Résumé
The dynamics of systolic and diastolic strains and torsional mechanics of the left ventricle (LV) and their relation to diastolic filling never have been evaluated at various exercise intensities.
Speckle tracking echocardiography was performed in 20 healthy sedentary subjects at rest and during a progressive submaximal exercise test at 20%, 30%, and 40% of maximal aerobic power. LV twist increased progressively with exercise intensity (10.5 ± 3.2 to 15.8 ± 4.5°; P<0.001), whereas longitudinal strain remained unchanged after the first workload, underlining the key role of torsional reserve in systolic-diastolic coupling during exercise. The increase in diastolic untwisting (-88.7 ± 34.2 to -182.9 ± 53.5 deg · s(-1); P<0.01) was correlated to enhanced systolic twist (R=0.61; P<0.001), and its magnitude of increase was significantly higher compared to diastolic longitudinal and circumferential strain rates (119 ± 64% versus 65 ± 44% and 57 ± 24%, respectively), emphasizing its contribution to diastolic filling. The timing of peak untwisting and the chronology of diastolic mechanical events were unchanged during effort. Untwisting was driven mainly by apical rotation and determined mitral opening and isovolumic relaxation time (R=0.47 and 0.61, respectively; P<0.001), whereas basal rotation and longitudinal and circumferential diastolic strain rates were major determinants of increased early diastolic filling (R=0.64, 0.79, and 0.81, respectively; P<0.001).
The use of speckle tracking echocardiography gives new insights into physiological adaptive LV mechanics during incremental exercise in healthy subjects, underlining the key role of torsional mechanics. It might be useful to better understand the mechanisms of diastolic dysfunction and exercise intolerance in various pathological conditions.