Activation patterns in atrial fibrillation

Isochronal activation maps obtained from the right atrial free wall during atrial fibrillation show four distinct patterns of myocardial activation, indicated by black arrows. Activation from a localizable site which spreads in all directions away from the site is termed focal atrial activation (upper left). Type I activation is a single broad wavefront that propagates without conduction delay (upper right). Type II activation is a single wavefront that is associated with conduction slowing or block, or with two wavefronts (lower left). Type III activation results from the presence of three or more wave fronts associated with areas of slow and blocked conduction (lower right).