Let’s say you admit a 75 year old man with pneumonia and sepsis. His EKG shows atrial fibrillation, which as far as anyone knows, is new. He is treated with antibiotics, fluids, and started on a heparin drip for the atrial fibrillation.
Two days later, his telemetry shows normal sinus rhythm. The patient feels much better than when he came in. Past medical history is significant for hypertension and hyperlipidemia. A TTE shows no valvular disease. The patient asks you, “Doc, do I have to keep taking a blood thinner? Do I have to take it for the rest of my life?”
In this case, the conversion to NSR was spontaneous. My brief search did not turn up studies looking at anticoagulation dosing/duration in patients who spontaneously convert to NSR, so I’m extrapolating from recommendations for patients who undergo planned cardioversion.
In cases of planned cardioversion, short-term vs. long-term anticoagulation afterwards is based on the CHADS VASC score and patient-specific risk factors for stroke/thromboembolism. This is regardless of how long atrial fibrillation has been present for (the all-important “48 hours” is arbitrary and most helpful for categorizing afib for study purposes).
CHADS VASC=0 : most cardiologists would anticoagulate for 4 weeks
CHADS VASC ≥ 1: most cardiologists would anticoagulate for at least 4 weeks…and might continue long-term anticoagulation if the CHADS VASC is considered “high risk,” and definitely if there is history like valve disease or replacement, or past stroke.
Our patient in the case above is relatively healthy but has a CHADS VASC score of 3. It would be reasonable to keep him anticoagulated and discharge with your favorite anticoagulant. He and his primary care doctor should discuss risks/benefits of anticoagulation, and if the patient agrees, it would be preferable for him to continue anticoagulation long-term.
Remember: when making decisions about anticoagulation, it’s not the kind of atrial fibrillation that matters (it doesn’t matter if it’s unprovoked, provoked, or new onset)–it’s the patient’s underlying risk factors.