AHA Relents on CT Imaging for Intermediate-Risk Coronary Patients

DALLAS, Oct. 12 -- CT imaging of coronary calcification by electron beam or multidetector devices is appropriate for patients at an intermediate risk, according to an American Heart Association statement. It represents an about face for the organization.

The AHA maintained its position that imaging plaque calcification may not give additional useful information about patients known to be at high or low coronary risk. But the statement acknowledged that EBCT imaging may be helpful in making the difficult treatment decisions for the millions of intermediate-risk patients, defined as having a 10% to 20% 10-year Framingham risk score.

"If you know they are high risk, it's easy -- they get treated," said Matthew J. Budoff, M.D., of the Harbor-University of California Los Angeles Medical Center. "If they are low risk, it's easy -- you just tell them to stay healthy But it's all those people in the middle where guidelines tend to fall out. This is where coronary artery calcification is going to play a huge role."

For these patients, "elevated calcium scores may trigger more vigorous application of both lifestyle and/or pharmacological therapies targeted to lower cardiovascular risk," Dr. Budoff and colleagues wrote in the Oct. 17 issue of Circulation, Journal of the American heart Association.

The AHA statement cited rapidly evolving technology and literature for its change of heart regarding EBCT and multidetector CT (MDCT). The AHA's prior statements in 1994 and 2000 acknowledged CT's potential but because of conflicting data did not recommend routine scanning. Yet by 2005 the AHA had given CT the partial go-ahead in a statement targeted at women.

"I think this definitely represents a recognition that the science is getting better in this regard," Dr. Budoff said.

EBCT is a fast x-ray imaging modality that can detect and measure calcium deposits in the coronary arteries. MDCT, also called multirow or multislice CT, is more commonly available.

The recommendations suggested that cardiac CT in asymptomatic patients has:

• No benefit for patients at low (Framingham risk score <10% 10-year risk) or high cardiovascular risk (Framingham risk score >20% 10-year risk), and
• Reasonable benefit for clinically selected, intermediate-risk patients to refine clinical risk prediction and to select patients for more aggressive target values for lipid-lowering therapies.

Because calcified plaque can be present in nonobstructive coronary plaque lesions but is not highly specific for obstructive lesions, a positive finding in asymptomatic patients "does not provide a rationale for revascularization but rather for risk factor modification and possible further functional assessment," the authors wrote.

"Clinicians must understand that a positive calcium scan indicates atherosclerosis but most often no significant stenosis," they added.

The recommendations said that cardiac CT in symptomatic patients is:

• Reasonable for coronary calcium assessment, especially in the setting of equivocal treadmill or functional testing.
• May be considered for coronary artery calcified plaque measurement in symptomatic patients to determine the cause of cardiomyopathy.
• May be considered for coronary artery calcification assessment in patients with chest pain with equivocal or normal electrocardiograms and negative cardiac enzyme studies.

Noninvasive CT angiography performed by either EBCT or MDCT "may develop into a clinically useful tool" to evaluate the lumen and wall of the coronary artery, especially in the context of ruling out stenosis in patients with low to intermediate likelihood of disease. The recommendations said that CT coronary angiography is:

• Reasonable for the assessment of obstructive disease in symptomatic patients,
• Not recommended for detecting restenosis after stent placement due to lack of evidence,
• Not recommended as a screening test for atherosclerosis (noncalcific plaque) in asymptomatic patients in part because of the higher radiation doses, and
• Similarly not recommended as a screening tool for assessment of occult coronary artery disease in asymptomatic patients due to the higher radiation dose.

Though the clinical relevance of the radiation dose from cardiac CT remains unknown, higher radiation doses are generally associated with a small increase in cancer risk.

Other recommendations included:

• CT evaluation of noncalcified plaque is "promising but premature" as is serial imaging for assessment of progression of coronary calcification and hybrid scanning to assess cardiovascular risk or presence of obstructive disease,
• Both EBCT and MDCT "might be reasonable in most cases" to assess the patency of a bypass graft and the presence of coronary stenoses in the course of the bypass graft, at the anastomotic site, and in the native coronary artery system, and
• CT is a reasonable first-choice imaging modalities in the workup of known and suspected coronary anomalies.

For coronary artery calcified plaque assessment, the authors "strongly" recommended using a low radiation-dose cardiac CT technique with prospective cardiac gating (starting data acquisition based on a signal from the electrocardiogram to avoid blurring of the image as the heart pumps). MDCT may be preferable for larger patients since EBCT's lower power may cause image quality to suffer from noise, the authors noted.

The statement acknowledged that "EBCT is one of many contenders in a crowded field of emerging [coronary artery disease] risk-assessment tools," such as carotid intima-media thickness and blood tests like homocysteine and C-reactive protein.

It also noted that there is not evidence that screening with EBCT improves clinical outcomes by reducing mortality or morbidity from coronary artery disease.

The recommendations came out just ahead of the American College of Cardiology's appropriateness statement on the same topic and within a month of the expected November arrival of the ACC's similar guidelines.

The authors disclosed various conflicts with companies including: Merck, Pfizer, Wyeth, AstraZeneca, KOS, General Electric, Siemens Medical Systems, Novartis, and Toshiba.