How Much Atrial Fibrillation Is Too Much Atrial Fibrillation?

Modern cardiac pacemakers and defibrillators function as permanently implanted cardiac monitors, detecting atrial and ventricular arrhythmias. Although the principal purpose of collecting this information is to manage the patient's cardiac rhythm, these data can also be used to detect and study clinically inapparent arrhythmias and their consequences. In this issue of the Journal, Healey and coworkers 1 report the results of a prospective study involving patients in whom a pacemaker or defibrillator had recently been implanted (Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial [ASSERT] 1 , 2 ; ClinicalTrials.gov number, NCT00256152). This study . . .