CT adds value on top of clinical data, calcium score, and ECG
NOVEMBER 2, 2011
Rotterdam, the Netherlands - A new comparative study shows that coronary computed tomography angiography (CCTA) has incremental prognostic value over exercise testing in patients with symptoms of coronary disease [1].
The study, by Dr Admir Dedic (Erasmus University Medical Centre, the Netherlands) and colleagues, published in the November 2011 issue of Radiology, also found that patients in whom a diagnostic exercise test is impossible are more likely to have an unfavorable outcome, independent of traditional risk factors, than those who can exercise for an ECG stress test.
In the study, 471 patients with chest pain but no known coronary disease underwent exercise ECG and dual-source CT scanning at a rapid-assessment outpatient chest-pain clinic. The CT scan identified coronary calcification and the presence of coronary stenosis of 50% or greater diameter in one or more vessels, and the exercise ECG results were classified as normal, ischemic, or nondiagnostic. The researchers were able to follow 424 of the patients for an average of 2.6 years, during which 30 patients suffered a total 44 major adverse cardiac events, including four cardiac deaths and six nonfatal MIs.
The three univariable predictors of major adverse coronary events in the study were the presence of coronary calcification (hazard ratio 8.22), obstructive coronary disease (HR 6.22), and nondiagnostic stress-test results (HR 3.00). A multivariable analysis showed that obstructive coronary disease found by CCTA (HR 5.0) and nondiagnostic exercise ECG results (HR 2.9) were independent predictors of major adverse events and that the CCTA findings provided incremental prognostic value beyond clinical predictors and stress-test results alone.
Exercise testing has been "the diagnostic cornerstone" for evaluating ischemic heart disease for the past decade, Dedic et al explain. ECG's power as a predictor of coronary disease events is confirmed in the study insofar as the inability to perform and complete an exercise ECG predicted unfavorable outcomes, because exercise capacity represents contractile left ventricular function and overall physical health, but ischemic ECG changes were not associated with more adverse events in the study. "Presumably, patients with these changes were treated more aggressively, explaining their better event-free survival," the authors note.
Combining functional and anatomical information
"Because the two tests address a different aspect of CAD, I don't think CTA can fully replace stress testing," Dedic toldheartwire. "They should be used as complementary to each other, focusing on their strengths.
In the study, coronary calcium scores did not add further incremental value over CCTA. "It appears that the information obtained with calcium scanning largely overlaps with the information obtained with CT angiography, while the latter also provides such additional characteristics as total plaque burden and luminal obstruction," the authors explain in the paper. But because absence of calcium is associated with a very good prognosis in this population, Dedic said "the general outpatient population with stable anginal complaints would benefit most from an initial calcium scan, [and then] patients with no or abundant calcium should not undergo CCTA," he said.
Above a certain arbitrary calcium score, the positive predictive value of CCTA drops off and the scans become noninterpretable. For these patients and any patients with an intermediate-sized coronary lesion on CCTA or a contraindication for CT, exercise testing is necessary to assess their ischemia, he said. Also, patients with disease in their left main or proximal left anterior descending artery or in three vessels should be referred to invasive angiography, and patients with obstructive disease in one or two nonmajor vessels should be treated with optimal medical therapy and then reevaluated with exercise testing if necessary, he said.
Patients with nonobstructive coronary plaque appearing on CCTA can be reassured that their risk of future events is relatively low, but they should focus on modifying any risk factors they may have through diet, exercise, smoking cessation, etc, Dedic said.
Although the study enrolled "all-comers," it was a single-center trial and therefore may not necessarily reflect the entire chest-pain population. A large randomized trial is now needed to compare the efficacy, safety, and cost-effectiveness of a diagnostic workup strategy including CCTA and exercise testing. Dedic et al hope that the ongoing Computed Tomography Versus Exercise Testing in Suspected Coronary Artery Disease (CRESCENT) trial will provide answers to these questions. CRESCENT is randomizing patients with stable chest pain to one of two diagnostic strategies: cardiac CT followed by stress testing, invasive angiography, or neither depending on the CT scan result; or standard diagnostic management, including stress testing and/or invasive angiography.
| The authors have no potential relevant conflicts of interest to disclose. |
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