Spontaneous conversion of long-standing atrial fibrillation.

Spontaneous conversion to sinus rhythm after prolonged atrial fibrillation is uncommon, with only 11 recorded cases to our knowledge in the English language literature. We report four cases of spontaneous conversion to an organized atrial rhythm (either sinus rhythm or atrial tachycardia with block) after nine to 16 years of established atrial fibrillation. One case was due to a toxic reaction to digitalis. In the other three cases there was no apparent reason. M-mode and two-dimensional echocardiography in three patients showed an akinetic and noncontractile left atrium in each case. This lends support to an earlier hypothesis that complete fibrosis of the left atrium may be responsible for the conversion from atrial fibrillation.