P1538 Light exercise may induce an increase in the propagation velocity of naturally occurring shear waves

Abstract

Abstract Background Shear waves (SW) are induced in the myocardium by the closure of the valves. Recent studies show variations in their propagation velocity with age, gender or pathology. However, these valve-induced waves occur during relaxation and contraction. This means that the instantaneous SW velocity, as measure for stiffness, might not only depend on the intrinsic elastic properties of the relaxed myocardium, but also on its contractility and the exact moment of valve closure. The latter can change with heart rate and loading conditions, which could induce variance in measurement. Purpose This study aimed to investigate the effect of light exercise on the propagation velocity of naturally occurring shear waves. Methods Ten healthy volunteers underwent high frame rate (over 500 Hz) color TDI studies at rest and during light physiological stress (handgrip exercise). Shear wave velocities were averaged over several heart beats. Values obtained were compared by using the Wilcoxon signed ranks test and a Bland-Altman analysis. Results The light physiological exercise test induced a small but statistically significant rise in diastolic blood pressure and heart rate (table). The shear wave velocity after aortic valve closure (ASW) could be quantified in each subject at rest and during stress. The shear wave tracking after mitral valve closure (MSW) was only feasible for 8 subjects at rest and 6 during stress. There was an average difference of 0.4 ± 0.3 m/s (LOA= -0.18 to 0.97 m/s) between stress and rest measurements for the ASW velocity, which was statistically significant(p = 0.01, Figure). For the MSW the average difference was 0.02 ± 0.5 m/s (LOA= -1.02 to 1.06 m/s), p = 0.9. Conclusion We observed a statistically significant rise in the shear wave velocity after aortic valve closure but not after mitral closure during a light exercise. Although the statistical power of this study is relatively small, the results may suggest that naturally occurring shear waves velocity can be influenced by heart rate and loading conditions. Table Parameter Rest Stress P Age [yr] 30 ± 6 - - BMI [kg/m2] 22 ± 2 - - Heartrate [bpm] 62 ± 7 67 ± 8 <0.01 Systolic blood pressure [mmHg] 106 ± 13 110 ± 10 0.08 Diastolic blood pressure [mmHg] 62 ± 9 67 ± 9 0.01 Aortic shear wave velocity [m/s] 3.26 ± 0.4 3.65 ± 0.7 0.01 Mitral shear wave velocity [m/s] 4.56 ± 0.7 4.83 ± 0.8 0.9 Abstract P1538 Figure