December 4, 2009 (Chicago, IL) - Evaluating chest-pain patients with coronary CT angiography (CCTA) is preferable to the "standard" nuclear stress-testing technique in the population whose prevalence of coronary disease is under 50%, according to a study by Dr Ethan Halpern (Jefferson University, Philadelphia, PA) .
CCTA evaluation of chest pain in this population reduces the number of unnecessary cardiac catheterization procedures, reduces radiation exposure, and leads to a more cost-effective cardiac workup overall, Halpern said during a presentation at the Radiological Society of North America (RSNA) 2009 Scientific Assembly. Halpern's was among over a dozen presentations at the RSNA meeting on cardiac risk stratification with CT or MRI.
"Both CCTA and nuclear myocardial perfusion scintigraphy [MPS] testing are used to evaluate coronary artery disease. The key question is: Are they competing or complementary studies? In some cases you can decide on one test or the other to exclude a diagnosis, and in some cases the two studies may combine to provide additional information," he explained. "The purpose of this study was to define the optimum combination of coronary CT and perfusion studies for the evaluation of coronary disease."
Halpern and colleagues evaluated the published literature and Medicare cost data to develop a decision-tree model to calculate the expected values of cost and radiation exposure for evaluation of the coronary arteries with MPS alone, CCTA alone, and CCTA followed by MPS over a range of probabilities of flow-limiting coronary disease. They found that the cost of imaging and the effective radiation exposure increases linearly with prevalence of CAD.
The model assumes that patients are referred to diagnostic catheterization only if both the CCTA and MPS results find flow-limiting CAD. Each diagnostic catheterization costs about $3000, so reducing unnecessary cath-lab referrals is a key to containing the cost of evaluating chest-pain patients, Halpern explained. "And we haven't even talked about the morbidity associated with those caths--at least a 1% morbidity for events like strokes."
The model shows that as long as the prevalence of CAD was below 50%, evaluation with CCTA reduced imaging costs and effective radiation dose relative to MPS, because CCTA delivers less radiation and reduces the number of false positives referred for unnecessary cardiac catheterizations. The combination of CCTA plus MPS testing resulted in slightly higher radiation exposure than the use of CCTA alone but reduced imaging costs by further reducing the number cardiac catheterization studies.
Halpern suggested that the decision model should be relatively easy to apply because "we should be able to figure out what the prevalence of the CAD is based on patient history and presentation," he said. "And we're going to reduce the radiation exposure with CT and have a more cost-effective cardiac workup."
Triple-rule-out helps sort out the muddled middle
During the same session at RSNA, Dr Kevin Takakuwa (Jefferson University) presented an analysis of the factors that predicted acute coronary syndrome, coronary disease, or extracoronary disease in 446 chest-pain patients undergoing a "triple-rule-out" CT scan for coronary disease, pulmonary embolism, and thoracic dissection .
Takakuwa and colleagues found that age, TIMI risk scores, and various cardiac risk factors predicted which patients have a higher than 50% chance of developing coronary disease. However, only TIMI risk scores and hypercholesterolemia predicted acute coronary syndrome, and indeterminate myoglobin or troponin rise predicted significant risk of extracoronary problems. Takakuwa explained that demographic and historical features of patients' presentation when they arrive at the hospital do not usually predict ACS or extracoronary findings, but they may predict non-ACS coronary atherosclerosis.
This suggests a great need for the triple-rule-out CT study to diagnose the large group of patients whose underlying risk of coronary disease based on their risk factors is neither especially high nor low but present to the emergency room with chest pain. "The number of people in that indeterminate middle group, where you're not sure what they have, is actually quite high," but the percentage of these patients who actually have an acute coronary syndrome is probably less than half, Takakuwa estimates.
"It's this middle group that we really struggle with in emergency departments, and that's why I think the triple-rule-out study is going to be very valuable. We can take them out of an observational protocol--where we may watch them for up to 36 hours and do stress tests--and instead do a six-hour protocol with the triple-rule-out study and actually be able to send them directly home."
Evidence base for imaging more critical than ever
At the opening of the session on cardiac risk stratification, Dr Arthur Stillman (Emory University, Atlanta, GA) emphasized the importance of studies like those presented by Takakuwa and Halpern to prevent unnecessary, costly, and sometimes dangerous testing.
He also said that promising protocols should be evaluated in population studies to understand the best application of different imaging modalities before governments make certain tests mandatory. "We really need to have answers that are evidence-based and not let medicine be dictated to us by Congress--by people who are not medical professionals and don't really understand all of the issues."
He cited the recently enacted Texas Heart Attack Prevention Bill, reported by heartwire , which forces health-benefit plans to provide coverage for certain screening tests for early coronary artery disease, including some repetitive tests for which there is no evidentiary support or professional society guidelines. Dr Richard D White (University of Florida College of Medicine-Jacksonville) referred to the Texas mandate as an example of "government making some very important decisions that are not necessarily very well thought out or based on evidence."
Halpern disclosed support from Lantheus Medical Imaging and equipment support from Toshiba. Takakuwa disclosed having no conflicts of interest.
Heartwire from Medscape © 2009 Medscape, LLC
Cite this: CCTA Testing Reduces Cost, Radiation in Population With Less Than 50% Prevalence of CAD - Medscape - Dec 04, 2009.