Rationale Atrial fibrillation (AF) often occurs transiently in the setting of an acute stressor (e.g.

medical illness or surgery). Uncertainty exists as to whether AF Occurring Transiently with Stress (AFOTS) is secondary to a reversible precipitant and is benign, or is a first presentation of paroxysmal AF and associated with a risk of stroke. AFOTS is a common occurrence (>40% in some intensive care settings), but there is a lack of evidence to guide its management and guidelines have called for further research in this area. Retrospective data suggest that many patients with AFOTS (>50%) will experience recurrent AF. These estimates were obtained without using sensitive methods for AF detection, which raises the possibility that the true rate of recurrent AF is much higher. As the rate of recurrent AF increases, it becomes increasingly likely that AFOTS is just the first detection of typical "clinical" AF.

Objective To use a sensitive strategy to determine the rate of recurrent AF among patients who experienced AFOTS following i) non-cardiac surgery OR ii) medical illness, compared to matched controls.

Methods Two multi-centre, 138-patient, observational cohorts. AFOTS patients will have new AF, documented by 12-Lead ECG or surface monitoring, during hospitalization for non- cardiac surgery (Cohort 1) or medical illness (Cohort 2).

Controls will be patients without a history of AF who are matched for age (within 5 years), sex and exposure to stressor. Participants will wear a 14-day ECG monitor at 1 and 6 months after discharge. The endpoint is detection of AF.

Impact

If the incidence of AF after AFOTS is >80%, clinicians could be advised to treat AFOTS like "clinical" AF and initiate anticoagulation according to guidelines. Otherwise, a strategy of surveillance for AF would be advised.

Hypothesis

1. Patients who experience AFOTS will have a higher future incidence of AF and of stroke compared to patients exposed to a similar stressor but who did not develop AF.
2. The risk of recurrent AF after AFOTS will be sufficiently high (> 80%) to warrant routine initiation of long-term OAC in all cases.

Inclusion Criteria:

Cases will be patients without a history of AF who experience new AFOTS during hospital admission for non-cardiac surgery (non-cardiac surgery study) OR medical illness (medical illness study) Controls will be patients who were exposed to a similar stressor but did not develop AF (matched for age within 5 years, sex and stressor).

All participants will have a CHA2DS2-VaSc score >1 for men, >2 for women.

Exclusion Criteria:

1. Documented prior history of AF.

2. Patients whose rhythm is AF at the time of discharge from hospital

3. Patients unsuitable for study follow-up because the patient:

   1. is unreliable concerning the follow-up schedule
   2. cannot be contacted by telephone
   3. has a life expectancy less than one year

4. Unwilling or unable to participate in the study

5. Presence of an implanted pacemaker or defibrillator.

6. Documented significant allergy to ECG electrode adhesive.

7. Residence in a chronic care facility

8. Diagnosed with Ischemic Stroke or Systemic embolism on admission

9. Primary cardiac admitting diagnosis (i.e. myocardial infarction, heart failure, pericarditis, arrhythmia)

10. Patients with Stage V Chronic Kidney Disease

Patients admitted for non-cardiac surgery OR medical Illness, who develop new Atrial Fibrillation Occurring Transiently With Stress (AFOTS) during hospital admission (case group), OR who are exposed to the same stressor, but did not develop AF (control group).

All patients will be candidates for OAC therapy as per the Canadian Cardiovascular Society (CCS) AF algorithm [12]. Patients with a history of AF will be excluded from the study.