Atrial flutter

Abstract

Atrial flutter is caused by either macro or micro re-entry circuits within either the right atrium or left atrium. It is broadly divided into either typical or atypical forms. Typical atrial flutter involves the cavotricuspid isthmus as part of the circuit with either a counter-clockwise or clockwise activation. The cavotricuspid isthmus extends from the tricuspid valve to the inferior vena cava, which supports slow conduction. Atypical atrial flutter involves non-cavotricuspid isthmus dependent circuits in the right atrium, septum or left atrium. Right atrial flutters which are not dependent on the cavotricuspid isthmus include upper loop re-entry, lower loop re-entry, right lateral wall incisional type atrial flutter and circuits around the fossa ovalis. Upper loop re-entry tends to occur around the superior vena cava with slow conduction through the upper component of the crista terminalis. Lower loop re-entry occurs around the inferior vena cava with slow conduction through the lower portion of the crista terminalis. Left atrial flutters tend to occur around the mitral valve annulus, the ostia of the pulmonary veins or the fossa ovalis on the left side. Mitral annular flutter may propagate either in a clockwise or counterclockwise direction.