Validation of the Appropriate Use Criteria for Coronary Angiography

Editors' Notes Context Criteria to determine the appropriateness of diagnostic testing might help guide practice, reduce wasteful testing, and aid performance evaluation. The validity of recently developed appropriate use criteria for diagnostic cardiac catheterization has not been established. Contribution Despite an association between appropriateness ratings and the presence of obstructive coronary artery disease (CAD), only approximately half of angiographic studies classified as appropriate demonstrated obstructive CAD. Furthermore, obstructive CAD was reported at about one third of tests designated as inappropriate or uncertain. Implication Current appropriateness criteria for diagnostic coronary angiography may not be suitable to guide clinical practice. Expenditures in health care, particularly in the field of cardiovascular disease, are increasing dramatically, threatening its sustainability (1, 2). Diagnostic cardiac catheterization is an example of a widely used investigation with substantial geographic variability (3, 4) for which there have been questions of overuse, given its suboptimal diagnostic yield in stable ischemic heart disease (IHD) (5, 6). In response, more rational consumption of resources has been emphasized. One such effort was the development of appropriate use criteria (AUC) for diagnostic catheterization, led by the American College of Cardiology Foundation in collaboration with other professional organizations (7). The implicit rationale for a procedure being defined as appropriate is that its anticipated benefit outweighs its potential harm. However, there is a paucity of empirical evidence validating this conceptual framework. Previous work by our group has helped to validate the AUC for revascularization by showing that revascularization in patients with appropriate indications is associated with a reduction in mortality (8). The validity of the recent appropriateness criteria for diagnostic coronary angiography is less clear. Our goal in this study was to address this gap in knowledge. In suspected stable IHD, coronary angiography is done to confirm or rule out the presence of obstructive coronary artery disease (CAD) such that appropriate secondary prevention medications can be initiated and the need for coronary revascularization can be assessed. Thus, the diagnostic yield for an appropriate coronary angiographic study should be higher, in terms of the proportion of obstructive CAD, than for one that is deemed inappropriate. It follows that more appropriate angiography should more frequently lead to subsequent revascularization. Accordingly, the objective of this study was to evaluate the validity of the appropriateness criteria in predicting obstructive CAD in patients having elective coronary angiography for suspected stable IHD. Methods This population-based, observational, multicenter cohort study was approved by the Institutional Research Ethics Board at Sunnybrook Health Sciences Centre (Toronto, Ontario, Canada). The need for patient consent was waived under Ontario's Personal Health Information Protection Act (www.ipc.on.ca). Data Sources The Cardiac Care Network (CCN) is a network of 19 hospitals providing cardiac services in Ontario, Canada. The CCN maintains a prospective clinical registry of all patients in the province who have advanced cardiac procedures, such as angiography, percutaneous coronary intervention (PCI), or coronary artery bypass grafting (CABG). This registry contains detailed information on demographic characteristics, symptom severity, and comorbid conditions as well as results of noninvasive cardiac testing done before coronary angiography. Detailed information on the results of the angiographic study is also available. Data for the registry are obtained by dedicated clinical care coordinators at each hospital, and the accuracy of the anatomical and clinical data in the CCN registry has been assessed through chart audits and angiographic core laboratory validation (9, 10). Data from the CCN registry were linked by using encrypted unique identifiers to population-based administrative databases containing information on all Ontario residents. Ontario has more than 13 million residents, who have universal access to physician and hospital services through a single-payer, publicly funded health care program administered by the Ontario Ministry of Health and Long-Term Care (MOHLTC). These databases are available from the Institute for Clinical Evaluative Sciences (ICES). The Canadian Institute for Health Information Discharge Abstract Database (CIHI-DAD) contains data on all hospitalizations as well as diagnostic codes to identify comorbid conditions. Sex was confirmed by using the Ontario Registered Persons Database, and data on postal codes (for income status and rural residence) were obtained from Statistics Canada. Presence of hypertension and diabetes was cross-referenced with the Ontario Hypertension Database