Coronary CTA, CAC scoring offer advantages as primary prevention tool
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Coronary CT angiography and coronary artery calcium scoring each have their benefits as a primary prevention tool, two experts said.
This debate comparing coronary CTA with CAC scoring took place at the virtual American Society for Preventive Cardiology Congress on CVD Prevention.
Comprehensive evaluation with coronary CTA
“There’s 20-plus years of calcium scoring data, but what you’ll see at the end of this talk is that calcium scoring is obsolete and coronary CT angiography should be the primary modality used for primary prevention,” James Min, MD, founder and CEO of Cleerly Inc., said in support of coronary CTA.
The issue is the sole dependence on risk factors, according to the presentation.
“A risk factor is a variable that’s associated with but not necessarily pathognomonic for disease,” Min said. “As a result, risk factors are really not disease, so there’s a problem with diagnosis.”
Another issue related to risk factors is that the absence of them does not indicate the absence of disease or risk for disease. Therapy based on risk factors also does not ensure disease prevention or reduction in disease risk. Following risk factors over time does not guarantee this prevention or reduction in risk. Lastly, risk factors are for populations and not individual people.
CAC is not a risk factor, but rather a risk marker of CAD. It is also advocated as more of an individualized approach compared with risk factor scoring. An American College of Cardiology expert consensus document defined CAC as part of the development of atherosclerosis that occurs exclusively in the atherosclerotic arteries and is typically absence in the normal vessel wall.
“All of that is true, but the converse isn’t true,” Min said. “The absence of coronary calcium does not dictate the absence of atherosclerosis, and there lies the problem.”
CAC may be better at prognostic risk stratification than clinical risk factor scoring. Beyond risk stratification, Min said CAC is not a great strategy.
“If you look at the essential criteria of an effective primary prevention tool, risk factors are superior to calcium scoring,” Min said. “The only one that guides clinical decision-making in a manner that improves patient outcomes is risk factors. Beyond prognosis, calcium scoring is actually less useful as a primary prevention tool than conventional risk factors.
Min said CTA overcomes limitations of risk factors and risk markers by performing comprehensive quantitative assessment of pathologic diseases, which can lead to adverse events. This makes CTA an ideal test for diagnosis, staging, personalized treatment and improved outcomes.
During the past 15 years, CTA has evolved so that it can perform whole-heart imaging in less than a second with radiation doses that are one-third of what CAC scoring emits and at a comparable cost.
CTA succeeds at meeting essential criteria of an effective primary prevention tool because it directly measures pathologic disease. It also shows that the absence and presence of results truly indicate the absence or presence of disease. This leads to personalized treatment and the ability to follow the disease or the risk for disease over time.
Min said coronary CTA is the best noninvasive test for CAD diagnosis because CAC often fails to diagnose it in many patients. Coronary CTA also evaluates CAD across the entire spectrum of disease severity compared with CAC that diagnoses only late-stage disease. This modality stratifies both high- and low-risk atherosclerosis while CAC scoring combined high- and low-risk atherosclerosis. Unlike CAC scoring, coronary CTA enables response assessment over time.
Other reasons why coronary CTA should be used for primary prevention is because atherosclerosis treatment based upon these findings improve patient outcomes compared with CAC scoring. Evaluation with coronary CTA allows comprehensive evaluation of individual CAD risk vs. CAC scoring.
“CTA is ready for prevention,” Min said. “It does comprehensive visualization of pathologic disease, it can assess the presence, the extent, the severity, the type, which allows us to personalize the treatment, directly visualize disease over time to make sure that we’re actually stabilizing the disease, and then it does improve the outcomes. In contrast, coronary calcium scoring does none of that.”
Power of zero with CAC scoring
Extensive screening with sophisticated tools like coronary CTA in addition to aggressive management has marginal utility, Khurram Nasir, MD, MPH, MSc, FASPC, Jerold B. Katz Investigator at the Academy of Translational Research, chief of the division of cardiovascular prevention and wellness at DeBakey Heart & Vascular Center and co-director of the Center for Outcomes Research at Houston Methodist, said during his presentation on CAC scoring. The guidelines have been liberal with treatment criteria, and Nassir said screening for additional risk markers should be questioned if the CAC gives sufficient guidance for statin therapy, for example.
In 2015, Nasir said he decided that it was time to move on from screening from additional risk factors. In a study that he and colleagues published in the Journal of the American College of Cardiology that year, results showed that two of every three adults aged 45 years and older without atherosclerotic CVD were candidates for statin therapy, and patients who were not candidates had very low risk.
CAC scoring should be used as a decision aid and a tool for de-risking uncertain patients who are candidates for therapy. From 2015 to 2018, the “power of zero” was confirmed in additional studies, some of which showed that a CAC score of zero was the strongest negative predictor for ASCVD risk. These studies also showed that avoiding treatment in patients with a CAC score of zero was cost-effective, and there was no benefit of statin therapy in patients with a CAC score of zero.
“In the summer of 2018, we made a clear message out to the guidelines and said it’s time to accept the facts, accept the power of zero, forget this screening paradigm strategy, focus more on what we have seen in the real world where the value is going to be,” Nasir said.
The guidelines then accepted the power of zero, he said.
According to Nasir, coronary CTA may be the next frontier in understanding coronary atherosclerotic plaque.
“I truly want to understand where is the added value apart from my major interest in understanding the biology of the coronary atherosclerotic plaque,” he said.
Three perspectives must be viewed when thinking about this next frontier, Nasir said, including the prevalence of noncalcified plaque, whether prognostic value of coronary CTA is above CAC and the role of vulnerable plaque features.
Several studies have already determined that the additional risk-predictive advantage of coronary CTA is not clinically meaningful in patients without chest pain syndrome compared with a CAC score-based risk model, he said.
“CTA may provide you with some fancy pictures, but does it add any hard, rock-solid data? The answer at least in the short period is no,” Nasir said.
A study published in the European Heart Journal: Cardiovascular Imaging in 2017 focused on the long-term data potentially obtained from CAC scoring. In 3,000 patients who were referred for coronary CTA and CAC scoring, 52% had a CAC score of zero and 0.5% had missed CAD. During a 13-year follow-up period, no patients with a CAC score of zero died of a coronary event.
“That is the power of zero,” Nasir said.
The PROMISE trial found that an optimal diagnostic strategy may start with CAC scoring followed by a second test. In addition, the CRESCENT trial determined that there is no indication that calcium scans in patients with low to intermediate probability for disease is unsafe.
“I think that CTA with its fancy picture is a lot of hype,” Nasir said. “It’s overvalued like Tesla. Investigators are treating this too much like this is the next messiah and it’s going to change the world of prevention. What I’m just going to ask you is be pragmatic. Accept the power of zero. Just ignore the CTA hype in primary prevention. Trust the rock-hard data and just don’t fall apart for pretty pictures.”
References:
- Mittal TK, et al. Eur Heart J Cardiovasc Imaging. 2017;doi:10.1093/ehjci/jex037.
- Nasir K, et al. J Am Coll Cardiol. 2015;doi:10.1016/j.jacc.2015.07.066.
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Min J.
Nasir K. SCCT Debate: CTA vs. CAC. Both presented at: American Society for Preventive Cardiology Congress on CVD Prevention; July 25-26, 2020 (virtual meeting).
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