Relevant Terms and Definitions Arrhythmia/Term Definition Supraventricular tachycardia (SVT) An umbrella term used to describe tachycardias (atrial and/or ventricular rates in excess of 100 bpm at rest), the mechanism of which involves tissue from the His bundle or above. These SVTs include inappropriate sinus tachycardia, AT (including focal and multifocal AT), macroreentrant AT (including typical atrial flutter), junctional tachycardia, AVNRT, and various forms of accessory pathway-mediated reentrant tachycardias. In this guideline, the term does not include AF. Paroxysmal supraventricular tachycardia (PSVT) A clinical syndrome characterized by the presence of a regular and rapid tachycardia of abrupt onset and termination. These features are characteristic of AVNRT or AVRT, and, less frequently, AT. PSVT represents a subset of SVT. Atrial fibrillation (AF) A supraventricular arrhythmia with uncoordinated atrial activation and, consequently, ineffective atrial contraction. ECG characteristics include: 1) irregular atrial activity, 2) absence of distinct P waves, and 3) irregular R-R intervals (when atrioventricular conduction is present). AF is not addressed in this document. Sinus tachycardia Rhythm arising from the sinus node in which the rate of impulses exceeds 100 bpm. Physiologic sinus tachycardia Appropriate increased sinus rate in response to exercise and other situations that increase sympathetic tone. Inappropriate sinus tachycardia Sinus heart rate >100 bpm at rest, with a mean 24-h heart rate >90 bpm not due to appropriate physiological responses or primary causes such as hyperthyroidism or anemia. Atrial tachycardia (AT) Focal AT An SVT arising from a localized atrial site, characterized by regular, organized atrial activity with discrete P waves and typically an isoelectric segment between P waves. At times, irregularity is seen, especially at onset ( warm-up ) and termination ( warm-down ). Atrial mapping reveals a focal point of origin. 