Pacemakers as Atrial Fibrillation Detectors: Finding Racial Differences and Opportunities for Preventing Stroke

Implantation of permanent pacemakers has become routine and pervasive. Overall use increased by 53% between 1993 and 2009, with a significant steady decline in singlechamber ventricular devices throughout this time period and a significant steady rise in dual-chamber devices until around 2002, when the rates stabilized. Beyond their self-evident therapeutic benefits, pacemakers can have important diagnostic utility. With atrial leads and current detection algorithms, these devices can detect atrial tachycardia with 95% accuracy. In this issue of JAHA, Kamel et al performed an observational study exploiting the fact that pacemakers can act as atrial fibrillation (AF) detectors; they analyzed administrative records from 2005–2006 to 2010–2011 from California, Florida, and New York of patients with permanent pacemakers and no history of AF. After adjusting for demographic and clinical differences, investigators found a significantly lower risk of developing AF among black patients relative to white patients (hazard ratio 0.91). The study has several strengths, including its size, involving >100 000 participants. Furthermore, incident AF was assessed in a manner less prone to ascertainment bias than review of administrative records of a population lacking pacemakers. The study, however, relied on administrative records rather than direct interrogation of the pacemakers and may still have suffered from some level of ascertainment bias because transient runs of AF may not have been documented with the same rigor across racial groups. In addition, although the study adjusted for pacemaker interrogations, it did not adjust for type of device, atrial lead placement, or diagnostic algorithm, all of which may contribute to variations in sensitivity for detecting AF. The findings of Kamel et al were largely consistent with those of ASSERT, the Asymptomatic AF and Stroke Evaluation in Pacemaker Patients and the AF Reduction Atrial Pacing Trial, which also found lower rates of AF in black participants relative to white participants. Table compares key features of the 2 studies. Differences in population genetics may explain the lower risk of AF among black participants relative to white participants. An approach to testing this hypothesis is through admixture mapping, which assumes that differences in rates of a phenotype are caused by differences in the frequency of phenotype-causing genetic variants between populations. After adjusting for numerous potential confounders including age, sex, body mass index, diabetes mellitus, and heart failure, a meta-analysis of Atherosclerosis Risk in Communities (ARIC), which included 4543 white and 822 black participants, and the Cardiovascular Health Study (CHS), which included 10 902 white and 3517 black participants, showed that for every 10% increase in European ancestry, there was a 13% increase in the risk of AF. The findings in ARIC and in CHS were not statistically heterogeneous. In the case of ARIC, a significant relationship between European ancestry and risk of AF was independently observed using 2 separate arrays of ancestry-informative markers. Nevertheless, among postmenopausal women in the Women’s Health Initiative (WHI), genomewide ancestry did not associate with AF, even though self-reported African American race/ethnicity was negatively associated with AF. The reasons for failure to replicate are uncertain, but the degree of European ancestry in the WHI cohort was low, and classification of AF relied on self-report, potentially compromising power to detect differences. Kamel et al evaluated patients for the presence or absence of AF; however, the arrhythmia is not a dichotomous trait. The reality is more complex. Patients with AF are more appropriately seen as having varying degrees of disease burden. The risk of stroke is higher for patients with permanent versus nonpermanent AF, and, somewhat surprisingly, anticoagulation may not negate this difference. The AMADEUS study found that the risk of cardiovascular death, stroke, or systemic embolism is 68% higher in anticoagulated patients with permanent versus nonpermanent AF. For every The opinions expressed in this article are not necessarily those of the editors or of the American Heart Association. From the Department of Neurology, Mayo Clinic, Jacksonville, FL. Correspondence to: James F. Meschia, MD, Department of Neurology, Mayo Clinic, 4500 San Pablo Road, Jacksonville, FL 32224. E-mail: Meschia.james@ mayo.edu J Am Heart Assoc. 2016;5:e003090 doi: 10.1161/JAHA.115.003090. a 2016 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.