Anticoagulation and Thrombotic Events

Understanding the Risk: Anticoagulation Does Not Eliminate Thrombotic Events

An INR of 2.9 falls within the therapeutic range (2.0-3.0) recommended for most indications including PE treatment and atrial fibrillation, as suggested by the British Thoracic Society and the American College of Chest Physicians 1, 2
The American Heart Association recommends that warfarin prevents thrombus formation on existing clots or in low-flow states (atrial fibrillation, mechanical valves, venous thromboembolism) 3, 4

If clinical suspicion exists for PE or MI, proceed with full diagnostic evaluation regardless of INR 2.9, as recommended by the British Thoracic Society 1, 5, 6
The British Thoracic Society guidelines emphasize that therapeutic INR (2.0-3.0) is the target for PE treatment, but this does not preclude diagnosis of new or recurrent PE 1, 7, 8

Patients with atrial fibrillation are at increased risk for stroke and systemic embolism even with anticoagulation, according to the American College of Cardiology 9
Mechanical heart valve patients have an annual thromboembolic risk of 1-2% despite anticoagulation, as reported in the journal Circulation 3
Active malignancy may overwhelm anticoagulation due to a hypercoagulable state, as noted in the journal Chest 2

The American College of Cardiology notes that approximately 28% of patients who experienced ischemic stroke had strokes despite adequate anticoagulation, with 72% of patients having either discontinued anticoagulation or had INR <2.0 10
The American College of Cardiology and Chest guideline societies suggest that INR levels >3.0-3.5 are associated with significantly increased bleeding risk, including intracranial hemorrhage, which can present as stroke-like symptoms 11, 12

The Stroke journal reports that the risk of intracranial hemorrhage increases dramatically at INR values >4.0 13
The American College of Cardiology recommends that patients believed to be in sinus rhythm after cardioversion still require ongoing anticoagulation, as 75% of thromboembolic events in rhythm-control patients occurred when they were thought to be in sinus rhythm 10