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Hamilton, Canada: Cerebrovascular disease (50-60%) and clinically documented atrial fibrillation (AF) (25%) account for significant number of stroke. However, the etiology of majority of other strokes (cryptogenic) in still unclear. A recent study conducted by the Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) has attempted to test the hypothesis that there is a link between subclinical AF and the occurrence of stroke.
The study followed a total of 2,580 patients between 2004 and 2009. Patients older than 65 years of age with current hypertension, no previous history of AF/atrial flutter, and with recent pacemaker or ICD implantation (within 8 weeks) were enrolled in the study. Patients who required anticoagulation for other indications were not included in the study. Episodes of atrial tachyarrhythmias (190 beats per minute and lasting more than 6 minutes) detected during device interrogation were defined as subclinical atrial arrhythmias. Devices were interrogated at 3 month follow up clinic visit. The second part of the study was to assess the effectiveness of overdrive pacing in preventing AF development. At 3 months, a portion of patients with pacemakers were randomly assigned to receive continuous atrial overdrive pacing. The primary outcome of the first part of the study assessing the prognostic value of subclinical AF was thrombo-embolic event. The primary outcome of the second part was atrial tachyarrhythmia detected on surface ECG.
By the first 3-month clinic visit, 261 patients (10.1%) experienced at least one episode of subclinical atrial tachyarrhythmia. Over subsequent follow up duration of 2.5 years, close to 16% of patients with subclinical atrial tachyarrhythmia developed clinical atrial tachycardia compared to 3% in non-subclinical atrial tachyarrhythmia group. In the subclinical atrial tachyarrhythmia group, 4.2% experienced a thrombo-embolic event compared to 1.7% in latter patient cohort. The risk of thrombo-embolic event was greater (HR 1.76, 95% CI 0.99 -3.11) in subclinical atrial tachyarrythmia group compared to latter patient group. Patients with subclinical tachyarrhythmias have 2.5 times increased risk of thrombo-embolism compared to patients without atrial tachycardias. The risk of thrombo-embolic event also appeared to increase in number and duration of sub-clinical atrial tachyarrhythmias. The study also demonstrated that continuous atrial overdrive pacing was unsuccessful in preventing atrial fibrillation.
In conclusion, the study supported the proposed relationship between subclinical atrial tachyarrhythmia and an increased risk of developing ischemic stroke. This is a significant finding, and it may explain the etiology behind cryptogenic strokes. It is important to note that patients with subclinical tachyarrhythmia may develop future clinical AF, and that atrial overdrive pacing is ineffective in preventing atrial tachyarrhythmias.
Reference: 1. Healey JS, Connolly SJ, Gold MR, Israel CW, Van Gelder IC, Capucci A, et al. Subclinical atrial fibrillation and the risk of stroke. The New England journal of medicine. 2012;366(2):120-9.
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