2001 ValidationofClinicalClassificat
- (Gage et al., 2001) ⇒ Brian F Gage, Amy D Waterman, William Shannon, Michael Boechler, Michael W Rich, and Martha J Radford. (2001). “Validation of Clinical Classification Schemes for Predicting Stroke.” In: JAMA: the journal of the American Medical Association. doi:10.1001/jama.285.22.2864
Subject Headings: Hazard Rate
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Cited By
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Abstract
- Context
Patients who have atrial fibrillation (AF) have an increased risk of stroke, but their absolute rate of stroke depends on age and comorbid conditions.
- Objective
To assess the predictive value of classification schemes that estimate stroke risk in patients with AF.
- Design, Setting, and Patients
Two existing classification schemes were combined into a new stroke-risk scheme, the CHADS2 index, and all 3 classification schemes were validated. The CHADS2 was formed by assigning 1 point each for the presence of congestive heart failure, hypertension, age 75 years or older, and diabetes mellitus and by assigning 2 points for history of stroke or transient ischemic attack. Data from peer review organizations representing 7 states were used to assemble a National Registry of AF (NRAF) consisting of 1733 Medicare beneficiaries aged 65 to 95 years who had nonrheumatic AF and were not prescribed warfarin at hospital discharge.
- Main Outcome Measure
Hospitalization for ischemic stroke, determined by Medicare claims data.
- Results
During 2121 patient-years of follow-up, 94 patients were readmitted to the hospital for ischemic stroke (stroke rate, 4.4 per 100 patient-years). As indicated by a c statistic greater than 0.5, the 2 existing classification schemes predicted stroke better than chance: c of 0.68 (95% confidence interval [CI], 0.65-0.71) for the scheme developed by the Atrial Fibrillation Investigators (AFI) and c of 0.74 (95% CI, 0.71-0.76) for the Stroke Prevention in Atrial Fibrillation (SPAF) III scheme. However, with a c statistic of 0.82 (95% CI, 0.80-0.84), the CHADS2 index was the most accurate predictor of stroke. The stroke rate per 100 patient-years without antithrombotic therapy increased by a factor of 1.5 (95% CI, 1.3-1.7) for each 1-point increase in the CHADS2 score: 1.9 (95% CI, 1.2-3.0) for a score of 0; 2.8 (95% CI, 2.0-3.8) for 1; 4.0 (95% CI, 3.1-5.1) for 2; 5.9 (95% CI, 4.6-7.3) for 3; 8.5 (95% CI, 6.3-11.1) for 4; 12.5 (95% CI, 8.2-17.5) for 5; and 18.2 (95% CI, 10.5-27.4) for 6.
- Conclusion
The 2 existing classification schemes and especially a new stroke risk index, CHADS2, can quantify risk of stroke for patients who have AF and may aid in selection of antithrombotic therapy.
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Methods
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Statistical Analyses
To calculate the stroke rate as a function of CHADS2, we used an exponential survival model.27 We used the survival model to measure how the hazard rate for stroke was affected by each 1-point increase in CHADS2 and by prescription of aspirin. We also used the model to predict the annual rate of stroke as a function of CHADS2 and of aspirin use. We confirmed the appropriateness of using an exponential survival model graphically (by plotting the negative of the logarithm of the survival curve vs time).28 We performed our survival analyses in SAS (Version 6.12; SAS Institute Inc; Cary, NC) using the LIFEREG and LIFETEST procedures.28 We calculated the RR reduction from aspirin therapy as 1 minus the relative hazard of prescribing aspirin (as obtained from the exponential model).
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Results
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Stroke Rate in the NRAF Cohort
The 1733 patients were followed up for a mean (median) of 1.2 (1.0) years. During the 2121 patient-years of follow-up, 94 NRAF patients were readmitted for an ischemic event (rate, 4.4 per 100 patient-years), 71 patients were admitted for a stroke as indicated by ICD-9-CM codes 434 or 436, and 23 patients were admitted for transient cerebral ischemia as indicated by ICD-9-CM code 435. We refer to all of these events as stroke for simplicity and because 8 of the 23 patients had a subsequent hospitalization with ICD-9-CM code 434 or 436. Of the 94 patients admitted for a stroke, 25 (27%) died within 30 days of the hospital admission.
The stroke rate was lowest among the 120 patients in the NRAF cohort who had a CHADS2 score of 0, a crude stroke rate of 1.2, and an adjusted rate of 1.9 per 100 patient-years without antithrombotic therapy (Table 2). 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 (P<.001). 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 = .27).
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References
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| Author | volume | Date Value | title | type | journal | titleUrl | doi | note | year | |
|---|---|---|---|---|---|---|---|---|---|---|
| 2001 ValidationofClinicalClassificat | Brian F Gage Amy D Waterman William Shannon Michael Boechler Michael W Rich Martha J Radford | Validation of Clinical Classification Schemes for Predicting Stroke | 10.1001/jama.285.22.2864 |