Michelle J. Keyes

Changes in Arterial Stiffness and Wave Reflection With Advancing Age in Healthy Men and Women The Framingham Heart Study

With advancing age, arterial stiffness and wave reflections increase and elevate systolic and pulse pressures. An elevated central pulse pressure is generally ascribed to increased wave reflection and portends an unfavorable prognosis. Using arterial tonometry, we evaluated central (carotid-femoral) and peripheral (carotid-brachial) pulse wave velocity, amplitudes of forward and reflected pressure waves, and augmentation index in 188 men and 333 women in the Framingham Heart Study offspring cohort who were free of clinical cardiovascular disease, hypertension, diabetes, smoking within the past 12 months, dyslipidemia, and obesity. In multivariable linear regression models, advancing age was the predominant correlate of higher carotid-femoral pulse wave velocity; other correlates were higher mean arterial pressure, heart rate, and triglycerides and walk test before tonometry (model R2 = 0.512, P < 0.001). A similar model was obtained for carotid-brachial pulse wave velocity (model R2 = 0.227, P < 0.001), although the increase with advancing age was smaller. Owing to different relations of age to central and peripheral stiffness measures, carotid-femoral pulse wave velocity was lower than carotid-brachial pulse wave velocity before age 50 years but exceeded it thereafter, leading to reversal of the normal central-to-peripheral arterial stiffness gradient. In this healthy cohort with a minimal burden of cardiovascular disease risk factors, an age-related increase in aortic stiffness, as compared with peripheral arterial stiffness, was associated with increasing forward wave amplitude and pulse pressure and reversal of the arterial stiffness gradient. This phenomenon may facilitate forward transmission of potentially deleterious pressure pulsations into the periphery.

Cross-Sectional Relations of Digital Vascular Function to Cardiovascular Risk Factors in the Framingham Heart Study

Background— Digital pulse amplitude augmentation in response to hyperemia is a novel measure of peripheral vasodilator function that depends partially on endothelium-derived nitric oxide. Baseline digital pulse amplitude reflects local peripheral arterial tone. The relation of digital pulse amplitude and digital hyperemic response to cardiovascular risk factors in the community is unknown. Methods and Results— Using a fingertip peripheral arterial tonometry (PAT) device, we measured digital pulse amplitude in Framingham Third Generation Cohort participants (n=1957; mean age, 40±9 years; 49% women) at baseline and in 30-second intervals for 4 minutes during reactive hyperemia induced by 5-minute forearm cuff occlusion. To evaluate the vascular response in relation to baseline, adjusting for systemic effects and skewed data, we expressed the hyperemic response (called the PAT ratio) as the natural logarithm of the ratio of postdeflation to baseline pulse amplitude in the hyperemic finger divided by the same ratio in the contralateral finger that served as control. The relation of the PAT ratio to cardiovascular risk factors was strongest in the 90- to 120-second postdeflation interval (overall model R2=0.159). In stepwise multivariable linear regression models, male sex, body mass index, ratio of total to high-density lipoprotein cholesterol, diabetes mellitus, smoking, and lipid-lowering treatment were inversely related to PAT ratio, whereas increasing age was positively related to PAT ratio (all P<0.01). Conclusions— Reactive hyperemia produced a time-dependent increase in fingertip pulse amplitude. Digital vasodilator function is related to multiple traditional and metabolic cardiovascular risk factors. Our findings support further investigations to define the clinical utility and predictive value of digital pulse amplitude.

Clinical Correlates and Heritability of Flow-Mediated Dilation in the Community: The Framingham Heart Study

Background—Studies in selected samples have linked impaired endothelial function with cardiovascular disease and its risk factors. The clinical correlates and heritability of endothelial function in the community have not been described. Methods and Results—We examined a measure of endothelial function, brachial artery flow-mediated dilation (FMD), expressed as both percent (FMD%) and actual dilation by ultrasound with the occlusion cuff below the elbow in 2883 Framingham Study participants (52.9% women; mean age, 61 years). A subset of 1096 participants performed a 6-minute walk test before FMD determination. Mean FMD% was 3.3±3.0% in women and 2.4±2.4% in men. In stepwise multivariable linear regression models, FMD% was inversely related to age, systolic blood pressure, body mass index (BMI), lipid-lowering medication, and smoking, whereas it was positively related to female gender, heart rate, and prior walk test. The estimated heritability of FMD% was 0.14. FMD actual dilation findings were similar, except that female sex and BMI were not significantly associated. Conclusions—Increasing age, systolic blood pressure, BMI, and smoking were associated with lower FMD% in our community-based sample, whereas prior exercise and increasing heart rate were associated with higher FMD%. The estimated heritability of FMD was modest. Future research will permit more complete characterization of the genetic and environmental determinants of endothelial function and its prognostic value in the community.

