In a study from Healey et al, a cohort of 2580 patients with pacemakers or defibrillators were monitored for 3 months to detect subclinical atrial tachyarrhythmias. Patients with subclinical atrial tachyarrhythmias had a significantly increased risk of subsequent ischemic stroke.
Atrial fibrillation may be asymptomatic and consequently subclinical. Epidemiologic studies indicate that many patients with atrial fibrillation on screening electrocardiograms had not previously received a diagnosis of atrial fibrillation.
• What percentage of strokes are attributable to atrial fibrillation?
About 15% of strokes are attributable to documented atrial fibrillation, and 50 to 60% to documented cerebrovascular disease, but in about 25% of patients who have ischemic strokes, no etiologic factor is identified. Subclinical atrial fibrillation is often suspected to be the cause of stroke in these patients.
• How is the CHADS2 score used?
The CHADS2 score is used to predict the risk of stroke in patients with atrial fibrillation. Scores range from 0 to 6, with higher scores indicating a greater risk of stroke; the categories of congestive heart failure, hypertension, diabetes, and an age of 75 years or older are each assigned 1 point, and the category of prior stroke or transient ischemic attack is assigned 2 points.
Morning Report Questions
Q: What is the relationship between subclinical atrial tachyarrhthmias and stroke or systemic embolization?
A: In this study published in this week’s Journal, 4.2% of patients in whom subclinical atrial tachyarrhythmias had been detected before 3 months had an ischemic stroke or systemic embolism (a rate of 1.69% per year), as compared with 1.7% (0.69% per year) in whom subclinical atrial tachyarrhythmias had not been detected (hazard ratio, 2.49; 95% CI, 1.28 to 4.85; P=0.007). The risk was virtually unchanged after adjustment for baseline risk factors for stroke and was similar in an analysis in which data from patients were censored once clinical atrial fibrillation developed. The population attributable risk of ischemic stroke or systemic embolism associated with subclinical atrial tachyarrhythmia was 13%.
Q: How common is the presence of subclinical tachyarrhythmia in patients who have implanted pacemakers or defibrillators?
A: In this study of patients 65 years of age or older with a history of hypertension who had undergone implantation of a pacemaker or ICD and were free from clinical atrial fibrillation, there was a substantial incidence of subclinical atrial tachyarrhythmias. Subclinical atrial tachyarrhythmias were detected in one tenth of the patients within 3 months after implantation and were detected at least once during a mean follow-up period of 2.5 years in 35% of the patients. Episodes of subclinical atrial tachyarrhythmias were almost eight times as common as episodes of clinical atrial fibrillation. During the course of the study, clinical atrial fibrillation developed in only 16% of the patients with subclinical atrial tachyarrhythmias, suggesting that there can be a lag between subclinical events and clinical detection.