Detection of Atrial Fibrillation Using Insertable Cardiac Monitors in Patients With Cryptogenic Stroke in Japan (the LOOK Study): Protocol for a Prospective Multicenter Observational Study
Authors: Suda Satoshi , Katano Takehiro , Kitagawa Kazuo , Iguchi Yasuyuki , Fujimoto Shigeru , Ono Kenjiro , Kano Osamu , Takekawa Hidehiro , Koga Masatoshi , Ihara Masafumi , Morimoto Masafumi , Yamagami Hiroshi , Terasaki Tadashi , Yamaguchi Keiji , Okubo Seiji , Ueno Yuji , Ohara Nobuyuki , Kamiya Yuki , Takeuchi Masataka , Yazawa Yukako , Terasawa Yuka , Doijiri Ryosuke , Tsuboi Yoshifumi , Sonoda Kazutaka , Nomura Koichi , Shimoyama Takashi , Kutsuna Akihito , Kimura Kazumi 
Published: April 2023

Background
Paroxysmal atrial fibrillation (AF) is a probable cause of cryptogenic stroke (CS), and its detection and treatment are important for the secondary prevention of stroke. Insertable cardiac monitors (ICMs) are clinically effective in screening for AF and are superior to conventional short-term cardiac monitoring. Japanese guidelines for determining clinical indications for ICMs in CS are stricter than those in Western countries. Differences between Japanese and Western guidelines may impact the detection rate and prediction of AF via ICMs in patients with CS. Available data on Japanese patients are limited to small retrospective studies. Furthermore, additional information about AF detection, including the number of episodes, cumulative episode duration, anticoagulation initiation (type and dose of regimen and time of initiation), rate of catheter ablation, role of atrial cardiomyopathy, and stroke recurrence (time of recurrence and cause of the recurrent event), was not provided in the vast majority of previously published studies.

Objective
In this study, we aim to identify the proportion and timing of AF detection and risk stratification criteria in patients with CS in real-world settings in Japan.

Methods
This is a multicenter, prospective, observational study that aims to use ICMs to evaluate the proportion, timing, and characteristics of AF detection in patients diagnosed with CS. We will investigate the first detection of AF within the initial 6, 12, and 24 months of follow-up after ICM implantation. Patient characteristics, laboratory data, atrial cardiomyopathy markers, serial magnetic resonance imaging findings at baseline, 6, 12, and 24 months after ICM implantation, electrocardiogram readings, transesophageal echocardiography findings, cognitive status, stroke recurrence, and functional outcomes will be compared between patients with AF and patients without AF. Furthermore, we will obtain additional information regarding the number of AF episodes, duration of cumulative AF episodes, and time of anticoagulation initiation.

Results
Study recruitment began in February 2020, and thus far, 213 patients have provided written informed consent and are currently in the follow-up phase. The last recruited participant (May 2021) will have completed the 24-month follow-up in May 2023. The main results are expected to be submitted for publication in 2023.

Conclusions
The findings of this study will help identify AF markers and generate a risk scoring system with a novel and superior screening algorithm for occult AF detection while identifying candidates for ICM implantation and aiding the development of diagnostic criteria for CS in Japan.

Trial Registration
UMIN Clinical Trial Registry UMIN000039809; https://tinyurl.com/3jaewe6a

International Registered Report Identifier (IRRID)
DERR1-10.2196/39307