Long-term Outcomes in Individuals With Prolonged PR Interval or First-Degree Atrioventricular Block

CONTEXT Prolongation of the electrocardiographic PR interval, known as first-degree atrioventricular block when the PR interval exceeds 200 milliseconds, is frequently encountered in clinical practice. OBJECTIVE To determine the clinical significance of PR prolongation in ambulatory individuals. DESIGN, SETTING, AND PARTICIPANTS Prospective, community-based cohort including 7575 individuals from the Framingham Heart Study (mean age, 47 years; 54% women) who underwent routine 12-lead electrocardiography. The study cohort underwent prospective follow-up through 2007 from baseline examinations in 1968-1974. Multivariable-adjusted Cox proportional hazards models were used to examine the associations of PR interval with the incidence of arrhythmic events and death. MAIN OUTCOME MEASURES Incident atrial fibrillation (AF), pacemaker implantation, and all-cause mortality. RESULTS During follow-up, 481 participants developed AF, 124 required pacemaker implantation, and 1739 died. At the baseline examination, 124 individuals had PR intervals longer than 200 milliseconds. For those with PR intervals longer than 200 milliseconds compared with those with PR intervals of 200 milliseconds or shorter, incidence rates per 10 000 person-years were 140 (95% confidence interval [CI], 95-208) vs 36 (95% CI, 32-39) for AF, 59 (95% CI, 40-87) vs 6 (95% CI, 5-7) for pacemaker implantation, and 334 (95% CI, 260-428) vs 129 (95% CI, 123-135) for all-cause mortality. Corresponding absolute risk increases were 1.04% (AF), 0.53% (pacemaker implantation), and 2.05% (all-cause mortality) per year. In multivariable analyses, each 20-millisecond increment in PR was associated with an adjusted hazard ratio (HR) of 1.11 (95% CI, 1.02-1.22; P = .02) for AF, 1.22 (95% CI, 1.14-1.30; P < .001) for pacemaker implantation, and 1.08 (95% CI, 1.02-1.13; P = .005) for all-cause mortality. Individuals with first-degree atrioventricular block had a 2-fold adjusted risk of AF (HR, 2.06; 95% CI, 1.36-3.12; P < .001), 3-fold adjusted risk of pacemaker implantation (HR, 2.89; 95% CI, 1.83-4.57; P < .001), and 1.4-fold adjusted risk of all-cause mortality (HR, 1.44, 95% CI, 1.09-1.91; P = .01). CONCLUSION Prolongation of the PR interval is associated with increased risks of AF, pacemaker implantation, and all-cause mortality.

Adiposity, Cardiometabolic Risk, and Vitamin D Status: the Framingham Heart Study

OBJECTIVE Because vitamin D deficiency is associated with a variety of chronic diseases, understanding the characteristics that promote vitamin D deficiency in otherwise healthy adults could have important clinical implications. Few studies relating vitamin D deficiency to obesity have included direct measures of adiposity. Furthermore, the degree to which vitamin D is associated with metabolic traits after adjusting for adiposity measures is unclear. RESEARCH DESIGN AND METHODS We investigated the relations of serum 25-hydroxyvitamin D (25[OH]D) concentrations with indexes of cardiometabolic risk in 3,890 nondiabetic individuals; 1,882 had subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT) volumes measured by multidetector computed tomography (CT). RESULTS In multivariable-adjusted regression models, 25(OH)D was inversely associated with winter season, waist circumference, and serum insulin (P < 0.005 for all). In models further adjusted for CT measures, 25(OH)D was inversely related to SAT (−1.1 ng/ml per SD increment in SAT, P = 0.016) and VAT (−2.3 ng/ml per SD, P < 0.0001). The association of 25(OH)D with insulin resistance measures became nonsignificant after adjustment for VAT. Higher adiposity volumes were correlated with lower 25(OH)D across different categories of BMI, including in lean individuals (BMI <25 kg/m2). The prevalence of vitamin D deficiency (25[OH]D <20 ng/ml) was threefold higher in those with high SAT and high VAT than in those with low SAT and low VAT (P < 0.0001). CONCLUSIONS Vitamin D status is strongly associated with variation in subcutaneous and especially visceral adiposity. The mechanisms by which adiposity promotes vitamin D deficiency warrant further study.

