The study aims to evaluate and compare the incidence of atrial arrhythmias (including Post-Operative Atrial Fibrillation (POAF), atrial flutter, and atrial tachycardia) stratified by baseline Utah fibrosis stages and overall fibrosis (%) of the left atrial wall area. The investigators hypothesize that patients with a higher baseline Utah fibrosis staging will experience a higher incidence of POAF.

The study also aims to evaluate and compare the in-hospital mortality, length-of-stay (LOS), complication rates (strokes, pneumonia, respiratory failure etc.) of the different Utah fibrosis stage cohorts. Perform cost analysis and compare between patients with POAF and patients without POAF. The investigators hypothesize that patients experiencing POAF will have a higher mortality rate, longer LOS, greater complications, and therefore, additional hospital costs.

The study is a a prospective, observational cohort study. 50 patients undergoing cardiac surgery (Coronary Artery Bypass Graft (CABG), valvular etc.) without a history of atrial fibrillation will be given a baseline Magnetic Resonance Imaging (MRI) upon which patients will be assigned Utah stages I-IV based on their left atrial fibrosis pattern. Overall fibrosis (%) of the left atrial wall area will also be collected. Patients will then undergo their planned surgeries receiving management adherent to current guidelines and standard of care procedures. Atrial arrhythmia incidence after surgical procedure will be collected using in-hospital telemetry or serial Electrocardiogram (ECG) from all patients in their respective cohorts. Cardiac surgery type, duration and any intraoperative complications will be recorded. Other clinical and relevant demographical data will be collected at admission and throughout patients' hospital stay.

All cardiac surgeries will be performed by experienced surgeons at Tulane Medical Center, Washington University Medical Center Barnes Jewish Hospital, and University Medical Center New Orleans, adhering to all relevant standard-of-care guidelines. MRI imaging will be performed by experienced technicians and operators at Tulane Medical Center, Washington University Medical Center Barnes Jewish Hospital, and University Medical Center New Orleans. MRI Utah fibrosis staging will be performed and assessed by experienced operators at MARREK, Inc., by using the Corview processing software with de-identified images.

The investigators expect a total recruitment of 50 subjects over a period of 6 months from the Tulane Medical Center Cardiology and Cardiothoracic Surgery Clinics, Washington University Medical Center Barnes Jewish Hospital Cardiology and Cardiothoracic Surgery Clinics, as well as University Medical Center New Orleans Cardiology and Cardiothoracic Surgery Clinics in order to complete the study. They expect to recruit 40 patients from Washington University Medical Center and 10 patients from either Tulane Medical Center or University Medical Center New Orleans.

Inclusion Criteria:

• Male or female patients age 40 years of age or older
• Patients with no history of atrial arrhythmia (atrial fibrillation, atrial flutter, atrial tachycardia) scheduled to undergo cardiac surgery (These surgeries include but are not limited to coronary artery bypass graft (CABG), valvular repair/reconstruction, aneurysm repair, and insertion of pacemaker).

Exclusion Criteria:

• Patients with a history of atrial arrhythmia (atrial fibrillation, atrial flutter, atrial tachycardia)
• Patients with a history of cardiac or open chest surgery
• Patients with a history of catheter ablation
• Patients under the age of 40
• Patients with left ventricular assist device (LVAD) or scheduled to have LVAD implanted
• Patients who have previously undergone extracorporeal membrane oxygenation (ECMO)
• Patients who have undergone or will undergo heart transplantation
• Patients with any health related Late Gadolinium Enhancement (LGE)-MRI contraindications (including previous allergic reaction to gadolinium, pacemakers, defibrillators, other devices/implants contraindicated for MRI)
• Acute or chronic severe renal disease with a low glomerular filtration rate (GFR), <30 mL per minute per 1.73 m2 will be excluded from the trial. (A creatinine measurement should be available within the last 6 months. If not, a creatinine blood test will be drawn to assess for renal function before the MRI acquisition).
• Patients weighing > 300 lbs. (MRI image quality decreases due to increased body mass index)
• Patients currently pregnant or breastfeeding, or plan to become pregnant during the study period
• Patients with cognitive impairment preventing them from giving informed consent will be excluded from the study
• Patients who cannot read, speak, and/or understand English

The study population is any patient with no history of atrial arrhythmia scheduled to undergo cardiac surgery and meets other inclusion/exclusion criteria).

Each Site:

• Approximately 10 Patients from either Tulane Medical Center and/or University Medical Center New Orleans.
• Approximately 40 Patients from Washington University Medical Center (Barnes Jewish Hospital).

The PIs and co-PI will have access to recruit patients through their cardiology and cardiothoracic surgery clinics.

Participants may also be recruited from the community by direct advertising; emails, TV, flyers posted in public places, as well as online postings to study-site affiliated websites, social media platforms (Facebook, Twitter, Instagram) and LinkedIn.