Abigail May Khan

Cardiac Natriuretic Peptides, Obesity, and Insulin Resistance: Evidence from Two Community-Based Studies

BACKGROUND The natriuretic peptides play an important role in salt homeostasis and blood pressure regulation. It has been suggested that obesity promotes a relative natriuretic peptide deficiency, but this has been a variable finding in prior studies and the cause is unknown. AIM The aim of this study was to examine the association between obesity and natriuretic peptide levels and evaluate the role of hyperinsulinemia and testosterone as mediators of this interaction. METHODS We studied 7770 individuals from the Framingham Heart Study (n = 3833, 54% women) and the Malmö Diet and Cancer study (n = 3918, 60% women). We examined the relation of plasma N-terminal pro-B-type natriuretic peptide levels (N-BNP) with obesity, insulin resistance, and various metabolic subtypes. RESULTS Obesity was associated with 6-20% lower levels of N-BNP (P < 0.001 in Framingham, P = 0.001 in Malmö), whereas insulin resistance was associated with 10-30% lower levels of N-BNP (P < 0.001 in both cohorts). Individuals with obesity who were insulin sensitive had only modest reductions in N-BNP compared with nonobese, insulin-sensitive individuals. On the other hand, individuals who were nonobese but insulin resistant had 26% lower N-BNP in Framingham (P < 0.001) and 10% lower N-BNP in Malmö (P < 0.001), compared with nonobese and insulin-sensitive individuals. Adjustment for serum-free testosterone did not alter these associations. CONCLUSIONS In both nonobese and obese individuals, insulin resistance is associated with lower natriuretic peptide levels. The relative natriuretic peptide deficiency seen in obesity could be partly attributable to insulin resistance, and could be one mechanism by which insulin resistance promotes hypertension.

Low Serum Magnesium and the Development of Atrial Fibrillation in the Community The Framingham Heart Study

Background— Low serum magnesium has been linked to increased risk of atrial fibrillation (AF) after cardiac surgery. It is unknown whether hypomagnesemia predisposes to AF in the community. Methods and Results— We studied 3530 participants (mean age, 44 years; 52% women) from the Framingham Offspring Study who attended a routine examination and were free of AF and cardiovascular disease. We used Cox proportional hazard regression analysis to examine the association between serum magnesium at baseline and risk of incident AF. Analyses were adjusted for conventional AF risk factors, use of antihypertensive medications, and serum potassium. During up to 20 years of follow-up, 228 participants developed AF. Mean serum magnesium was 1.88 mg/dL. The age- and sex-adjusted incidence rate of AF was 9.4 per 1000 person-years (95% confidence interval, 6.7–11.9) in the lowest quartile of serum magnesium (⩽1.77 mg/dL) compared with 6.3 per 1000 person-years (95% confidence interval, 4.1–8.4) in the highest quartile (≥1.99 mg/dL). In multivariable-adjusted models, individuals in the lowest quartile of serum magnesium were ~50% more likely to develop AF (adjusted hazard ratio, 1.52; 95% confidence interval, 1.00–2.31; P=0.05) compared with those in the upper quartiles. Results were similar after the exclusion of individuals on diuretics. Conclusions— Low serum magnesium is moderately associated with the development of AF in individuals without cardiovascular disease. Because hypomagnesemia is common in the general population, a link with AF may have potential clinical implications. Further studies are warranted to confirm our findings and to elucidate the underlying mechanisms.

Ventricular-Arterial Coupling, Remodeling, and Prognosis in Chronic Heart Failure

