At times, irregularity is seen, especially at onset ( warm-up ) and termination ( warm-down ). Atrial mapping reveals a focal point of origin. Sinus node reentry tachycardia A specific type of focal AT that is due to microreentry arising from the sinus node complex, characterized by abrupt onset and termination, resulting in a P-wave morphology that is indistinguishable from sinus rhythm. Multifocal atrial tachycardia (MAT) An irregular SVT characterized by 3 distinct P-wave morphologies and/or patterns of atrial activation at different rates. The rhythm is always irregular. Atrial flutter Cavotricuspid isthmus dependent atrial flutter: typical Macroreentrant AT propagating around the tricuspid annulus, proceeding superiorly along the atrial septum, inferiorly along the right atrial wall, and through the cavotricuspid isthmus between the tricuspid valve annulus and the Eustachian valve and ridge. This activation sequence produces predominantly negative sawtooth flutter waves on the ECG in leads 2, 3, and aVF and a late positive deflection in V1. The atrial rate can be slower than the typical 300 bpm (cycle length 200 ms) in the presence of antiarrhythmic drugs or scarring. It is also known as typical atrial flutter or cavotricuspid isthmus dependent atrial flutter or counterclockwise atrial flutter. Cavotricuspid isthmus dependent atrial flutter: reverse typical Macroreentrant AT that propagates around in the direction reverse that of typical atrial flutter. Flutter waves typically appear positive in the inferior leads and negative in V1. This type of atrial flutter is also referred to as reverse typical atrial flutter or clockwise typical atrial flutter. Atypical or non cavotricuspid isthmus dependent atrial flutter Macroreentrant ATs that do not involve the cavotricuspid isthmus. A variety of reentrant circuits may include reentry around the mitral valve annulus or scar tissue within the left or right atrium. 