Detecting Paroxysmal Atrial Fibrillation After Ischemic Stroke and Transient Ischemic Attack: If You Don’t Look, You Won’t Find
To the Editor:
Paroxysmal atrial fibrillation (AF) is a major preventable cause of stroke worldwide. We congratulate Liao and colleagues for their systematic review of a series of cohort studies highlighting the important issue of screening for occult AF after ischemic stroke and transient ischemic attack (TIA).1 As their review indicates, extended duration ECG monitoring after stroke/TIA identifies more patients with AF than standard ECG and Holter monitoring alone.
Short duration monitoring (24- to 72-hour Holter) identifies new AF in only about 5% of patients poststroke.1 Longer monitoring (4- or 7-day event loop recorder) detects new AF in an additional 6% to 8% of patients after a nondiagnostic Holter.1 Repeated monitoring detects even more. The incremental yield of serial monitoring was demonstrated in recent study not included in the aforementioned systematic review, in which 7-day event recording at 0, 3, and 6 months detected new AF in 14% of patients with an initial negative Holter (26% among those patients with frequent atrial premature beats).2 Frequent atrial premature beats (>70 during a 24-hour Holter) was an independent predictor of AF (odds ratio 7).2 Because warfarin is significantly more effective at preventing recurrent strokes than standard antiplatlelet prophylaxis in AF, these data make a strong case for clinicians to consider more effective methods of detecting occult AF in patients with unexplained stroke/TIA.
Unfortunately, in current practice patients commonly receive only a single 24- or 48-hour Holter monitor, and unless AF occurs during that monitoring period, the diagnosis of AF is missed, warfarin is not given, and a proportion of patients will experience a recurrent stroke. Specific guidelines are lacking. Current Canadian practice recommendations for stroke (www.canadianstrokestrategy.ca) make no recommendation about screening for AF. An American Heart Association guideline states that cardiac monitoring “should be conducted routinely after an acute cerebrovascular event to screen for serious cardiac arrhythmias”.3 The issue, of course, is how, when, in which patients, and for how long?
Currently, available monitors have limitations. The adhesive skin contact electrodes cause skin irritation, making it difficult to wear for prolonged durations. Loop recorders rely on patients to recognize palpitations and, therefore, miss asymptomatic AF. A pilot study in Toronto (EMBRACE) is evaluating a novel ambulatory ECG monitor programmed for automatic detection of AF using high-impedance, nonadhesive (dry) electrodes that can be worn comfortably for 30 days.4
With over one-third of ischemic strokes currently classified as “undetermined etiology”, we speculate that a substantial proportion of these cryptogenic strokes result from (undiagnosed) paroxysmal AF, particularly in the elderly. This is especially likely for patients with an “embolic pattern” of ischemia on neuroimaging (ie, multiple areas of MRI diffusion restriction in different vascular territories), which may be seen in 12% of cryptogenic events. Such patients are prime targets for extended duration ECG monitoring.
To put this in perspective, we analyzed AF prevalence data from the prospective Registry of the Canadian Stroke Network, 2003 to 2007 (www.rcsn.org). Of 12 849 consecutive ischemic stroke patients presenting to hospital, 17% had a history of AF, and an additional 6% had new AF detected in hospital (4% detected on admission ECG and 2% detected later in hospital; median length of stay 7 days). For patients aged >75 years with <50% carotid artery stenosis, 1 in 10 had new AF detected in hospital; an additional 6% had new AF documented on a hospital readmission within 12 months. Therefore, detection of occult AF is an important function of inpatient stroke care for patients with unexplained cerebral ischemic events, but with current methods we are likely missing many patients with AF.
The public health implications of undiagnosed and untreated AF are enormous. Better strategies for detecting occult AF after stroke/TIA must continue to be explored if we are to improve secondary stroke prevention care.
Liao J, Khalid Z, Scallan C, Morillo C, O’Donnell M. Non-invasive cardiac monitoring for detecting paroxysmal atrial fibrillation or flutter following acute ischemic stroke: a systematic review. Stroke. 2007; 38: 2935–2940.
Wallmann D, Tuller D, Wustmann K, Meier P, Isenegger J, Arnold M, Mattle HP, Delacrétaz E. Frequent atrial premature beats predict paroxysmal atrial fibrillation in stroke patients: an opportunity for a new diagnostic strategy. Stroke. 2007; 38: 2292–2294.
Adams HP Jr, del Zoppo G, Alberts MJ Bhatt DL, Brass L, Furlan A, Grubb RL, Higashida RT, Jauch EC, Kidwell C, Lyden PD, Morgenstern LB, Qureshi AI, Rosenwasser RH, Scott PA, Wijdicks EF; American Heart Association; American Stroke Association Stroke Council; Clinical Cardiology Council; Cardiovascular Radiology and Intervention Council; Atherosclerotic Peripheral Vascular Disease and Quality of Care Outcomes in Research Interdisciplinary Working Groups. Guidelines for the early management of adults with ischemic stroke. Stroke. 2007; 38: 1655–1711.
Spring M, Dorian P, Fry B, Buck B, Sahlas DJ, Hopyan J, Korley V, Black SE, Gladstone DJ. A 30-Day Cardiac Event Monitor Belt for Recording Paroxysmal Atrial Fibrillation After a Cerebral Ischemic Event: The EMBRACE Pilot Study. Stroke. 2008. (abstract).