Studi Pilot Fibrilasi Atrium: Karakteristik Klinik Pasien Fibrilasi Atrium dan Penggunaan Pengobatan Antikoagulan Oral di Rumah Sakit Tersier di Indonesia = Atrial fibrillation pilot study: clinical characteristics of patients with atrial fibrillation and patteron of oral anticoagulant treatment in a tertiary hospital in Indonesia