Risk of stroke with AF

A simple clinical way of estimating the risk of stroke in patients with non-rheumatic atrial fibrillation [1].

Study

The patients in this study were 1733 people aged 65 to 95 years discharged from hospital with a diagnosis of non-rheumatic atrial fibrillation, without any treatment apart from aspirin in some. A national registry was generated using anonymous information from five quality improvement or peer review organizations serving seven US states. Medicare records could be reviewed for proper assessment and diagnosis of atrial fibrillation, documented risk factors, any therapy or comorbid conditions. Standardized abstraction forms were used, with excellent agreement between abstractors.

The study outcome was hospital admission for first ischemic stroke, as determined by Medicare claims. The minimum follow up was 365 days, and the maximum was 1000 days.

Risk classification scheme

Two risk classification schemes used in clinical trials to classify patients with atrial fibrillation at low, medium and high risk of stroke were combined. The new scheme involved independent risk factors identified in the original two schemes: one point was given for the presence of congestive heart failure, hypertension (systolic >160 mmHg), age greater than 75 years, and diabetes, and two points given for prior cerebral ischemia (Table 1). The name of the new classification scheme is CHAD2 (C for CHF, H for HBP, A for age, D for diabetes and 2 for CVA/TIA which gets two points.

 

Table 1: Components of CHAD2

 

CHAD2 item

Points

Congestive heart failure

1

Hypertension (systolic >160 mmHg)

1

Age greater than 75 years

1

Diabetes

1

Prior cerebral ischemia

2

Results

There were 94 strokes in the 1733 patients over an average 1.2 year follow up, a crude average rate of 4.5% a year. Within the cohort, the crude rate for patients with no risk factors (120 people) was 1.2%. With increasing risk scores, the crude annual risk rose also. Figure 1 shows the 95% confidence interval of the rate after smoothing through an exponential survival model. Table 2 gives the numbers..

Figure 1: CHAD score and risk of stroke

 

Table 2: CHAD score and risk of stroke

 

Number of:

 

CHAD2 score

Patients

Strokes

Adjusted annual stroke rate (95%CI)

0

120

2

1.9 (1.2 to 3.0)

1

463

17

2.8 (2.0 to 3.8)

2

523

23

4.0 (3.1 to 5.1)

3

337

25

5.9 (4.6 to 7.3)

4

220

19

8.5 (6.3 to 11.1)

5

65

6

12.5 (8.2 to 17.5)

6

5

2

18.2 (10.5 to 27.4)

Reference:

  1. BF Gage et al. Validation of clinical classification schemes for predicting stroke. Results from the national registry of atrial fibrillation. JAMA 2001 285: 2864-2870.