Noninvasive tests for arterial structure, function, and compliance: Do they identify risk or diagnose disease?

Predictors of the intima-media thickness of carotid artery in asymptomatic newly detected severe hypercholesterolemic patients

BACKGROUND

Data about predictors of intima-media thickness (IMT) of common carotid artery (CCA) in asymptomatic subjects with newly detected severe hypercholesterolemia is scarce.

AIM

This research is aimed at studying the predictors of the IMT of CCA among basic atherogenic risk biomarkers - lipid [total cholesterol (TC), triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein (LDL) cholesterol, Apolipoprotein-B, Apolipoprotein-Ai, Apolipoprotein-B/A(1) index] and non-lipid, [asymmetric dimethylarginine (ADMA), total homocysteine, cell adhesion molecules] in asymptomatic subjects with newly detected severe hypercholesterolemia.

METHODS

Two hundred and fifty asymptomatic patients with severe, newly hypercholesterolemia and 200 controls were evaluated. Hypercholesterolemia was defined as TC > 7.5 mm and LDL cholesterol > 4.9 mm. The ADMA and cell adhesion molecules were determined by ELISA and total homocysteine by high-performance liquid chromatography.

RESULTS

There was significant difference between the two groups in respect to all lipid biomarkers (P<0.001). Hypercholesterolemic patients had significantly higher level of ADMA, sVCAM-1, sICAM-1, IMT (P<0.001), whereas no significant difference was found between two groups with respect to total homocysteine, P-selectin and E-selectin (P>0.05). A strong positive correlation between IMT mean and age (r(xy) = 0.714; P<0.001), Apolipoprotein-B (r(xy) = 0.706; r(xy) < 0.001), Apolipoprotein-B/A(1) (r(xy) = 0.324; P<0.001), ADMA (r(xy) = 0.603; P<0.001) was found. The subsequent linear and multiple regression analysis selected age and Apolipoprotein-B as most significant factors in relation to IMT mean. Apolipoprotein-B is a better factor for assessment of risk, as LDL cholesterol underestimates the risk in asymptomatic subjects with newly detected severe hypercholesterolemia, until more rapid and feasible methods for measurement of small and dense LDL are available.

Influence of Cardiovascular Risk Factors on Total Arterial Compliance

BACKGROUND

Reduced total arterial compliance (TAC) may be a marker of preclinical vascular disease. Irreversible risk factors such as age and body habitus are determinants of TAC, the importance of which may have been hidden by reports in selected subgroups, such as the elderly and those with diabetes mellitus or hypertension. We sought the comparative influence of reversible and irreversible risk factors on TAC in a large primary prevention group.

MATERIALS AND METHODS

We studied 720 consecutive patients with and without cardiovascular risk factors but with no overt cardiovascular disease. TAC was calculated by the pulse-pressure method from simultaneous applanation tonometry and left ventricular outflow tract Doppler. Central pressure was derived using a transfer function from the radial tonometric waveform and calibrated using mean and diastolic brachial cuff pressure.

RESULTS

There were 192 patients with no cardiovascular risk factors, 180 patients with one cardiovascular risk factor, 173 patients with two cardiovascular risk factors, and 175 patients with three or more risk factors. Although age, gender, height, weight, hypertension, diabetes mellitus, hyperlipidemia, and number of risk factors were all significantly associated with TAC, age accounted for approximately 13% of the variance, and the only other independent predictors were height and weight. TAC was not significantly different in age-matched subgroups with single risk factors.

CONCLUSION

TAC is associated with multiple risk factors, but age is a major determinant. The influence of age and other correlates may dwarf the contribution of individual risk factors and therefore their alteration with therapy.

Carotid ultrasound assessment of patients with coronary artery disease: a useful index for risk stratification

Carotid disease is a common finding in patients with coronary artery disease (CAD) and its presence is associated with worse clinical outcomes. Intima-media thickness provides incremental value over traditional risk factors in predicting cardiovascular events; however, it does not predict the absence of CAD or its extent and severity. The presence of carotid plaques is associated with an increased risk of cardiovascular events in patients with CAD regardless of the treatment strategy (medical therapy alone or myocardial revascularization). Hence, we advocate the screening of patients with diagnosed CAD for carotid atherosclerosis. The prognostic impact of ultrasound characteristics of carotid plaques on cardiovascular outcomes of patients with CAD remains controversial.

