Carotid Atherosclerosis and Stroke in Atrial Fibrillation: The Atherosclerosis Risk in Communities Study

Background and Purpose - Whether consideration of carotid intima-media thickness (cIMT) and carotid plaque would improve risk prediction of ischemic stroke in persons with atrial fibrillation (AF) is unknown. The purpose of this study was to assess the improvement in risk prediction of stroke by adding cIMT and carotid plaque to the CHA₂DS₂-VASc (variables age, heart failure, hypertension, diabetes mellitus, myocardial infarction, and peripheral arterial disease) score. Methods - We included participants from the Atherosclerosis Risk in Communities (ARIC) study (mean age, 63 years) who developed AF within 5 years after carotid measurement, were not on warfarin, and had no prior stroke at AF diagnosis. AF was ascertained from study ECGs and diagnosis codes, and stroke was physician adjudicated. Multivariable Cox models were used to assess association between carotid indices and ischemic stroke. Improvement in 10-year risk prediction of stroke was assessed by the C-statistic, net reclassification improvement, and relative integrated discrimination improvement. Results - There were 81 (11.2%) stroke events that occurred among 724 participants with AF during a mean follow-up of 8.5 years. Increased cIMT and presence of carotid plaque were significantly associated with increased stroke risk. The addition of cIMT+plaque to the CHA₂DS₂-VASc score marginally increased the C-statistic (95% confidence interval) from 0.685 (0.623-0.747) to 0.698 (0.638-0.759). The net reclassification improvement and integrated discrimination improvement for cIMT+plaque were 0.091 (95% confidence interval, 0.012-0.170) and 0.101 (95% confidence interval, 0.002-0.226), respectively. Conclusions - Increased cIMT and presence of carotid plaque are associated with increased risk of ischemic stroke in individuals with AF. Furthermore, they may improve risk prediction of stroke, over and above the CHA₂DS₂-VASc score.