The long-term observational study in South Korea followed more than 4,000 individuals at intermediate risk per the Framingham risk score who underwent both CAC and CCTA. The researchers found that CCTA had incremental value over CAC in predicting all cardiac events and major cardiac events. On the other hand, CAC did not add prognostic value over CCTA.
"CCTA has incremental prognostic value over CAC scoring in asymptomatic subjects at intermediate risk," said presenter Dr. Soo Jin Hong from Seoul National University Hospital. The difference between the two exams is large enough that CCTA could potentially replace CAC in such individuals, she added.
CAC is good, as far as it goes
The coronary calcium score has proved very useful for determining incremental prognostic risk of heart disease over the Framingham score. But it has limitations in representing the entire spectrum of risk in atherosclerosis, principally because it does not show noncalcified plaques, Hong said.
A key problem in treating coronary artery disease is the long delay between the development of subclinical atherosclerosis and the manifestation of coronary artery disease (CAD), she said.
"About 50% of patients with cardiac death due to coronary artery disease do not experience prior symptoms of CAD, so the unexpected cardiac death is the initial symptom," she said. "About 20% of deaths occur in the absence of any major risk factor. And the Framingham risk score has other limitations, such as the misclassification of high-risk individuals as low or intermediate risk."
However, there is no prognostic data on the value of CCTA in asymptomatic subjects at intermediate risk. Therefore, this ongoing study aimed to determine the prognostic value of CCTA over CAC and the Framingham risk score, as well as define the prevalence and characteristics of subclinical coronary atherosclerosis in these asymptomatic individuals at intermediate risk (Framingham risk score of 10 to 20), Hong said.
Known as ESCORT, the study examined 5,142 asymptomatic Koreans with both CAC and 64-detector-row CCTA in 2006 and 2007, following them for 10 years. Many dropped out over the years or were excluded for reasons such as insufficient medical history or poor image quality, leaving 1,155 individuals with complete data in the study.
Plaque was evaluated according to American Heart Association guidelines, whereby luminal stenosis of at least 50% was considered obstructive disease. Plaques were segregated into calcified, mixed, and noncalcified categories.
Over a mean follow-up of 76 months to date, major cardiac events occurred in 5.2% (n = 60) of the subjects, including cardiac death, myocardial infarction, and unstable angina requiring hospitalization.
CCTA correlated with multiple risk parameters
For predicting major adverse cardiac events, all of the CCTA parameters correlated significantly with outcomes (p < 0.01).
"There were differences between individuals with and without major events for all major risk factors except dyslipidemia," Hong said.
Nearly half of subjects (48.3%) had evidence of subclinical atherosclerosis, and obstructive stenosis was found in 10.7%. The presence of any plaque, or of mixed and calcified plaques, correlated significantly with outcomes for all cardiac events and major events. The presence of obstructive coronary disease was the largest factor separating all events from major events, according to Hong.
|Predictive value of CCTA for major adverse cardiac events|
|CCTA findings||Subjects with events -- hazard ratio corrected for Framingham risk score||p-value|
|Presence of any plaque||15.34||< 0.001|
|Plaque with obstructive stenosis||21.55||< 0.001|
|Presence of noncalcified plaque||9.05||< 0.001|
|Mixed plaque||5.45||< 0.001|
|Calcified plaque||2.82||< 0.001|
|Plaque in proximal segments||15.50||< 0.001|
|Plaque with obstructive stenosis at proximal segments||18.67||< 0.12|
As for calcium scores, adding CAC to Framingham increased the area under the curve (AUC) from 0.65 to 0.80, while adding CCTA to Framingham increased the AUC from 0.65 to 0.90, the group reported.
For predicting all cardiac events, the AUC of Framingham (0.64), Framingham plus CAC (0.81), and Framingham plus CCTA (0.91) showed gradual increases, Hong said. Still, adding coronary calcium to CCTA plus Framingham did not add to the prognostic power of the analysis.
"In conclusion, CCTA has incremental prognostic value over [Framingham risk score] and CAC score in individuals at intermediate risk," she said. "Therefore, CCTA may have the potential to replace CAC or evolve into a potential complementary approach with CAC."
The major factor driving the superiority of CCTA in these individuals is the exam's ability to evaluate soft plaque, which is often vulnerable to rupture, Hong explained in response to questions after the talk. CAC simply cannot evaluate many of the risk factors that were significantly associated with cardiac events.