The risk of thrombosis is first assessed before anticoagulation in atrial fibrillation (AF) (Thrombosis Risk Assessment System – CHA2DS2-VASc, see Table 1). If the CHA2DS2-VASc score is 0, patients with AF can take 75-325 mg of oral aspirin without antithrombotic therapy; if the CHA2DS2-VASc score is 1, oral anticoagulants or aspirin are preferred; if the CHA2DS2-VASc score is ≥2 oral anticoagulants, such as vitamin K antagonists (warfarin) should be used for long-term Anticoagulation to maintain INR 2.0-3.0. Anticoagulation in specific situations Paroxysmal AF: Paroxysmal AF anticoagulation should be applied according to the CHA2DS2-VASc score results. Perioperative anticoagulation: Vitamin K antagonists (warfarin) should be withheld before interventional or surgical procedures, and many surgeons require a preoperative INR adjustment of <1.5. Preoperative (even for minor outpatient procedures) assessment of bleeding and risk of stroke and thrombosis should be performed. Because of the warfarin half-life of 36-42 hours, it should be discontinued for more than 5 days before surgery. If the INR is still higher than 1.5, oral vitamin K (1-2 mg) may be considered to adjust the INR. oral warfarin should be resumed the same evening or the next morning after surgery at the same dose as preoperatively, without loading dose. In patients with mechanical flaps or greater risk of thrombosis, preoperative discontinuation of warfarin should be considered with low-molecular heparin or plain heparin. Atrial fibrillation combined with stable vascular disease: In patients with stable coronary artery disease, carotid lesions or peripheral arterial disease, the usual anticoagulation therapy is vitamin K antagonist + antiplatelet agents (aspirin), but some studies suggest that vitamin K antagonist + aspirin, instead of reducing the occurrence of stroke or vascular events such as myocardial infarction, increases the risk of bleeding. Acute coronary syndrome and emergency PCI: The traditional anticoagulation strategy after acute coronary syndrome and/or PCI is combined clopidogrel + aspirin anticoagulation for 4 weeks in patients with implanted bare stents and combined clopidogrel + aspirin anticoagulation for 6 to 12 months in patients with implanted drug stents. Adding a vitamin K antagonist to the above two-combination anticoagulation, the triple anticoagulation does not increase the risk of bleeding in the short term (4 weeks). However, the expert consensus issued by the European Society of Cardiology Thrombosis Working Group concluded that pharmacological stenting should be avoided in such patients and that clopidogrel + aspirin + vitamin K antagonist triple anticoagulation should be followed by vitamin K antagonist + clopidogrel 75 mg/day or aspirin 75-100 mg/day long-term anticoagulation. Vitamin K antagonist anticoagulation alone may be considered if the patient has stable vascular disease such as no acute bleeding events within the past year, no PCI, and no stent implantation. Elective PCI with atrial fibrillation: clopidogrel + aspirin + vitamin K antagonist anticoagulation for ≥3 months in patients with drug-coated stents such as sirolimus, everolimus and tacrolimus, and clopidogrel + aspirin + vitamin K antagonist anticoagulation for ≥6 months in patients with paclitaxel-coated stents, followed by vitamin K antagonist + clopidogrel 75 mg/day or aspirin 75- 100 mg/day long-term anticoagulation, with the addition of proton pump inhibitors, H2 receptor antagonists, or antacids in patients with a propensity for gastric mucosal bleeding. Patients with bare stent implantation, stable coronary artery disease, combined with atrial fibrillation, vitamin K antagonist + clopidogrel 75mg/day or aspirin 75-100mg/day anticoagulation therapy for 12 months. To protect the gastric mucosa proton pump inhibitors, H2 receptor inhibitors, and antacids are available. Acute non-ST-segment elevation myocardial infarction combined with atrial fibrillation: Patients with acute non-ST-segment elevation myocardial infarction combined with atrial fibrillation are at moderate to severe risk of stroke. The acute phase should be anticoagulated with a combination of clopidogrel + aspirin + regular heparin or low-molecular heparin or bivalirudin or platelet glycoprotein IIb/IIIa inhibitor; anticoagulation should be uninterrupted, and PCI is the preferred treatment modality for long-term treatment, with vitamin K antagonist + aspirin + clopidogrel anticoagulation for 3-6 months in the initial phase, and the duration of triple anticoagulation can be extended if the patient is at minimal risk of bleeding. For patients at high risk of cardiovascular thrombosis, vitamin K antagonist + clopidogrel 75 mg/day or aspirin 75-100 mg/day anticoagulation may be chosen for 12 months, and proton pump inhibitors or H2 receptor antagonists or antacids may be added for patients with a propensity for gastric mucosal bleeding. Acute ST-segment elevation myocardial infarction + PCI combined with atrial fibrillation: clopidogrel + aspirin + heparin therapy is an option in the acute phase; additional anticoagulation with bivalirudin or platelet glycoprotein IIb/IIIa inhibitors may be considered in patients with very high thrombotic risk; if INR > 2, no additional bivalirudin or platelet glycoprotein IIb/IIIa inhibitors should be added. Try to remove the thrombus intraoperatively. For medium- and long-term anticoagulation, in the initial phase, vitamin K antagonist + aspirin + clopidogrel anticoagulation for 3 to 6 months; the duration of triple anticoagulation may be extended if the patient is at minimal risk of bleeding. For patients at high risk of cardiovascular thrombosis, vitamin K antagonist + clopidogrel 75 mg/day or aspirin 75-100 mg/day anticoagulation for 12 months may be chosen, and proton pump inhibitors or H2 receptor antagonists or antacids may be added for patients with a tendency to bleed from the gastric mucosa. Acute stroke combined with atrial fibrillation: There is limited evidence-based medical information on anticoagulation in patients with acute stroke combined with atrial fibrillation. The risk of recurrent thrombosis within 2 weeks of the acute phase of thrombotic stroke is high, but the risk of cerebral hemorrhage is greatly increased if anticoagulation is administered. Acute phase of stroke or transient cerebral ischemia with uncontrolled hypertension should be accompanied by cranial CT or MRI to exclude intracranial hemorrhage. If there is no intracranial hemorrhage, anticoagulation will be performed after 2 weeks; if there is intracranial hemorrhage, anticoagulation is contraindicated. In patients with transient cerebral ischemia combined with atrial fibrillation, intracranial infarction or hemorrhage is excluded, and anticoagulation therapy should be started as early as possible. Asymptomatic stroke combined with atrial fibrillation: Patients with atrial fibrillation are prone to cerebral embolism, and cranial CT or MRI examinations show that asymptomatic stroke occurs significantly more frequently in patients with atrial fibrillation than in patients with sinus rhythm. Cerebral flow Doppler examinations may reveal asymptomatic patients with acute embolism, or patients with prior cerebral embolism who are at high risk of reoccurring embolism. Anticoagulation should be administered early in such patients. Atrial flutter: As with previous guidelines, anticoagulation for atrial flutter is the same as for atrial fibrillation. Anticoagulation for atrial fibrillation reversal: Patients with unknown duration of atrial fibrillation or atrial fibrillation lasting >48 hours who require pharmacological or electrical reversal should take oral vitamin K antagonists (INR 2.0-3.0) for at least 3 weeks before reversal and for at least 4 weeks after reversal; if reversal fails or if patients are at high risk of thrombosis should be on long-term anticoagulation. Atrial fibrillation lasting <48 hours prior to definitive conversion, with plain heparin or low-molecular heparin before conversion; patients without thrombotic risk do not require anticoagulation after conversion. Patients at high risk of thrombosis should be placed on long-term oral vitamin K antagonists (INR 2.0-3.0) until the INR is reached, and regular or low molecular heparin and vitamin K antagonists should be used overlappingly. Atrial fibrillation lasting >48 hours prior to definitive conversion and hemodynamic instability such as angina pectoris, myocardial infarction, shock and pulmonary edema require immediate cardioversion. Normal heparin or low-molecular heparin should be used before resuscitation, and after resuscitation normal heparin or low-molecular heparin should be overlapped with oral vitamin K antagonists until the INR is reached (INR 2.0 to 3.0). The duration of oral vitamin K antagonist, long-term or 4 weeks, depends on the high or low thrombotic risk.