular palpitations.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.AVNRT is typically paroxysmal and may occur spontaneously or upon provocation with exertion, caffeine, alcohol, beta-agonists (salbutamol) or sympathomimetics (amphetamines). This is the commonest cause of palpitations in patients with structurally normal hearts.
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