Spontaneous reversion from long-lasting atrial fibrillation to sinus rhythm.

We have collected 23 cases with atrial fibrillation (AF) of 3-29 years' duration with spontaneous reversion to sinus rhythm (SR). We have also identified 22 similar cases in the literature. Several of our patients spent several years with different atrial arrhythmias before a stable SR was established. Of all the 45 cases, 39 had significant rheumatic mitral valve disease. In the majority of these patients the ECG shows first degree AV block after return to SR and a low-amplitude P-wave--as if the left atrial P component was lacking. There are no signs of left atrial mechanical activity after re-establishment of SR in our mitral valve disease group, as judged from phonocardiograms, apexcardiograms, echocardiograms and left atrial pressure recordings in selected patients. Heart muscle biopsy was obtained from two patients who underwent mitral valve surgery. Left atrial speciments showed almost complete lack of all muscle structures. There is thus electrical, mechanical and histological evidence of left atrial muscle deterioration. It is likely that the electrophysiological factors responsible for initiation and maintenance of AF have disappeared with this deterioration, thereby allowing SR to be re-established. The return of SR might indicate a progress of the heart disease although the patient may benefit from normalization of cardiac rate and regularity. The easy identification of our 23 patients makes us believe that the phenomenon of appearance of late SR is far more common than suggested up to now.