supraventricular tachycardia

A supraventricular tachycardia (SVT) is a rapid rhythm of the heart in which the origin of the electrical signal is either the atria or the AV node. These rhythms require the atria or the AV node for either initiation or maintenance. This is in contrast to ventricular tachycardias, which are tachycardias that are not dependant on the atria or AV node.

Types of SVTs

Supraventricular tachycardia is a general term that describes a number of different arrhythmias of the heart, each with a different mechanism of impulse maintenance. While some treatment modalities can be applied to all SVTs with impunity, there are specific therapies that are available that can cure many of these arrhythmias that require intimate knowledge of how the arrhythmia is propogated. The SVTs can be simplistically separated into two groups, based on whether they involve the AV node for impulse maintenance or not. Those that involve the AV node can be terminated by maneuvers that decrease conduction through the AV node, while those that do not involve the AV node may be unmasked by the transient AV block caused by the decreased conduction through the AV node. SVTs that require the AV node for impulse maintenance include:

AV nodal reentrant tachycardia (AVNRT)
AV reentrant tachycardia (AVRT)
Permanent junctional reciprocating tachycardia (PJRT)
Junctional tachycardia

SVTs that do not require the AV node for impulse maintenance include:

Sinoatrial node reentrant tachycardia (SANRT)
Multifocal atrial tachycardia (MAT)
(Unifocal) Atrial tachycardia (AT)

Diagnosis

In the clinical setting, it is important to determine whether a wide-complex tachycardia is an SVT or a ventricular tachycardia, since they are treated differently. Ventricular tachycardia has to be treated appropriately, since it can quickly degenerate to ventricular fibrillation and death. A number of different algorithms have been devised to determine whether a wide complex tachycardia is supraventricular or ventricular in origin.¹ In general, a history of structural heart disease dramatically increases the likelyhood that the tachycardia is ventricular in origin.

References

1. Lau EW, Ng GA. Comparison of the performance of three diagnostic algorithms for regular broad complex tachycardia in practical application. Pacing Clin Electrophysiol. 2002 May;25(5):822-7. (Medline abstract)

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