Chicago, IL—Diagnostic accuracy is the primary determinant of cost-effectiveness of medical imaging for patients with chronic coronary artery disease (CAD), stated Matthew J. Budoff, MD, Professor of Medicine at David Geffen School of Medicine at University of California Los Angeles (UCLA), and Director of Cardiac CT at Harbor-UCLA Medical Center, Torrance, CA, at the 2012 American College of Cardiology meeting.
Coronary computed tomography angiography (CTA) as currently performed has the highest diagnostic accuracy, with a sensitivity of 95% and specificity of 83%, followed by pharmacology nuclear imaging (89% sensitivity, 75% specificity). Exercise electrocardiogram has the lowest diagnostic accuracy (68% sensitivity, 77% specificity).
Patient selection for testing is poor, and improvement is needed to achieve cost-effectiveness. A total of 62% of patients sent to the diagnostic catheterization laboratory to rule out CAD do not have it, according to data from the 2005 to 2007 National Cardiovascular Data Registry published in 2010.
On average, catheterization laboratory testing costs >$10,000 per patient; this adds hundreds of millions of dollars in healthcare costs, according to Dr Budoff.
CTA as a “Gatekeeper” to Invasive Coronary Angiography
CTA can prevent the need for invasive coronary angiography (ICA) in a percentage of patients. A recent study showed a combined 73% rate of falsepositives in 241 patients with abnormal findings on myocardial perfusion imaging (MPI)—23% had normal coronary arteries, 40% had nonsignificant disease, and 10% had mild disease (Patel N, et al. Am J Cardiol. 2012;109: 165-168). This translated to a net savings of $1295 per patient (a 51% savings) and a total savings of $320,000, based on Medicare costs.
A larger, 2007 study also provides evidence that “correlates to the idea that dollars can be saved by not having to perform invasive coronary angiography,” commented Dr Budoff. In 421 patients with intermediate risk of CAD and an abnormal MPI result, an 80% reduction in ICA with CTA was demonstrated. Safety of this strategy was confirmed by event-free survival at 15 months. Of the total patients, 6 had a late ICA, 1 patient had revascularization, and no myocardial infarctions or deaths occurred.
A 2007 study of 206 patients with mildly abnormal or equivocal tests (only 32% had obstructive CAD) showed that selective catheterization saved $1454 per patient. Dr Budoff noted the relation between cost-savings and pretest probability of prevalence of disease, with CTA saving the most money in lower-probability patients and the savings decreasing as the probability increased. “At a prevalence of CAD of about 80%, CTA is cost-effective as a gatekeeper to ICA,” said Dr Budoff.
Cost per Correct Diagnosis, Quality-Adjusted Life-Year
Imaging can save downstream costs, and the savings differ by imaging modality. In a 2008 study of patients at intermediate risk for CAD, the downstream costs in patients without known CAD was $1572 for CTA (N = 1647) and $2531 for single-photon emission computed tomography (N = 6588) at 1 year, based on Medicare data.
The average savings was $1075, which increased to $1838 per person when the observation was expanded to include 39,174 patients.
CTA was shown in one series to be cost-effective in terms of cost per correct diagnosis in patients with a low prevalence of CAD, whereas ICA performed better in patients with higher probability of disease, which Dr Budoff noted is concordant with other trials. In patients with a 10% disease probability, CTA alone reduces costs, at a cost per correct diagnosis of $81,591 compared with $349,880 for ICA.
The cost for CTA per correct diagnosis was $17,516 with a 30% CAD probability, $9847 with a 40% probability, and $5281 with a 50% probability; the corresponding costs with ICA were $73,175, $43,008, and $25,315, respectively.
The cost per quality-adjusted lifeyear (QALY), the gold standard for measuring cost-effectiveness, varies by age but not by sex. For example, at a 30% CAD probability, the cost per QALY for CTA alone is $18,862 and $594,264 for ICA at age 60 years; this shifts to $21,636 and $162,229, respectively, at age 80 years.
For patients in their 40s and 50s, the cost for CTA alone is $39,574 and $23,440, respectively, but ICA was the dominant strategy in this series.
CTA: Cost-Effective Triage for Acute Coronary Syndrome
In a 2007 single-center study of 197 patients presenting with chest pain at the emergency department, CTA used immediately to exclude or identify CAD resulted in an approximate 15% cost-savings, at a cost of $1586 per patient compared with $1872 in the standard- of-care arm.
The time to diagnosis was significantly reduced with CTA compared with standard of care (3.4 hours vs 15.0 hours, respectively), and its diagnostic accuracy was 75%.
The 16-center, international Coronary Computed Tomographic Angiography for Systematic Triage of Acute Chest Pain Patients to Treatment (CTSTAT) trial exhibited a significant 38% reduction in cost of care with CTA ($2137 with CTA, $3458 with MPI) in 699 patients presenting to the emergency department and a 54% reduction in time to diagnosis (Goldstein JA, et al. J Am Coll Cardiol. 2011;58:1414-1422).