Association of arterial wave properties and diastolic dysfunction in patients with type 2 diabetes mellitus

Left ventricular (LV) diastolic dysfunction and increased arterial stiffness are prevalent in patients with type 2 diabetes mellitus (DM). Because the systemic vasculature plays a pivotal role in myocardial loading, this study aimed to determine the effect of arterial characteristics on LV diastolic function in patients with type 2 DM. Conventional echocardiography and tissue Doppler imaging were performed in 155 patients with type 2 DM (88 men; mean age 55 +/- 11 years) with preserved LV ejection fractions (>50%). Patients were stratified into groups on the basis of LV diastolic function (normal, n = 53; delayed relaxation, n = 79; pseudonormal, n = 23). Arterial wave reflection parameters and central blood pressure were determined by radial tonometry. Arterial (brachial and carotid) structure and function were determined by standard ultrasound methods. There were no significant differences among the groups on central pressure or arterial function. LV filling pressure, determined by the ratio of early transmitral inflow velocity to diastolic early tissue velocity (E/E'), was significantly correlated with central pulse pressure (r = 0.21, p <0.05). Late diastolic inflow velocity (A) was significantly associated with central pulse pressure (r = 0.32, p <0.001), total arterial compliance (r = -0.35, p <0.001), and carotid artery stiffness (r = 0.34, p <0.001). Multiple regression analysis found central but not brachial pulse pressure independently predicted E/E' and A. In conclusion, increased central pulse pressure, possibly due to amplified pressure wave reflections, is independently associated with abnormal LV diastolic function in patients with type 2 DM.

Effect of weight loss due to lifestyle intervention on subclinical cardiovascular dysfunction in obesity (body mass index >30 kg/m2)

Subclinical myocardial and vascular dysfunctions occur in subjects with obesity. We investigated whether these changes were reversible with weight loss due to lifestyle intervention. Quantitative assessment of myocardial and vascular functions was performed at baseline and after a minimum of 8 weeks of a lifestyle intervention program in 106 subjects with significant risk factors but no history of cardiovascular disease and normal ejection fractions. Myocardial function was assessed using strain rate, strain, regional myocardial systolic velocity, and diastolic velocity (e(m)). Myocardial reflectivity was assessed by calibrated integrated backscatter. Vascular function was assessed using brachial arterial reactivity and arterial compliance. Exercise capacity was measured by peak oxygen consumption per unit time (VO(2)). Weight loss (-4.5 +/- 2.0%) was achieved by 48 subjects, and 58 maintained or increased weight (+1 +/- 1.5%, p <0.001). Compared with the stable weight group, the weight loss group showed significant improvement in brachial arterial reactivity (8.6 +/- 4.9% vs 6.7 +/- 4.9%, p <0.05), e(m) (6.4 +/- 1.9 vs 5.5 +/- 1.9 cm/s, p <0.01), and reflectivity (calibrated integrated backscatter, 18.3 +/- 4.9 vs 16.2 +/- 5.2 dB, p <0.01). The magnitude of weight change correlated with changes in e(m) (r = 0.36) and calibrated integrated backscatter (r = 0.33). The change in e(m) correlated with peak VO(2) (r = 0.38, p <0.001) and was an independent predictor for peak VO(2) even after adjustment for age and body mass index in a multivariate model (R(2) = 0.45, p <0.001). Weight loss was not associated with a significant change in systolic parameters (regional myocardial systolic velocity, global strain, and strain rate) or arterial compliance.

Free fatty acids are associated with obesity, insulin resistance, and atherosclerosis in renal transplant recipients

BACKGROUND

Insulin resistance (IR) may be implicated in the pathogenesis of atherosclerosis in renal transplant recipients (RTRs) and be contributed to, in part, by free fatty acids (FFAs), produced in excess in centrally obese individuals. The aim of this study was to determine the prevalence of IR and the relationships between FFAs, central obesity, and atherosclerosis in a cohort of prevalent RTRs.

METHODS

Observational data were collected on 85 RTRs (mean age 54 years; 49% male, 87% Caucasian). Fasting serum was analyzed for FFAs, glucose, and insulin; IR was calculated using the homeostasis model assessment (HOMA-IR) score. Vascular structure was assessed by carotid intima-media thickness (IMT) measurement. Linear regression analyses were performed to determine the factors associated with IR and atherosclerosis.

