Wednesday, February 17, 2016

Why is there a need to shift from CHADS2 score to the new evolved CHA2DS2-VASc score? Which one is better predictor of stroke risk?

The CHADS2 scoring system is used to stratify stroke risk in patients with nonvalvular atrial fibrillation. Guidelines (Circulation 2006; ) recommend aspirin for patients with CHADS2 scores of 0 (low risk), warfarin or aspirin for patients with scores of 1 (intermediate risk), and warfarin for patients with scores of ≥2 (high risk). CHADS2, however, classifies many patients as intermediate risk, and clinicians struggle with committing these patients to long-term warfarin anticoagulation. In this study involving 74,000 patients with nonvalvular atrial fibrillation, Danish investigators compared CHADS2 with a new system, CHA2DS2-VASc. CHA2DS2-VASc also classifies patients with scores of 0 as low risk, 1 as intermediate risk, and ≥2 as high risk .
Of 16,000 patients in the low-risk CHADS2 category, 40% were categorized as intermediate risk and 22% as high risk by CHA2DS2-VASc. Of 24,000 patients categorized by CHADS2 as intermediate risk, 93% were categorized as high risk by CHA2DS2-VASc. The 1-year event rate of hospital admission and death due to thromboembolism (e.g., stroke) per 100 person-years was 1.7, 4.8, and 12.3 for patients with low-, intermediate-, and high-risk CHADS2 scores and 0.8, 2.0, and 8.8 for patients with low-, intermediate-, and high-risk CHA2DS2-VASc scores. Similar patterns were found during 5 to 10 years of follow-up. For both scoring systems and all risk categories, the estimated event rate was lower in patients treated with vitamin K antagonists (e.g., warfarin), except for patients with CHA2DS2-VASc scores of 0, in whom the event rate was unchanged.

Simple clinical risk score is required to help assess the risk of stroke in patients with atrial fibrillation. Atrial fibrillation increases the risk of stroke but this risk is not homogenous and depends on the presence of various stroke risk factors; hence, there isn’t one size which fits all. The older CHADS2 score which was described in 2001 includes five common stroke risk factors seen in non-warfarin arm in the historical trials. However in these trials the patients were not truly representative, because they only randomized <10% of the patients screened . Many of the stroke risk factors that we see in routine practice are not recorded properly or they are inadequately defined . hence we extended this in 2009 , including common risk factors that we see in our practice , including those seen in large observational trials . CHADS2 and CHA2DS2-VASc have 5 common risk factors, but why CHA2DS2-VASc is particularly good is because it reliably identifies patients at truly low risk of ischemic stroke; and these truly low risk are CHA2Ds2-VASc of zero in men and CHA2Ds2-VASc of one in females. These patients who are at truly low risk do not need any antithrombotic therapies. The next step is to offer anti-thrombotic therapy to those who have one or more stroke risk factors, in other words a CHA2DS2-VASc score of one in men and CHA2SS2-VASc of two in women and it really doesn’t matter whether the score 1, 2 or 8; we need to offer anti-thrombotic therapy to these patients, if we are serious about stroke prevention.

Final message

CHA2DS2-VASc is better than CHADS2 at predicting which patients with nonvalvular atrial fibrillation are at high risk for thromboembolism. CHA2DS2-VASc also appears to be better at predicting which patients are truly at low risk. Broad use of the CHA2DS2-VASc scoring system could lower the number of patients treated with vitamin K antagonists who will not benefit from them and raise the number of patients treated with vitamin K antagonists who will.

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