Warfarin is a complex but highly effective treatment for decreasing thromboembolic risk in atrial fibrillation (AF). We examined contemporary warfarin treatment rates in AF before the expected introduction of newer anticoagulants and extent of practice-level variation in warfarin use. Within the National Cardiovascular Data Registry Practice Innovation and Clinical Excellence program from July 2008 through December 2009, we identified 9,113 outpatients with AF from 20 sites who were at moderate to high risk for stroke (congestive heart failure, hypertension, age, diabetes, stroke score >1) and would be optimally treated with warfarin. Using hierarchical models, the extent of site-level variation was quantified with the median rate ratio, which can be interpreted as the likelihood that 2 random practices would differ in treating “identical” patients with warfarin. Overall rate of warfarin treatment was only 55.1% (5,018 of 9,913). Untreated patients and treated patients had mean congestive heart failure, hypertension, age, diabetes, stroke scores of 2.5 (p = 0.38) and similar rates of heart failure, hypertension, diabetes mellitus, and previous stroke, suggesting an almost “random” pattern of treatment. At the practice level, however, there was substantial variation in treatment ranging from 25% to 80% (interquartile range for practices 50 to 65), with a median rate ratio of 1.31 (1.22 to 1.55, p <0.001). In conclusion, within the Practice Innovation and Clinical Excellence registry, we found that warfarin treatment in AF was suboptimal, with large variations in treatment observed across practices. Our findings suggest important opportunities for practice-level improvement in stroke prevention for outpatients with AF and define a benchmark treatment rate before the introduction of newer anticoagulant agents.
The emergence of the National Cardiovascular Date Registry (NCDR) Practice Innovation and Clinical Excellence (PINNACLE) program for cardiac outpatients represents a unique data source to evaluate warfarin treatment patterns in a contemporary United States outpatient cohort. Results from a contemporary registry can provide important baseline treatment rates with warfarin before the introduction of newer anticoagulants such as dabigatran and rivaroxaban. Accordingly, within the PINNACLE program we examined (1) treatment rates with warfarin in outpatients with nonvalvular atrial fibrillation (AF) who are at moderate to high risk for stroke and (2) extent of patient- and practice-level variations in warfarin use. Presence of significant site-level variation would identify opportunities for quality improvement and our findings will provide important benchmark rates of warfarin treatment before the introduction of newer anticoagulants into routine practice.
Methods
The PINNACLE program has been previously described. Briefly, in 2008 the American College of Cardiology Foundation’s NCDR launched PINNACLE (formerly known as the Improving Continuous Cardiac Care program [IC ]), the first national prospective office-based cardiac quality improvement registry in the United States. Academic and private practices were invited to participate in PINNACLE through the American College of Cardiology’s Web site, e-mails, brochures, and information Webinars. Physicians or practice representatives (e.g., administrators) in interested practices underwent a series of educational training sessions before data submission.
Within participating practices different patient data were collected at the point of care including patients’ symptoms, vital signs, co-morbidities, and medications. In addition, data for established performance measurements for coronary artery disease, heart failure, and AF were collected. Data collection was achieved through 1 of 2 mechanisms: (1) paper forms completed at the time of clinic visits or (2) modification of a practice’s electronic medical record data-collection system to comprehensively capture requisite PINNACLE data elements. Data from practices are routinely submitted to the NCDR and data quality checks and analyses were performed at Saint Luke’s Mid America Heart Institute (Kansas City, Missouri), the primary analytic center for the PINNACLE program.
For the purposes of this study, of 136,796 patients enrolled into PINNACLE from July 1, 2008 through December 31, 2009, we included 18,393 patients with nonvalvular AF. We further restricted the cohort to only those patients at moderate to high risk for stroke (i.e., a congestive heart failure/hypertension/age/diabetes/stroke [CHADS 2 ] score >1) in whom warfarin therapy is considered a performance measurement of high-quality care and included patients from practices with ≥10 eligible patients (total of 9,280 patients excluded). The final study sample consisted of 9,113 patients with nonvalvular AF at moderate to high risk for stroke from 20 practices at 51 different office locations.
Coprimary outcomes were (1) rate of warfarin treatment in patients with AF at moderate to high risk for stroke and (2) extent of practice-level variation in warfarin use. To minimize over-representation by patients with multiple visits we included data from only the baseline enrollment visit of each patient.
Baseline characteristics between patients treated and not treated with warfarin were compared using t tests for continuous variables and chi-square test for categorical variables. Warfarin treatment rates were determined for each practice and examined with descriptive plots.
To examine extent of practice-level variation in warfarin use multivariable hierarchical regression models were constructed to determine the median rate ratio (RR). These were 2-level hierarchical models with the practice modeled as a random effect and patient covariates as fixed effects. Because treatment rates exceeded 10% we used log-binomial or modified Poisson regression models at all steps, which estimate an RR directly. The resulting median RR can be interpreted as the likelihood that 2 random practices would differ in treating “identical” patients with warfarin. Median RR is always ≥1, with a median RR >1.20 suggesting significant practice-level variation.
In addition, we examined in these models whether patient-level predictors were stronger determinants of warfarin treatment than practice-level variation. This is possible because the median RR permits meaningful comparisons with effect sizes of patient factors (e.g., age, gender) included in hierarchical models, thus overcoming interpretational limitations that are inherent with the intraclass correlation coefficient. In these models we included as covariates the following patient characteristics: age (<70, 70 to <80, ≥80 years), gender, insurance type (private, Medicare, public, none), congestive heart failure, hypertension, diabetes mellitus, peripheral arterial disease, concomitant use of thienopyridine therapy, and previous stroke or transient ischemic attack, coronary artery disease, or systemic embolism.
