Atrial fibrillation (AF) is the most common cardiac arrhythmia in the United States, and treatment by AF ablation is quickly becoming the favored definitive therapy. Nonetheless, AF ablation comes with some risk, including bleeds related to vascular access and myocardial damage, as well as the rare incidence of clinical stroke from blood clots that travel from the heart to the brain, termed "cerebrothromboemboli." In fact, cerebrothromboemboli without any symptoms have been detected by special imaging procedures called brain magnetic resonance imaging (MRI) in as many as 22% of cases.(1-6) There remains clinical equipoise amongst experts regarding balancing the risks and benefits of continued versus interrupted blood thinning, or "anticoagulation" during AF ablation as they pertain to risk of bleed and cerebrothromboemboli prevention, respectively, and the potentially more subtle sequelae of these apparently silent cerebrothromboemboli remain unknown. In fact, both interruption and continuation of anticoagulation during AF ablation are the standard of care. The investigators will perform the first randomized trial of uninterrupted versus interrupted anticoagulation in patients undergoing AF ablation to determine if it mitigates neurologic injury. The objective of this research is to investigate the effect of continued anticoagulation for AF ablation on cerebrothromboemboli, and the neurocognitive sequelae of embolic lesions, which to this point are considered subclinical. The investigators hypothesize that continued anticoagulation will both reduce cerebrothromboemboli and mitigate any potential decline in neurocognitive function post-procedurally. The investigators also hypothesize that the incidence of cerebrothromboemboli (CTE) by MRI will mediate that difference.

Inclusion Criteria:

• Patients 18 years old and older with AF (paroxysmal or persistent) who are to undergo an elective AF ablation procedure at UCSF will be eligible for enrollment.

Exclusion Criteria:

• Patients will be excluded if they have:
• A contraindication of warfarin therapy (pregnancy, recent bleed, inability of have serial INR checks)
• A contraindication or relative contraindication to interruption of anticoagulation (e.g. mechanical valve, clotting disorder such as antiphospholipid syndrome, recent history of pulmonary embolism or history of recurrent pulmonary embolism)
• A contraindication to transesophageal echocardiogram; any contraindication to MRI
• Have a diagnosed condition of dementia or a diagnosis that precludes accurate assessment of neurocognitive function
• Non-English speakers
• Inability to give informed consent.