OBJECTIVES The objective of this study was to compare the physiological determinants of ejection fraction (EF)-ventricular size, contractile function, and ventricular-arterial (VA) interaction-and their associations with clinical outcomes in chronic heart failure (HF). BACKGROUND EF is a potent predictor of HF outcomes, but represents a complex summary measure that integrates several components including left ventricular size, contractile function, and VA coupling. The relative importance of each of these parameters in determining prognosis is unknown. METHODS In 466 participants with chronic systolic HF, we derived quantitative echocardiographic measures of EF: cardiac size (end-diastolic volume [EDV]); contractile function (the end-systolic pressure volume relationship slope [Eessb] and intercept [V0]); and VA coupling (arterial elastance [Ea]/Eessb). We determined the association between these parameters and the following adverse outcomes: 1) the combined endpoint of death, cardiac transplantation, or ventricular assist device (VAD) placement; and 2) cardiac hospitalization. RESULTS Over a median follow-up of 3.4 years, there were 76 deaths, 52 transplantations, 14 VAD placements, and 684 cardiac hospitalizations. EF was independently associated with death, transplantation, and VAD placement (adjusted hazard ratio [HR]: 3.0; 95% confidence interval [CI]: 1.8 to 5.0 comparing third and first tertiles), as were EDV (HR: 2.6; 95% CI: 1.5 to 4.2); V0 (HR: 3.6; 95% CI: 2.1 to 6.1); and Ea/Eessb (HR: 2.1; 95% CI: 1.3 to 3.3). EDV, V0, and Ea/Eessb were also associated with risk of cardiac hospitalization. Eessb was not significantly associated with any adverse outcomes in adjusted analyses. CONCLUSIONS Left ventricular size, V0, and VA coupling are associated with prognosis in systolic HF, but end-systolic elastance (Eessb) is not. Assessment of VA coupling via Ea/Eessb is an additional noninvasively derived metric that can be used to gauge prognosis in human HF.

Preload Dependency of Left Ventricular Torsion: The Impact of Normal Saline Infusion

Background—Left ventricular (LV) rotation results from contraction of obliquely oriented myocardial fibers. The net difference between systolic apical counterclockwise rotation and basal clockwise rotation is left ventricular torsion (LVT). Although LVT is altered in various cardiac diseases, determinants of LVT are incompletely understood. Methods and Results—LV end-diastolic volume, LV apical and basal rotation, peak systolic LVT, and peak early diastolic untwisting rate were measured by speckle-tracking echocardiography in healthy subjects (n=8) before and after infusion of a weight-based normal saline bolus (2.1±0.3 L). Saline infusion led to a significant increase in end-diastolic LV internal diameter (45.9±3.7 versus 47.6±4.2 mm; P=0.002) and LV end-diastolic volume (90.0±21.6 versus 98.3±19.6 mL; P=0.01). Stroke volume (51.3±10.9 versus 63.0±15.5 mL; P=0.003) and cardiac output (3.4±0.8 versus 4.4±1.5 L/min; P=0.007) increased, whereas there was no change in heart rate and blood pressure. There was a significant increase in the magnitude of peak systolic apical rotation (7.5±2.4° versus 10.5±2.8°; P<0.001) but no change in basal rotation (−4.1±2.3° versus −4.8±3.1°; P=0.44). Accordingly, peak systolic LVT increased by 33% after saline infusion (11.2±1.3° versus 14.9±1.7°; P<0.001). This saline-induced increase in LVT was associated with a marked increase in peak early diastolic untwisting rate (72.3±21.4 versus 136.8±30.0 degrees/s; P<0.001). Conclusions—Peak systolic LVT and peak early diastolic untwisting rate are preload-dependent. Changes in LV preload should be considered when interpreting results of future LVT studies.Background— Left ventricular (LV) rotation results from contraction of obliquely oriented myocardial fibers. The net difference between systolic apical counterclockwise rotation and basal clockwise rotation is left ventricular torsion (LVT). Although LVT is altered in various cardiac diseases, determinants of LVT are incompletely understood. Methods and Results— LV end-diastolic volume, LV apical and basal rotation, peak systolic LVT, and peak early diastolic untwisting rate were measured by speckle-tracking echocardiography in healthy subjects (n=8) before and after infusion of a weight-based normal saline bolus (2.1±0.3 L). Saline infusion led to a significant increase in end-diastolic LV internal diameter (45.9±3.7 versus 47.6±4.2 mm; P =0.002) and LV end-diastolic volume (90.0±21.6 versus 98.3±19.6 mL; P =0.01). Stroke volume (51.3±10.9 versus 63.0±15.5 mL; P =0.003) and cardiac output (3.4±0.8 versus 4.4±1.5 L/min; P =0.007) increased, whereas there was no change in heart rate and blood pressure. There was a significant increase in the magnitude of peak systolic apical rotation (7.5±2.4° versus 10.5±2.8°; P <0.001) but no change in basal rotation (−4.1±2.3° versus −4.8±3.1°; P =0.44). Accordingly, peak systolic LVT increased by 33% after saline infusion (11.2±1.3° versus 14.9±1.7°; P <0.001). This saline-induced increase in LVT was associated with a marked increase in peak early diastolic untwisting rate (72.3±21.4 versus 136.8±30.0 degrees/s; P <0.001). Conclusions— Peak systolic LVT and peak early diastolic untwisting rate are preload-dependent. Changes in LV preload should be considered when interpreting results of future LVT studies.

