Prevention Conference V: Beyond secondary prevention: identifying the high-risk patient for primary prevention: noninvasive tests of atherosclerotic burden: Writing Group III

Clinical trials: surrogate endpoints or hard endpoints?

A man, aged 50, has about a 50% risk and a 50-year-old woman a 35% risk of having a myocardial infarction during their lifetime. The extent of atherosclerosis is the primary determinant of the risk of myocardial infarction. We will be unable to substantially reduce the lifetime risk of coronary artery disease without primary prevention of atherosclerosis. Noninvasive methods to measure subclinical atherosclerosis and its progression offer a unique opportunity to improve individual patient preventive strategies, based both on pharmacologic and nonpharmacologic therapies, as well as an opportunity to study and develop new drug therapies. The use of subclinical disease as a surrogate marker of atherosclerosis and the study of plaque characteristics will greatly enhance our understanding of the role of new risk factors for atherosclerosis, lipoprotein metabolism, and genetic-lifestyle interactions.

Carotid ultrasound

This article provides an overview of basic diagnostic carotid ultrasound applications, and emphasizes practical aspects of this examination. Areas currently being investigated include carotid plaque characterization and applications relative to IMT measurements. Contrast-enhanced ultrasound imaging also offers promise to improve plaque characterization, which in turn may link these evaluations to outcome studies.

Diabetes and the associated incidence of subclinical atherosclerosis and coronary artery disease: Implications for management

BACKGROUND

We sought to examine the prevalence, sensitivity, and specificity of coronary calcium (CC), a marker of atherosclerosis, in a population of symptomatic and asymptomatic diabetic persons.

METHODS

We used electron beam tomography (EBT) to quantitate CC in 168 symptomatic (chest pain or anginal equivalent) persons with diabetes who underwent coronary angiography and then compared this with a cohort of 155 asymptomatic persons with diabetes.

RESULTS

In the 168 symptomatic diabetic persons, 124 (74%) had obstructive coronary artery disease (CAD) by angiography. Receiver-operator characteristic curve analysis was used to maximize sensitivity and specificity for obstructive CAD (>50% stenosis), which established a CC score of 102 as optimal. With use of this cut point, EBT has a sensitivity of 77% and a specificity of 77% for detecting obstructive CAD. Of the 155 asymptomatic diabetic persons, 72% had CC and 48% had a CC score >102. The presumed prevalence of obstructive disease (on the basis of EBT scores and prevalence of CC) among asymptomatic diabetic persons is quite high (as high as symptomatic persons without diabetes). Analyzing the 323 diabetic patients demonstrated no significant age difference in CC scores between women and men.

CONCLUSIONS

This study confirms that higher CC scores should be used in diabetic patients to improve the specificity of CC to determine obstructive disease. EBT can allow a noninvasive diagnosis of CAD before clinical presentation, allowing for more therapy for those in which CC is detected. These results suggest that asymptomatic diabetic persons have the same atherogenic burden of those patients with CAD without diabetes. The high prevalence of CC in asymptomatic persons with diabetes supports the need for aggressive management of diabetes and associated risk factors.

Do conventional risk factors predict subclinical coronary artery disease? Results from the Prospective Army Coronary Calcium Project

BACKGROUND

Recent guidelines recommend against the routine use of coronary artery calcification (CAC) detection because the additive value over clinical prediction tools is uncertain. We compared CAC, with use of electron-beam computed tomography (EBCT), with clinical and serologic coronary risk factors for the identification of patients with increased coronary heart disease risk.

METHODS AND RESULTS

We studied 630 active-duty US Army personnel (39-45 years old) without known coronary artery disease (CAD) who were undergoing a routine physical examination as required by regulations. Each participant underwent clinical and serologic risk factor screening and EBCT. The cohort (mean age 42 +/- 2 years, 82% male) had a low predicted risk of coronary events (mean 5-year Framingham risk index [FRI] 1.6% +/- 1.2%). The prevalence of coronary calcification was 17.6% (male 20.6%, female 4.3%). Significant univariate correlates of CAC were total and low-density lipoprotein [LDL] cholesterol, triglycerides, systolic blood pressure, and body mass index. However, only LDL cholesterol was independently associated with CAC. There was a significant but weak relationship between CAC and the Framingham risk index (FRI) (receiver-operator characteristic [ROC] curve area 0.62 +/- 0.03, P <.001), which was not different from the relationship between CAC and LDL cholesterol alone (ROC curve area 0.61 +/- 0.03, P <.001). The prevalence of any CAC in men increased slightly across increasing quartiles of FRI: 17.0%, 20.8%, 33.0%, and 29.2% (P =.033). Other risk factors (family history, homocysteine, insulin, lipoprotein[a], and fibrinogen) were not related to CAC.

CONCLUSIONS

In this age-homogeneous, low-risk screening cohort, conventional coronary risk factors significantly underestimated the presence of premature, subclinical calcified coronary atherosclerosis. These data support the potential of CAC detection as an anatomic, plaque-burden diagnostic test to identify patients who may require more intensive risk-reduction therapies, independent of predicted clinical risk.

Coronary calcium: the case for helical computed tomography

This article provides the rationale for using helical (aka spiral, conventional, and mechanical) computed tomography (CT) systems from measuring coronary calcium. The current state and active research concerning measuring coronary calcium with single- and multi-slice systems is reviewed. The components of image quality, which are important to cardiac imaging with CT, are discussed. Companion articles will review electron beam CT (EBCT) for measuring coronary calcium and perhaps most importantly the scientific data relating coronary calcium to coronary heart disease and atherosclerosis.