Left ventricular functional, structural and energetic effects of normal aging: Comparison with hypertension

Abstract

Objectives: Both aging and hypertension are significant risk factors for heart failure in the elderly. The purpose of this study was to determine how aging, with and without hypertension, affects left ventricular function.

Methods: Cross-sectional study of magnetic resonance imaging and 31P spectroscopy-based measurements of left ventricular structure, global function, strains, pulse wave velocity, high energy phosphate metabolism in 48 normal subjects and 40 treated hypertensive patients (though no other cardiovascular disease or diabetes) stratified into 3 age deciles from 50-79 years.

Results: Normal aging was associated with significant increases in systolic blood pressure, vascular stiffness, torsion, and impaired diastolic function (all P<0.05). Age-matched hypertension exacerbated the effects of aging on systolic pressure, and diastolic function. Hypertension alone, and not aging, was associated with increased left ventricular mass index, reduced energetic reserve, reduced longitudinal shortening and increased endocardial circumferential shortening (all P<0.05). Multiple linear regression analysis showed that these unique hypertensive features were significantly related to systolic blood pressure (P<0.05).

Conclusions: 1) Hypertension adds to the age-related changes in systolic blood pressure and diastolic function; 2) hypertension is uniquely associated with changes in several aspects of left ventricular structure, function, systolic strains, and energetics; and 3) these uniquely hypertensive-associated parameters are related to the level of systolic blood pressure and so are potentially modifiable.

Fig 1. Healthy young: Illustration of epicardial torsion and endocardial circumferential shortening used in the calculation of the torsion to shortening ratio (TSR) and relationship to subepicardial and subendocardial fiber orientations.

Epicardium is red and endocardium blue. A. Obliquely oriented subepicardial fibers produce rotation of the apex with respect to the base (B.) in a counterclockwise direction when looking from the apex to base, which is quantified in terms of the circumferential-longitudinal shear angle (C.). Epicardial torsion acts on the subendocardium with its greater mechanical advantage due to its larger radius, forcing subendocardial fiber bundles to shorten in a direction at almost 90° away from the subendocardial fiber direction (in the circumferential plane) (D.). This subepicardial to subendocardial interaction is quantified as the torsion to shortening ratio (TSR), and an increase in the TSR suggests reduced subepicardial influence over the subendocardium. Healthy aging: Rotational angle E and torsional angle F are increased compared to healthy young, there is no change in endocardial circumferential shortening and so the TSR is increased indicating reduced interactions between subepicardium and subendocardium. Hypertension: Rotational and torsional angles are unchanged compared to healthy young (angle G), though there is increased endocardial circumferential shortening (thick blue arrows, shortening H) indicating increased interaction between the subepicardium and subendocardium and therefore TSR is decreased.

Fig 2

Scatter plots of the effects of aging on A. systolic blood pressure, B. early filling percentage (measure of diastolic function), C. left ventricular mass index, D. endocardial circumferential (endo. circ.) shortening, E. longitudinal shortening and F. PCr/ATP ratio. Both aging and hypertension are associated with significant effects on A and B (linear regression slope increases in both groups and shifted parallel in hypertension), however for C-F there is no significant relationship of aging. Normal subjects are in blue and hypertensive patients in red.

Fig 3

Scatter plots of A. left ventricular (LV) mass index, B. endocardial circumferential (endo. circ.) shortening, C. longitudinal shortening and D. PCr/ATP ratio versus systolic pressure with univariate linear regression analysis. Normal subjects are in blue and hypertensive patients in red. The regression line refers to the combined cohort.

Fig 4. Summary results figure.

Both aging and hypertension are associated with unique effects, and additive effects are shown in the overlapping center. In particular, systolic blood pressure has a significant relationship to left ventricular mass index, longitudinal shortening, endocardial circumferential shortening, and the PCr/ATP ratio (highlighted with ‘*’) suggesting that these effects are potentially modifiable. Abbreviations as in Tables 2 and 3.