Lack of association between serum magnesium and the risks of hypertension and cardiovascular disease

BACKGROUND Experimental studies have linked hypomagnesemia with the development of vascular dysfunction, hypertension, and atherosclerosis. Prior clinical studies have yielded conflicting results but were limited by the use of self-reported magnesium intake or short follow-up periods. METHODS We examined the relationship between serum magnesium concentration and incident hypertension, cardiovascular disease (CVD), and mortality in 3,531 middle-aged adult participants in the Framingham Heart Study offspring cohort. Analyses were performed using Cox proportional hazards regressions, adjusted for traditional CVD risk factors. RESULTS Follow-up was 8 years for new-onset hypertension (551 events) and 20 years for CVD (554 events). There was no association between baseline serum magnesium and the development of hypertension (multivariable-adjusted hazards ratio per 0.15 mg/dL 1.03, 95% CI 0.92-1.15, P = .61), CVD (0.83, 95% CI 0.49-1.40, P = .49), or all-cause mortality (0.77, 95% CI 0.41-1.45, P = .42). Similar findings were observed in categorical analyses, in which serum magnesium was modeled in categories (<1.5, 1.5-2.2, >2.2 mg/dL) or in quartiles. CONCLUSIONS In conclusion, data from this large, community-based cohort do not support the hypothesis that low serum magnesium is a risk factor for developing hypertension or CVD.

FGF-23 and the Progression of Coronary Arterial Calcification in Patients New to Dialysis

BACKGROUND AND OBJECTIVE Fibroblast growth factor 23 (FGF-23), a regulator of phosphorus metabolism, is a risk marker in CKD. FGF-23 has been associated with coronary arterial calcification (CAC), but it is not known whether FGF-23 predicts CAC progression in CKD. The aim of this study was to evaluate the association of FGF-23 with CAC progression in advanced CKD. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS FGF-23 levels and CAC were measured by electrocardiography-triggered multislice computed tomography in 99 individuals initiating dialysis. Patients were enrolled in the study from April 2008 to July 2010. CAC was calculated using Agatston and calcium volume score. Sixty-seven study participants had repeat CAC measures at 1 year. Linear regression was used to assess the association of FGF-23 with CAC. RESULTS The mean age of study participants was 50 years; 33% were women, and 64% were black. The median FGF-23 level was 1238 relative units (RU)/ml (interquartile range, 515-2218 RU/ml). According to Agatston score, FGF-23 was not associated with baseline CAC (P=0.14) but was significantly associated with CAC progression. There was a 192.3-Agatston unit change in CAC score per 1-SD change in FGF-23 (P=0.008) in models adjusting for known risk factors for CAC and serum phosphate. This association persisted after adjustment for high-sensitivity C-reactive protein, 25-OH vitamin D levels, and the use of phosphorus binders. Results were similar when change in calcium volume score was used. CONCLUSIONS In individuals with advanced CKD, serum FGF-23 is strongly associated with CAC progression. FGF-23 may be a marker of cardiovascular risk in CKD.

