Peter Ott
Sarver Heart Center, USA
Title: Subclinical atrial fibrillation: diagnosis and therapeutic challenges
Biography
Biography: Peter Ott
Abstract
Advances in pacemaker technology and expanding use of cardiac rhythm monitoring devices have resulted in detection of thus far undiagnosed atrial fibrillation (AF). These device-detected episodes, typically brief in duration (minutes to hours) and mostly asymptomatic, are often referred to as “subclinical atrial fibrillation” (SCAF). While clinical atrial fibrillation, typically diagnosed by routine EKG/48 hour Holter recording is a well-known risk factor for stroke, the therapeutic implications for device detected SCAF remain unknown.
Three recent long-term studies investigated the incidence of SCAF by means of implanted loop recorder devices in a total of 950 patients deemed at risk for AF based on age (>65-70 years) plus additional risk factors. The incidence of SCAF (defined as > 6 minutes in duration) ranged from 22-34% at 18 months follow up. Most episodes were asymptomatic and brief in duration (<30 minutes). Episode duration > 24 hours comprised only 10% of all SCAF episodes.
Several studies in patients undergoing pacemaker or ICD implantation investigated the prevalence and clinical implications of device detected SCAF. The patient populations (some trials enrolled patients with a prior history of stroke and AF) and definitions of SCAF varied (ranging from > 5 minutes to > 24 hours), the incidence of SCAF ranged from approximately 20-50% at 12-18 months follow up. Overall there were no important differences in clinical risk factors such as age, CHADS score, comorbidities, etc, between patients with and without SCAF. Compared to patients without SCAF those with SCAF had a higher incidence of subsequent diagnosis of clinical AF (HR 5-6) and an increase in rates of thrombo-embolic (TE) complications (HR 2-2.5). The absolute number of stroke events was small, and none of these trials controlled for use of anticoagulation or antiplatelet therapy. While the relative risk of TE events was increased in patients with SCAF the absolute risk varied 1.0–2.5%/year. The stroke risk was highest in patients with increased CHADS stroke risk score and/or prolonged SCAF episode duration. A recent analysis in 2,580 pacemaker recipients > 65 years of age and no prior history of AF showed increased stroke rates only in patients with SCAF > 24 hrs duration. In this large trial the overall incidence of SCAF was approx. 20% at 1-2 year follow up, and only 25% of SCAF episodes were > 24 hours in duration.