Reentry circuit location and left atrial three-dimensional activation patterns in left atrial flutter

We report the case of a patient with left atrial flutter (LAF) in whom the reentry circuit location was mapped with a 64-electrode basket catheter dep loyed in the left atrium. Left atrial three-dimensional activation patterns were constructed with a software program and presented as color-coded isoc hrones. The reentrant activation traveled preferentially around the mitral annulus in a clockwise direction. It consisted of a single reentry confined anteriorly by the mitral annulus and posteriorly by an anatomic-functional barrier composed of a functional conduction block extending between pulmon ary veins and surrounding a part of the posterior wall of the left atrium. The lower portion of the posterior wall and the anterior wall in close prox imity to mitral annulus were preferentially used by the reentrant impulse.