Atrial fibrillation
Atrial fibrillation represents a common electrical malady in the heart that appears during the time interval of atrial systole (see figure at right margin). Theory suggests that an ectopic focus, usually situated within the pulmonary trunks, competes with the sinoatrial node for electrical control of the atrial chambers and thereby diminishes the performance of the atrial myocardium, or atrial heart muscle. The ordered, sinoatrial control of atrial electrical activity is disrupted, causing the loss of coordinated generation of pressure in the two atrial chambers. Atrial fibrillation represents an electrically-disordered but well perfused atrial mass working (in an uncoordinated fashion) with a (comparatively) electrically-healthy ventricular systole.