Abstract 2546: Mechanism of Left Ventricular Untwist Rate: Is it All About End-Systolic Volume?
Background: Left ventricular diastolic untwist may account for diastolic suction. The mechanisms of diastolic untwist, however, are not well defined. This study investigates the relationship between diastolic untwist rate (UTR) and contractility, loading conditions and myocardial ischemia, respectively.
Methods: In 9 anesthetized dogs with micromanometers we measured LV twist by sonomicrometry as the difference between apical and basal rotation, and twist rate as the time derivate of twist. In addition we measured apical rotation and rotation rate by speckle tracking echocardiography (STE). LV volume was measured by sonomicrometry. Measurements were done during different loading conditions, increased contractility by dobutamine, and during LAD occlusion.
Results: Volume loading increased UTR and end-systolic volume (ESV) from 67 ± 7 (SEM) and 43 ± 3 to 92 ± 10 °/s (P<0.05) and 45 ± 3 ml (P<0.05), respectively. Dobutamine increased UTR to 132 ±13 °/s (P<0.01), and decreased ESV to 38 ± 2 ml (P<0.01), whereas LAD occlusion decreased UTR to 55 ± 5 °/s (P<0.05) and increased ESV to 57 ± 4 ml (P<0.01). Importantly, at comparable ESV levels measurements during dobutamine showed essentially similar UTR as during baseline and volume loading. Furthermore, there was no reduction of UTR during ischemia at comparable ESV levels before ischemia. Similar results were observed for apical rotation by STE.
Conclusions: Changes in diastolic untwist rate during changes in contractility and ischemia were attributed to accompanying changes in end-systolic volume. These results support that diastolic untwist is caused by restoring forces which are determined by LV end-systolic dimension.