AMSTERDAM, THE NETHERLANDS — Positron emission tomography (PET) is more accurate for diagnosing myocardial ischemia than several other commonly used functional and anatomic imaging methods, with invasive fractional-flow reserve (FFR) readings as the reference standard, according to a rare study that used the range of imaging modalities in all patients[1].
In the single-center PACIFIC study, 208 patients with suspected CAD underwent PET imaging and invasive FFR assessment along with SPECT perfusion imaging and coronary computed tomographic angiography (CCTA).
The diagnostic accuracy of PET was 85% compared with 77% for SPECT and 74% for CCTA. A hybrid approach of CCTA coupled with SPECT or PET, combining anatomical and functional assessments, did not improve diagnosis.
Sensitivity was 90% for CCTA, 57% for SPECT, and 87% for PET. Specificity was 60% for CCTA, 94% for SPECT, and 84% for PET.
The results were published online August 16 in JAMA Cardiology with lead author Dr Ibrahim Danad (VU University Medical Center, Amsterdam, the Netherlands).
Not More Accuracy, Just More Radiation
Some investigators believe that the hybrid approach would keep the high sensitivity of CCTA but with better specificity, the group notes. But Danad and colleagues found it exposed patients to more radiation without increasing diagnostic ability of the single test alone.
But given the results, using CCTA may lead to overdiagnosis of CAD with very high sensitivity, and using SPECT may lead to underdiagnoses of CAD with very low sensitivity and very high specificity, senior author Dr Paul Knaapen (VU University Medical Center) told theheart.org | Medscape Cardiology.
He cautioned that this study was small, and guidelines don’t weigh in on which screening to use, but given the findings, “If you were to do a first-line test, it would be PET, but if it’s not available, you’d rather have a CT scan than a SPECT based on the fact that you’d rather not miss patients who have coronary artery disease.”
“If you have an ambiguous result with one test or a positive result you don’t trust, it makes no sense to answer it with another test,” he added. “That’s what the PACIFIC trial clearly demonstrated.”
Following a positive CT scan with another test to see if it’s a false positive, for instance, doesn’t add to diagnostic accuracy, it just lowers the sensitivity of the CT scan.
“So you’re actually going to miss patients by ordering another test,” Knaapen said.
This is the first head-to-head comparison study of three modern imaging modalities that included a hybrid approach and involved sending every patient to the cath lab for the FFR reference standard, according to the report.
Ethics of Sending All Patients to the Cath Lab
Researchers in prior studies have not wanted to send patients to the cath lab if all three noninvasive tests were negative because they saw that as unethical, Knaapen said.
“We completely disagree,” he said. “We think these types of studies need to be done because then you avoid selection bias in which patients go to the cath lab. We had zero complications in conducting the protocol.”
Dr Matthew Tong (Ohio State University Wexner Medical Center, Columbus) told theheart.org | Medscape Cardiology that this study does what others before have not in identifying the strengths and weaknesses of each modality in one report.
He said that though the study found PET had the highest accuracy, it is expensive and mostly available at larger centers, so it won’t be a choice for many.
He noted that the most surprising aspect was the conclusion that adding the functional aspect to the anatomical does not help with clinical decisions.
In an accompanying editorial[2], Drs Pamela Douglas and Leslee Shaw agreed that was a surprise.
“This is unexpected and contradicts the conventional wisdom that anatomy and function are essential in evaluating coronary artery disease,” they write.
Although it was not a randomized trial and was conducted at a single center, they write, it adds significantly to the limited evidence available from patients who have undergone PET, SPECT, and CCTA, and then FFR.
As to the cost of PET, Shaw told theheart.org | Medscape Cardiology that it is more expensive than the other tests, though compared with SPECT, not by much.
“PET also benefits from enhanced resolution, much lower radiation exposure, and the ability to measure absolute blood flow as well as regional myocardial perfusion,” she said.
She said the similarity in specificity between PET and SPECT was surprising, given PET’s enhanced resolution abilities. She added that clinicians should note that both tests were able to exclude flow-limiting CAD quite well, both with a low rate of false positives.
Shaw said that in a larger trial a next step might be testing a strategy of PET and selective CT angiography vs standard SPECT imaging alone.
Such a study, she said, might help answer the question: “How do we incorporate both regional perfusion and myocardial blood flow to then selectively apply noninvasive CT angiography and reserve invasive cath for only those with obstructive CAD?”
“This would limit further testing to few patients and save money when compared with the high rates of diagnostic caths performed now,” she said.
Danad, Douglas, and Shaw reported no conflicts of interest. Disclosures for the coauthors are listed in the paper.
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