Local Shear Stress and Brachial Artery Flow-Mediated Dilation The Framingham Heart Study

Endothelium-dependent flow-mediated dilation is a homeostatic response to short-term increases in local shear stress. Flow-mediated dilation of the brachial artery in response to postischemic reactive hyperemia is impaired in patients with cardiovascular disease risk factors and may reflect local endothelial dysfunction in the brachial artery. However, previous studies have largely neglected the effect of risk factors on evoked shear stress, which is the stimulus for dilation. We evaluated brachial artery percent dilation and evoked diastolic shear stress during reactive hyperemia using high-resolution ultrasound and Doppler in 2045 participants (1107 women, mean age 61 years) in the Framingham Offspring Study. In age- and sex-adjusted models, baseline and hyperemic shear stress were related to brachial artery percent dilation. In stepwise multivariable analyses examining clinical correlates of percent dilation (without shear stress in the model), age, sex, mean arterial pressure, pulse pressure, heart rate, body mass index, lipid medication use, and hormone replacement therapy were related to percent dilation (R2 =0.189; P <0.001). When hyperemic shear stress was incorporated, the overall R2 improved (R2 =0.335; P <0.001), but relationships between risk factors and percent dilation were attenuated (age and mean arterial pressure) or no longer significant (all others). In contrast, risk factors were related to baseline and hyperemic shear stress in multivariable analyses. Evoked hyperemic shear stress is a major correlate of brachial artery flow–mediated dilation. The associations between many risk factors and brachial artery flow–mediated dilation may be attributable to reduced stimulus for dilation rather than impaired local conduit artery response during hyperemia.

LDL Particle Number and Risk of Future Cardiovascular Disease in the Framingham Offspring Study – Implications for LDL Management

BACKGROUND The cholesterol content of LDL particles is variable, causing frequent discrepancies between concentrations of LDL cholesterol and LDL particle number. In managing patients at risk for cardiovascular disease (CVD) to LDL target levels, it is unclear whether LDL cholesterol provides the optimum measure of residual risk and adequacy of LDL lowering treatment. OBJECTIVE To compare the ability of alternative measures of LDL to provide CVD risk discrimination at relatively low levels consistent with current therapeutic targets. METHODS Concentrations of LDL cholesterol (LDL-C) and non-HDL cholesterol (non-HDL-C) were measured chemically and LDL particle number (LDL-P) and VLDL particle number (VLDL-P) were measured by nuclear magnetic resonance (NMR) in 3066 middle-aged white participants (53% women) without CVD in the Framingham Offspring cohort. The main outcome measure was incidence of first CVD event. RESULTS At baseline, the cholesterol content per LDL particle was negatively associated with triglycerides and positively associated with LDL-C. On follow-up (median 14.8 yrs), 265 men and 266 women experienced a CVD event. In multivariable models adjusting for non-lipid CVD risk factors, LDL-P was related more strongly to future CVD in both sexes than LDL-C or non-HDL-C. Subjects with a low level of LDL-P (<25(th) percentile) had a lower CVD event rate (59 events per 1000 person-years) than those with an equivalently low level of LDL-C or non-HDL-C (81 and 74 events per 1000 person-years, respectively). CONCLUSIONS In a large community-based sample, LDL-P was a more sensitive indicator of low CVD risk than either LDL-C or non-HDL-C, suggesting a potential clinical role for LDL-P as a goal of LDL management.

