Multicentre, prospective cohort study in patients with a history of HF with preserved or reduced ejection fraction admitted to hospital with acutely decompensated HF. Eligible and consenting patients will be enrolled at 3 Hamilton, Ontario area hospitals and receive 28-day ECG monitoring implemented at the time of hospital discharge. Patients will be followed for a total of 1 year from hospital discharge.

In patients discharged from hospital after an admission for acute heart failure (HF) decompensation, subclinical atrial fibrillation (AF) of 30 minutes or greater in duration is common (at least 15% of patients without prior AF) and is associated with increased risk of re-hospitalization within 30-days.

Study Objectives:

1. To evaluate the prevalence of subclinical AF ≥30 minutes in duration in patients discharged from hospital following an admission for acute HF exacerbation and who have no known history of clinical AF.
2. To examine the temporal association between subclinical AF ≥30 minutes in duration and 30-day hospital readmission for HF.

Inclusion Criteria:

1. Hospitalized with a most responsible diagnosis of acute decompensated heart failure.
2. Clinical signs and symptoms of heart failure as per the Boston criteria (i.e. score ≥8)

Exclusion Criteria:

1. History of clinical atrial fibrillation
2. History of hypertrophic cardiomyopathy or congenital heart disease.
3. End stage renal disease or advanced renal dysfunction (e.g. estimated glomerular filtration rate, eGFR < 15 mL/min/1.73 m2)
4. Cardiothoracic surgery in the past 30 days or imminently planned (does not include percutaneous procedures).
5. Unable or unwilling to provide informed consent.
6. Presence of a pacemaker or an ICD with an atrial lead (which can already diagnose AF).

Patients with a history of HF who are admitted to hospital with acutely decompensated HF and have no prior history of AF.