Atrial fibrillation is a very common arrhythmia in clinical practice, and it is feared due to the risk of embolic complications. In recent years, there has been a significant increase in interest in the arrhythmia, with improvements in the treatment and prevention of these complications.
Studies show that it is possible to stratify the risk of embolic phenomena based on clinical parameters, currently with the Chads-Vasc score. It is important to note that, in this score, the clinical manifestation of the way atrial fibrillation presents (paroxysmal, persistent, or permanent) does not increase or decrease the risk. Whatever this form, a patient with a high score has an increased risk and may benefit from prevention.
This concept has been corroborated by data from clinical studies. In the Active study, patients with different forms of presentation of the arrhythmia were evaluated. At the end of the follow-up, the authors observed that patients with the paroxysmal form had the same risk of thromboembolic complications compared to other patients (with permanent or persistent AF). Thus, even short episodes of arrhythmia pose a greater risk of embolism.
More recently, other data sources have brought more arguments that support this statement. The Assert study evaluated patients with artificial pacemakers capable of diagnosing short episodes of arrhythmia. Of the 2580 patients, who did not have documented atrial fibrillation, 261 presented, in the follow-up of 2.5 years, episodes of atrial tachyarrhythmias (heart rates above 190 beats per minute for more than 6 minutes). These patients not only had more clinically documented episodes of atrial fibrillation but also a risk of embolic events.
Another study that highlighted the importance of detecting episodes of atrial arrhythmias was Crystal-AF. In it, patients with cryptogenic stroke (of unknown or obscure origin) were evaluated with an implantable monitor adjusted to detect episodes of atrial fibrillation lasting more than 30 seconds. Prolonged monitoring detected arrhythmias in 8.9% of patients, compared to 1.4% of those monitored for 24 hours in the first 6 months, and 12.4% versus 2.0% at the end of one year.
Based on these findings, it is increasingly common to use longer monitoring periods. Devices like the CardioSeven can extend patient monitoring for up to 7 days. This feature has expanded the use of this tool in a simple and practical manner.
Even with all this evidence, new questions arise: how much time in atrial fibrillation is sufficient to result in an increased risk of embolic events? What is the most appropriate monitoring time for detecting unsuspected arrhythmias in clinical practice? Is anticoagulant treatment effective and safe for the prevention of events? 
Medical science is like this… The more data, the more questions arise, providing hypotheses for new studies, and thus knowledge grows, leading to improvements in the care of our patients. 
1.  Hohnloser SH, Pajitnev D, Pogue J, Healey JS, Pfeffer MA, Yusuf S, et al. Incidence of Stroke in Paroxysmal Versus Sustained Atrial Fibrillation in Patients Taking Oral Anticoagulation or Combined Antiplatelet Therapy. J Am Coll Cardiol [Internet]. 2007 Nov;50(22):2156–61. 2.  Healey JS, Connolly SJ, Gold MR, Israel CW, Van Gelder IC, Capucci A, et al. Subclinical Atrial Fibrillation and the Risk of Stroke. N Engl J Med [Internet]. 2012 Jan 12;366(2):120–9.3.  Sanna T, Diener H-C, Passman RS, Di Lazzaro V, Bernstein RA, Morillo CA, et al. Cryptogenic Stroke and Underlying Atrial Fibrillation. N Engl J Med [Internet]. 2014 Jun 26;370(26):2478–86.

Dr. Márcio Jansen de Oliveira Figueiredo
Professor of the Cardiology Discipline, responsible for the Arrhythmias Service at UNICAMP,
Specialist in Cardiology by SBC, and in Electrophysiology by SOBRAC.