The purpose of this protocol is to assess the sensitivity and specificity of a photoplethysmography (PPG)-based algorithm for the detection of atrial fibrillation as compared to a gold-standard assessment (wearable ECG patch) among a population of individuals with known atrial fibrillation and without known atrial fibrillation over a 7-day study period.

Atrial fibrillation (Afib) is the most common cardiac arrhythmia in the United States, affecting up to one in four individuals across the lifespan, and is associated with substantial morbidity and mortality. Fifteen percent of strokes in the United States are attributable to Afib, and nearly 20% of these occur in individuals with no prior Afib history. Because Afib is often paroxysmal, one-time screening is unlikely to capture those at risk. Thus, there has been an increasing interest in leveraging monitoring for Afib via wearable devices, which provide a novel method to detect Afib and determine the burden of Afib in the general population. Devices such as the WHOOP 4.0 strap use advanced sensors to detect pulse rate and other physiologic metrics in real-time. Given the high degree of pulse-rate variability in Afib, it is clear that algorithms evaluating data from these devices may be able to detect asymptomatic Afib. However, the sensitivity and specificity of the algorithm operating on data from the WHOOP 4.0 strap have not been formally evaluated in a clinical setting.

The WHOOP strap measures changes in blood flow via photoplethysmography (PPG), from which timing between successive heartbeats ("beat-to-beat intervals") is measured. While normal sinus rhythm tends to display beat-to-beat intervals of similar magnitude, those of cardiac arrythmias are characterized by higher variability and may follow particular patterns.

The primary objective of this study is to assess the sensitivity and specificity of the WHOOP Strap ANF 1.0 classification algorithm for the detection of Afib as compared to a gold-standard assessment (one-week ECG patch monitoring using the BioTel ePatch).

Inclusion Criteria:

• Age >= 22 years
• Known diagnosis of atrial fibrillation OR no history of arrhythmia as documented in the patient medical record
• Seen in a Yale New Haven Hospital-associated Primary Care or Cardiology Clinic
• Cell phone (IOS 15.0 or greater or Android 10 or greater) with an active data plan and willing to install the WHOOP Mobile Application software
• Full-time US resident
• Able to read, understand, and provide written informed consent in English
• Willing and able to participate in the study procedures as described in the consent form
• Able to communicate effectively with and follow instructions from the study staff

Exclusion Criteria:

• Pre-existing WHOOP user with active account
• Has implantable cardiac device (e.g., pacemaker, ICD, LVAD)
• Solid organ transplant
• Sensitivity or allergy to ECG patch or skin glue
• Unwilling to wear WHOOP 4.0 strap for one week
• Unwilling to wear BioTel (ECG patch) ePatch for one week
• WHOOP strap should be the only wearable on the arm. Individuals unwilling to adhere to the proper usage of the WHOOP strap will be excluded.
• Unwilling to install the WHOOP Mobile Application software
• Unable to provide informed consent
• Non-English speaking (as the WHOOP Mobile Application software is English only)
• Known sensitivity to medical adhesives, isopropyl alcohol, watch bands, or electrocardiogram (ECG) electrodes including known allergy or sensitivity to polyamide, polyester, or elastane bands primarily used in wrist worn fitness devices
• Symptomatic (or active) allergic skin reactions
• Significant tremor that prevents the subject from being able to hold still.
• Acute myocardial infarction (MI) within 90 days of screening or other cardiovascular disease that, in the opinion of the investigator, increases the risk to the subject or renders data uninterpretable.
• Pregnant women: Women who report being pregnant at the time of study participation.
• Subjects taking rhythm control drugs including amiodarone, dronedarone, dofetilide, sotalol, flecainide, ibutilide, lidocaine, procainamide, propafenone, quinidine, tocainide.

The study population will include adults seen in primary care and cardiology clinics associated with a single health system. The prospective cohort will comprise three distinct populations - individuals with a known history of persistent atrial fibrillation, individuals with paroxysmal atrial fibrillation, and individuals without a history of cardiac arrhythmia of any kind.