Atrial fibrillation (AF) is a major cause of ischemic strokes. AF-related strokes are more severe than those of other etiologies [1] and stroke patients with AF exhibit a high risk of recurrent ischemic events [2]. AF might escape routine stroke etiology work-up as paroxysmal AF (pAF) occurs intermittently. The identification of pAF is of major clinical importance as it usually changes the secondary stroke prevention strategy with respect to the initiation of oral anticoagulation instead of antiplatelet therapy. This leads to a 40% relative risk reduction of recurrent strokes events [3].

So far, three randomized trials have demonstrated that a high proportion of patients with pAF can be identified by prolonged electrocardiography (ECG)-monitoring [4-6] compared to a standard stroke workup. However, the clinical relevance of AF detected by different means is unknown. For instance, short episodes detected by implantable cardiac monitors are a frequent finding in patients with cardiovascular risk factor (29% within 18 months) while the overall stroke rate is low [7].

A latent or early symptomatic stage is a key principle of a screening program [8]. This principle has not yet been proven for AF detection in stroke patients. We aimed to follow-up patients after a 6-month monitoring period for additional 2.5 years to investigate if (1) detection rate of AF during follow-up is different between both study arms and (2) ischemic stroke rate is different between both study arms.

Baseline characteristics and results until 12 months of follow-up have been published and are included here to depict the full study results [6]. One thousand six hundred four patients ≥60 years with International Classification of Diseases (ICD) diagnosis 63.x were screened and finally 402 patients were enrolled and randomized at four study centers in Germany from May 8th, 2013 until August 31st, 2014. Four patients were randomized erroneously (two in each group) and were excluded from the final analysis. Two hundred patients were assigned to the intervention group and 198 to the control group. The study population had a mean±SD age of 73±7 years (range, 60 to 96). Forty percentage (160 patients) were female.

Details on the monitoring in the intervention and control group have been published previously [6]. In brief, in the intervention group, 197 patients (99.5%), 128 (75.3% of those remaining in the study and without detected AF) and 116 patients (75.8%) underwent study monitoring at baseline, after 3 and after 6 months, respectively.

In the control group, 188 of 198 patients (95%) underwent Stroke-Unit telemetry for a median duration of 73 hours (IQR, 54 to 84) and 149 of 198 patients (75%) received additional Holter-ECG-monitoring for a median of 24 hours (IQR, 22 to 25). One hundred and eighty-one of 198 patients (91.4%) in the control arm and 178 of 200 patients (89.0%) in the intervention arm had at least 24 hours of monitoring outside the study monitoring.

The primary trial ended as planned after all patients had completed 12 months of follow-up and the last patient’s final visit took place on September 16th, 2015. After 12 months, all 342 patients still in the trial were offered an extended follow-up for an additional 2 years, and 274 (80.1%) consented for the extended follow-up. Details are shown in Figure 1 and baseline characteristics of patients consenting for extended follow-up are shown in Table 1. Patients consenting for extended follow-up were on average 3 years younger than those who did not give consent, tended to have less comorbidities, more often had a history of myocardial infarction and coronary artery disease, and had lower initial National Institutes of Health Stroke Scale (NIHSS) score (Supplementary Table 1).

We present data on 3 years of follow-up in a study randomizing patients aged ≥60 years with acute ischemic strokes to enhanced and prolonged ECG-monitoring by means of three 10-day Holter-ECGs (EPM) or standard-of care to detect pAF. While there was a significant difference in the primary endpoint of first detection of atrial fibrillation prior to recurrent stroke after 6 and 12 months in the EPM group, this difference diminished over time due to a higher detection rate of AF in the control group and became non-significant beyond 2 years of follow-up. We found a high adherence to anticoagulation in patients with detected new-onset AF. Importantly, there were numerically less strokes, TIAs, and deaths in the EPM arm compared to the control arm.

To date, three large randomized trials for intensified AF detection have been performed in ischemic stroke patients. The 0-Day Cardiac Event Monitor Belt for Recording Atrial Fibrillation After a Cerebral Ischemic Event (EMBRACE) trial [4] applied a 30-day external event recorder in 572 patients with cryptogenic stroke, starting 75 days after the stroke event, while the Study of Continuous Cardiac Monitoring to Assess Atrial Fibrillation After Cryptogenic Stroke (CRYSTAL-AF) study [5] used an implantable cardiac monitor in 441 patients with cryptogenic stroke starting 38 days after the stroke event. The third trial is the Find-AF trial [6], which also included approximately 50% of non-cryptogenic stroke patients and initiated the intervention within a median of 3 days after the qualifying ischemic stroke. All three trials found significantly more cases of AF in the intervention as compared to the control arm. However, the follow-up in EMBRACE was only 90 days and no information on ischemic cerebral events beyond 90 days of follow-up has been reported so far. In CRYSTAL-AF, the minimum duration of follow-up was 12 months, but only a minority of patients was followed beyond 2 years. There were numerically less strokes and TIAs in the intervention arm, but only the combined number of strokes and TIAs (20 vs. 24) has been reported and these events were not blindly adjudicated [12].

