'Lone Atrial Fibrillation' is a Four Letter Word.

The term "lone atrial fibrillation" ("lone AF") was commonly used in prior decades to describe atrial fibrillation with no apparent clinical cause. In those years, "lone AF" was denoted in up to 30% of patients. However, with modern diagnostic methodologies, many experts now feel that a cause for atrial fibrillation can be found in virtually all patients such that most recent major-organization guidelines state that the term "lone AF" should no longer be used. Nonetheless, from a clinical rather than micro-diagnostic viewpoint, this position can be challenged as lessons of continued clinical relevance can be learned from an examination of the "lone AF" era, several of which are reviewed herein for the aid of current practitioners.