Effect of Weight Loss After Weight Loss Surgery on Plasma N-Terminal Pro-B-Type Natriuretic Peptide Levels

Natriuretic peptides have multiple beneficial cardiovascular effects. Previous cross-sectional studies have indicated that obese subjects have lower natriuretic peptide concentrations than those of normal weight. It is not known whether this relative natriuretic peptide deficiency is reversible with weight loss. We studied 132 obese subjects undergoing weight loss surgery with serial measurement of plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations at preoperative, early (1 to 2 months), and late postoperative (6 months) points. In addition, 20 subjects also underwent echocardiography at baseline and 6 months after surgery. Significant weight loss was observed after surgery (median body mass index 45.1, 41.0, and 32.9 kg/m(2) for the 3 corresponding points, analysis of variance p <0.001). The median NT-proBNP levels increased substantially (31.6, 66.9, and 84.9 pg/ml; p <0.001). The average intrasubject increase in NT-proBNP at the 2 postoperative points was 3.4 and 5.0 times the preoperative level (p <0.001 for both points vs preoperatively). In the multivariate regression models adjusted for clinical characteristics and insulin resistance, the strongest predictor of the change in NT-proBNP level 6 months after weight loss surgery was the change in weight (p = 0.03). Echocardiography showed a mean intrasubject reduction in left ventricular mass index of 18% (p <0.001) and mild improvements in diastolic function, with no change in ejection fraction. In conclusion, we have demonstrated that weight loss is associated with early and sustained increases in NT-proBNP concentrations, despite evidence of preserved systolic and improved diastolic function. These findings suggest a direct, reversible relation between obesity and reduced natriuretic peptide levels.

Arterial Stiffness, Central Pressures, and Incident Hospitalized Heart Failure in the Chronic Renal Insufficiency Cohort Study

Chronic kidney disease (CKD) is independently associated with an increased risk of cardiovascular disease1;2. Patients with CKD are also at an increased risk of heart failure (HF), which is a major cause of morbidity and mortality in this population 3-6. Whereas several studies have been performed regarding predictors of overall cardiovascular risk in CKD (assessed using composite cardiovascular endpoints), the predictors of HF as a specific endpoint have not been adequately characterized in subjects with CKD. Of note, composite cardiovascular endpoints usually include several atherosclerotic and non-atherosclerotic events, for which risk factors may differ. HF in CKD has been proposed to be largely independent of atherosclerotic occlusive disease and more closely related to structural myocardial disease 3. Elevated blood pressure is a well-known risk factor for HF in the general population and a candidate mechanism for increased HF risk in CKD 7. However, a recent study reported that moderate CKD increases the risk of HF even in the absence of hypertension (defined from brachial pressure measurements) or diabetes mellitus at baseline 4. Central pressure profiles have been investigated in the prediction of cardiovascular risk in patients with end-stage kidney disease 8, but the relationship between central pressures and incident HF has never been examined in earlier stages of CKD. Similarly, increased large artery stiffness has been proposed as a major contributor to HF risk in CKD 3 due to its well-known effects on left ventricular pulsatile afterload 9, which promote left ventricular hypertrophy and myocardial dysfunction. Despite these important physiologic considerations, the relationship between large artery stiffness, central pressures and incident HF in CKD has not been investigated. In this study, we aimed to evaluate the role of large artery stiffness, brachial and central blood pressure as predictors of incident hospitalized HF in the Chronic Renal Insufficiency Cohort (CRIC), a multi-ethnic multi-center prospective observational study of patients with CKD10.Background—Chronic kidney disease is associated with an increased risk of heart failure (HF). We aimed to evaluate the role of large artery stiffness, brachial, and central blood pressure as predictors of incident hospitalized HF in the Chronic Renal Insufficiency Cohort (CRIC), a multiethnic, multicenter prospective observational study of patients with chronic kidney disease. Methods and Results—We studied 2602 participants who were free of HF at baseline. Carotid-femoral pulse wave velocity (CF-PWV; the gold standard index of large artery stiffness), brachial, and central pressures (estimated via radial tonometry and a generalized transfer function) were assessed at baseline. Participants were prospectively followed up to assess the development of new-onset hospitalized HF. During 3.5 years of follow-up, 154 participants had a first hospital admission for HF. CF-PWV was a significant independent predictor of incident hospitalized HF. When compared with the lowest tertile, the hazard ratios among subjects in the middle and top CF-PWV tertiles were 2.33 (95% confidence interval, 1.37–3.97; P=0.002) and 5.24 (95% confidence interval, 3.22–8.53; P<0.0001), respectively. After adjustment for multiple confounders, the hazard ratios for the middle and top CF-PWV tertiles were 1.95 (95% confidence interval, 0.92–4.13; P=0.079) and 3.01 (95% confidence interval, 1.45–6.26; P=0.003), respectively. Brachial systolic and pulse pressure were also independently associated with incident hospitalized HF, whereas central pressures were less consistently associated with this end point. The association between CF-PWV and incident HF persisted after adjustment for systolic blood pressure. Conclusions—Large artery stiffness is an independent predictor of incident HF in chronic kidney disease, an association with strong biological plausibility given the known effects of large artery stiffening of left ventricular pulsatile load.

