Study supports CTA in high-risk asymptomatic patients

September 1, 2006

Technique proves more useful than calcium scoring in triaging patients for coronary catheterization

Anecdotal evidence abounds for coronary CT angiography's value in detecting heart disease in high-risk asymptomatic patients, and referring cardiologists are increasingly enthusiastic about its use. But do the facts support the confidence? A small new study suggests they do, at least for some referring doctors.

"In our study, coronary CTA detected a 20% rate of silent ischemia in high-risk patients with no chest pain. The positive predictive value of CTA was 96%, and the study did not lead to a high rate of unnecessary cardiac catheterizations. Coronary CTA is more useful than calcium scoring in triaging patients for coronary catheterization," said Dr. Jeffrey Goldman, director of cardiovascular CT/MR at Manhattan Diagnostic Radiology in New York City, in a presentation at the Stanford Multidetector-Row CT symposium.

Silent myocardial ischemia (SMI) is defined as myocardial ischemia in the absence of angina. Patients may have nonspecific symptoms like dyspnea, anxiety, and overwhelming fatigue, and the condition is difficult to diagnose. When older patients present with shortness of breath, it's hard to know if the cause is cardiac-related or not, Goldman said.

In the general population, about 2.5% of people have SMI, and in the high-risk population, that figure rises to 10% to 20%. Risk factors include age, hypertension, smoking, obesity, and diabetes. Interest in coronary CTA is growing, but its use in asymptomatic patients at high risk for SMI is controversial and confusing for the general public, he said.

Many referring cardiologists swear by CCTA for picking up SMI in high-risk patients and marvel at the profound impact of the study on clinical practice. Goldman analyzed referrals from two physicians who were true believers in CCTA for SMI. He performed a retrospective review of all patients referred by these doctors for 64-slice CT. All patients were over 55 and had two or more risk factors for coronary artery disease. None had chest pain, and 7% had dyspnea.

The study involved 240 patients with an average age of 73 and a mean calcium score of 600. The CCTA studies were performed to determine if patients needed cardiac catheterization. Of the total, 49 (25%) were recommended for conventional angiography. Of those who underwent this procedure, 47 had an obstructive lesion and required stent placement. Six needed coronary artery bypass surgery, and two false positives appeared on CCTA.

Overall, coronary CTA had a 96% positive predictive value. Researchers did not analyze performance on a per-segment basis.

The rate of silent ischemia in this particular patient population was 20%. There was no statistically significant difference in the calcium scores between those who had SMI and those who did not, Goldman said.

Marked differences emerged in the prevalence of disease, however, depending on the referring physician. For one doctor, the rate of SMI was 13% versus 46% for the second doctor. There is obviously a difference in the way these two doctors go about selecting high-risk patients for CCTA, Goldman said.

"Is there a role for CT in screening asymptomatic patients over 55 and at high risk? Further studies are needed to compare CTA with stress ECG, stress echocardiogram, and stress valium tests," he said. "As new technology evolves to lower the CT radiation dose, the role of CTA in screening high-risk patients becomes more attractive."