Left ventricular torsion, energetics, and diastolic function in normal human aging

Abstract

This study determined, for the first time, whether the effects of normal aging on systolic and diastolic left ventricular function in subjects without cardiovascular disease are related to underlying energetic defects. Cardiac magnetic resonance imaging with tissue tagging and (31)P spectroscopy was used to determine global structure, function, myocardial strains, and the phosphocreatine-to-ATP ratio (PCr/ATP) in 49 healthy subjects aged 20-69 yr. The three major abnormalities that developed with increasing age were the early filling percentage (EFP, the left ventricular volume increase from end systole to mid-diastole divided by stroke volume × 100), which decreased with age, indicating impaired early diastolic filling (r = -0.72, P < 0.0001), the torsion-to-shortening ratio (TSR, measure of subepicardial torsion exerting mechanical advantage over subendocardial shortening), which increased with age indicating relative subendocardial dysfunction (r = 0.44, P < 0.02), and the PCr/ATP (decreased with increasing age, r = -0.52, P < 0.003). EFP and TSR were strongly correlated (r = -0.63, P < 0.0001), although they were not related to PCr/ATP [EFP vs. PCr/ATP: r = 0.34, not significant (NS) and TSR vs. PCr/ATP: r = -0.3, P = NS]. In normal aging, changes in EFP and TSR likely share the same pathophysiology, although it is unlikely that energetics have a major role in the functional effects of aging.

Figures

Fig. 1.

A: cardiac cine imaging (top) and cardiac tagging (bottom) at diastole (left) and systole (right), showing how a rectangular grid of nulled signal applied at diastole remains with the tissue through the cardiac cycle, allowing calculation of strain and torsion. B: tagging in two parallel sections allows the calculation of the torsion (the longitudinal-circumferential shear angle γ) between two short-axis planes a distance d apart with radius r where one short-axis plane rotates through Δϕ relative to the other. γ = tan−1{[2r sin(Δϕ/2)]/d}.

Fig. 2.

Key cardiac parameters plotted against subject age. A: early filling percentage, representing the percentage of stroke volume due to ventricular relaxation. B: cardiac energetics represented by the ratio of phosphocreatine to ATP (PCr/ATP ratio). C: cardiac wall motion represented by the torsion-to-shortening ratio. rad, Radians.

Fig. 3.

Sample cardiac phosphorus spectra from a young subject (with PCr/ATP = 1.95, A) and an older subject (with PCr/ATP = 1.55, B). A difference in PCr concentration is seen. The spectra are presented as acquired before correction for saturation due to heart rate, flip angle experienced at the cardiac tissue, and blood content. 2,3-DPG, 2,3-diphosphoglycerate; ppm, parts/million; PDE, phosphodiesters.