Cardiovascular

Supraventricular Tachycardia (SVT)

A re-entry circuit running through the atrioventricular (AV) node, either within it or looping via an accessory pathway, fires at a fixed rate and gives abrupt regular narrow-complex tachycardia.

Definition

Supraventricular tachycardia is any tachycardia arising above the ventricles. In practice the SVT pathway means a regular narrow-complex paroxysmal tachycardia, most often AVNRT or orthodromic AVRT. Atrial fibrillation, atrial flutter, focal atrial tachycardia and sinus tachycardia are separated out because their treatment differs.

First principles

SVT names where the rhythm starts, not how it works

Any rhythm arising above the ventricles is supraventricular, but atrial fibrillation, atrial flutter, focal atrial tachycardia and sinus tachycardia behave nothing like the re-entry circuits this chapter covers. In practice the SVT pathway means a regular narrow-complex tachycardia, usually AV nodal re-entrant tachycardia (AVNRT) or orthodromic AV re-entrant tachycardia (AVRT). Flutter with fixed block is the mimic that catches people out.

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