Clinical Review

ABC of clinical electrocardiography

Junctional tachycardias

BMJ 2002; 324 doi: 10.1136/bmj.324.7338.662 (Published 16 March 2002)
Cite this as: BMJ 2002;324:662.1

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  1. Demas Esberger,
  2. Sallyann Jones,
  3. Francis Morris

    Any tachyarrhythmia arising from the atria or the atrioventricular junction is a supraventricular tachycardia. In clinical practice, however, the term supraventricular tachycardia is reserved for atrial tachycardias and arrhythmias arising from the region of the atrioventricular junction as a result of a re-entry mechanism (junctional tachycardias). The most common junctional tachycardias are atrioventricular nodal re-entrant tachycardia and atrioventricular re-entrant tachycardia.

    Mechanism of atrioventricular nodal re-entrant tachycardia showing the slow and fast conduction routes and the final common pathway through the lower part of the atrioventricular node and bundle of His

    Atrioventricular nodal re-entrant tachycardia

    Atrioventricular nodal re-…

    This is the most common cause of paroxysmal regular narrow complex tachycardia. Affected individuals are usually young and healthy with no organic heart disease.

    Mechanism

    In atrioventricular nodal re-entrant tachycardia there are two functionally and anatomically different distinct pathways in the atrioventricular node, with different conduction velocities and different refractory periods. They share a final common pathway through the lower part of the atrioventricular node and bundle of His. One pathway is relatively fast and has a long refractory period; the other pathway is slow with a short refractory period. In sinus rhythm the atrial impulse is conducted through the fast pathway and depolarises the ventricles. The impulse also travels down the slow pathway but terminates because the final common pathway is refractory.

    A premature atrial impulse finds the fast pathway refractory, allowing conduction only down the slow pathway (left). By the time the impulse reaches the His bundle, the fast pathway may have recovered, allowing retrograde conduction back up to the atria—the resultant “circus movement” gives rise to slow-fast atrioventricular nodal re-entrant tachycardia (right)

    The slow pathway has a short refractory period and recovers first. An atrioventricular nodal re-entrant tachycardia is initiated, for example, if a premature atrial beat occurs at the critical moment when the fast pathway is still …

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