Predicting Risk in Atrial Fibrillation

During my medical shadowing block in January, a decision was made for a patient I was looking after to be started on warfarin for anticoagulation. She had been admitted to the hospital with congestive cardiac failure secondary to atrial fibrillation. Patients who have AF are at increased risk of developing a systemic embolism and an ischamic stroke. On admission, this patient was on a low dose of daily aspirin (75mg once daily) however she had several risk factors which put her at increased risk of stroke. The question is which patients with AF should be anticoagulated, if not all of them. Warfarin is a dangerous drug, associated with an increased risk of haemorrhage, particularly if dosing is poorly controlled. In order to justify starting a patient on warfarin, it must be judged that the benefits of reducing risk of stroke outweigh the disadvantage of increased risk of harm.

In the BMJ this week, an editorial was sent on this topical subject titled 'Anticoagulation in people with atrial fibrillation'. The author argued that anticoagulants are underprescribed. In the past, the CHADS2 classification scale has been used to predict patients with AF at risk of stroke. The patient gains a point for each of: Congestive Heart Failure, Hypertension, Age >75, Diabetes and 2 points for stroke. Patients with a score of 2 or more are recommended to be started on warfarin. Now, a new index has been developed called the CHA2DS2VASc score which takes more relevant risk factors into consideration. This new score takes into account sex of the patient and history of vascular disease. The results of the new index is that more patients are recommended to be anticoagulated. In fact, only 8.6% of patients with AF in general practice would be considered low risk. An advantage of the new CHA2DS2VASc score is that it is better than CHADS2 at predicting patients at low risk of developing a stroke.

There has been much discussion recently about developing new anticoagulants to replace vitamin K antagonists. It will be interesting to see whether development of new, safer anticoagulants will result in doctors lowering the threshold for prescribing anticoagulants. Dabigratan is a direct thrombin inhibitor which may result in fewer intracranial haemorrhages than warfarin. It remains unclear whether prescribing trends with anticoagulants will change in the forthcoming years as they become safer.