RESULTS

IR occurred in 75% of RTRs, and FFA levels were independently associated with its occurrence (beta: -0.55, 95% CI: -1.02 to -0.07, P = 0.02). Other variables independently associated with IR were male sex, body mass index, central obesity, diabetes, systolic blood pressure and corticosteroid use. There was a significant correlation between FFA levels and IMT (r = 0.3, P=0.01). On multivariate analysis, IMT correlated with elevated FFA (beta: 0.07, 95% CI: 0.02-0.12, P = 0.007), diabetes mellitus (P = 0.05), older age (P < 0.002), and a body mass index >25 kg/m (P = 0.002).

CONCLUSIONS

FFAs are associated with the development of IR and may be involved in the pathogenesis of atherosclerosis in RTRs. Additional studies are required to explore these associations further before considering whether an interventional trial aimed at lowering FFA would be a worthwhile undertaking.

Myocardial and vascular dysfunction and exercise capacity in the metabolic syndrome

The metabolic syndrome (MS) is associated with cardiovascular risk exceeding that expected from atherosclerotic risk factors, but the mechanism of this association is unclear. We sought to determine the effects of the MS on myocardial and vascular function and cardiorespiratory fitness in 393 subjects with significant risk factors but no cardiovascular disease and negative stress echocardiographic findings. Myocardial function was assessed by global strain rate, strain, and regional systolic velocity (s(m)) and diastolic velocity (e(m)) using tissue Doppler imaging. Arterial compliance was assessed using the pulse pressure method, involving simultaneous radial applanation tonometry and echocardiographic measurement of stroke volume. Exercise capacity was measured by expired gas analysis. Significant and incremental variations in left ventricular systolic (s(m), global strain, and strain rate) and diastolic (e(m)) function were found according to the number of components of MS (p <0.001). MS contributed to reduced systolic and diastolic function even in those without left ventricular hypertrophy (p <0.01). A similar dose-response association was present between the number of components of the MS and exercise capacity (p <0.001) and arterial compliance. The global strain rate and e(m) were independent predictors of exercise capacity. In conclusion, subclinical left ventricular dysfunction corresponded to the degree of metabolic burden, and these myocardial changes were associated with reduced cardiorespiratory fitness. Subjects with MS who also have subclinical myocardial abnormalities and reduced cardiorespiratory fitness may have a higher risk of cardiovascular disease events and heart failure.

Screening for coronary artery disease in patients with diabetes: a Bayesian strategy of clinical risk evaluation and exercise echocardiography

OBJECTIVE

Screening for coronary artery disease is constrained by its low prevalence in unselected patients. We compared the ability of clinical scores to identify a high-risk group with diabetes mellitus and investigated a Bayesian strategy by combination with exercise echocardiography (ExE).

METHODS

The Framingham risk score (FRS), a score based on the American Diabetes Association (ADA) screening guidelines, the United Kingdom Prospective Diabetes Study (UKPDS) risk engine, and a disease-specific diabetic cardiac risk score (DCRS) were calculated in 199 asymptomatic patients with type 2 diabetes mellitus undergoing ExE. The frequency of abnormal ExE and the proportion of these with coronary stenoses were sought in groups designated as high risk on the basis of optimal cutoffs for each score. All patients were followed up for 1 year.

RESULTS

High risk was identified in fewer patients with the DCRS (27%) than FRS (38%, P = .02), ADA (41%, P = .004), and UKPDS (43%, P = .001). Exercise echocardiography was positive in 27 (14%); 11 of 23 proceeding to angiography showed significant stenoses. Areas under the receiver operator characteristic curves for prediction of a positive ExE were similar for DCRS, UKPDS, and FRS but less for ADA (P = .04). Positive ExE was uncommon in low-risk patients (8%-11%) and most were false positives (58%-80%). Cardiovascular events (n = 9) were more likely in the high-risk compared with the low-risk UKPDS (9% vs 2%, P = .03) and DCRS (12% vs 2%, P = .01).

CONCLUSION

Combination of the UKPDS or DCRS with ExE may optimize detection of coronary artery disease and cardiac events in asymptomatic patients, while minimizing the numbers of ExE and false-positive rate.