Occurrence and Natural History of Clinically Silent Episodes of Atrial Fibrillation in Hypertrophic Cardiomyopathy

Overt symptomatic atrial fibrillation (AF) occurs in over 20% of patients with hypertrophic cardiomyopathy (HC) leading to impaired quality of life, loss of productivity, and the risk for embolic stroke. However, the overall burden presented by AF in the HC population is unresolved due to the unknown frequency of silent asymptomatic episodes that do not necessarily achieve clinical recognition but nevertheless may have important disease-related implications. Therefore, stored electrograms were analyzed retrospectively for AF in 75 consecutive patients with HC (without AF history) implanted with dual-chamber cardioverter-defibrillators. Patients were followed for 5.0 ± 4.1 years at the Tufts Medical Center HCM Institute; ages were 50 ± 15 years, and 55% were male. Implantable cardioverter-defibrillator interrogation in the 75 patients showed AF to be absent in 54 (72%), 18 (24%) had clinically silent AF episodes, and the remaining 3 (4%) without previous asymptomatic episodes developed symptomatic and clinically overt paroxysmal AF. Of the 18 patients with clinically silent AF, 8 developed symptomatic AF, 4.1 ± 1.5 years later. Nonfatal embolic stroke occurred in 1 patient associated with asymptomatic AF and without other risk factors. In conclusion, clinically silent AF appears to be common in HC, occurring in almost 25% of patients. Such asymptomatic episodes of AF have important future implications, including potential thromboembolic risk, and development of symptomatic and clinically overt AF requiring prophylactic anticoagulation.