This release from Johns Hopkins describes results from a head-to-head comparison study that found computed tomography (CT) scans of the heart’s vessels outperformed single-photon emission computed tomography (SPECT) stress tests in detecting clogged arteries. The analysis came from a trial that compared how well the two noninvasive imaging techniques (CT scans and SPECT stress tests) matched up with invasive coronary angiography.
A quick read of this news release could erroneously lead readers to believe the current standard initial imaging test for a blocked heart artery, SPECT stress testing, should be immediately tossed aside in favor of CT angiography, and that the switch would improve heart attack prevention.
While the release had several strengths, it inflated the benefits and soft-pedaled study limitations. Our reviewers suggest the findings are of modest importance because while identifying blocked arteries is important, the bigger question is: What is the prognosis (what will happen to me if I don’t do anything differently?) and how should patients be treated? Identifying blocked vessels is part of that, but it doesn’t provide a complete picture. The release doesn’t mention that elements of the standard stress test, unlike the CT scan, can help predict prognosis. The release presumes that finding blocked arteries is the goal when really what patients and providers need to know is whether or not to undergo additional interventions.
About 15 million Americans seek medical attention each year for chest pain, shortness of breath and extreme fatigue — symptoms that may signal a clogged artery. A study that definitively showed that one non-invasive imaging test outperformed another in accurately detecting clogged arteries would be of wide interest. However, one study rarely changes clinical practice. And even when results clearly indicate a newer test does a better job of measuring what it measures, that doesn’t necessarily mean it will automatically improve the health of patients. News releases shouldn’t confuse advancing the ball with scoring a touchdown.
The release says the price tags of the two tests are similar, between $750 and $1200. But the release says it is unclear whether there are differences in total costs, after taking into account follow-up testing.
The journal article provides a clearer picture by citing some other studies that found CT angiography may lead to more follow-up testing and higher rates of revascularization and one study that did not see a difference.
The reported findings appear impressive: the CT scans correctly identified blockages in nine out of 10 people, while stress tests picked up blockages in six out of 10. The release further quantifies the findings when it says:
Overall, non-invasive CT angiograms accurately detected or ruled out artery blockages in 91 percent of patients, compared with 69 percent for stress testing. When researchers analyzed test performance in a subgroup of 111 patients with very high-risk disease as identified on traditional angiography, the diagnostic accuracy of CT angiograms went up to 96 percent, compared with 80 percent for stress testing.
Here again, the release soft-pedals concerns that are pointed out in the journal article. All the tests looked at in the study expose patients to radiation. The journal article notes that while the latest-generation CT angiography machine that they used in the study exposes patients to less than half as much radiation as the SPECT machine they used, the older CT angiography machines in general used around the country actually expose patients to higher doses of radiation than their SPECT machine, and there are ways of doing SPECT that can reduce radiation exposure.
In contrast, the release gave only a muddled nod to the issue, saying “While many newer CT scans deliver substantially lower doses of radiation than the scans used in nuclear stress tests, the dose and protocols can vary widely from hospital to hospital.” It never says the average doses in clinical practice are higher.
The release says that this is the first head-to-head comparison of CT angiography and SPECT stress testing that also included coronary angiography (inserting a catheter to directly check suspected blockages) and that it included many more participants than earlier studies. The release includes a pretty good description of what happened in the study.
But we had a problem with the lead sentence of the release, which says CT scans of heart arteries “are far better at spotting clogged arteries that can trigger a heart attack” (emphasis added). However, this study did not look at heart attack rates or other real health outcomes. The researchers looked only at how well the two noninvasive imaging techniques matched up with coronary angiography, which includes threading a catheter directly into the heart artery to directly measure a suspected blockage. The release should have been more clear that the study did not look at how patients fared after the tests.
The release notes in the lead sentence and in the body of the release that the study involved only patients who had chest pain or other symptoms that could indicate a blocked heart artery. However, it should have mentioned that the researchers cautioned their results may not apply to low-risk patients.
The release got this one only half right. It mentions that the study was partly funded by Toshiba Medical Systems, the maker of the CT angiography device they tested. However, it fails to include that some of the researchers receive other grant funding, consulting or speaker’s fees from Toshiba and other device makers, even though these financial relationships are clearly noted in the journal article.
The release is clear that the point of the study was to compare CT angiography with the current standard imaging test for these patients. It would have been beneficial to also mention what follows the test.
The release notes that both types of testing are available so we gave it a satisfactory. However, it would have been beneficial if the release had noted somewhere the differences between the machines and methods used by the researchers and those commonly used in clinical practice.
The release notes that for the first time in a trial, patient volunteers underwent all three tests (the two imaging tests) as well as invasive cardiac angiography as part of the study.
While the tone of the release is measured, it suggests that clinicians should go ahead and switch tests now, without acknowledging that other experts may want to see confirmation or other kinds of studies before changing how they practice. Our reviewers saw this as problematic.