March 14th, 2015
Has CT Angiography Lived Up to Its Early Promise?
Computed tomographic angiography (CTA) enjoyed an explosion of growth over the past decade or more, fueled by enthusiasm for its ability to deliver speedy, high-resolution images of the coronary arteries. Many anticipated that CTA would prove its worth and justify its expense and radiation dose. As explained by one cardiologist, Duke University’s Dan Mark, with CTA “only the patients who needed revascularization would actually go to the cath lab and the rest would avoid it,” leading to a reduced use of invasive tests, fewer unnecessary revascularizations, fewer false positives, and, therefore, significant economic advantages. Many years later, however, there is still little agreement about CTA and how it should be used in the diagnosis and management of people with chest pain.
Results of the NHLBI-supported Prospective Multicenter Imaging Study for Evaluation of Chest Pain (PROMISE), presented at the American College of Cardiology meeting in San Diego and published simultaneously in the New England Journal of Medicine, provide the best evidence yet for the evaluation of CTA. The trial included 10,003 patients with chest pain randomized to CTA or functional exercise testing, consisting of either a standard exercise ECG test, a nuclear stress test, or stress echocardiography.
After two years the trial showed that CTA brought no improvement to the long-term outcome of the patients. The primary endpoint of the trial — the composite endpoint of death, MI, hospitalization for unstable angina, or major procedural complication — occurred in 3.3% of patients in the CTA group versus 3% in the control group. The results were consistent across different subgroups of patients.
A major goal of these procedures is to reduce highly invasive cardiac catheterizations. But within the first three months, 12.2% in the CTA group and 8.1% of the control group underwent cardiac catheterization. However, fewer patients in the CTA group who underwent catheterization were found to have no obstructive disease (27.9% in the CTA group and 52.5% in the control group).
The low number of events in the trial “probably reflects an excellent prognosis for patients with similar, new-onset, stable chest pain in real-world settings in which contemporary testing methods are used,” the authors wrote. “Showing a difference in patient outcomes with different testing strategies given this excellent midterm prognosis would require a large incremental test effect driving differences in downstream care or an extremely large study sample.”
“These findings highlight a substantial opportunity to improve the selection of patients for noninvasive testing beyond currently accepted approaches,” they wrote.
Although PROMISE didn’t provide a definitive answer to the role of CTA in clinical practice, it also didn’t give a broad endorsement to CTA, which makes doing CTA “less necessary,” said John Ryan. It “slows down the CTA train a little.”
In an accompanying editorial, Christopher Kramer terms the result a “tie” and asks how it will alter clinical practice.
Dan Mark, a PROMISE investigator who presented the results of the PROMISE economic substudy, said that CTA “may not be the ‘holy grail’ of diagnostic testing once hoped for” but that more liberal use “will improve some aspects of care without causing a major new economic burden on the health care system.” After more than two years of followup the use of CTA resulted in only a small, nonsignificant increase in cost (less than $500) and resulted in fewer patients going on to have an invasive cardiac catheterization with normal findings, he said.
The principal investigator of PROMISE, Pam Douglas, also at Duke, told CardioExchange that although they had expected CTA to lead to more catheterizations and revascularization procedures, “we were surprised by how much it improved the cath yield (rate of finding obstructive CAD at cath).” She said that CTA “is now proven to be a very viable alternative to functional testing. It should be considered as a first-line tool for patients with stable chest pain.”