Coronary angiography rates were strongly correlated with population based rates of revascularization. However, when comparing coronary angiography individually to the two interventional options very different patterns emerged. Compared with the modestly sloped coronary angiography-CABG relationship with a suggestion of a threshold effect, the coronary angiography-PCI relationship was steep and linear.
The simple explanation for the tight relationship between coronary angiography and overall revascularization rates is that there is a large reservoir of undiagnosed coronary artery disease, more of which is discovered in areas with higher coronary angiography rates. However, we have previously shown that rates of hospitalization for acute myocardial infarction are uncorrelated with revascularization rates (R2
= 0.03) 3
. The different relationship between angiography and PCI versus CABG further suggests that disease burden alone is unlikely to be the primary factor explaining these findings. Coronary disease burden could only explain these relationships if there are extremely different distributions of coronary artery disease severity and anatomy between populations, unaccounted for by age, sex, and race.
Indications for CABG are fairly specific12,13
and most studies suggest that CABG is currently performed for combinations of anatomy and function for which surgical revascularization improves long term survival, at least in comparison to older medical therapy, or for patients with multi-vessel disease to relieve symptoms and improve quality of life. The modest relationship between angiography and CABG suggest that while more cases are found for surgical intervention as coronary angiography rates increase, beyond a certain point increasing rates do not identify additional patients for which CABG is the preferred intervention. However, the picture for PCI is quite different. There is a much more positive relationship between coronary angiography and PCI rates and there is no place on the coronary angiography/PCI curve that suggests that all patients with lesions that could undergo a PCI have been identified. What accounts for the apparent lack of a threshold for intervention with a catheter?
When we look for coronary artery disease in an elderly population, we find it. However, the coronary angiography-CABG relationship suggests that the ‘marginal yield’ of severe coronary artery disease falls with higher rates of coronary angiography. Therefore, it appears that the marginal disease found at very high rates of angiography is predominantly non-surgical one- and two-vessel disease. Unlike CABG, there are almost no absolute indications for PCI 14
, the exception being primary PCI for AMI. Thus, it must be patient and/or physician preferences for PCI versus medical management that drives the tight diagnostic-therapeutic relationship for PCI.
The limited data that exists suggests that patients’ and physicians’ preferences for treatment of coronary artery disease may be in conflict. Only one randomized trial of patient preferences for treatment of coronary artery disease has been performed15
. In this study, patients on the waiting list for revascularization in Ontario Canada, a geographic region that had lower rates of intervention than that in any HRR in the United States, were randomized to usual care versus an interactive decision aid designed to assist patients in making complex medical decisions. Patients in the decision aid arm were 28% more likely to choose medical treatment over either PCI or CABG than those in the control arm. Lin and colleagues found that cardiologists, despite acknowledging the lack of evidence of mortality and AMI prevention benefit stated they would provide PCI for minor lesions unrelated to symptoms16
. The authors (and the cardiologists interviewed) attributed these findings to the ‘occulostenotic reflex’17
, the impulse to fix a stenosis even if it is unlikely to cause future problems. Cardiologists also reported a bias towards intervention because of a belief, despite evidence18,19,20,21
that an open artery provided benefit and because of concerns about ‘regret’ if they failed to act and a patient suffered a subsequent event. Combined, these studies suggest that patients with coronary artery disease may be more risk averse than cardiologists when considering treatment options.
Other factors may also play a role in the tight, linear relationship between angiography and PCI. Often, the same cardiologist is both diagnostician and the interventionalist. Potential issues related to ‘self-referral’ are compounded by clinically significant intra-observer and inter-observer variability in interpretation of angiograms 22
and the need to make rapid, rather than measured, decisions on whether and where to intervene. This propensity to intervene has been given a clear push by private insurers. Since the early 1990s, insurance companies have encouraged the use of ‘ad hoc’ angioplasty through explicit payment policies that discourage staged procedures - a diagnostic event followed by an interventional event. This policy may have made sense from the standpoint of reducing episode based costs; however, it may have had the unanticipated consequence of increasing the numbers of PCIs performed.
Our study has some limitations. First, we limited our analysis to the aged Medicare population. However, we have no reason to believe that patterns of care across geographic regions vary systematically by age or insurance status. Variation in Medicare rates is reflected in younger populations (www.bcbsm.com/atlas
). We are unable to assess the indication for testing nor of the results of the coronary angiography and indications for revascularization. However, this is only an important limitation if disease patterns vary remarkably across geographic areas and we have previously found little evidence of large disparities in disease distribution across geographic regions.
The tight relationship between diagnostic intensity and therapeutic intensity with PCI raises a fundamental challenge to those managing patients with coronary artery disease. There is established evidence of benefit of PCI in unstable coronary syndromes24
, and current guidelines recommend such a strategy in these patients25
. However, several recent studies have suggested that patients with stable coronary disease who undergo PCI may receive no marginal benefit, or worse, face increased risk of death and AMI compared to those managed medically26,27,28
. We would contend that unstable patients are more likely to receive intervention no matter where they live, but the marginal patients in high rate areas are likely to be those who are less symptomatic in whom the benefit is much less well defined. Our models suggest that, in areas with high rates of coronary angiography, at most 0.2 patients with serious coronary anatomy eligible for CABG would be identified for each 10 angiograms performed. Thus, the ‘cost’ of, at most, 0.2 appropriate CABGs would be 10 additional angiograms and 3.4 additional PCIs. Given the ‘diagnostic-therapeutic yield’, a fundamental question needs to be asked: in the low and moderate risk patient, do we even want to know their anatomy?