Association of Estimated Sodium Intake With Adverse Cardiac Structure and Function: From the HyperGEN Study

Abstract

Background: The optimal level of sodium intake remains controversial.

Objectives: This study sought to determine whether examination of left ventricular longitudinal strain (LS), circumferential strain, and e' velocity can provide insight into thresholds for the detrimental effects of estimated sodium intake (ESI) on subclinical cardiovascular disease.

Methods: We performed speckle-tracking analysis on HyperGEN (Hypertension Genetic Epidemiology Network) study echocardiograms with available urinary sodium data (N = 2,996). We evaluated the associations among ESI and LS, circumferential strain, and e' velocity using multivariable-adjusted linear mixed-effects models (to account for relatedness among subjects) with linear splines (spline 1: ESI ≤3.7 g/day, spline 2: ESI >3.7 g/day based on visual inspection of fractional polynomial plots of the association between ESI and indices of strain and e' velocity). We performed mediation analysis to understand the indirect effects of systolic blood pressure and serum aldosterone on the relationship between ESI and strain and e' velocity.

Results: Mean age of participants was 49 ± 14 years, 57% were female, 50% were African American, and 54% had hypertension. The median ESI was 3.73 (interquartile range: 3.24, 4.25) g/day. ESI >3.7 g/day was associated with larger left atrial and left ventricular dimensions (p < 0.05). After adjusting for speckle-tracking analyst, image quality, study site, age, sex, smoking status, alcohol use, daily blocks walked, diuretic use, estimated glomerular filtration rate, left ventricular mass, ejection fraction, and wall motion score index, ESI >3.7 g/day was associated with both strain parameters and e' velocity (p < 0.05 for all comparisons), but ESI ≤3.7 g/day was not (p > 0.05 for all comparisons). There were significant interactions by potassium excretion for circumferential strain. Mediation analysis suggested that systolic blood pressure explained 14% and 20% of the indirect effects between ESI and LS and e' velocity, respectively, whereas serum aldosterone explained 19% of the indirect effects between ESI and LS.

Conclusions: ESI >3.7 g/day is associated with adverse cardiac remodeling and worse systolic strain and diastolic e' velocity.

Keywords: echocardiography; sodium intake; strain; urinary sodium.

Figure 1. Unadjusted fractional polynomial plots of estimated urinary sodium excretion and strain, e′ velocity, and E/e′ ratio

(A) longitudinal strain, (B) circumferential strain, (C) early diastolic (e′) velocity, and (D) E/e′ ratio. A reference line is drawn at an estimated sodium intake value of 3.7 g/day. The 95% confidence intervals are noted by dashed lines. Plots are shown for the unadjusted relationship. Note: Tissue velocity values derived from speckle-tracking software are lower than values derived from tissue Doppler imaging. Thus, e′ is lower and E/e′ is higher in the present study compared to other studies that use conventional tissue Doppler imaging to measure tissue velocities.

Central Illustration. Urinary Sodium and Cardiac Mechanics: Estimated Sodium Intake and Adverse Cardiac Structure and Function as well as heart failure

Increased sodium intake has been associated with cardiac fibrosis, endothelial dysfunction, and arterial stiffness, which can lead to systemic hypertension. Together, these derangements may lead to adverse myocardial strain and e′ velocity as detected by speckle-tracking echocardiography in our study. In addition, increased sodium intake increases fluid retention, and when coupled with adverse strain and e′ velocity, may predispose individuals to heart failure.