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Re: atrial fibrillation burden is crucial to evaluation of suspected cardioembolic stroke

In his allusion to the uncertain significance of "brief and infrequent paroxysms of AF(atrial fibrillation) noted on the event monitor"(1) the author highlighted the thorny issue of the relationship between AF burden and embolic risk(2). The author's misgivings resonated with the comment which has been made that "it is not well known if a "small" AF burden presents any lesser risk of morbidity and mortality compared with a "large" burden", and the rider that "the quantitative cutoff point for defining a "low risk" AF burden has never been defined"(2). Two approaches have neen made to adress these issues. One approach has been to presribe uniform criteria for evaluating recurrences of AF and, hence, AF burden. In the opinion of a recent consensus conference, seven day Holter ECG recording is as "powerful" as daily plus symptom-activated transtelephonic ECG(electrocardiographic)monitoring to detect AF recurrence, being capable of detecting approximately 70% of AF recurrences. Holter ACG recordings, however, had the advantage of documenting the duration of AF episodes(3). The second approach is to correlate the duration of AF episodes with embolic risk, and this was done in a cohort of 725 patients suffering from bradycardia, who were implanted with dual-chamber pacemakers. These pacemakers had 100% sensitivity and 97% specificity for detection of atrial tachyarrhythmias. In that study AF episodes longer than one day were the ones thet appeared to be independently associated with arterial embolism(3.1 hazard ratio, 95% confidence interval 1.1 to 10.5, p=0.044)(4). Further studies are needed to assess whether these conclusions can be extrapolated to Holter monitoring, in which the negative predictive value for "freedom from AF" is 25-40% in paroxysmal AF(3), and whether they are relevant to patients with different baseline charcteristics. References (1) Weir NU An update on cardioembolic stroke Postgraduate Medical Journal 2008:84:133-42 (2) Verma A., Natale A Controversies in Cardiovascular Medicine:Should atrial fibrillation ablation be considered first line therapy for some patients? Why atrial fibrillation ablation should be considered first-line therapy for some patients Circulation 2005:112:1214-31 (3) Kirchhof P., Auricchio A., Bax J et al Outcome parameters for trials in atrial fibrillation: executive summary Recommendations from a consensus conference organized by the German Atrial Fibrillation Competence NETwork(AFNET) and the European Heart Rhythm Association(EHRA) European Heart Journal 2007:28:2803-17 (4) Capucci A., Santini M., Padeletti L et al Monitored atrial fibrillation duration predicts arterial embolic events in patients suffering from bradycardia and atrial fibrillation implanted with antitachycardia pacemakers Journal of the American College of Cardiology 2005:46:1913-20

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Re: Response to letter by Dr Jolobe

I am grateful to Dr Jolobe for drawing attention to the dilemma of just how much paroxysmal AF (pAF) is sufficient to produce a clinically important risk of stroke and systemic embolism. So far, research in this field has been limited, focused on primary prevention populations (those with pacemakers for bradycardia), and unclear as to whether several hours or just a few minutes of rapid AF are required.[1][2] Hopefully the recent completion of a further large study on this topic should help clarify matters.[3] However, none of these data properly address the related dilemma that may soon face clinicians in the field of secondary prevention, namely just how much pAF is required to justify long-term anticoagulation in patients with an otherwise unexplained stroke.

This question follows on the publication of several small studies that have used automatic loop recording (ALR) devices to monitor the ECG over many days in patients with a stroke or TIA and reported unsuspected episodes of AF in 5.7% to 14.2% of consecutive cases [4][5][6] and in 14.3% to 23% of cases with cryptogenic events.[4][7] Not surprisingly, these data have generated considerable interest in the stroke community. However, several difficulties prevent their simple interpretation data, not least of which is the fact that most of the episodes of AF detected using ALR devices last only a few seconds; for example, in one study 77% of all the episodes of AF lasted < 30 seconds.[7]

It is, of course, not unreasonable to set a lower threshold for starting anticoagulation in secondary prevention populations given that the patients have declared themselves to be ‘stroke prone’. As such, even if primary prevention studies suggest that only pAF measured in hours merits anticoagulation, I suspect most clinicians would still anti- coagulate a patient with a recent cryptogenic stroke and, say, a single 15 minute episode of AF. The real dilemma relates to the majority in whom the burden of pAF is measured in seconds. Some will regard these brief episodes as ‘biomarkers of more prolonged and clinically significant AF’ and proceed with anticoagulation.[7] Others will regard them as a common and incidental finding in elderly populations, and, noting that they have hitherto been ignored by arrhythmia investigators,[8] continue with aspirin. Given the non-trivial implications of error either way, this dilemma must be resolved before ALR use creeps into routine practice. To do so, future studies in this field must shift from case-series that simply describe the prevalence of unsuspected AF to analyses that compare it between large and representative cohorts with explained and unexplained stroke.

References

1. Capucci A, Santini M, Padeletti L et al. Monitored atrial fibrillation duration predicts arterial embolic events in patients suffering from bradycardia and atrial fibrillation implanted with antitachycardia pacemakers. J Am Coll Cardiol 2005;46:1913-20

2. Glotzer TV, Hellkamp AS, Zimmerman J et al. Atrial high rate episodes detected by pacemaker diagnostics predict death and stroke. Report of the Atrial Diagnostics Ancillary Study of the MOde Selection Trial (MOST). Circulation 2003;107:1614-19

3. Glotzer TV, Daoud EG, Wyse DG et al. Rationale and design of a prospective study of the clinical significance of atrial arrhythmias detected by implanted device diagnostics: the TRENDS study. J Interventional Cardiac Electrophysiology 2006;15:9-14

4. Barthelemy JC, Feasson-Gerard S, Garnier P et al. Automatic cardiac event recorders reveal paroxysmal atrial fibrillation after unexplained strokes or transient ischemic attacks. Ann Noninvasive Electrocardiology 2003;8:194-199

5. Jabaudon D, Sztajzel J, Sievert K et al. Usefulness of ambulatory 7-dayECG monitoring for the detection of atrial fibrillation and flutter after acute stroke and transient ischemic attack. Stroke 2004;35:1647-51

6. Wallmann D, Tüller D, Wustmann K et al. Frequent atrial premature beats predict paroxysmal atrial fibrillation in stroke patients. An opportunity for a new diagnostic strategy. Stroke 2007;38:2292-94

7. Tayal AH, Tian M, Kelly KM et al. Atrial fibrillation detected by mobile cardiac outpatient telemetry in cryptogenic TIA or stroke. Neurology 2008;71:1696-1701

8. Kirchhof P, Auricchio A, Bax J et al. Outcome parameters for trials in atrial fibrillation. Recommendations from a consensus conference organized by the German Atrial Fibrillation Competence NETwork and the European Heart Rhythm Association. Europace 2007;9:1006-23