Subclinical Atrial Fibrillation

Posted by Sara Fazio • January 13th, 2012

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.

Clinical Pearls

• 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%.

Table 2. Clinical Outcomes Occurring after the 3-Month Visit, According to Whether Subclinical Atrial Tachyarrhythmias Were or Were Not Detected between Enrollment and the 3-Month Visit.

Figure 1. The Risk of Clinical Atrial Tachyarrhythmias and of Ischemic Stroke or Systemic Embolism, According to the Presence or Absence of Subclinical Atrial Tachyarrhythmias.

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.

One Response to “Subclinical Atrial Fibrillation”

  1. Gaetano Santulli says:

    Healey et al. report that subclinical atrial fibrillation (AF) is associated with an increased risk of ischemic stroke or systemic embolism (1). This finding is really intriguing, but the interpretation is problematic in that the Authors did not mention in their analysis some widely recognized independent risk factors for ischemic stroke, such as smoking status and left atrial size (2, 3). These factors clearly partake in the pathophysiology of AF-associated stroke, which is indeed mainly due to embolism of thrombus formed during stasis of blood in the left atrial appendage (2). Furthermore, there is a well-known connection between atrial dimensions and new-onset AF (4). Thus, subclinical episodes of AF could be simply a marker of stroke risk, indicating another underlying disease (2).
    In this trial (1), the risk of stroke was improperly assessed using the CHADS2 score (5), which was instead specifically designed just for patients with overt AF. To better understand the prognostic clinical implications of asymptomatic AF, it would be of interest to validate the significancy of provided results after correction for the omitted risk factors.

    Disclosures: None.

    References
    1. Healey JS, Connolly SJ, Gold MR, et al. Subclinical atrial fibrillation and the risk of stroke. N Engl J Med 2012;366:120-9.
    2. Sacco RL, Benjamin EJ, Broderick JP, et al. American Heart Association Prevention Conference. IV. Prevention and Rehabilitation of Stroke. Risk factors. Stroke 1997;28:1507-17.
    3. Benjamin EJ, D’Agostino RB, Belanger AJ, Wolf PA, Levy D. Left atrial size and the risk of stroke and death. The Framingham Heart Study. Circulation 1995;92:835-41.
    4. Tsang TS, Barnes ME, Bailey KR, et al. Left atrial volume: important risk marker of incident atrial fibrillation in 1655 older men and women. Mayo Clin Proc 2001;76:467-75.
    5. Gage BF, Waterman AD, Shannon W, Boechler M, Rich MW, Radford MJ. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA 2001;285:2864-70.

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