CHADS2 score
Synonyms and keywords: CHADS score

# Overview
CHADS2 score is a clinical prediction rule for the estimation of the risk of stroke among patients with non-rheumatic atrial fibrillation (AF), a common and serious cardiac arrhythmia associated with an increased risk of thromboembolic stroke.  AF can cause stasis of blood in the atria, leading to the formation of a mural thrombus that can dislodge into the blood flow, reach the brain, and cause a stroke.  CHADS2 score is used to assess the risk of stroke and determine whether or not antithrombotic therapy is required with either anticoagulants therapy or antiplatelets for the prevention of thromboembolism.  A high CHADS2 score corresponds to a greater risk of stroke, while a low CHADS2 score corresponds to a lower risk of stroke. The CHADS2 score was validated by a study on non-rheumatic AF patients aged 65 to 95 who were not prescribed the anticoagulant warfarin.

# CHADS2 Score Original Study

## Description
The CHADS2 index was developed by the Gage et al., published in the Journal of the American Medical Association in June 2001, with the objective of assessing the predictive value of classification schemes that estimate stroke risk in patients with AF. To develop the index, two existing classification schemes from the Atrial Fibrillation Investigators (AFI), and the Stroke Prevention and Atrial Fibrillation investigators (SPAF) were combined, and all 3 classification schemes were validated. 1 point each was assigned for the presence of congestive heart failure, hypertension, age 75 and older, and diabetes mellitus, and 2 points were assigned for history of stroke or transient ischemic attack. Data was obtained from peer review organizations representing 7 different states to create a National Registry of Atrial Fibrillation consisting of 1733 Medicare beneficiaries aged 65 to 95 years who had non-rheumatic AF and were not prescribed warfarin at discharge. The outcome measured was the hospitalization for ischemic stroke, which was determined by medicare claims data. The 1733 patients were followed for a median of 1.2 years.
The results were as follows;
- During the 2121 patient-years of follow up, 94 patients were re-admitted for an ischemic event; 73 of these patients were admitted for stroke, and 23 patients for transient cerebral ischemia.
- The stroke rate was lowest amongst the 120 patients who had a CHADS2 score of 0.
- The stroke rate increased by a factor of 1.5 (95% CI, 1.3-1.7) for each 1 point increase in the CHADS2 score.
- Aspirin was associated with a hazard rate of 0.80 (95% CI, 0.5-1.3) corresponding to a nonsignificant 20% RR reduction in the rate of stroke (p=0.27)
- Compared to the schemes developed by the AFI and SPAF, the CHADS2 index was the most accurate predictor of stroke with a c-statistic of 0.82 (95% CI, 0.80-0.84).

## Strengths
- The CHADS2 study used chart reviews rather than ICD-9-CM claims to document the presence of AF and to identify stroke risk factors.
- The chart reviews included patients who received aspirin after being discharged from the hospital, enabling adjustment for the use of aspirin in the calculation of the CHADS2 specific stroke rate.
- The cohort of persons used in the study were Medicare beneficiaries from 7 different states, and all geographic regions of the United States were represented.
- As the CHADS2 study used Medicare beneficiaries who were recently hospitalized rather than healthier individuals, it is thought that CHADS2 should be generalizable to frail and elderly individuals

## Limitations
- The CHADS2 score has various limitations, which have been debated.  Notably, many stroke risk factors have not been included, and whilst simple, the score has only modest predictive value for thromboembolism.
- The CHADS2 score may underestimate the risk of stroke in those patients over the age of 75 years. For this reason, some authors have advocated the use of anticoagulation among patients who are over the age of 75 years if there are no contraindications.
- When compared to data from clinical trials from The Stroke Prevention and Atrial Fibrillation investigators (SPAF) and the Atrial Fibrillation Investigators (AFI), the CHADS2 study used participants who were older and sicker. The CHADS2 study was based on the SPAF and AFI schemes; therefore, the study may have performed better if it was used in a younger cohort of patients.
- A single chart review was used to measure the stroke risk factors, and therefore the study was unable to capture new stroke risk factors that may have developed in the cohort participants.
- The study only looked at patients who were hospitalized and were not prescribed warfarin.
- As Medicare claims were used to ascertain the number of ischemic events, there was no way to verify these events.
- The 20% risk reduction of stroke with aspirin administration was not statistically significant in this study (however there is clinical significance when the study is combined with other research).
- While the CHADS2 score provides prognostic information regarding the natural history of non-valvular AF in the absence of warfarin therapy, it should be noted that warfarin therapy also has an associated stroke risk (particularly hemorrhagic stroke) and a risk of major bleeding, and these considerations were taken into account in the development of the recommendations in the next section.

# CHADS2 Risk Score Calculator

## Calculation of the CHADS2 Score for Atrial Fibrillation Stroke Risk
function calcScore(){
var score = 0;
if(document.forms.checked == 1){score += 1;}
if(document.forms.checked == 1){score += 1;}
if(document.forms.checked == 1){score += 1;}
if(document.forms.checked == 1){score += 1;}
if(document.forms.checked == 1){score += 2;}
document.forms.value = score;
if(score == 0){document.forms.value = "Low risk (1.9% stroke risk, 95% CI 1.2-3.0); Consider Aspirin daily";}
if(score == 1){document.forms.value = "Moderate risk (2.8% stroke risk, CI 2.0-3.8); Consider Aspirin or Warfarin";}
if(score == 2){document.forms.value = "Moderate risk (4% stroke risk, 95% CI 3.1-5.); Warfarin with an INR target of 2-3";}
if(score == 3){document.forms.value = "Moderate risk (5.9% stroke risk, 95% CI 4.6-7.3); Warfarin with an INR target of 2-3";}
if(score == 4){document.forms.value = "High risk (8.5% stroke risk, 95% CI 6.3-11.1); Warfarin with an INR target of 2-3";}
if(score == 5){document.forms.value = "High risk (12.5% stroke risk, 95% CI 8.2-17.5); Warfarin with an INR target of 2-3";}
if(score == 6){document.forms.value = "High risk (18.2% stroke risk, 95% CI 10.5-27.4); Warfarin with an INR target of 2-3";}

## Interpretation of the CHADS2 Score for Atrial Fibrillation Stroke Risk
Shown below is the probability of the annual stroke risk by the corresponding CHADS2 score value.
- Score 0: Low risk (1.9% stroke risk, 95% CI 1.2-3.0); Consider Aspirin daily
- Score 1: Moderate risk (2.8% stroke risk, CI 2.0-3.8); Consider Aspirin or Warfarin depends on patient preference
- Score 2: Moderate risk (4% stroke risk, 95% CI 3.1-5.); Warfarin with an INR target of 2-3, unless contraindicated
- Score 3: Moderate risk (5.9% stroke risk, 95% CI 4.6-7.3); Warfarin with an INR target of 2-3, unless contraindicated
- Score 4: High risk (8.5% stroke risk, 95% CI 6.3-11.1); Warfarin with an INR target of 2-3, unless contraindicated
- Score 5: High risk (12.5% stroke risk, 95% CI 8.2-17.5); Warfarin with an INR target of 2-3, unless contraindicated
- Score 6: High risk (18.2% stroke risk, 95% CI 10.5-27.4); Warfarin with an INR target of 2-3, unless contraindicated

# 2014 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation (DO NOT EDIT)

## Prevention of Thromboembolism