Page 47 - The role of advanced echocardiography in patients with ischemic heart disease - Rachid Abou

DISCUSSION
While data on global LV longitudinal strain are accumulating in healthy volunteers and
individuals without structural or functional heart disease, data on level- and layer- 2 specific longitudinal strain are scarce.2,3,10 A recent meta-analysis of 24 studies totalling
2,597 individuals without structural heart disease (mean age 47 ± 11 years, 51% men)
reported that the normal values of global LV longitudinal strain ranged from –15.9% to
–22.1%.11 Clinical characteristics of the included individuals and the vendor-specific
software used to analyse longitudinal strain may explain the disparate values of global
LV longitudinal strain. In the present study, the mean value of global LV longitudinal
strain for the overall population was -18.9% and did not differ significantly across the
different age categories.
In terms of level-specific LV longitudinal strain, previous studies have shown a gradient in longitudinal strain from the base to the apex, showing the basal segments a smaller magnitude of longitudinal strain as compared with the apical segments.2,3,12 During systole, wall stress decreases towards the apex due to smaller circumferential radius of curvature which leads to higher magnitude of longitudinal strain in the apex compared with the base.13 Furthermore, this gradient can be also explained by the different composition of the myocardium with more cross-fiber shortening in the apex compared with the LV base.13 However, changes in the gradient across different age categories in a real-world ageing population have not been studied so far. The present study shows that the gradient in longitudinal strain from base to apex is kept constant across the age categories. Interestingly, aging was associated with a borderline significant decline in LV longitudinal strain magnitude in the basal segments and significant enhancement of longitudinal strain magnitude in apical segments. Aging is known to be associated with fibrotic remodeling of the LV while having preserved function and contractility.14 The increase of interstitial fibrosis and LV mass leads to increased stiffness of the LV myocardium and impaired diastolic relaxation as demonstrated in our study. To maintain low LV filling pressures, the LV shows an increase of the longitudinal strain in the apical segments during systole as a compensatory mechanism.15
To further explore the effect of aging on LV mechanics, the present study evaluated the layer-specific longitudinal strain (from endocardium to epicardium). The larger magnitude of longitudinal strain in the endocardium compared with the epicardium can be explained by the larger end-diastolic wall stress in the endocardium which leads to larger fiber stretch at end-diastole and larger shortening during systole.13 Layer- specific longitudinal strain analysis is increasingly being used in the detection of global
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