Increased Small Low-Density Lipoprotein Particle Number A Prominent Feature of the Metabolic Syndrome in the Framingham Heart Study

Background— Levels of LDL cholesterol (LDL-C) are frequently not elevated in individuals with the metabolic syndrome (MetSyn). However, the atherogenic potential of LDL may depend on the number and size of LDL particles in addition to the cholesterol content of LDL. Methods and Results— We examined the sex-specific cross-sectional relations of small LDL particle number (determined by nuclear magnetic resonance spectroscopy) to the presence of MetSyn and its components in 2993 Framingham Heart Study participants (mean age, 51 years; 53% women) without cardiovascular disease (CVD) and the relations of small LDL particle number to CVD incidence in people with MetSyn. The MetSyn (≥3 of 5 traits as defined by the National Cholesterol Education Adult Treatment Panel III) was present in 27% of men and 17% of women. In both sexes, small LDL particle number increased from 0 to 5 MetSyn traits, a pattern partly accounted for by strong correlations between small LDL particle number and serum triglycerides (r=0.61, P<0.0001) and HDL-C (r=−0.55, P<0.0001). Compared with participants without the MetSyn, those with the MetSyn had a higher CVD event rate. However, among participants with the MetSyn, CVD rates were similar for groups with an elevated versus a lower number of small LDL particles (defined by the sex-specific median). Conclusions— Small LDL particle number is elevated in the MetSyn, increases with the number of MetSyn components, and most prominently is correlated with triglycerides and HDL-C. Whereas increased small LDL particle number identified the MetSyn with high sensitivity, a higher small LDL particle number was not associated with greater CVD event rates in people with the MetSyn.

Cross-Sectional Relations of Peripheral Microvascular Function, Cardiovascular Disease Risk Factors, and Aortic Stiffness The Framingham Heart Study

Background— Aortic stiffness and small-artery structure and function share various risk factors; however, relations between these 2 measures of vascular function are complex and incompletely understood. Methods and Results— We examined hyperemic forearm blood flow, an indicator of microvascular structure and function, and aortic stiffness in 2045 participants (1107 women, mean age 61±9 years) in the Framingham Heart Study offspring cohort. Using arterial tonometry, we evaluated 3 measures of aortic stiffness: brachial pulse pressure; carotid-femoral pulse wave velocity (CFPWV), which is related directly to aortic wall stiffness; and forward pressure wave amplitude (Pf), which is related directly to aortic wall stiffness and inversely to aortic diameter. Using high-resolution ultrasound and Doppler, we evaluated brachial artery diameter, blood flow, and forearm vascular resistance (FVR) at baseline and during reactive hyperemia after 5 minutes of forearm ischemia. In multivariable models that adjusted for cardiovascular disease risk factors, local brachial pulse pressure, CFPWV, and Pf, considered separately, were associated with increased baseline and hyperemic FVR (P<0.001). In models that further adjusted for mean arterial pressure, each measure of aortic stiffness was associated with reduced hyperemic flow (P<0.001). In risk factor–adjusted models that simultaneously considered CFPWV and Pf, both were associated with increased FVR at baseline (P<0.01) and during hyperemia (P<0.001). Conclusions— Our findings indicate that abnormal aortic stiffness and increased pressure pulsatility are associated with blunted microvascular reactivity to ischemic stress that is in excess of changes attributable to conventional cardiovascular disease risk factors alone, including mean arterial pressure.

Cross-Sectional Correlates of Increased Aortic Stiffness in the Community The Framingham Heart Study

Background— Increased aortic stiffness is associated with numerous common diseases of aging, including heart disease, stroke, and renal disease. However, the prevalence and correlates of abnormally high aortic stiffness are incompletely understood. Methods and Results— We evaluated 2 aortic stiffness measures, carotid-femoral pulse wave velocity and forward pressure wave amplitude, in a pooled sample of the Framingham Original, Offspring, and minority Omni cohorts (mean age, 62 years; 56% women). Abnormal stiffness of each measure was defined as a value exceeding the sex-specific 90th percentile of a reference group with a low burden of conventional cardiovascular disease risk factors. Applying this criterion to the entire sample identified a 24% to 33% prevalence of abnormal stiffness measures. The prevalence of abnormal stiffness increased markedly with age, eg, for pulse wave velocity, from a few percent in both sexes aged <50 years to 64% (men) to 74% (women) in those aged ≥70 years. With adjustment for age, important correlates of abnormal aortic stiffness included higher mean arterial pressure, greater body mass index, impaired glucose metabolism, and abnormal lipids. Correlates of aortic stiffness were similar if we used age-specific rather than fixed criteria for defining abnormal stiffness. Conclusions— The prevalence of abnormal aortic stiffness increases steeply with advancing age in the community, especially in the presence of obesity or diabetes. Our data suggest that the burden of disease attributable to aortic stiffness is likely to increase considerably over the next few years as the population ages.