The LOOP study aims to determine whether screening for atrial fibrillation (AF) with implantable loop recorder and initiation of oral anticoagulation (OAC) if AF is detected will reduce the risk of stroke and systemic arterial embolism in patients with risk factors for stroke.

Background:

Ischemic stroke is an increasing health problem world-wide (Heidenreich PA, et al. Circulation 2011; PMID 21262990). At least 20% of ischemic strokes are attributable to atrial fibrillation (AF) (Marini C, et al. Stroke J Cereb Circ 2005; PMID 15879330). Another 30% are so-called cryptogenic, possibly related to undiagnosed AF (Brachmann J, et al. Circ Arrhythm Electrophysiol 2015; PMID 26763225). In approximately 30% of a general population of pacemaker or cardioverter defibrillator patients, previously unknown AF will be detected during the first 2-3 years after implantation (Healey JS, et al. N Engl J Med 2012; PMID 22236222; ASSERT). Although the majority of these AF episodes are short-lasting and asymptomatic, the ASSERT study found that such AF is associated with risk of stroke. Since this was published, screening for AF has received intensified attention by researchers and the industry, although available evidence does not yet support systematic mass screening.

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Aims:

The LOOP study will determine whether long-term continuous screening and initiation of OAC for AF episodes lasting ≥6 minutes will reduce the risk of stroke in patients with stroke risk factors.

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Methods:

Patients from the general population will receive a letter of invitation from one of four study centers located in 3 of Denmark's 5 administrative regions.

Eligible study participants must be ≥70 years old and have ≥1 of the following stroke risk factors; hypertension, diabetes, heart failure or previous stroke, while any history of AF or existing cardiac implantable electronic device are exclusion criteria.

A total of 6000 participants will be randomized 3:1 to control (n=4500) or to receive an implantable loop recorder with continuous remote monitoring (n=1500) and initiation of OAC if AF is detected.

The primary endpoint is time to first stroke or systemic arterial embolism. The trial is event-driven and planned to continue until 279 adjudicated primary events have occurred.

Sub-studies include AF characterization, health economic analyses, quality-of-life assessments, cognitive function assessments, and studies of risk markers from 12-lead ECG, genetics, cardiac and brain imaging, biochemistry, and more.

Inclusion Criteria:

• Age 70-90 years, and

• Previously diagnosed with ≥1 of:

  • Diabetes mellitus (type 1 or type 2, with or without medical therapy)
  • Hypertension (with or without medical therapy)
  • Heart failure
  • Previous diagnosed stroke (previous transient ischemic attack is not considered an inclusion criterion)

Exclusion Criteria:

• History of atrial fibrillation or flutter irrespective of type
• Cardiac pacemaker or defibrillator (with or without re-synchronization therapy)
• Contraindication to oral anticoagulation therapy
• Anticoagulation therapy; vitamin K antagonists, direct oral anticoagulants, or (low-molecular) heparins. Therapy with platelet inhibitors such as acetyl-salicylic acid, clopidogrel, persantine is not considered an exclusion criterion
• Renal failure treated with permanent dialysis
• Uncorrected congenital heart disease, or severe valvular stenosis, obstructive cardiomyopathy, active myocarditis, or constrictive pericarditis.
• On a waiting list for major surgery (cardiac, thoracic or abdominal)
• Cardiac or thoracic surgery has been performed within 3 months from inclusion
• Any major organ transplant (e.g. lung, liver, heart, or kidney)
• Cytotoxic or cytostatic chemotherapy and/or radiation therapy for treatment of a malignancy within 6 months before randomization or clinical evidence of current malignancy with the following exceptions: Basal or squamous cell carcinoma of the skin, cervical intraepithelial neoplasia, prostate cancer (if stable, localized disease with a life expectancy of > 2.5 years in the opinion of the investigator)
• Life-expectancy shorter than 6 months
• Known to be human immunodeficiency virus (HIV) positive with an expected survival of less than 5 years due to HIV infection
• Recent (within 3 months) history of alcohol or drug abuse based on self-reporting
• Any condition (e.g. psychiatric illness, dementia) or situation, that in the investigators opinion could put the subject at significant risk, confound the study results, or interfere significantly with the subject participation in the study
• Unwillingness to participate or patient does not understand Danish language