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Estimating Risk for Thromboembolism in Atrial Fibrillation: The ATRIA Risk Score

2016 06 28 9 45 57Atrial fibrillation, or Afib, is essentially a temporary, semi-permanent, or permanent change in the electrophysiology of the atria of the heart. Afib is the abnormal rapid contraction of the atria, resulting in an irregular atrioventricular contraction rhythm. This decreases the heart’s ability to eject blood through the body efficiently (decreased cardiac output), thus increasing stasis of pooled blood within the chambers of the heart. Patients with atrial fibrillation are at an increased risk for arterial thromboembolic events because of the procoagulant effect of hemostasis.

The most common arterial thromboembolic event correlated with atrial fibrillation is ischemic stroke. Determining the risk for thromboembolism in these patients is multifactorial and risk factors such as concurrent valvular heart disease (i.e. mitral valve stenosis, prosthetic valves etc.), significantly increase the risk for thromboembolism.1 In patients with valvular heart disease, the risk for thromboembolism high and anticoagulation or antiplatelet therapy should be utilized, barring significant contraindications to either warfarin (Coumadin) or aspirin. Hospice patients with prosthetic valves, mechanical valves, or significant valvular stenosis should maintain anticoagulation or antiplatelet therapy until the patient loses the ability to swallow, or a bleeding diathesis poses a greater risk to the patient and family than the benefit of preventing an ischemic stroke.

In patients with non-valvular atrial fibrillation, the risk of stroke is less significant and warrants an investigation into the patient’s risk of having an ischemic event. There are several modalities by which to estimate risk for thromboembolism in patients with non-valvular atrial fibrillation. The CHADS2 and CHA2DS2-VASc scores are the most common scoring tools utilized by clinicians. Each scoring system is briefly described below.2

CHADS2 - Assigns points to patients based upon risk factors proven in various trials to increase the risk for ischemic stroke in patients with atrial fibrillation. Does not take into account previous history of arterial vascular disease (aortic plaque, myocardial infarction, peripheral arterial disease, etc.) or sex. Assigns 1 point for: congestive heart failure, hypertension, age greater than 74, or the presence of diabetes mellitus. Assigns 2 points to patients with a history of stroke/TIA. In this scoring system, patients with a score of 0 are considered low risk, a score of 1 equates to a moderate risk, and 2 or greater indicates a high risk patient.

CHA2DS2-VASc - Broadens stroke risk assessment for patients between the ages of 65-74, adds increased risk points for age greater than 74, and includes history of arterial vascular disease and female sex as additional risk factors. Assigns 1 point for: congestive heart failure, hypertension, presence of diabetes mellitus, arterial vascular disease, age between 65-74, or female sex. Assigns 2 points for an age greater than 74 years and history of stroke/TIA. This risk estimation system utilizes the same risk score-based anticoagulation parameters as CHADS2.

The 2014 AHA/ACC/HRS guidelines recommends utilizing vitamin K antagonists (i.e. warfarin) or novel oral anticoagulants (rivaroxaban [Xarelto ®] or apixaban [Eliquis ®]) with a CHADS2 or CHA2DS2-VASc score of 2 or greater (moderate-high risk).3 The downfall to utilizing these risk assessments is the underestimation of low risk in patients who fit parameters for high risk of stroke.

The ATRIA (Anticoagulation and Risk Factors in Atrial Fibrillation) risk score is a novel tool designed to more accurately define high risk versus low risk patients.4 The ATRIA score includes risk factors addressed with CHADS2/CHA2DS2-VASc and adds the presence of renal dysfunction as an additional risk factor (eGFR < 45 mL/min or ESRD and proteinuria). The ATRIA risk score, however, stratifies patients into two categories based on the presence/absence of stroke/TIA in the past medical history. This unique feature of ATRIA may provide additional clinical significance in avoiding anticoagulation when it may actually not be clinically necessary.

In hospice patients, the need for anticoagulation is a clinical conundrum that frequently leaves clinicians wondering if anticoagulation is necessary. Patients may or may not be able to swallow, which complicates matters further. The ATRIA risk score may provide hospice clinicians a better picture as to whether anticoagulation is necessary. The scoring system is more time-intensive in comparison to the CHADS2/CHA2DS2-VASc stroke risk scores, but in the end may be able to help prevent adverse bleeding events and can become a cost-effective approach to anticoagulation in hospice patients. The scoring system is as follows:4

Risk Factor Points without prior stroke Points with prior stroke
Age (years)
            85 or greater 6 9
               75-84 5 7
               65-74 3 7  
               Less than 65 0 8
Female 1 1
Diabetes 1 1
CHF 1 1
Hypertension 1 1
Proteinuria 1 1
eGFR less than 45 mL/min 1 1

In patients with an ATRIA risk score of 6 or below, the risk of stroke per 100 patient years is approximately that of a CHADS2/CHA2DS2-VASc stroke risk score or 0-1.2 In patients scoring above a 6, the benefits of stroke prevention most likely outweigh the risk of major bleeding with anticoagulation. In patients with a score less than 6, it may be feasible to discontinue anticoagulation or downgrade the intensity of anticoagulation. Downgrading anticoagulation could include discontinuing warfarin or the novel oral anticoagulants, discontinuing clopidogrel, and switching the patient to low-dose aspirin (81 mg orally once daily). If the patient’s ATRIA scores are as low as 2, anticoagulation is most likely unnecessary.

Most clinicians are familiar with the CHADS2/CHA2DS2-VASc stroke risk scores. Some hospice patients may require a more rigorous assessment of stroke risk, and the benefits of anticoagulation should be weighed versus the risks of adverse bleeding events, drug interactions, and the evolving issue of polypharmacy. It may be advantageous to consider utilizing the ATRIA risk score to assist with anticoagulation decision making at the end-of-life in patients with non-valvular atrial fibrillation. Populations that may particularly benefit from an ATRIA risk assessment include patients with no history of stroke/TIA and those at an older age without renal dysfunction or other significant comorbidities.


References:
1. Nishimura R, Otto C, Bonow R et al. 2014 AHA/ACC Guideline for the Management of Patients With Valvular Heart Disease: Executive Summary: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation. 2014;129(23):2440-2492. Accessed December 14th 2015.
2. Friberg L, Rosenqvist M, Lip G. Evaluation of risk stratification schemes for ischaemic stroke and bleeding in 182 678 patients with atrial fibrillation: the Swedish Atrial Fibrillation cohort study. European Heart Journal. 2012;33(12):1500-1510. Accessed December 14th 2015.
3. January C, Wann L, Alpert J et al. 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation: Executive Summary.Journal of the American College of Cardiology. 2014;64(21):2246-2280. Accessed December 15th 2015.
4. Singer D, Chang Y, Borowsky L et al. A New Risk Scheme to Predict Ischemic Stroke and Other Thromboembolism in Atrial Fibrillation: The ATRIA Study Stroke Risk Score. Journal of the American Heart Association. 2013;2(3):e000250-e000250. Accessed December 17th 2015.

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