Atrial fibrillation (AF) often starts with short episodes of rapid irregular heartbeats that are only detected by implanted pacemakers or defibrillators. Usually people don't know that they have these episodes. Over time, these episodes can happen more often and last for longer periods. In some people, the heart eventually remains permanently in a fast irregular rhythm, known as atrial fibrillation. This condition can lead to strokes and blood clots. If physicians could detect atrial fibrillation at a very early stage they could treat people early and possibly prevent the condition from becoming permanent. People with implanted devices allow a unique opportunity to constantly monitor the heart rhythm so investigators can detect any irregularities immediately.

Investigators don't know which people are at risk of developing short episodes of fast irregular heartbeats that can lead to atrial fibrillation. The purpose of this study is to find out if there are proteins or chemical changes in the blood that can predict the risk of developing atrial fibrillation. These chemical changes, also known as biomarkers, may also be able to give investigators other clues about atrial fibrillation.

Atrial fibrillation (AF) is considered to be a progressive condition that starts with episodes of paroxysmal AF (short runs of AF), progresses to persistent AF (can be reverted to normal rhythm) and eventually to permanent AF. More than 25% of people with paroxysmal AF will go on to develop persistent or chronic atrial fibrillation. The progression rate is around 5% per annum. AF can result in devastating outcomes such as stroke/TIA and systemic embolic events. In people with implanted devices such as ICDs, investigators can detect non-symptomatic rapid atrial arrhythmia, known as subclinical atrial fibrillation (SCAF), before it becomes symptomatic. In the ASSERT trial, SCAF was detected in 10% of patients with newly implanted devices within the first 3 months. Of these, nearly 16% developed clinical atrial fibrillation within 2.5 years vs 3% in those who did not exhibit SCAF within the first 3 months. During the follow up period, a further 24.5% of patients developed SCAF. People with SCAF also had a higher risk of stroke and systemic embolism.

Earlier diagnosis and treatment of AF may lead to better prevention and outcomes. The availability of serum based biomarkers that can predict the early onset of atrial fibrillation, may help in the identification of patients at risk for developing AF early. This would also allow the identification of the patient population most suitable for the evaluation of possible future intervention strategies to prevent the onset of atrial fibrillation, and alter its natural history and complications.

In this study investigators will study patients that have a permanent pacemaker or defibrillator implanted. These devices continuously monitor the patient's heart rhythm, detecting any irregularities. Patients with these devices are followed up in outpatient clinics on a regular basis. The information from the devices is downloaded at each follow up visit and analyzed by staff in the clinic.

Investigators will recruit patients for this study after the device was implanted. After obtaining consent, investigators will collect a blood sample for measuring biomarkers. They will interview the participant in regards to previous health history, smoking, alcohol consumption, family history and current medications. Participants' medical records will be reviewed annually for the next 10 years, to monitor for any irregular heart rhythms, hospitalizations and death.

Inclusion Criteria:

• Dual chamber permanent pacemaker or defibrillator implanted within previous 10 years

Exclusion Criteria:

• Clinical atrial fibrillation documented by surface ECG (12 lead ECG, Telemetry, Holter)
• Participants considered by the investigator to be unsuitable for the study for the following reason: life expectancy less than 2 years due to concomitant disease
• Participants who are pregnant or breast-feeding
• Congenital heart disease
• Inherited arrhythmia syndrome, i.e. Brugada, long QT interval

Investigators will recruit patients with a permanent defibrillator or pacemaker who have an upcoming appointment at the Device Clinic.