Some disease processes can be analyzed with sufficient sensitivity and specificity on a large scale by identifying procedures related to their advanced stage. For example, early diagnosis and aggressive treatment of Helicobacter pylori
infection has led to decreased incidence of advanced gastrointestinal ulcer hemorrhage or bowel perforation, and as result fewer surgical procedures related to this diagnosis 
. Alternatively, improved diagnosis and aggressive treatment may lead to increased frequency of procedures secondary to efficacy as with surgical procedures for ischemic stroke 
In this manuscript, we used well-established surrogates for advanced coronary artery disease, coronary artery bypass graft and percutaneous transluminal coronary angioplasty, and investigated their relationship with socioeconomic factors 
The number of cardiac revascularization procedures was inversely related to highest education levels of the patients. This coincides with an established body of evidence that the highest formal education level corresponds to known risk factors for heart disease, such as obesity 
, diabetes 
, and hypertension 
. Education level is also an established and well known correlate of non-cardiac related conditions, such as cancer 
, rheumatoid arthritis 
, cerebrovascular disease 
, and back pain 
. Education level is an important marker of socioeconomic status not only because it describes the educational attainment that may confer a better understanding and self-management of preventative health measures, but it also indirectly relates to earning potential (household income) and employment status that can both influence ones ability to obtain routine healthcare.
Coronary artery disease often results from a culmination of multiple patient-centered factors such as diet and exercise 
. Lifestyle choices such as diet and activity level influence cardiovascular disease risk factors such as hypertension and diabetes mellitus and in turn the development of coronary atherosclerosis 
. Education, both in the classroom setting and via a healthcare provider are likely to influence patient compliance with healthy lifestyle choices as they relate to cardiovascular disease prevention. This provides some explanation to the strong negative correlation of education and the decreased prevalence of coronary artery disease.
Another finding of this study was that income levels correlate with the prevalence of advanced coronary artery disease. Household income levels have previously been associated with health insurance status, medical care use, health, and employment 
. In a complex interplay of these factors, household income provides a summative metric to compare groups. We chose a value much higher than the defined poverty level in an effort to compensate for the anticipated costs of a balanced diet and healthcare coverage. Even at the generous mark of $ 50,000 USD, a strong correlation was present. It should be noted that no accounting could be made for household size in relationship to income level, as this data does not exist in the accessed databases.
Additional factors that likely influence the development of advanced cardiovascular disease include biological differences in certain ethnic and gender groups not accounted for in this study, such as factors that alter the interaction between prothrombotic factors and atherosclerosis 
. It has been shown that living in a disadvantaged neighborhood is a risk factor for coronary heart disease, even after controlling for income and education 
The strength of this study includes the use of two well-established national databases that encompass hundreds of thousands of people, enabling a robust comparison between study and control groups. Limitations include the geographic reporting at the state level that make regional differences at the neighborhood or even city level difficult to account for. There also exist state-to-state differences in practice patterns between CABG and PTCA. In one of the largest studies of regional discrepancies in treatment modalities for acute myocardial infarction cardiac revascularization, state specific CABG rates varied from 9.3% to 13.1% 
. The state specific rates for PTCA associated with acute myocardial intervention varied much more widely, ranging from 16.8 to 36.0% 
. State specific factors may influence whether one is more likely to undergo CABG or PCTA for acute myocardial infarction, however no data currently exist regarding the prevalence of these procedures in all settings.
Inherent to national databases is the potential for geographical biases with respect to aggressiveness of intervention. For example, a patient with multiple medical comorbidities in poor clinical condition may be considered a candidate for CABG in one state but perhaps not in another. These differences are difficult to quantify from a population-based standpoint and are best addressed with prospective, intention to treat analysis. These databases also lack information on the degree of severity of the coronary artery blockage and do not capture clinical data points such as time interval from symptom onset to treatment. All data recorded in national databases are subject to various coding anomalies. We attempted to eliminate this bias by focusing exclusively on the principal diagnosis (that is the major determinant of reimbursement rates) with the assistance of CCS grouping that systematically and compressively identifies key ICD-9-CM procedure codes. Additionally, not all states participate in the BRFSS, limiting the analysis to the data of 30 states. This study is expected to generally underestimate differences in health status, as the amount of undiagnosed disease in those without any access to care is impossible to report.