Atrial fibrillation (AF), with an annual incidence of 5.38 per 1,000 person-years[2, 3], is one of the most common clinical arrhythmias. A large body of literature has documented that Atrial fibrillation is a potent risk factor for stroke, and early detection may allow timely therapeutic intervention. As a supplement to qualitative diagnosis, the application of long-term continuous ECG monitoring technology brought the concept of a quantitative diagnosis of atrial fibrillation and also led to the study on the relationship between atrial fibrillation burden. But there remains no clear consensus on whether the burden of atrial fibrillation independently influences the risk of thromboembolism.
Some studies have recently documented that device-detected atrial fibrillation burden, expressed as a percentage of time spent in atrial fibrillation, may have a biological gradient relation with stroke risk and could be combined with the CHA2DS2-VASc score as a predictor of stroke[4]. However, other studies declare that AF burden has no association with ischemic stroke after adjusting for traditional risk scores (CHA2DS2-VASc score)[5] [6].
In our cohort, we identified 210 patients with atrial fibrillation by ambulatory electrocardiogram, and 18 stroke events occurred at a median follow-up of 11 months preceding the ambulatory electrocardiogram. We did not detect any strong association between AF burden, AF frequency and subsequent stroke, whereas Clinical characteristics-based stratifications such as CHA2DS2-VASc score were highly predictive of new stroke, with a predictive value of 92% when using CHA2DS2-VASc score of 4.5 as a cutoff. In this regard, our findings are more consistent with the concept that AF is a marker of an underlying atrial myopathy[7] [8, 9]and that once AF occurs, stroke risk can be best predicted by underlying risk factors (as quantified by the CHA2DS2-VASc score) in patients with atrial fibrillation;conversely, the specific burdens become less relevant.
This difference in findings across studies may lie in the heterogeneity of study cohorts. Most researchers restricted study participation to patients with paroxysmal AF and excluded all other patterns of AF[10], while all patterns of AF patients were included in our cohort. Therefore, AF burden was high in both the stroke group and the control group in our study, which attenuated the difference between the two groups. Meanwhile, compared with those earlier studies, most patients were of advanced age, and had multiple comorbidities known to be risk factors for ischemic stroke events in our cohort, with the preponderant high CHA2DS2-VASc score. These findings further highlight the impact of the clinical characteristics and effectiveness of the CHA2DS2-VASc scoring system, thus AF burden may become less predictive of stroke among higher risk patients.
In a prospective study of 9850 patients with cardiac implantable electronic device, a strong relationship of temporal proximity of AF with ischemic stroke was found, which was highest in the 5 to 10 days after the episode of AF events (odds ratio 17.4, 95% confidence interval, 5.39–73.1), and no longer elevated by 30 days[11]. It was suggested that rapidly acting anticoagulants should be transient used as a stroke-preventive strategy during onset and offset of paroxysmal or persistent AF. However, a great portion of the subjects had been on medication such as anticoagulant, antiplatelet agents and statins in our cohort, which reflected good control of ischemic factors and might lead to low and delayed occurrence of endpoint events. Therefore, ischemic stroke occurred at a median of 6.5 months rather than the extremely short-time stroke in the above mentioned studies. AF burden varies in a short time, and its impact on embolism occurs quickly and once the period of atrial fibrillation ends, its impact will disappear rapidly. Our results raise the hypothesis that whether higher CHADS2-vasc increases the risk of relatively long-term stroke while AF burden confers a short-term increase in stroke risk. Further investigation is deserved.
AF was detected by ambulatory electrocardiogram in our cohort, which was simple, convenient, operable, and more typical of the general AF population. Screening tools such as pacemakers, implantable loop recorders, and even wearable continuous monitors can identify AF better and yield more information related to the variation of AF burden which requires long-term or frequent ECG monitoring[12]. Nonetheless, AF was arbitrarily defined as a HAR event lasting longer than 5–6 min in these studies, and AF may be missed if the onset of AF is short or slow. Additionally, on account of AT or frequent premature atrial complexes and far-field R-wave over-sensing, there was a 17.3% false-positive rate of cardiovascular implanted electronic devices(CIEDs)detected short period of AF[1, 13]. Such bias could be substantially under control in ambulatory electrocardiography monitoring because the 12-lead electrocardiogram can detect and analyze atrial waves synchronously, which is helpful to distinguish atrial fibrillation from atrial premature beats, atrial tachycardia, atrial flutter, and pseudo-error. Meanwhile, The cost and invasiveness of these devices limit their widespread adoption, Only a few people are implanted with CIEDs, thus it remains unclear whether the conclusions obtained from the small population of CIEDs detected AF could be directly extrapolated to the practice population, not to mention those without CIEDs More detailed exploration of the CIEDs-detected AF burden as a novel variable for stroke might need tries in a more comprehensive study cohort with multiple risk factors, and leadless pacemaker may come to the fore, because the overall accuracy of the leadless ICM for AF duration based on the incoherence of the R–R interval is 98.5%[14].