A Risk Score to Predict Arrhythmias in Patients with Unexplained Syncope

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Abstract
Objectives: To develop and validate a risk score predicting arrhythmias for patients with syncope remaining unexplained after emergency department (ED) noninvasive evaluation. Methods: One cohort of 175 patients with unexplained syncope (Geneva, Switzerland) was used to develop and cross‐validate the risk score; a second cohort of 269 similar patients (Pittsburgh, PA) was used to validate the system. Arrhythmias as a cause of syncope were diagnosed by cardiac monitoring or electrophysiologic testing. Data from the patient's history and 12‐lead emergency electrocardiography (ECG) were used to identify predictors of arrhythmias. Logistic regression was used to identify predictors for the risk‐score system. Risk‐score performance was measured by comparing the proportions of patients with arrhythmias at various levels of the score and receiver operating characteristic (ROC) curves. Results: The prevalence of arrhythmic syncope was 17% in the derivation cohort and 18% in the validation cohort. Predictors of arrhythmias were abnormal ECG (odds ratio [OR]: 8.1, 95% confidence interval [CI] = 3.0 to 22.7), a history of congestive heart failure (OR: 5.3, 95% CI = 1.9 to 15.0), and age older than 65 (OR: 5.4, 95% CI = 1.1 to 26.0). In the derivation cohort, the risk of arrhythmias ranged from 0% (95% CI = 0 to 6) in patients with no risk factors to 6% (95% CI = 1 to 15) for patients with one risk factor, 41% (95% CI = 26 to 57) for patients with two risk factors, and 60% (95% CI = 32 to 84) for those with three risk factors. In the validation cohort, these proportions varied from 2% (95% CI = 0 to 7) with no risk factors to 17% (95% CI = 10 to 27) with one risk factor, 35% (95% CI = 24 to 46) with two risk factors, and 27% (95% CI = 6 to 61) with three risk factors. Areas under the ROC curves ranged from 0.88 (95% CI = 0.84 to 0.91) for the derivation cohort to 0.84 (95% CI = 0.77 to 0.91) after cross‐validation within the same cohort and 0.75 (95% CI = 0.68 to 0.81) for the external validation cohort. Conclusions: In patients with unexplained syncope, a risk score based on clinical and ECG factors available in the ED identifies patients at risk for arrhythmias.