Once 64-slice MDCT was implemented, CCTA was rapidly adopted within the practice. During the first full year of availability, 1,405 CCTA procedures were performed. During the second year, fewer CCTA procedures were performed as other community CTs became available and as cardiologists became familiar with indications and utility of CCS testing. Increased reliance on CCS might have played a role in a lower second year volume of CCTA and going forward physicians focused on measurable plaque burden and altered their medical approach. We have previously reported in this cohort that the findings of calcified and non-calcified plaque on Cardiac CT lead to a change in medical strategy for CAD with aggressive reduction of LDLs, this despite near normal LDL values at baseline [20
The adoption of CCTA was also associated with a significant reduction in SPECT MPI, suggesting that CCTA replaced SPECT MPI to some extent. The reduction in SPECT MPI may be explained by a shift in diagnostic paradigm in which CCTA was performed as a first line test instead of SPECT MPI for evaluation of patients with intermediate pretest risk of CAD, consistent with current appropriateness criteria [8
]. Further, the strong negative predictability of CCTA would support a decreased need for downstream SPECT MPI [10
]. Also, the number of stress echocardiograms performed in the last 2 years of the study is greater than the first 2 years, most likely reflecting some substitution of SPECT MPI to stress echocardiography, perhaps due to the desire to avoid a second test utilization radiation.
The reduced number of patients referred for invasive coronary angiography and SPECT MPI was partially offset by the number of patients getting CCTA, Calcium scores. However, this resulted in a substitution of very high cost invasive coronary angiography by lower cost office based testing. Since diagnostic cardiac catheterization is associated with severe adverse events in 0.7–1.5% of patients and associated deaths in 0.07% the avoidance of unnecessary cardiac catheterization in subjects at relatively low risk of cardiac events is clinically significant and with substantial cost savings [23
Others have predicted or have estimated that the potential reductions in myocardial perfusion imaging and invasive coronary angiography might be considerable in the setting of the utilization of CCTA as the first test for the intermediate risk patient or the patient with acute coronary syndrome [26
]. Such estimates suggest reductions in excess of 74%. [26
]. However, this is the first report in a “real world” uncontrolled setting which documents dramatic reductions in ICA and simultaneous reduced downstream testing of SPECT MPI and TME. Even more appropriate and cost efficient testing might be achievable by only considering patients for provocative testing who have failed medical management and or have suspicious narrowing’s on CCTA that require invasive coronary for clarification or intervention.
In this practice, implementation of CCTA was associated with a significant 45% decrease in ICA over the study period (from 2,083 procedures in 2004 to 1,150 in 2007, P
= 0.012) but had no significant impact on the number of percutaneous revascularization procedures performed. As a result, implementation of CCTA was associated with a significant 53% increase (P
= 0.008) in the proportion of ICA studies showing significant angiographic narrowing’s resulting in the need for percutaneous coronary intervention. This implies that there was more accurate detection of disease that ultimately underwent PCI with fewer patients with normal or non occlusive disease undergoing invasive coronary angiography. Following publication of the COURAGE trial in the spring of 2007 [30
] this practice experienced a trend toward reduced incidence of PCI (425 in 2006 vs. 326 in 2007) which did not achieve statistical significance. Further evaluation will need to assess utilization rates over the next few years to determine whether there is a significant lasting change in the intervention strategy and resulting impact on ICA and PCI utilization. Finally, this study performed in a private practice cardiology group, parallels a university medical center study which showed a 30% decrease in non-invasive imaging after introduction of CCTA [31
]. However, in that study there was a reported growth of the invasive angiography practice and also decisions may have been controlled by multiple individuals in an academic setting thus confounding the ability to implement and measure an opportunity to reduce the incidence of invasive angiography.
The limitations of our study need consideration: (1) The trends in noninvasive and invasive procedures reported in this study should be viewed with some caution, given the short observation period (2 years before and 2 years after installation of the 64-slice MDCT) and the potential confounding factors of an uncontrolled retrospective study in the setting of concerns about late stent stenosis [32
] improved medical management [33
] and modest trends towards general reduction in both invasive angiography and PCI in similar practices of approximately 10% (MedAxiom, Neptune Beach Florida-private communication). The utilization of angiography is dynamic and under many influences and therefore CCTA may not solely account for the reduction found in this study. (2) The effects of availability of the calcium score on downstream testing independent of CCTA cannot be determined from this study. (However, identification of non calcified plaque found on CCTA enhanced lipid management [20
]). (3) The findings of a normal or non occlusive CCTA may have lead to fewer MPI-SPECT testing and invasive coronary angiography downstream over the entire 4 years once significant occlusive CAD was excluded. Thus, the ability to analyze each year effects sequential is impaired.