Report questions evidence for coronary CTA

June 26, 2006

Definitive evidence that coronary CT angiography can replace conventional angiography is lacking, according to a report presented on the last day of the 8th Annual International Symposium on Multidetector-Row CT in San Francisco.

Definitive evidence that coronary CT angiography can replace conventional angiography is lacking, according to a report presented on the last day of the 8th Annual International Symposium on Multidetector-Row CT in San Francisco.

The evidence-based report from Duke University was commissioned by the Agency for Healthcare Quality and Research and presented to the Centers for Medicare and Medicaid Services within the last month. It finds that published coronary CTA trials are often biased and too small and that elderly people are underrepresented, making it difficult to generalize positive results for Medicare patients, in whom disruptive calcification might be more common.

"Utilization of CTA is exceeding evidence in routine clinical practice and substantiates the need for appropriateness criteria, as we await further trials that will clarify its role in treatment and decision making," said presenter Dr. David Kandzari, John B. Simpson assistant professor of interventional cardiology and genomic sciences at the Duke Center for Evidence-based Practice. "There is no definitive evidence that CTA provides a useful adjunct to x-ray coronary angiography for native coronary evaluation. There are no empirical data about availability, convenience, or resource implications."

The doctor's comments appeared almost blasphemous following days of impressive presentations about the seemingly endless potential of multislice CT technology in clinical practice. In the moderator's words, Kandzari's lecture was "like a bucket of cold water."

The evidence-based approach in the Duke research used a higher yardstick for measuring a technology's worth. As defined by Sackett et al, evidence-based medicine is "the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research."

The Duke review sought to identify key articles that support the use of CTA versus conventional angiography for assessing native coronary arteries. Articles had to be peer-reviewed and published (abstracts and presentations were excluded). Researchers paid particular attention to answering several questions:

  • Were the trials prospective?

  • Were consecutive patients analyzed?

  • Was the imaging technique standardized and interpretation blinded?

  • Are the patients in the trials representative of Medicare beneficiaries?

They also assessed variability in reported outcomes, including per-segment and per-patient analyses.

"When considering these studies, as with all trials, it is noteworthy to recall that sensitivity and specificity may vary according to populations tested. This is especially relevant [in this report], because of the rapid evolution of CTA. Proof-of-concept studies often use clinically obvious cases for initial evaluation of diagnostic performance. This overestimates performance," Kandzari said.

Researchers identified 29 multislice CT studies. The prevalence of ischemic heart disease in the CT studies was 54% compared with 7% in the general population, he said. Only one study had subjects with a mean age of more than 65 years, and subgroup analyses by age were not generally available. Trials often excluded poor quality studies, leading to biased results. Up to 12% of segments were excluded.

Overall, per-patient sensitivity ranged from 85% to 100%, specificity from 49% to 98%, segmental sensitivity from 30% to 99%, and segmental specificity from 49% to 98%.

The rapid evolution and advancement of CTA technology makes it difficult to produce a definitive assessment of CTA test performance, Kandzari said. Of the 16-slice CT studies, only four had more than 100 patients. There were six trials of 64-slice CT, but the total number of patients in all of these studies was lower than 400.

In the largest 16-slice CT study, which included 149 patients, about one-quarter of coronary segments were of poor quality due to problems with motion or calcification. Per-segment sensitivity was low at 30%, and per-patient specificity was just 50%.

Performance was better with 64-slice scanners. In one study of 70 patients, 88% of segments were interpretable and sensitivity/specificity were high. Nevertheless, Kandzari said, this paper reminded readers that performance may be weaker in more challenging or complex cases, such as those with extensive calcification, which may include the elderly population, obese subjects, and patients with higher heart rates.

"Sensitivity, specificity, and predictive values may drop precipitously in these patients," he said. "MDCTA is less accurate than coronary invasive angiography but may be similar in select patient populations. Test performance overall cannot be assessed at present due to limitations, in particular rapid changes in noninvasive technologies."

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