Strain improves risk prediction beyond ejection fraction in chronic systolic heart failure.

Background The utility of longitudinal, circumferential, and radial strain and strain rate in determining prognosis in chronic heart failure is not well established. Methods and Results In 416 patients with chronic systolic heart failure, we performed speckle‐tracking analyses of left ventricular longitudinal, circumferential, and radial strain and strain rate on archived echocardiography images (30 frames per second). Cox regression models were used to determine the associations between strain and strain rate and risk of all‐cause mortality, cardiac transplantation, and ventricular‐assist device placement. The area under the time‐dependent ROC curve (AUC) was also calculated at 1 year and 5 years. Over a maximum follow‐up of 8.9 years, there were 138 events (33.2%). In unadjusted models, all strain and strain rate parameters were associated with adverse outcomes (P<0.001). In multivariable models, all parameters with the exception of radial strain rate (P=0.11) remained independently associated, with patients in the lowest tertile of strain or strain rate parameter having a ≈2‐fold increased risk of adverse outcomes compared with the reference group (P<0.05). Addition of strain to ejection fraction (EF) led to a significantly improved AUC at 1 year (0.697 versus 0.633, P=0.032) and 5 years (0.700 versus 0.638, P=0.001). In contrast, strain rate did not provide incremental prognostic value to EF alone. Conclusions Longitudinal and circumferential strain and strain rate, and radial strain are associated with chronic heart failure prognosis. Strain provides incremental value to EF in the prediction of adverse outcomes, and with additional study may be a clinically relevant prognostic tool.

Weight Loss, Saline Loading, and the Natriuretic Peptide System

Background In epidemiologic studies, obesity has been associated with reduced natriuretic peptide (NP) concentrations. Reduced NP production could impair the ability of obese individuals to respond to salt loads, increasing the risk of hypertension and other disorders. We hypothesized that weight loss enhances NP production before and after salt loading. Methods and Results We enrolled 15 obese individuals (mean BMI 45±5.4 kg/m2) undergoing gastric bypass surgery. Before and 6 months after surgery, subjects were admitted to the clinical research center and administered a large‐volume intravenous saline challenge. Echocardiography and serial blood sampling were performed. From the pre‐operative visit to 6 months after surgery, subjects had a mean BMI decrease of 27%. At the 6‐month visit, N‐terminal pro‐atrial NP (Nt‐proANP) levels were 40% higher before, during, and after the saline infusion, compared with levels measured at the same time points during the pre‐operative visit (P<0.001). The rise in Nt‐pro‐ANP induced by the saline infusion (≈50%) was similar both before and after surgery (saline, P<0.001; interaction, P=0.2). Similar results were obtained for BNP and Nt‐proBNP; resting concentrations increased by 50% and 31%, respectively, after gastric bypass surgery. The increase in NP concentrations after surgery was accompanied by significant decreases in mean arterial pressure (P=0.004) and heart rate (P<0.001), and an increase in mitral annular diastolic velocity (P=0.02). Conclusion In obese individuals, weight loss is associated with a substantial increase in the “setpoint” of circulating NP concentrations. Higher NP concentrations could contribute to an enhanced ability to handle salt loads after weight loss.