The relative impact of circumferential and longitudinal shortening on left ventricular ejection fraction and stroke volume

Abstract

In vivo data have been unable to provide conclusive results with regard to the relative impact of circumferential and longitudinal shortening on stroke volume. The objective of the present study was to assess the relative contribution of circumferential and longitudinal myocardial shortening to left ventricular stroke volume and ejection fraction, and to evaluate the effect of left ventricular hypertrophy. A two-shell, three-dimensional mathematical model was used to assess the individual contributions of longitudinal and midwall circumferential shortening (or strain) to stroke volume and ejection fraction. Reducing either circumferential or longitudinal shortening resulted in a reduced ejection fraction and stroke volume. The stroke volume fell by 43% when circumferential strain was reduced from -20% to -5%, but only by 19% when longitudinal strain was similarly reduced. The sole contribution of circumferential and longitudinal shortening to stroke volume was 67% and 33%, respectively. These proportions were independent of wall thickness. The present study demonstrated that both longitudinal and midwall circumferential shortening contribute to different extents depending on the degree of abnormality of myocardial shortening. Contrary to most previous studies, the present study shows that circumferential shortening has a relatively greater contribution to stroke volume (ie, two-thirds) and ejection fraction than longitudinal shortening. These observations have important clinical and research implications in the assessment of left ventricular function.

Keywords: Ejection fraction; Mathematical modelling; Myocardial mechanics; Myocardial strain; Stroke volume.

Figure 1)

Left ventricular contraction. Figure represents diastole (external dashed lines) and systole (shaded figure). Stroke volume is determined from the difference in internal end-diastolic and end-systolic volumes. It is also determined by the change in total external volume assuming the myocardium is incompressible. Therefore, the stroke volume is the sum of the volume of atrioventricular displacement (red arrows) and is disc shaped. In addition, there is a smaller contribution from external epicardial displacement (blue arrow heads) and is approximately cylindrically shaped). Note that epicardial fractional shortening is less than midwall fractional shortening and midwall fractional shortening is less than endocardial fractional shortening (green arrows)

Figure 2)

Effect of myocardial shortening (peak systolic strain) and left ventricular end-diastolic wall thickness on ejection fraction. The ejection fraction increases with increasing left ventricular end-diastolic wall thickness. Worsening longitudinal strain leads to a reduction in ejection fraction. Reducing circumferential strain results in a relatively greater fall in ejection fraction compared with longitudinal strain. A Effect of peak systolic longitudinal strain on ejection fraction (midwall circumferential strain normal). B Effect of peak systolic midwall circumferential strain on ejection fraction (longitudinal strain normal)

Figure 3)

Effects of peak systolic strain on stroke volume. Stroke volume remains constant as end-diastolic wall thickness increases. Reducing longitudinal strain resulted in a fall in stroke volume. A relatively greater reduction in stroke volume occurs when midwall circumferential strain is reduced compared with longitudinal strain. A Effect of reducing peak systolic longitudinal strain on stroke volume. B Effect of reduction in peak systolic mid-wall circumferential strain on stroke volume

Figure 4)

Effects of peak systolic strain on ejection fraction. Ejection fraction falls with reducing strain. Reducing longitudinal strain resulted in a fall in ejection fraction. A relatively greater reduction in ejection fraction occurs when midwall circumferential strain is reduced compared with longitudinal strain. A Effects of altering longitudinal and circumferential peak systolic strain on ejection fraction (normal wall thickness). B Effect of altering longitudinal and circumferential peak systolic strain on stroke volume (normal wall thickness)

Figure 5)

Effect of altering longitudinal and midwall circumferential peak systolic strain on the percentage reduction in stroke volume (normal wall thickness). Reducing circumferential strain results in a greater percentage reduction in stroke volume than longitudinal strain

Figure 6)

Effect of strain on endocardial, midwall and epicardial fractional shortening (normal wall thickness). Note longitudinal and midwall strains are the same and midwall fractional shortening is identical to circumferential strain. As strain increases, endocardial fractional shortening rises to a greater extent than epicardial fractional shortening (see Table 1 for clinical trial results)

Figure 7)

Association of circumferential and longitudinal strain using speckle tracking. AS Aortic stenosis; cLVH Concentric left ventricular hypertrophy; HFPEF Heart failure with a preserved ejection fraction; HFREF Heart failure with a reduced ejection fraction. Plot derived from data presented in Table 2