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Estimating Stroke Risk in Atrial Fibrillation
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco does research for Medtronic, is a consultant for Medtronic, Novartis, and St. Jude, and is a speaker for Boston Scientific.
Source: Daccarett M, et al. Association of left atrial fibrosis detected by delayed-enhancement magnetic resonance imaging and the risk of stroke in patients with atrial fibrillation. J Am Coll Cardiol. 2011; 57:831-838.
In this paper, daccarett and colleagues from the University of Utah assessed the potential contribution of cardiac magnetic resonance imaging for detection of left atrial fibrosis to risk stratify patients for stroke with atrial fibrillation. The authors assessed patients at their institutions who were scheduled for pulmonary vein isolation for the treatment of atrial fibrillation (AF). Patients underwent delayed enhancement magnetic resonance imaging (DE-MRI) using special analysis methods that allow detection and quantification of left atrial scarring. After DE-MRI patients were assigned to one of four quartiles based on the severity of structural remodeling or scarring as follows: Stage I (< 8.5% DE), Stage II (8.6% to 16% DE), Stage III (16.1% to 21% DE), and Stage IV (>21% DE). A CHADS2 score was calculated based on clinical data. Patients with and without prior stroke were then compared.
The study includes data from 387 patients. Of these, 36 (9.3%) had a history of stroke. Patients with stroke were older and predominantly female. Four of the CHADS2 risk factors, (congestive heart failure, hypertension, age > 75 and diabetes), as well as the patterns of AF were similar between those with and without a history of stroke. More severe scarring by DE-MRI was strongly associated with a history of stroke (24.4 + 12.4% vs. 16.1 + 9.8% scarring, p < 0.001, with and without prior stroke, respectively). Patients with only Stage I remodeling had a low stroke incidence (2.8%), whereas 52.8% of patients with Stage IV remodeling had suffered a prior stroke. Higher CHADS2 scores were associated with increased left atrial fibrosis, By multivariate logistic regression analysis, AF remodeling was independently associated with stroke risk. Patients with Stage IV remodeling had a four times higher prevalence of stroke than patients with only Stage I remodeling.
The authors conclude that adding a quantitative measure of left atrial scar remodeling or scarring determined by DE-MRI may enhance risk stratification in patients with atrial fibrillation.
Stroke is the most feared complication of atrial fibrillation. Unfortunately, anticoagulation to prevent stroke is associated with its own set of problems with serious or major bleeding noted with a rate of approximately 2% per year. Effective risk stratification is, therefore, a key to successful management. Current risk stratification schemes including the CHADS2 score cited here and the updated CHA2DS2VASc score cited in the recent European Society of Cardiology guidelines are frequently used but have only modest predictive power. They are, however, easily calculated based only on easily obtained clinical findings. In this paper, Daccarett and his colleagues show that adding information about left atrial scarring may enhance our ability to predict stroke risk. The correlations made here were in a population of patients referred for ablation and the strokes occurred before the DE-MRI studies were performed. Prospective use of the proposed scoring scheme needs to be tested in future trials. Even with new agents for anticoagulation becoming available, the risks, costs, and inconvenience of such therapy are substantial. Techniques such as these that may enhance our ability to predict stroke may prove to be very valuable.