Myocardial Contraction during the Diastolic Isovolumetric Period: Analysis of Longitudinal Strain by Means of Speckle Tracking Echocardiography

Abstract

Background: According to the ventricular myocardial band model, the diastolic isovolumetric period is a contraction phenomenon. Our objective was to employ speckle-tracking echocardiography (STE) to analyze myocardial deformation of the left ventricle (LV) and to confirm if it supports the myocardial band model.

Methods: This was a prospective observational study in which 90 healthy volunteers were recruited. We evaluated different types of postsystolic shortening (PSS) from an LV longitudinal strain study. Duration of latest deformation (LD) was calculated as the time from the start of the QRS complex of the ECG to the latest longitudinal deformation peak in the 18 segments of the LV.

Results: The mean age of our subjects was 50.3 ± 11.1 years. PSS was observed in 48.4% of the 1620 LV segments studied (19.8%, 13.5%, and 15.1% in the basal, medial, and apical regions, respectively). PSS was more frequent in the basal, medial septal, and apical anteroseptal segments (>50%). LD peaked in the interventricular septum and in the basal segments of the LV.

Conclusions: The pattern of PSS and LD revealed by STE suggests there is contraction in the postsystolic phase of the cardiac cycle. The anatomical location of the segments in which this contraction is most frequently observed corresponds to the main path of the ascending component of the myocardial band. This contraction can be attributed to the protodiastolic untwisting of the LV.

Keywords: diastolic contraction; helical ventricular myocardial band; longitudinal strain; speckle-tracking echocardiography; ventricular torsion.

Figure 1

Morphological types of longitudinal deformation observed in healthy subjects. a: Duration of systolic deformation; b: Duration of postsystolic deformation. AVC: Aortic valve closure. PSS: Postsystolic shortening. (Referred only to the morphology, regardless of its amplitude).

Figure 2

Postsystolic shortening (PSS) (A). PSS of the medial (light blue) and basal (yellow) segments of the interventricular septum, indicated by arrows in (B) (enlarged) (C). PSS of the medial (light blue) and basal (yellow) segments of the interventricular septum, and lateral basal (red) segment, indicated by arrows in (D) (enlarged). AVC: Aortic valve closure.

Figure 3

Bull’s eye map showing the frequency of PSS (%) in the different segments.

Figure 4

Segmental sequence of the mean time to longitudinal latest deformation (LD) in the 18 segments of the LV. The segments where LD occurs earliest are in yellow, and those where the peak of deformation occurs latest are in red.

Figure 5

Frontal view. Diagram showing the behavior of the descending (green) and ascending (discontinuous purple) components of the apical loop. (1): In a telediastole, with the myocardium inactivated. (2): In a systole, electromechanical activation begins at the mid-septum and basal-lateral (asterisk), and spreads towards the apex and base, and from the endocardium to the epicardium. Contraction of the descending fibers (thick green) causes basal and apical rotation in opposite directions (twist) and longitudinal shortening of the ventricles by displacement of the base towards the apex, which results in stretching of the more epicardial ascending fibers (discontinuous purple). (3): The subsequent contraction of the ascending fibers (heavy discontinuous purple) causes longitudinal straightening and untwisting of the ventricle, coinciding with the period of isovolumetric filling. (4): Myocardial relaxation concludes during the diastole. NOTE: The basal loop, which wraps up and is stimulated simultaneously by the descending portion of the apical loop, is not represented in the graph.

Figure 6

Diagram showing the behavior of the descending (green) and ascending (discontinuous purple) components of the apical loop viewed from the apex as a complement to the previous figure. (1): In a telediastole with the myocardium inactivated; (2a): The contraction of the descending fibers (thick green) causes basal and apical rotation in opposite directions (twist), and ventricular radial thickening; (2b): At the same time, the more epicardial ascending fibers (discontinuous purple) stretch at the ends (white arrows); (3): During the subsequent period of isovolumetric filling, the contraction of the ascending fibers (thick discontinuous purple) causes the longitudinal straightening and untwisting of the ventricle while relaxation of the descending fibers (thin green) takes place; (4): Myocardial relaxation concludes during the diastole.

Figure 7

The simultaneous rotation in opposite directions of the base and the apex can be observed in the representation of the twist of a healthy adult subject obtained with EST.