TCT: Will CT develop into useful tool to ID vulnerable plaque?
SAN FRANCISCO—A debate, conducted at the annual Transcatheter Cardiovascular Therapeutics (TCT) scientific symposium on Monday, highlighted the difficulties in assessing whether multidetector CT is capable of accurately identifying vulnerable plaque.

Norman E. Lepor, MD, associate professor of medicine at Geffen School of Medicine-UCLA Cedars-Sinai Medical Center in Los Angeles, noted that  64-slice CT has been commercially available in the U.S. since 2004, and that the large volume of data that the technology has yielded is “tremendously useful in terms of potential applications.”

However, he added that there is a lack of larger, population-based clinical trials to prove its worth.

Lepor, who presented the affirmative side of the debate, said that the technology has evolved to provide a spatial resolution of 0.4 mm, which can identify the lumenology of the plaque with a “fair degree of certainty. With a high level of technical expertise, we are also able to evaluate plaque morphology, and perhaps, plaque vulnerability.”

Stephan Achenbach, MD, of the department of cardiology at University of Erlangen–Nürnberg in Erlangen, Germany, said that he has his doubts about the value of CT in this area. To prove its worth, he said it needs to be established whether CT can identify plaques that are vulnerable; whether these plaques will lead to an event; and whether local treatment with these vulnerable plaques will be beneficial to the patient.

Achenbach noted that local treatment has not been proven beneficial, adding that it could be beneficial only if it is shown that vulnerable plaques caused those events, and if those plaques would reliably cause events.

“However, that is not the case: there can lots of vulnerable and even ruptured plaques, which are not associated with a clinical events,” he said. “By far, the majority of vulnerable plaque present in the population will never lead to an event.”

In terms of a comprehensive plaque analysis, Lepor said that CT is used to define plaque architecture, plaque volume, the length of plaque and impact of plaque on luminal dimensions. He added that CT may be to the point of defining the physiology of the plaque, by virtue of performing a stress test with adenosine (Adenoscan, Astellas Pharma) with the modality. To “some extent,” CT can define the content of the plaque, he said.

“CT allows for high-resolution contrast-enhanced lumenograms, similar to that of conventional angiography,” Lepor said. “However, because of the differential tissue attenuation capabilities, it can also provide IVUS [intravascular ultrasound]-like characterization of intramural atherosclerosis.”

Achenbach acknowledged that there are examples where CT can “impressively” identify vulnerable features and find these lesions, but that only occurs “sometimes.” He also spoke to the difficulty of obtaining a uniform high-quality image for all patients, especially with obese patients.

“CT is good enough to rule out the presence of stenosis,” he said, “but not good enough to also identify whether plaque is present, or if plaque were present, it cannot identify its size.”

Yet, Lepor said that CT has the “particular capability to enhance the visualization in patients with chronic total occlusions.”

As a result, Lepor said that there is “certainly reasonable data that just the presence of obstructive coronary artery disease [CAD], seen on cardiac CT, has critical implications.”

Lepor referenced a series of small- to medium-size trials (between 100-800 participants), which support his premise that the presence of significant obstructive CAD, as well as the presence of coronary plaque, provides “significant prognostic information, in terms of major adverse cardiovascular events.”

Lepor went on to examine the characteristics of plaque, which could determine the lesion’s vulnerability, including spotty calcifications and more expansive remodeling. He also said that CT has the potential to recognize the number of vulnerable plaques, as well as the unstable versus stable plaques in a patient with multi-vessel disease.

“CT recognizes the culprit complex plaque and plaque extension not evident on conventional angiography and therefore may impact the decision on stent placement,” he said.

“CT is unreliable in finding or excluding vulnerable plaque, especially in real-life clinical practice,” according to Achenbach.  “Moreover, there are plaques that do not have the typical features of vulnerability on a CT scan. In fact, most plaques that look vulnerable on a CT will not cause an event, especially in asymptomatic patients; and conversely, plaques that look harmless on a CT can cause events.”

Lepor acknowledged that there is not a lot of data that provides clinical implications.

In his concluding statement, Achenbach expressed his doubts about CT becoming a useful tool to identify vulnerable plaque in the foreseeable future.

Lepor concluded that it is “clear that CT has the capability to define with high negative predictive value the presence of obstructive disease. Plaque characterization can be accomplished with CT, and certain plaque characteristics present in vulnerable lesions may help direct therapy. It also can be used to define physiology of the obstructive disease.”

However, he acknowledged that prospective follow up was needed to define the implications of CT regarding vulnerable plaque.