Detection of atrial fibrillation in the post‐stroke setting: challenges and opportunities on the horizon

Atrial fibrillation (AF) is an important risk factor for recurrent stroke. The study by Bugnicourt et al. [1] describes the incidence of newly diagnosed AF (NDAF) in a clinical cohort of stroke patients in whom no obvious cause could be elucidated (cryptogenic stroke). Using information obtained through a telephone-based interview (which was subsequently corroborated by hospital medical records), the investigators observed NDAF in one in eight patients approximately 2.3 years following their incident stroke [1]. Noteworthy is that two-thirds of patients with NDAF presented with vascular events while, in the remaining one-third, NDAF was detected asymptomatically during prolonged cardiac monitoring [1]. Previous population-based studies have focused largely on the contribution of AF to the development of stroke [2] and the prevalence of AF during acute ischaemic stroke [3]. Few studies have evaluated the incidence of AF following incident stroke. Using clinical trial data from the Virtual International Stroke Trials Archive (VISTA), Kamel et al. [4] observed delayed detection of AF in 7% of stroke patients who were followed up to 90 days. By contrast, investigators of the current study reported detection rates of 13% in a clinical cohort that was followed for a longer duration of 2.3 years [1]. The actual rates are likely higher given the opportunistic manner in which AF was elicited (often at the discretion of the attending physician). In several studies, despite a relatively short period of cardiac monitoring of 7–14 days, AF was detected in approximately one in 20 stroke patients [5]. These rates double when patients are selected a priori for cardiac monitoring on the basis of cryptogenic stroke etiology [5]. The importance of asymptomatic AF as a risk factor for recurrent stroke is further emphasized in the recent Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) trial, which observed greater risk of ischaemic stroke and systemic embolism in patients with subclinical atrial tachyarrhythmias [6]. How should stroke patients be screened for AF paroxysms? Several non-invasive and invasive methods exist [such as ambulatory (Holter) electrocardiography, patient-triggered event recorder, mobile cardiovascular telemetry and implantable loop recorder] [5]. In practice, however, the optimal choice of monitoring depends on the availability of devices and relevant expertise, cost considerations, convenience and acceptability to patients and the desired duration of monitoring. By modeling the lifetime cost and utility of warfarin therapy, prolonged cardiac monitoring was considered to be cost-effective in detecting NDAF [7]. Should AF be screened in patients with cryptogenic stroke or also in those with lacunar or large artery thrombosis? Monitoring for AF paroxysms in patients with cryptogenic stroke is intuitive as AF detection may better characterize mechanisms underlying stroke and indicate a cardioembolic etiology. A randomized prospective study [the Cryptogenic Stroke and Underlying Atrial Fibrillation (CRYSTAL AF) study] is currently being performed to compare the performance of a subcutaneous cardiac monitor (Reveal XT; Medtronic, Minneapolis, MN, USA) and standard arrhythmia monitoring (control arm) [8]. On the other hand, it is also arguable that AF screening in stroke patients with presumed lacunar or atherothrombotic etiology may be justifiable as smaller cardioembolic thrombi are prone to spontaneous recanalization resulting in minor lesions mimicking lacunar infarcts, while larger thrombi may occlude larger arteries resembling large artery thrombosis. In the study, stroke patients with lacunar infarcts with no evidence of small vessel disease were considered to be at risk of NDAF, whereas lacunar stroke patients with either leukoaraiosis or microbleeds were deemed not likely to have coexistent cardioembolism [1]. The authors proposed a clinical risk score to identify cryptogenic stroke patients who are at risk of developing NDAF, where age 72 years = 2 points, coronary artery disease = 1 point, previous stroke = 1 point and left atrial area 16 cm = 2 points (total score range, 0–6) [1]. A score of 0–1 effectively rules out the development of NDAF in patients with a cryptogenic stroke etiology. Contingent on independent validation in a multi-center prospective cohort, these scores may assist in the selection of stroke patients in whom prolonged cardiac monitoring is warranted. Although randomized data on the optimal management of AF detected after stroke are lacking, the advent of novel classes of oral anticoagulants (i.e. direct thrombin inhibitors and factor Xa inhibitors) and left atrial appendage closure devices are likely to contribute to this changing landscape.