Clinical meaning
Supraventricular tachycardia (SVT) is a broad term for tachyarrhythmias originating above the bundle of His, but clinically it most often refers to paroxysmal SVT (PSVT) — a regular, narrow-complex tachycardia with sudden onset and termination. The two most common mechanisms are: (1) AV Nodal Reentrant Tachycardia (AVNRT, ~60% of PSVT) — involves dual AV nodal pathways (fast and slow) creating a micro-reentry circuit within or near the AV node. Typically, the impulse travels antegrade down the slow pathway and retrograde up the fast pathway, producing a narrow QRS with P waves buried in or just after the QRS (short RP tachycardia). (2) AV Reciprocating Tachycardia (AVRT, ~30%) — involves an accessory pathway (bypass tract) connecting atria and ventricles outside the AV node. In orthodromic AVRT, the impulse travels antegrade through the AV node and retrograde through the accessory pathway, producing a narrow QRS. In antidromic AVRT, the direction reverses, producing a wide QRS that mimics ventricular tachycardia. Wolff-Parkinson-White (WPW) syndrome is the most recognized accessory pathway condition, characterized by a delta wave, short PR interval, and wide QRS on baseline ECG. Rates in SVT are typically 150–250 bpm, regular, with abrupt onset and offset. The rapid rate reduces diastolic filling time and may compromise cardiac output.