Saturday, September 26, 2009

When Should We Anticoagulate a Patient with Non-Valvular AF? The use of CHADS2 score

Do we need to anticoagulate all patients with non-valvular or non-rheumatic AF?

Not so, according to the CHADS2 score (furthermore, the use of warfarin is not without risk. It can complicate an intracranial bleeding).

CHADS2 score is a scoring system to identify risk factors for developing stroke in patients with nonrheumatic atrial fibrillation.

CHADS2 score is a combination of two previous scoring systems:

The Atrial Fibrillation Investigators (AFI) pooled data from several trials to form a unified stroke classification scheme. Among trial participants who did not receive antithrombotic therapy, these researchers found that the risk of stroke increased by a factor of 1.4 per decade of age and by 3 clinical risk factors:
1. Hypertension
2. Previous cerebral ischemia (either stroke or transient ischemic attack [TIA]), and
3. Diabetes mellitus (DM)

On the other hand, the Stroke Prevention and Atrial Fibrillation (SPAF) investigators reported their classification scheme from SPAF participants who were treated with aspirin therapy. Based on data from their first 2 trials, the SPAF investigators identified 4 independent risk factors for stroke:
1. Blood pressure higher than 160 mm Hg
2. Previous cerebral ischemia
3. Recent heart failure (ie, active within the past 100 days) or documented by echocardiography, or
4. the combination of 75 years or older and being female
Do we need to anticoagulate all patients with Atrial fibrillation?

CHADS2 score has been shown to be more accurate predictor of stroke compared to the Atrial Fibrillation Investigators (AFI) and the Stroke Prevention in Atrial Fibrillation (SPAF) predictors.

Gage BF, Waterman AD, ShannonW, et al. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA 2001;285:2864–70. Download the full text here.

**Also download a copy of the management guidelines of AF 2006 here.

The acronym of CHADS2 stands for:
C = Congestive Heart Failure
H = Hypertension or treated hypertension
A = Age 75 yrs or older
D = DM
S = Stroke or TIA previously

C-H-A-D each component: 1 point
S (previous stroke or TIA) = 2 points

If patient has 0 point: it is classified under low risk = aspirin daily will do
If patient has 1 point: it is classified under moderate risk: either aspirin, or warfarin with INR target 2 - 3
If patient has 2 or more points: it is classified under high risk: warfarin with INR 2 - 3 is needed

The higher the score, the higher the stroke risk

Patient with mitral stenosis or prosthetic heart valve is classified as high risk, and therefore warfarin is needed.

In A&E, although we may not follow-up the patient for long term, at least, CHADS score it is good predictive tool for risk stratification.

In a recent article published in September 2009, a cohort of 13,559 patients with nonvalvular atrial fibrillation (66,000 person-years of follow-up) was studied.

In that study, net clinical benefit was defined as the annual combined rate of ischemic stroke and systemic emboli that was prevented by warfarin, minus the annual rate of intracranial hemorrhages that were attributable to warfarin multiplied by 1.5 (the multiplier was included to give greater clinical weight to intracranial hemorrhage).

Generally, the net clinical benefit of warfarin, adjusted for stroke and hemorrhage risk factors, was shown to be 0.68% annually.

The annual adjusted benefit was higher for those with past ischemic stroke (2.48%) and for elders (age, ≥85; 2.34%).

No net clinical benefit was found for patients with CHADS2 risk scores (1 point each for congestive heart failure, hypertension, age ≥75, or diabetes; 2 points for past stroke) of 0 or 1.

For those with scores of 4 to 6, net benefit was 2.22%.

In other words, those with single or no stroke risk factors will not benefit from anticoagulation. In contrast, those with high risk for stroke will benefit from anticoagulation.

Singer DE et al. The net clinical benefit of warfarin anticoagulation in atrial fibrillation. Ann Intern Med 2009 Sep 1; 151:297.

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