|Pub Date:||Monday, May 4, 2009|
|Authors:||Jeffrey Anderson, MD, FAHA|
|Article:||Diagnostic-Therapeutic Cascade Revisited: Coronary Angiography, Coronary Artery Bypass Graft Surgery, and Percutaneous Coronary Intervention in the Modern Era|
- Lucas FL, Siewers AE, Malenka DJ, Wennberg DE, , Diagnostic-therapeutic cascade revisited: coronary angiography, coronary artery bypass graft surgery, and percutaneous coronary intervention in the modern era., Circulation, 118 (25) 2797-802. View in PubMed
Wide variations in rates of coronary angiography and revascularization across geographic regions of the United States have been known to exist for over a decade. Population-based rates of coronary artery bypass graft surgery (CABG) have been reported to vary by fivefold and percutaneous coronary interventions (PCI) by sixfold or greater. Further, variations in revascularization rates are not explained by differences in demographic characteristics or disease prevalence (as measured by rates of acute myocardial infarction), whereas they are highly correlated with variations in rates of coronary angiography. Factors identified as correlating with, and likely driving, rates of angiography include use of imaging-enhanced stress tests, the supply of interventional cardiologists, and the density of catheterization laboratories. The observed tight correlation between diagnostic testing for coronary artery disease (CAD) and therapeutic revascularization has been called the “diagnostic-therapeutic cascade.”
Missing from earlier assessment of the diagnostic-therapeutic cascade was an understanding of the separate correlations of angiography with CABG and with PCI. Further, since the 1990s, major changes have occurred in the use of these two approaches to coronary revascularization, with rates of CABG decreasing and PCI increasing. In addition, important outcome studies have emerged that have improved our understanding of the utility and limitations of PCI. Hence, the objective of this study was to re-evaluate the relationship between diagnostic testing and therapeutic application and to evaluate this separately for PCI and CABG.
The investigators reviewed the Medicare Part B (physician and supplier) claims data base to identify coronary angiography and revascularization procedures occurring during 2005 using current procedural terminology (CPT) codes for a 10% random sample of Medicare beneficiaries. The Medicare Denominator File was used to identify all beneficiaries eligible for Part B (i.e., approximately 5.4 million beneficiaries). Each beneficiary was assigned to a hospital referral region (HRR) based on ZIP code of residence. (Hospital referral regions represent geographic patterns of tertiary care, including PCI and cardiac surgery.) To account for differences in patient characteristics by HRR, procedural rates were adjusted for age/sex/race distributions of the local Medicare population. A standard method was used to calculate the expected number of events expected in each HRR assuming national (standard population) age/sex/rates. The observed number of events was then divided by the expected number of events, and the resulting ratio was multiplied by the national rate to produce the adjusted rate. A least-squares regression method was used to assess the relationship between rates of coronary angiography and revascularization.
In 2005, PCI rates far exceeded CABG rates in all Medicare groups, especially in older patients, women, and blacks. As observed in the mid 1990s, coronary angiography rates were highly variable across geographic regions (HRRs), ranging from 16.2 to 77.0 procedures per 1,000 beneficiaries, a 4.8-fold variation (mean rate, 37.2). The respective range for CABG was 1.1 to 10.1, a ninefold variation (mean rate, 4.9). The range of PCI rates was even greater, 4.2 to 44.7, a nearly 11-fold variation (mean rate, 13.2).
As in the 1990s, revascularization rates remain highly associated with angiography rates (r2 = 0.84). However, the relationships between angiography rates and CABG or PCI, considered separately, showed substantial differences. Angiography rates correlated only modestly with CABG rates (r2 = 0.41), with a linear relationship and a modest slope at lower angiography rates before reaching a plateau at 50 procedures per 1,000 beneficiaries. In contrast, the relationship with PCI was much stronger (r2 = 0.78) and linear across essentially the entire range of angiography rates observed: an increase of 10 in the coronary angiography rate was associated with an estimated increase of 3.4 in the PCI rate regardless of the baseline angiography rate.
The modern assessment of the "diagnostic-therapeutic cascade," more than a decade after its description, indicates a continued strong correlation between rates of coronary angiography, which continue to vary widely (up to fivefold), and revascularization. However, very different patterns were discovered for this relationship between CABG and PCI. CABG rates plateaued beyond 50 procedures per 1,000, whereas PCI rates continued to climb as angiographic rates increased. CABG indications are quite specific, with the added morbidity of and contraindications to CABG versus PCI further reinforcing limiting its application to those at higher risk and with more extensive and symptomatic disease. In contrast, PCI has few absolute indications beyond acute MI. These observations suggest that the marginal use of PCI over CABG at high regional rates of angiography likely represents nonsurgical one and two-vessel disease, with medical management being the alternative to PCI. The strong tendency to dilate or stent marginally significant lesions has long been known and termed the "occulo-stenotic reflex." Further, limited evidence suggests that it is physician- rather than patient-related factors that are the principal drivers of this preference for PCI over medical therapy. However, recent studies  have suggested that in patients with stable CAD, PCI may offer minimal incremental benefit or even increase procedure-related risk and cost. On the other hand, coronary stenoses resulting in objective evidence of ischemia, e.g., by radionuclide perfusion studies  or, more precisely, by fractional flow reserve measurements , does appear to select a group of patients for which revascularization may provide incremental symptomatic and outcomes benefits.
Taken in context with other recent supporting evidence, the implications of this study are potentially broad. The high rate of angiography and PCI in many care regions of the United States raises fundamental questions about cost effectiveness and clinical value. A thorough examination of practice patterns appears to be in order. Further clinical effectiveness and outcomes research is needed to guide optimization of strategies for both patients and society. Meanwhile, physicians and care systems should review, and potentially revise, practice patterns to ensure that coronary angiography and PCI are driven by high-risk features such as objective evidence of ischemia.
- Wennberg DE, Kellett MA, Dickens JD, et al. The association between local diagnostic testing intensity and invasive cardiac procedures. JAMA 1996;275:1161-1164.
- Kuhn EM, Hartz AJ, Baras M. Correlation of rates of coronary artery bypass surgery, angioplasty, and cardiac catheterization in 305 large communities for persons age 65 and older. Health Serv Res 1995;30:425-36.
- Verrilli D, Welch HG. The impact of diagnostic testing on therapeutic interventions. JAMA 1996;275:1189-91.
- Boden WE, O'Rourke RA, Teo KK et al. Optimal medical therapy with or without PCI for stable coronary disease. N Engl J Med 2007;356:1503-16.
- Shaw LJ, Berman DS, Maron DJ et al. Optimal medical therapy with or without percutaneous coronary intervention to reduce ischemic burden: results from the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial nuclear substudy. Circulation 2008;117:1283-91.
- Tonino PA, De Bruyne B, Pijls NH et al. Fractional flow reserve versus angiography for guiding percutaneous coronary intervention. N Engl J Med 2009;360:213-24.
-- The opinions expressed in this commentary are not necessarily those of the editors or of the American Heart Association. --