We conducted a population-based cohort study of elderly AMI patients living in US regions with vastly different practice patterns to assess which patients received more intensive treatment, and to study their associations with long-term population mortality. Patient baseline AMI severity was similar across regions; however, treatment differed dramatically after onset of AMI. Regions with more cardiac catheterization laboratory capacity had a commensurately more intensive invasive management style and provided higher rates of cardiac catheterization to all patients, regardless of age, risk profile, or clinical presentation. Availability of cardiac technology and lower patient risk appeared to be the factors driving invasive treatment, as others have also found.12,31,32,34,35,42
The treatment-risk paradox, whereby the propensity to receive treatment is inversely related to expected patient improvement when it is provided to patients at lower risk, possibly due to physician misconceptions about benefit-harm tradeoffs or concerns about treatment complications, has been shown for other cardiovascular therapies.43,44
Our study confirmed that clinicians were more likely to provide invasive treatments to lower-risk than higher-risk patients in this population, despite evidence demonstrating that these treatments are associated with greater absolute improvements in older, higher-risk patients.8–11
Second, a more intensive medical management style was associated with improved survival regardless of the level of invasive management in the region; however, in regions with high medical management intensity, there appeared to be little or no marginal improvement associated with additional invasive treatment, as was also found by McClellan et al.27
Although clinical trials have demonstrated that more intensive use of cardiac technology may improve survival for specific AMI subgroups under ideal conditions,2
this strategy does not always translate into population benefit because clinical settings do not replicate the ideal conditions of the trial. First, even for ideal patients, the benefits of receiving invasive care may not be achievable in routine clinical practice, especially in lower volume settings with less experienced clinicians, or with long transfer times to a hospital with an onsite cardiac catheterization laboratory. Second, the benefits have not been demonstrated in different subgroups of patients with AMI, even though our study and others show that invasive strategies are being routinely used in these patients.12
Finally, underuse of invasive cardiac technology in patients at high risk who could benefit most, serves to dilute population effectiveness. For the vast majority of patients, these findings point to the need for caution about the routine use of cardiac technology in populations in which the marginal improvements may be small, when simpler, lower-cost, evidence-based medical alternatives exist.
The regional exposure used in this study is an example of an “instrumental variable”27,45
or a “natural experiment.” By definition, an instrumental variable is associated with regional treatment intensity, but not with attributes that might affect mortality, such as AMI severity. It is a device that attempts to achieve pseudo-randomization so that the estimated treatment effects are not confounded by unmeasured selection bias from healthier patients receiving cardiac catheterization. Our regional intensity exposures appear to have these properties. Similar designs were used by McClellan et al27
and Fisher et al34,35
to assess the effects of regional exposures on survival of chronic disease populations. These types of analyses estimate treatment effects on the marginal patient, defined as those who would receive the treatment in a higher but not in a lower-intensity area.
Careful interpretation of the effects of the area-level exposures is necessary. Area-level analyses do not imply that the entire effect of the management strategy derives from the specific exposures that were measured, that is, prescription of β-blockers at discharge or use of cardiac catheterization. Instead, they imply that the survival effect is attributable to any and all treatments provided to the residents of the area. In this study, we documented that regions with a more intensive invasive management style provided more revascularization and less medical management. Regions prescribing more β-blockers at discharge also provided more intensive medical therapeutics of all types at discharge and less revascularization. The survival improvements observed are the combined effects of general management strategies that emphasize particular types of care.
Several limitations should be considered. Our results might be confounded by unmeasured regional AMI severity differences, although this is unlikely because mean baseline AMI severity risk was similar across regions. The risk adjustors were based on a systematic chart review and encompassed a rich mixture of patient characteristics that strongly predict mortality. Data were not available on postdischarge medications, but inpatient initiation of post-AMI therapies is strongly related to postdischarge use.46–48
Second, this study is somewhat dated in that current AMI treatment strategies include primary angioplasty and routine use of statins. However, unlike primary angioplasty, revascularization in the convalescent phase of AMI is likely to show improvement only after longer-term follow-up. In addition, only a minority of patients are eligible for primary angioplasty so that increasing use of this therapy is unlikely to significantly affect population outcomes. Studies such as this are the only way to evaluate long-term survival effects of different treatment styles in actual practice settings because population benefit is often not apparent for many years.49
Finally, we could not examine the implications of regional treatment intensity on severity of angina, quality of life, and functional status post-MI.
Debate continues regarding the value of routine use of high technology treatment for cardiac patients.50–53
While AMI survival has improved compared with 30 years ago, invasive treatment and medical management are not optimal as practiced in the United States. Administration of evidence-based medications has improved since 1994–1995,16,18
but invasive management rates have increased as well. Therefore, the message from our study regarding the need to direct optimal treatments to patients with the greatest expected improvement may still be relevant. We recommend first, that a comprehensive, systems-minded approach to delivering evidence-based medical management to AMI patients be a national priority. Second, because health care resources should be provided in such a way as to maximize clinical improvement and efficiency of Medicare spending, continuous large-scale population-based evaluations of the long-term community effectiveness of expensive, invasive cardiac technology must also be a national priority. The stakes are high in terms of patient outcomes and health care spending.