The remaining gaps in evidence for cardiac CT

These areas where more research is needed were outlined by Leslee Shaw, PhD, at the SCCT 2022 meeting last summer. Shaw was also was a co-author of the chest pain guidelines.

"There is a tremendous amount of evidence, with about 20 randomized trials for CT that went into the chest pain guidelines...but they are not complete," Shaw explained. "Particularly, we do not have trials showing that if you use CT, it results in improved outcomes."

She said there is secondary outcomes evidence from the SCOT-HEART and PROMISE trials that do show benefit to using cardiac CT as patients were followed for several years. But, more data would be helpful in shoring up those observations. 

She discussed several of the following areas where more evidence is needed for CCTA in a video interview she did with Health Imaging, attached to the top of this article.

What is the role of CT coronary plaque analysis?

One of the rising trends in cardiac CT technology is artificial intelligence (AI) algorithms that can automatically perform very detailed analysis of the soft coronary plaques to use as a baseline to monitor if statins or other drugs are reversing plaque buildup or reducing plaque inflammation that results in heart attacks. Many key cardiac CT experts believe this tool will be a paradigm shift in preventive medical therapy, enabling closer monitoring of patients decades before they would have presented with acute coronary syndromes. 

"Right now there is a lot of hype around atheroschlerotic plaque analysis, but how do we integrate that in order to make a difference in a patient's life?" Shaw said. "We all think it will add value, but demonstrating that in a randomized trial is totally different than actually making a statement."

What is the role of CT in patients who need revascularization?

Coronary CT angiography is very good at showing details of the anatomy, including calcified and soft plaques, vessel tortuosity, narrowing, blockages, remodeling, thrombus, dissections and evidence of previous revascularization with bypass grafts or stents. While CT can see plaque burden and narrowing of vessels, the functional data on these findings is missing and needs to be filled in with invasive angiography and catheter-based FFR, nuclear or MRI myocardial perfusion scans. This sometimes results in patients with intermediate lesions going to the cath lab and finding that they did not need to be catheterized and could be managed medically. 

"How much plaque is too much to where a patient should be sent to revascularization? Does the amount of plaque actually matter in what you are going to stent? Where are you going to stent? Are you going to cover the non-obstructive plaques?" Shaw said are the key questions. 

One technology that may help refine this and reduce unnecessary caths or additional testing is FFR-CT. This newer technology was also included in the new chest pain guidelines because it can non-invasively show if a narrowed artery has any hemodynamic impact causing ischemia. While appearing very useful for reducing costs in the management of intermediate lesion patients, she said add ons like this also increase the cost of CT, so clinical evidence needs to clearly show a cost vs benefit analysis. 

Additional costs from CT post-processing algorithms

Shaw said we are starting to see increased usage of FFR-CT, coronary plaque analysis and other image post-processing algorithms that increase costs for CT exams. She said additional evidence needs to be gatherer to show conclusively if these help improve care and are worth the additional expense. 

"All of this post-processing adds cost, and right now CT is a pretty inexpensive test. Certainly it is a fraction of the cost of a PET scan, and that is its value to society. But if we keep adding on these other costs, will it be the same if it is approaching the cost of a PET scan? Probably not," Shaw explained. 

Can cardiac CT play a role in the best patient selection for new drugs?

In the past couple of years, the U.S. Food and Drug Administration (FDA) has cleared a few novel lipid-lowering drug therapies that can significantly low cholesterol in patients who cannot be controlled by statins and diet alone. However, these new drugs come with very hefty price tags, so cardiologists are looking for more cost effective ways to screen patients who can benefit to justify the significant healthcare costs. 

Shaw said CTA might be the answer because it can help track plaque progression, especially using new AI plaque assessment software. Serial CT exams over time also could confirm if the agents are helping reverse plaque burden.

She said additional hard data from clinical studies will help answer these questions.