Atrial fibrillation

When the pulse rate is normal, and provided the patient is sufficiently well, exercise usually reduces the irregularity due to extrasystoles but increases that due to atrial fibrillation. If the pulse rate is above 100, atrial fibrillation is probably the cause of the irregularity. The electrocardiogram of atrial fibrillation is diagnostic since it shows that the P waves are absent and usually replaced by irregular fibrillary (f) waves. In cases of partial heart block with dropped beats and in atrial flutter with varying block, it can often be appreciated that runs of completely regular beats are occurring. If there is any doubt, an electrocardiogram must be taken for accurate diagnosis. Atrial fibrillation impairs the efficiency of the heart. The prognosis varies with the cause and is best when the underlying disease can be cured, e.g. thyrotoxicosis, or where no cause is found (idiopathic atrial fibrillation). In mitral stenosis the sudden onset of atrial fibrillation may precipitate cardiac failure or systemic or pulmonary embolism. In older subjects untreated atrial fibrillation is often associated with a normal ventricular rate and there may be little disability.