The purpose of this study is to determine if there is a rise in serum high sensitivity troponin T (a marker for heart muscle injury) following a direct current cardioversion (shock therapy) used for patients with atrial fibrillation. This will help us determine if direct current cardioversion results in damage to the heart muscles in a sufficient amount to cause a rise in high sensitivity troponin T.

High sensitivity Troponin T is a relatively new biomarker that is highly sensitive and specific for myocardial injury. Its widespread use has helped in the determination and investigation for myocardial ischemia in patients. Previous studies have shown a rise in creatine kinase (CK) and the more specific creatine kinase-MB isoenzyme (CKMB) after DC cardioversion. Studies on the earlier generation troponin T found that the levels don't rise or rise only minimally after DC cardioversion. The high sensitivity troponin T has never been studied in the setting of DC cardioversion.

Inclusion Criteria:

• Patients with atrial fibrillation / atrial flutter attending for direct current external cardioversion
• Age 18 or older

Exclusion Criteria:

• Myocardial infarction within the last 6 weeks
• Coronary artery bypass grafting, percutaneous coronary intervention or any other invasive cardiac procedure within the last 6 weeks

Patients with atrial fibrillation/flutter who attend the Coronary Care Unit of the University Hospital Limerick for a pre-organised appointment for direct current external cardioversion will be requested to participate in the study