CHADS Score

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

CHADS score or CHADS2 score is a clinical prediction rule for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. It is used to determine whether or not treatment is required with anticoagulation therapy or antiplatelet therapy,[1] since AF can cause stasis of blood in the upper heart chambers, leading to the formation of a mural thrombus that can dislodge into the blood flow, reach the brain, cut off blood supply to the brain, and cause a stroke. 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 of nonrheumatic atrial fibrillation patients aged 65 to 95 who were not prescribed the anticoagulant warfarin.[2]

Method

The CHADS2 scoring table is shown above:[3]

Adding together the points that correspond to the conditions that a patient has will result in the CHADS2 score. This score is used in the next section to estimate stroke risk.

Condition Points
 C   Congestive heart failure
1
 H  Hypertension: blood pressure consistently above 140/90 mmHg (or treated hypertension on medication)
1
 A  Age >/=75 years
1
 D  Diabetes Mellitus
1
 S2  Prior Stroke or TIA
2


Risk of stroke

Annual Stroke Risk[2]
CHADS2 Score   Stroke Risk %       95% CI      
0
1.9
 1.2–3.0
1
2.8
 2.0–3.8
2
4.0
 3.1–5.1
3
5.9
 4.6–7.3
4
8.5
 6.3–11.1
5
12.5
 8.2–17.5
6
18.2
10.5–27.4

According to the findings of the validation study, the risk of stroke as a percentage per year is shown in the table titled Annual Stroke Risk:

While the CHADS2 score provides prognostic information regarding the natural history of non-valvular atrial fibrillation (NVAF) in the absence of warfarin therapy, it should be noted that warfarin therapy also has an associated stroke risk[4] (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.

The CHADS2 score has various limitations, which have been debated [5]. Notably, many stroke risk factors have not been included, and whilst simple, the score has only modest predictive value for thromboembolism.

In order to improve upon the prognostic utility of the CHADS2 score and to incorporate additional stroke risk factors, the CHA2DS2-VASc score has been proposed [6]. These additional 'clinically relevant non-major' stroke risk factors include age 65-74, female gender and vascular disease. In the CHA2DS2-VASc score, 'age 75 and above' also has extra weight, with 2 points.

The CHA2DS2-VASc score has been used in the new European Society of Cardiology guidelines for the management of atrial fibrillation [7].

The European Society of Cardiology (ESC) guidelines recommend that if the patient has a CHADS2 score of 2 and above, oral anticoagulation (OAC) therapy is recommended. OAC options include warfarin with an INR target of 2-3 or dabigatran.

If the CHADS2 score is 0-1, other stroke risk modifiers should be considered: (i) If there are 2 or more risk factors (essentially a CHA2DS2-VASc score score of 2 or more), OAC is recommended; and (ii) If there is 1 risk factor (essentially a CHA2DS2-VASc score score=1), then antithrombotic therapy with either OAC or aspirin (OAC preferred) is recommended.

If patients have a CHA2DS2-VASc score of 0, then such patients are ‘truly low risk’[8]. The ESC guidelines recommend either aspirin or no antithrombotic therapy, but 'no antithrombotic therapy' is preferred[9].

Anticoagulation based on the CHADS2 score

The following treatment strategies are recommended in the table below entitled Anticoagulation based on the CHADS2 score:[1][2]

Score Risk Anticoagulation Therapy Considerations
0 Low Aspirin Aspirin daily
1 Moderate Aspirin or Warfarin Aspirin daily or INR to 2.0-3.0, depending on factors such as patient preference
2 or greater Moderate or High Warfarin INR to 2.0-3.0, unless contraindicated (e.g. clinically significant GI bleeding, inability to obtain regular INR screening)


For detailed recommendations on how the treatment recommendations based on the CHADS2 score are modified by considering additional 'stroke risk modifier' risk factors using the CHA2DS2-VASc score, see ESC guideline recommendations.

