Abstract & Commentary
Do Brief Episodes of Device-Detected Atrial Fibrillation Warrant Anticoagulation?
By Edward P. Gerstenfeld, MD
Professor of Medicine, Chief, Cardiac Electrophysiology, University of California, San Francisco
Dr. Gerstenfeld does research for Biosense Webster, Medtronic, and Rhythmia Medical.
Brambatti M, et al. Temporal relationship between subclinical atrial fibrillation and embolic events. Circulation 2014;129:2094-2099.
Asymptomatic episodes of atrial fibrillation (AF) are often detected when interrogating
implanted pacemakers or defibrillators. The Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) trial1 enrolled 2580 patients with risk factors for stroke (age ≥ 65 years, hypertension) but no history of AF who were undergoing pacemaker or defibrillator implantation and, therefore, had continuous monitoring to detect AF. It showed AF episodes in > 40% of the patients, but only 15% developed clinically documented AF. However, this subclinical AF was associated with a 2.5-fold increased risk of stroke. This study analyzed the temporal relationship between AF episodes and stroke. Fifty-one patients experienced stroke or systemic embolism during follow-up, and of these, 26 (51%) had AF episodes of > 6 minutes detected by the device. The AF was detected by the device before the stroke in 18 patients (35%), but only four patients had AF detected within the 30 days prior to stroke, and only one of these patients had AF detected during the time of stroke. Eight patients only had AF detected after the stroke. The authors concluded that asymptomatic AF is associated with a higher incidence of stroke; few had AF in the month before the event.
Commentary
Many cardiologists follow patients with implanted pacemakers and defibrillators, and the question of when to initiate anticoagulation for device-detected AF has always been a quandary. It was always thought that it required 48 hours of AF for a thrombus to form in the atrium. But what about 20 minutes or 1 hour of AF? Is this then a marker for future AF episodes that should prompt systemic anticoagulation with its attendant cost and bleeding risk? The original ASSERT trial raised eyebrows when it found that only > 6 minutes of detected AF was associated with a 2.5-fold increased risk of stroke, despite clinical ECG documented AF in only 15% of patients over the next 2.5 years. After ASSERT, some physicians have argued that any device-detected AF > 6 minutes is a marker of stroke and should warrant anticoagulation, even though there has yet to be a study proving that systemic anticoagulation would reduce stroke incidence in this population. The current study looked in more detail at the temporal relationship between stroke and detected AF. It is interesting that only one patient had AF during the time of their stroke, and only four had AF detected within 30 days of the stroke. This clearly raises the question of whether left atrial appendage stasis and thromboembolism was the primary reason for strokes in the ASSERT study, or whether AF is simply a marker for those at risk of stroke. There are certainly data that AF itself leads to a hypercoaguable state. It is possible the mere presence of AF increases the risk of thromboembolism — although the absence of AF within 30 days of the stroke in the majority of patients makes this unlikely. The other possible explanation is that AF is a marker of other high-risk features that put patients at risk of stroke. This latter option seems more tenable to me. We must also keep in mind that many of these strokes may be lacunar or due to cerebrovascular disease and not thromboembolic. Until prospective data showing a benefit to anticoagulation emerges, I am reassured that > 6 minutes of AF detected on a device interrogation does not clearly warrant systemic anticoagulation. The TRENDS study,2 a similar study that enrolled patients with stroke risk factors undergoing device implantation, found an increased risk of stroke for AF present > 5.5 hours. Similar to the current study, there was no AF detected within 30 days of stroke in 73% of patients. For now, I think a 6-hour AF duration cutoff before initiating anticoagulation in patients with stroke risk factors makes sense. For patients with high CHADS-Vasc scores and multiple shorter AF episodes, systemic anticoagulation is also reasonable. Remote telemetry of many devices can now transmit automatic alerts to the physician for AF episodes beyond a specified duration. This should allow close follow-up of patients with shorter AF episodes. A study is sorely needed to prospectively randomize patients with device-detected AF to systemic anticoagulation vs placebo.
REFERENCES
- Healey JS, et al. Subclinical atrial fibrillation and the risk of stroke. N Engl J Med 2012;366:120-129.
- Daoud EG, et al. Temporal relationship of atrial tachyarrhythmias, cerebrovascular events, and systemic emboli based on stored device data:
A subgroup analysis of TRENDS. Heart Rhythm 2011;8:1416-1423.
