Central versus peripheral cardiovascular risk in metabolic syndrome

Abstract

Individuals with metabolic syndrome (MetS; i.e., three of five of the following risk factors (RFs): elevated blood pressure, waist circumference, triglycerides, blood glucose, or reduced HDL) are thought to be prone to serious cardiovascular disease and there is debate as to whether the disease begins in the peripheral vasculature or centrally. This study investigates hemodynamics, cardiac function/morphology, and mechanical properties of the central (heart, carotid artery) or peripheral [total peripheral resistance (TPR), forearm vascular bed] vasculature in individuals without (1-2 RFs: n = 28), or with (≥3 RFs: n = 46) MetS. After adjustments for statin and blood pressure medication use, those with MetS had lower mitral valve E/A ratios (<3 RFs: 1.24 ± 0.07; ≥3 RFs: 1.01 ± 0.04; P = 0.025), and higher TPR index (<3 RFs: 48 ± 2 mmHg/L/min/m(2); ≥3 RFs: 53 ± 2 mmHg/L/min/m(2); P = 0.04). There were no differences in heart size, carotid artery measurements, cardiovagal baroreflex, pulse-wave velocity, stroke volume index, or cardiac output index due to MetS after adjustments for statin and blood pressure medication use. The use of statins was associated with increased inertia in the brachial vascular bed, increased HbA1c and decreased LDL cholesterol. The independent use of anti-hypertensive medication was associated with decreased predicted [Formula: see text] triglycerides, diastolic blood pressure, interventricular septum thickness, calculated left ventricle mass, left ventricle posterior wall thickness, and left ventricle pre-ejection period, but increased carotid stiffness, HDL cholesterol, and heart rate. These data imply that both a central cardiac effect and a peripheral effect of vascular resistance are expressed in MetS. These data also indicate that variance in between-group responses due to pharmacological treatments are important factors to consider in studying cardiovascular changes in these individuals.

Keywords: carotid distensibility; echocardiography; hemodynamics; metabolic syndrome; peripheral vasculature.

Figure 1

Indices of heart size in individuals with metabolic syndrome (MetS). After adjustment for statin and blood pressure medication use, compared with individuals with less than three risk factors for cardiovscular disease (<3 RFs) participants with MetS displayed no differences in (A) left ventricle mass (P = 0.49), (B) interventricular septal wall thickness (P = 0.12), or (C) left ventricular posterior wall thickness (P = 0.17). There were significant effects of anti-hypertension medication use and statin use in all variables (see Tables 4 and 5). Values are mean ± SD. Corresponding SE values are (A) 6.0 g (<3 RFs) and 6.3 g (MetS); (B) 0.02 cm (<3 RFs) and 0.01 cm (MetS); (C) 0.02 cm (<3 RFs) and 0.01 cm (MetS).

Figure 2

Echocardiography of individuals with metabolic syndrome (MetS). After adjustment for statin and blood pressure medication use, compared with individuals with less than three risk factors for cardiovscular disease (<3 RFs) participants with MetS displayed (A) lower mitral valve E/A ratio (MV E/A ratio; an indicator of left ventricle relaxation; P = 0.03) and (B) no difference in left ventricular pre-ejection period (LVPEP; P = 0.27). There were significant effects of anti-hypertension medication use on LVPEP (see Table 4). Values are mean ± SD. Corresponding SE values are (A) 0.07 (<3 RFs) and 0.04 (MetS); (B) 2.0 ms (<3 RFs) and 2.6 ms (MetS).

Figure 3

Carotid artery dynamics of individuals with metabolic syndrome (MetS). After adjustment for statin and blood pressure medication use, compared with individuals with less than three risk factors for cardiovascular disease (<3 RFs) participants with MetS were not different in carotid artery (A) strain (P = 0.34), (B) stiffness (P = 0.40), (C) distensibility (P = 0.75), and (D) elastic modulus (P = 0.23). There was a trend for an effect of anti-hypertension medication on carotid stiffness (see Table 4). There was a significant effect of anti-hypertension medication use on carotid distensibility (see Table 4). Values are mean ± SD. Corresponding SE values are (A) 0.005 cm⁻¹ (<3 RFs) and 0.004 cm⁻¹ (MetS); (B) 0.6 cm (<3 RFs) and 0.07 cm (MetS); (C) 0.0001 cm*mmHg⁻¹ (<3 RFs) and 0.0001 cm*mmHg⁻¹ (MetS); (D) 57 cm*mmHg (<3 RFs) and 67 cm*mmHg (MetS).

Figure 4

Hemodynamics of individuals with metabolic syndrome (MetS). After adjustment for statin and anti-hypertensive medication use, compared with individuals with less than three risk factors for cardiovascular disease (<3 RFs) participants with MetS displayed (A) no difference in stroke volume index (P = 0.19); (B) no difference in cardiac output index (P = 0.34); and (C) higher total peripheral resistance index (P = 0.04). There were no significant effects of anti-hypertension medication use or statin use for all variables. Values are mean ± SD. Corresponding SE values are (A) 0.9 mL/m² (<3 RFs) and 1.1 mL/m² (MetS); (B) 0.06 L/min/m² (<3 RFs) and 0.07 L/min/m² (MetS); (C) 1.8 mmHg/L/min/m² (<3 RFs) and 2.0 mmHg/L/min/m² (MetS).