Usefulness of carotid intimal medial thickness and flow-mediated dilation in a preventive cardiovascular practice.

I 1995, the University of Virginia started measuring common/mean carotid intimal medial thickness (IMT) and post–ischemia-induced flow-mediated dilation (FMD) as measures of subclinical arteriosclerosis. These tests were performed in patients with intermediate cardiovascular risk based on standard risk factors. IMT is a direct measure of carotid arteriosclerosis and an indirect measure of generalized atherosclerosis.1 O’Leary et al2 found that increased common carotid IMT predicted myocardial infarctions in elderly patients. FMD is a measure of nitric oxide release from the forearm arterial endothelium.3,4 In patients with a healthy endothelium, forearm ischemia induces greater nitric oxide release, and therefore, greater brachial artery dilation. Endothelial dysfunction is one the first abnormalities found in arteriosclerosis,5 dyslipidemia,6 and type 2 diabetes.7,8 Since 1995, 968 patients had FMD and IMT measured at the University of Virginia. It is known that age is a predictor of IMT9; FMD is less well characterized. Celermajer et al5 studied brachial and superficial femoral artery dilation and found an inverse relation between arterial diameter and percent artery dilation. We sought to more carefully characterize brachial artery FMD in addition to IMT. Therefore, we evaluated our cohort of patients to determine how to best interpret FMD and IMT results based on patient characteristics. • • • This investigation was performed retrospectively. All IMT and FMD studies performed at the University of Virginia were entered into a clinical database. For this analysis, a second database was created on July 17, 2002 that did not include any identifiers to a patients’ identity, as required by the University of Virginia’s Human Investigation Committee. The database included FMD, preischemic brachial artery diameter, common carotid IMT, systolic blood pressure, diastolic blood pressure, age, gender, height, weight, and histories of hypertension, smoking, or diabetes mellitus. The database was analyzed with SAS software (SAS Institute, Cary, North Carolina). There was no outside funding for this investigation. FMD was measured after an overnight fast. A blood pressure cuff was placed on the left upper arm (proximal to the brachial artery), and electrocardiography leads were attached. Blood pressure was measured after a 5-minute rest period. Cross-sectional and longitudinal brachial artery diameter was imaged with a Toshiba Powervision 6000 SSA370A ultrasound machine (Otawara-Shi, Tochigi, Japan) with an 11MHz vascular probe positioned distally to the blood pressure cuff. One cross-sectional brachial artery diFrom the Cardiovascular Division, Departments of Internal Medicine and Physiology, University of Virginia Health System, Charlottesville, Virginia. Dr. Christopher M. Rembold’s address is: Box 801395, Cardiovascular Division, University of Virginia Health System, Charlottesville, Virginia 22908-1395. E-mail: crembold@virginia.edu. Manuscript received December 10, 2003; revised manuscript received and accepted February 27, 2003. TABLE 1 Summary Statistics and Univariate and Multivariate Correlation Coefficients (r values) for Prediction of Brachial Artery Flow-mediated Dilation (FMD) on the Subset of Patients Without Known Arteriosclerosis Vascular Disease and Not Taking Medications (n 313)