For each analysis the null hypothesis was evaluated at a 2-sided significance level of 0.05 with 95% confidence intervals calculated. All analyses were performed with SAS 9.2 (SAS Institute, Cary, North Carolina) and R 2.7.0 (Foundation for Statistical Computing, Vienna, Austria).
Results
Of 9,113 patients with nonvalvular AF at moderate to high risk for stroke and eligible for warfarin treatment, 5,018 (55.1%) were treated with warfarin and 4,095 (44.9%) were not. Baseline characteristics of those treated and not treated with warfarin are listed in Table 1 . Compared to untreated patients, patients treated with warfarin were similar in CHADS 2 score, age, and rates of congestive heart failure, hypertension, diabetes mellitus, and previous stroke. However, patients treated with warfarin were more frequently men and were more likely to have dyslipidemia, peripheral arterial disease, and previous systemic embolism. In contrast, patients not treated with warfarin were more likely to have private health insurance and previous coronary artery disease. Notably, rates of percutaneous coronary intervention with a drug-eluting stent within the previous year, for which thienopyridine therapy would be warranted, were similar for the 2 groups.
| Covariates | Total Cohort (n = 9,113) | Warfarin Therapy | p Value | |
|---|---|---|---|---|
| Yes | No | |||
| (n = 5,018) | (n = 4,095) | |||
| Mean congestive heart failure/hypertension/age/diabetes/stroke score | 2.5 ± 0.8 | 2.5 ± 0.8 | 2.5 ± 0.8 | 0.38 |
| Age ≥75 years | 76.5 ± 9.9 | 76.3 ± 9.5 | 76.8 ± 10.4 | 0.45 |
| Age categories (years) | 0.07 | |||
| <70 | 21.1% | 21.4% | 20.9% | |
| 70–79 | 35.9% | 36.9% | 34.7% | |
| ≥80 | 43.0% | 41.8% | 44.4% | |
| Insurance type | <0.001 | |||
| Private | 61.9% | 60.4% | 63.8% | |
| Medicare | 33.7% | 34.4% | 32.9% | |
| Other public | 1.3% | 1.5% | 1.1% | |
| None | 3.0% | 3.6% | 2.2% | |
| Men | 51.3% | 52.6% | 49.7% | 0.005 |
| White | 87.2% | 87.1% | 87.3% | 0.80 |
| Coronary artery disease ⁎ | 47.4% | 45.6% | 49.6% | <0.001 |
| Dyslipidemia † | 60.8% | 62.9% | 58.3% | <0.001 |
| Diabetes mellitus | 37.1% | 36.8% | 37.5% | 0.50 |
| Hypertension ‡ | 93.4% | 93.8% | 93.0% | 0.14 |
| Previous stroke/transient ischemic attack | 10.3% | 9.9% | 10.7% | 0.18 |
| Congestive heart failure | 32.1% | 32.5% | 31.6% | 0.35 |
| Peripheral arterial disease | 6.1% | 5.1% | 7.3% | <0.001 |
| Previous systemic embolism | 2.1% | 2.8% | 1.1% | <0.001 |
| Stable angina pectoris | 5.1% | 4.9% | 5.3% | 0.39 |
| Percutaneous coronary intervention with drug-eluting stent in previous 12 months | 4.0% | 4.0% | 4.0% | 0.93 |
⁎ History of coronary artery stenosis ≥70%, percutaneous coronary intervention, or coronary artery bypass surgery.
† Assessed by individual physician most commonly because of low-density lipoprotein cholesterol level >130 mg/dL.
‡ Assessed by individual physician most commonly because of persistently increased systolic blood pressure (>140 mm Hg) or diastolic blood pressure (>90 mm Hg).
There was no relation between CHADS 2 score and treatment rates. Of 5,612 patients with a CHADS 2 score of 2, 3,086 (55.0%) were treated with warfarin. For the 2,510 patients with a CHADS 2 score of 3, 1,399 (55.7%) were treated with warfarin. For the 991 patients with a CHADS 2 score of ≥4, 533 (53.8%) were treated with warfarin. Table 2 lists use of antiplatelet therapies for patients treated and not treated with warfarin. Notably, of the 4,095 patients not treated with warfarin, 2,082 (50.8%) were treated with aspirin alone, 180 (4.4%) with a thienopyridine alone, 414 (10.1%) with aspirin and a thienopyridine, and 1,419 (34.7%) with neither aspirin nor thienopyridine therapy.
| Antiplatelet Therapy | Total Cohort (n = 9,113) | Warfarin Therapy | p Value | |
|---|---|---|---|---|
| Yes | No | |||
| (n = 5,018) | (n = 4,095) | |||
| Aspirin | 3,543 (38.9%) | 1,461 (29.1%) | 2,082 (50.8%) | <0.001 |
| Thienopyridine | 294 (3.2%) | 114 (2.3%) | 180 (4.4%) | <0.001 |
| Aspirin + thienopyridine | 589 (6.5%) | 175 (3.5%) | 414 (10.1%) | <0.001 |
| None | 4,687 (51.4%) | 3,268 (65.1%) | 1,419 (34.7%) | <0.001 |
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