Summary

We report a 55-year-old man who experienced proximal muscle weakness accompanied by the atrial flutter (AFL) with 1:1 conduction. Detailed examination revealed elevated antimitochondrial antibodies (AMA) and creatine kinase (CK). AFL was converted to sinus rhythm by cardioversion. He was diagnosed as AMA-positive myositis-associated AFL and was treated by prednisolone. Although his muscle weakness and CK level improved, AFL with 1:1 conduction reappeared. Therefore, radiofrequency catheter ablation (RFCA) was needed to treat the AFL, resulting in maintenance of sinus rhythm. This case report describes cardiac involvement in a patient with AMA-positive myositis.