Although the intervention only lasted 6 months in our study, EPM still remained superior to standard-of-care in detecting AF after 12 months (13.5% vs. 6.6%, P=0.021), yet losing significance after 24 months (14.0% vs. 9.1%, P=0.13) and 36 months (14.5% vs. 11.1%, P=0.37). While more patients with AF were detected in the intervention arm in the first 6 months after randomization, there were more AF cases detected in the standard-of-care arm during the following 2.5 years. This suggests that EPM mostly identified AF cases that otherwise would have been detected as clinical AF at a later stage. This is supported by the fact that most AF cases during extended follow-up were diagnosed by routine surface ECG, mostly done by the patients’ general practitioner or after having had a recurrent cerebrovascular event. Interestingly, EPM within the first 6 months found as much as 5/6 of all AF cases that were detected during the complete 3 years of follow-up. Our data suggest that AF episodes during a 10-day ECG monitoring are precursors of clinically relevant AF. This might be in contrast to AF episodes >2 minutes detected during continuous monitoring in CRYSTAL-AF: AF was diagnosed in 30% of patients during 36 months of follow-up with an implantable loop recorder, but the detection rate in the control arm was as low as 3% after 3 years [12]. While these differences may also partly be explained by different stroke characteristics (younger patients, lower NIHSS score), the minimum duration of AF that is of clinical relevance may depend on the duration and type of monitoring. We recently showed that AF episodes of 30 seconds or longer (detected by 7-day Holter-ECG) are associated with more severe strokes (comparable to strokes in patients with AF on surface ECG), while episodes lasting <30 seconds were associated with less severe strokes [13]. This is an argument that the threshold of 30 seconds duration of AF on a rhythm strip seems to be adequate for Holter monitoring ≤10 days. Interestingly, in patients with continuous monitoring by implanted pacemakers or defibrillators, but without prior stroke, it has recently been shown that mainly AF episodes that last for >24 hours are associated with a high stroke risk [14].

The adherence to anticoagulation in monitoring trials seems to be higher than in randomized anticoagulation trials, e.g., the discontinuation rate in Rivaroxaban Versus Aspirin in Secondary Prevention of Stroke and Prevention of Systemic Embolism in Patients With Recent Embolic Stroke of Undetermined Source (NAVIGATE-ESUS) [15] and Dabigatran Etexilate for Secondary Stroke Prevention in Patients With Embolic Stroke of Undetermined Source (RE-SPECT ESUS) [16] was 15% and 25%, respectively. The fact that anticoagulation therapy was mandated by a specific diagnosis (AF in this case) may explain the higher adherence rate in CRYSTAL-AF and Find-AF_RANDOMISED.

Although our data imply that short episodes of AF detected during 10-day Holter-ECG are of clinical relevance, this does not prove that they benefit from anticoagulation. Unfortunately, patients with short episodes of AF detected early after stroke have not been included in randomized anticoagulation trials. The question whether prolonged ECG-monitoring for AF after stroke not only increases the AF detection rate, but reduces the risk of recurrent stroke remains unknown and our trial was not powered to provide a definite answer. However, we previously reported numerically fewer stroke, TIAs, and deaths after 12 months in the EPM group [6] and this trend corroborated after 36 months. This is in line with a recent meta-analysis of randomized and observational studies that found a significant reduction of cerebral ischemic events by intensified ECG monitoring [17]. In summary, these findings would support the current clinical practice of treating patients with (short) AF-episodes detected after stroke with anticoagulation. Nevertheless, an adequately powered outcome trial with ischemic stroke and systemic embolism as the primary endpoint is needed to establish prolonged monitoring as an efficacious strategy for secondary stroke prevention. At least one trial, called Find-AF 2 (NCT 04371055) is underway and has already randomised more than 1,100 patients.

Find-AF_RANDOMISED should be interpreted in the context of its limitations. The trial was conducted in Germany and we cannot rule out that results would have differed in other countries, health systems or ethnicities. Only 68% and 65% of patients accepted the second and third Holter-ECG. This problem may be solved by more comfortable devices, such as adhesive ECG-patches and/or by an early risk stratification based on age [18], left atrial size and function [19], supraventricular ectopy [20], brain natriuretic peptides [21,22], or others as recommended in a recent consensus paper [23].

The decision to extent the follow-up was made during the study conduct and only 80% of patients consented, which is a potential bias. Differences between groups in number of visits to the general practitioner, access to care, socioeconomic status could have resulted in disparities in reporting AF-related symptoms and subsequently receiving an ECG. We tried to address this potential bias by competing risk analysis, but cannot totally excluded it. Moreover, we did not specifically assess the routine monitoring that patients received during extended follow-up. According to registry data from Germany [24], most patients are treated by their General Practitioner and do not frequently receive prolonged Holter-ECG monitoring. We suppose that our study patients were treated similarly which is in line with 2/3 of AF cases during extended follow-up being detected by 12-lead ECG, and only a minority by implantable loop recorder or prolonged Holter-ECG monitoring.

It was not possible to blind physicians and patients to study assignment. To overcome potential bias, we chose to assess the primary endpoint “detection of AF” and the major secondary endpoint “recurrent cerebral ischemic event” by blinded endpoint committees (prospective randomized open blinded endpoint [PROBE] design). In addition, the sample size and the number of stroke events of this trial were too small to give more than a trend for recurrent cerebral ischemic events. Finally, our results were obtained in stroke patients ≥60 years and AF prevalence is likely to be lower in younger patients [18].

In conclusion, the extended follow-up of Find-AF_RANDOMISED showed that enhanced and prolonged ECG-monitoring detected AF episodes that otherwise would have likely been detected later by clinical practice. The compliance with anticoagulation in AF patients was excellent (>90%) and there was a favorable trend towards fewer strokes, TIAs, and deaths in the EPM arm which might be the result of an earlier initiation of anticoagulation after AF detection. These findings provide the rationale for a larger randomized trial to prove that recurrent or continuous ECG-monitoring for AF and consecutive anticoagulation can reduce recurrent ischemic strokes.