and Ontario Diabetes Database, respectively. Details on the physician who performed the index angiographic study were obtained from the ICES physician database and the CCN registry. Physicians who performed both diagnostic catheterization and PCI were classified as interventional physicians, and those who performed only diagnostic angiography were classified as noninterventional physicians. Hospital-specific factors, such as on-site availability of PCI or CABG, were also obtained from the CCN registry. Study Population Our cohort comprised patients with an index angiographic study for the indication of suspected CAD, as documented at the time of referral for the procedure (obtained from the CCN registry), from 1 October 2008 to 30 September 2011. During this time, only 18 hospitals were providing diagnostic angiography in Ontario. Patients with multiple studies were categorized according to their first one. We did not include patients whose indications for angiography in the CCN registry were myocardial infarction (MI), acute coronary syndrome, valvular or structural heart disease, or arrhythmia. We excluded patients younger than 20 years and those who did not have a valid Ontario health card number. We also excluded all patients with a prior MI or revascularization (PCI or CABG) as indicated in either the CCN registry or the CIHI-DAD. Appropriateness Score Our primary exposure was the appropriateness score (scale of 1 to 9), as defined by the 2012 AUC for diagnostic catheterization (7). Scores were categorized as appropriate (7 to 9), uncertain (4 to 6), or inappropriate (1 to 3). Appropriateness was adjudicated on the basis of the data available at the time of referral for coronary angiography (as entered in the CCN registry) using an automated computer algorithm. The AUC consists of 102 indications for a spectrum of cardiovascular conditions, including acute coronary syndromes, valvular heart disease, and arrhythmias. As shown in Table 1, we restricted our analysis to 12 appropriateness indications relevant to patients with suspected stable IHD (indications 5 to 11, 13, 15, 17, 20, and 24 of the AUC). In particular, for the purposes of this study, we did not examine indications for patients with known CAD. We also did not consider advanced noninvasive testing, such as cardiac computed tomography or magnetic resonance imaging, because results of these tests are not available in the CCN registry. Table 1. Appropriateness Categories and Scores for Angiography, Based on the AUC* To determine the scores for patients, we applied a hierarchical approach (Figure 1), first based on whether they had noninvasive testing and on their symptom status. Noninvasive testing was divided into stress electrocardiographic (ECG) testing, stress testing with imaging (defined as either stress nuclear or stress echocardiographic studies), or echocardiography alone. Patients without prior noninvasive testing were evaluated on the basis of whether they were symptomatic or asymptomatic. Figure 1. Assignment of appropriateness scores according to the AUC. Indications are from Tables 1.2 and 1.3 in the AUC document (7). AUC = appropriate use criteria for diagnostic catheterization; GXT = stress echocardiographic testing; LV = left ventricular. For patients who had prior noninvasive testing, we applied indications 11, 13, 15, 17, 20, and 24 from the AUC. Patients with low-risk findings on stress testing with imaging but high-risk findings on stress ECG testing were specifically represented by indication 20 (Table 1). Otherwise, we applied scores based on the test result and the symptom status. Of note, the CCN registry restricts results from stress ECG testing and stress testing with imaging to either high- or low-risk, with no intermediate-risk category. If multiple noninvasive tests were done, we calculated a separate appropriateness score for each method for that patient and used the highest score as the final appropriateness score. For symptomatic patients without prior noninvasive testing (indications 8 to 10) (Table 1), we estimated pretest probabilities of CAD by using the DiamondForrester model referred to in the AUC (7, 11). Because we were unable to characterize symptom quality as typical, atypical, or nonanginal, we adopted a conservative assumption that all symptomatic patients had typical angina. With this approach, all symptomatic men younger than 40 years had an intermediate pretest probability of CAD, whereas those older than 40 years had a high pretest probability. For symptomatic women, the age cutoff between an intermediate and high pretest probability was 60 years. For asymptomatic patients without prior noninvasive testing (indications 5 to 7) (Table 1), we estimated overall global 10-year risk for CAD and categorized it as low (<10%), intermediate (10% to 20%), or high (>20%) using a modified Framingham risk score (the Appendix, provides details on how the score was calculated) (5, 12). Using this algorithm, we were able to determine an approp