Longitudinal and Circumferential Strain.
Concerning the shortening, and thickening in the circumferential, longitudinal, or radial dimensions, it is not addressed what it means or why this deformation occurs, which is linked to its helical morphology. Longitudinal strain reflects downward displacement of the AL fibers to generate the normal ejection fraction on average of 60%. (Figure 1: 3 DS-AS) In contrast, short-axis shortening arises from predominantly circumferential fiber deformation, but only a 30% ejection fraction occurs46 (Figure 1: 3 RS-LS) These changes in fiber angulation have implications because systolic contractile resistance Impaired AL develops when the ventricle becomes spherical and the AL muscle fibers lose their obliquity to a more transverse orientation. Longitudinal strain quantifies ventricular shortening and reflects the action of the DS and its sequential shortening in the base-apex direction, so ”pull-down” inferences contradict the helical dynamics of motion42.(Figure 4: 1A-C, predominance of vectors towards apical direction and endocardial direction.)
The short-axis shortening of the transverse fibers of the BL and the transverse shortening produced by subendocardial DS are two factors explaining why circumferential deformation produces ventricular compression or cardiac narrowing their contributions cannot be determined by the overlap within the free wall of the LV, the interventricular septum does not contain a circumferential envelope, so its measurement of longitudinal deformation is possible, this can be measured by recording the excursion of the mitral annulus towards the apex (MAPSE). Altered longitudinal strain is an early finding in ventricular dilatation and develops when the conical ventricular shape becomes spherical, causing the natural oblique fibers to develop a transverse configuration that disrupts their torsion capacity47. The functional validity of this concept is confirmed by the consistent return of cardiac torsion when the spherical shape of the failing heart is restored to its natural elliptical shape, as seen after properly performed ventricular restorative surgical procedures48, 49.