Use of the CHADS2 Score in Populations without Atrial Fibrillation

The CHADS2 score has been shown to also predict the risk of ischemic stroke among those patients who do not have atrial fibrillation [10] It should be noted however, that the CHADS2 Score has not been used to guide the selection of anticoagulation therapy in patients without atrial fibrillation.

Description of the Original Study

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 were recently hospitalized rather than healthier individuals, it is thought that CHADS2 should be generalizable to frail and elderly individuals

Validation_of_Clinical_Classification_Schemes_for_Predicting_Stroke.pptx‎

Limitations

  • 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 [11].
  • 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 that were older and sicker. The CHADS2 study was based on the SPAF and AFI schemes, therefore the study may have performed better if it were 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 for aspirin effectiveness in preventing stroke was not statistically significant in this study (however there is clinical significance when the study is combined with other research, and the results suggest that aspirin therapy should be prescribed for elderly patients with AF).


References

  1. 1.0 1.1 Gage BF, van Walraven C, Pearce L, et al. (2004). "Selecting patients with atrial fibrillation for anticoagulation: stroke risk stratification in patients taking aspirin". Circulation 110 (16): 2287–92. doi:10.1161/01.CIR.0000145172.55640.93. PMID 15477396.
  2. 2.0 2.1 2.2 Gage BF, Waterman AD, Shannon W, Boechler M, Rich MW, Radford MJ (2001). "Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation". JAMA 285 (22): 2864–70. PMID 11401607.
  3. Risk of Stroke with AF. VA Palo Alto Medical Center and at Stanford University: the Sportsmedicine Program and the Cardiomyopathy Clinic. Retrieved on 2007-09-14.
  4. Steiner, Thorsten; Jonathan Rosand, Michael Diringer (2006). "Intracerebral hemorrhage associated with oral anticoagulant therapy: current practices and unresolved questions.". Stroke 37 (1): 256–62. PMID 16339459 doi:10.1161/01.STR.0000196989.09900.f8.
  5. Karthikeyan G, Eikelboom JW. The CHADS2 score for stroke risk stratification in atrial fibrillation--friend or foe? Thromb Haemost. 2010 Jul 5;104(1):45-8.
  6. Lip GY, Nieuwlaat R, Pisters R, Lane DA, Crijns HJ. Refining clinical risk stratification for predicting stroke and thromboembolism in atrial fibrillation using a novel risk factor-based approach: the euro heart survey on atrial fibrillation. Chest. 2010 Feb;137(2):263-72.
  7. European Heart Rhythm Association; European Association for Cardio-Thoracic Surgery, Camm AJ, Kirchhof P, Lip GY, Schotten U, Savelieva I, Ernst S, Van Gelder IC, Al-Attar N, Hindricks G, Prendergast B, Heidbuchel H, Alfieri O, Angelini A, Atar D, Colonna P, De Caterina R, De Sutter J, Goette A, Gorenek B, Heldal M, Hohloser SH, Kolh P, Le Heuzey JY, Ponikowski P, Rutten FH. Guidelines for the management of atrial fibrillation: the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology (ESC). Eur Heart J. 2010 Oct;31(19):2369-429.
  8. Van Staa TP, Setakis E, Di Tanna GL, Lane DA, Lip GY. A comparison of risk stratification schema for stroke in 79884 atrial fibrillation patients in general practice. J Thromb Haemost. 2010 Oct 1. doi: 10.1111/j.1538-7836.2010.04085.x. [Epub ahead of print] PubMed PMID: 21029359.
  9. Lip GY, Halperin JL. Improving stroke risk stratification in atrial fibrillation. Am J Med. 2010 Jun;123(6):484-8.
  10. Welles CC, Whooley MA, Na B, et al. The CHADS(2) score predicts ischemic stroke in the absence of atrial fibrillation among subjects with coronary heart disease: Data from the Heart and Soul Study. Am Heart J. Sep 2011;162(3):555-61.
  11. Hobbs FD, Roalfe AK, Lip GY, et al. Performance of stroke risk scores in older people with atrial fibrillation not taking warfarin: comparative cohort study from BAFTA trial. BMJ. Jun 23 2011;342:d3653.

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