PET might be optimal imaging test for diagnosing coronary artery disease

By Marilynn Larkin

NEW YORK (Reuters Health) – Positron emission tomography (PET) is more accurate than single-photon emission tomography (SPECT) or coronary computed tomography angiography (CCTA) for diagnosing significant coronary artery disease (CAD) as determined by fractional flow reserve, a head-to-head comparison at a single center revealed.

“At present, the choice of noninvasive testing for a diagnosis of significant CAD is ambiguous,” and PET, SPECT or CCTA are the main imaging tests used for this purpose, according to Dr. Paul Knaapen of VU University Medical Center, Amsterdam, the Netherlands.

To compare the diagnostic accuracy of the three methods, Dr. Knaapen and colleagues recruited 208 patients (mean age, 58; about half women) with suspected CAD who presented to the medical center from 2012 to 2014. Participants underwent CCTA, technetium 99m/tetrofosmin-labeled SPECT, and 15OH2O PET, as well as examination of the arteries by fractional flow reserve (FFR). If any of the noninvasive anatomical or functional tests showed an abnormality, hybrid images were generated and interpreted.

As reported online August 16 in JAMA Cardiology, 92 patients (44.2%) had significant CAD, as indicated by a fractional flow reserve of 0.80 or less. The imaging tests showed that PET had 87% sensitivity and 84% specificity for detecting these cases, whereas CCTA had 90% sensitivity and 60% specificity, and SPECT, 57% sensitivity and 94% specificity.

Overall, diagnostic accuracy was higher for PET (85%) than for CCTA (74%) and SPECT (77%). Neither hybrid SPECT/CCTA nor PET/CCTA increased diagnostic accuracy; the hybrid images increased specificity but reduced sensitivity.

Summing up, Dr. Knaapen told Reuters Health by email, “In patients without a history of CAD but who are suspected of having CAD, PET has higher diagnostic value as opposed to SPECT or CCTA and should therefore be considered the diagnostic test of choice in these patients.”

“In addition,” he said by email, “SPECT and CCTA have comparable diagnostic accuracy, but SPECT was characterized by a lot of false negatives, whereas CCTA yields a lot of false positives. In other words, SPECT underdiagnoses CAD, whereas CCTA overestimates the extent of CAD.”

“Finally, and surprisingly,” he concluded, “hybrid imaging that combined CT with either SPECT or PET did not increase diagnostic accuracy and should therefore not be advocated in clinical practice.”

Dr. Leslee Shaw of Emory University School of Medicine, Atlanta, Georgia, coauthor of an accompanying editorial, told Reuters Health that because patients were scheduled for invasive angiography, “the results are from a higher-risk patient cohort than would normally be seen in the de novo chest pain evaluation and referral to stress imaging.”

The greater accuracy of PET is “not surprising,” she said by email, “given the better resolution of PET imaging when compared to SPECT.”

“However,” she noted, “the authors employed impaired hyperemic blood flow with 15O-water and not standard segmental interpretation. Thus, readers should take care to note the higher accuracy of hyperemic blood flow with PET versus myocardial perfusion abnormalities using standard segmental scoring.”

“These types of trials remain challenging, and more data in larger sample sizes are needed,” Dr. Shaw stressed. “Readers of this report should be encouraged by the use of FFR as the endpoint, as physiologic measures are increasingly the standard upon which ischemic evaluations are being undertaken.”

Editorial coauthor Dr. Pamela Douglas of Duke University School of Medicine, Durham, North Carolina, added in a separate email, “The most surprising finding . . . is that the diagnostic specificity of SPECT was noninferior to PET. This is contrary to prior data from other studies, such as EVINCI (http://bit.ly/2xtBaOm), which showed a lower value for SPECT.”

The discrepancy may be due in part “to the apples-and-oranges comparison employed of absolute blood flow (PET) versus relative blood flow (SPECT),” she said, “but also to other technical factors, such as attenuation correction algorithms.”

SOURCES: http://bit.ly/2v7uOTK and http://bit.ly/2vf2bnM

JAMA Cardiol 2017.

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