Abstract 552: How Twisted is the Left Ventricle?
Background: Conventional twist (RTwist) is calculated relative to end-diastolic (ED) LV configuration. The degree of diastolic untwisting may depend on the ED pressure. Hence, peak RTwist may not reflect how twisted the systolic LV configuration is. By calculating absolute twist (ATwist) relative to a fixed LV configuration we investigated the preload dependent untwisting of LV. We further investigated the influence of preload on peak RTwist and ATwist.
Methods: In 8 anesthetized dogs we assessed ED LV pressure (LVEDP) and measured LV twist by sonomicrometry which allowed assessment of twist relative to a fixed LV configuration. Both ED and peak ATwist was calculated relative to this configuration at baseline, during volume loading and caval constriction.
Results: Changes in LVEDP from 7.9 ± 1.1 (±SD) at baseline to 14.2±2.9 and 1.4±1.5 mmHg (both P<0.01) during volume loading and caval constriction, respectively, were associated with an increase in ED ATwist to 3.4±2.1 and a decrease to −4.4±1.5° (both P<0.01), during loading and caval constriction, respectively. A close correlation was observed between LVEDP and ED ATwist (R=0.90, P<0.01, Fig 1⇓). Peak ATwist demonstrated a positive correlation (R=0.61, P<0.01, Fig 2a⇓), whereas peak RTwist showed a negative correlation to LVEDP (R=0.61, P<0.01, Fig 2b⇓), indicating that peak RTwist and ATwist respond oppositely to preload.
Conclusion: The present study indicates that the absolute ED twist configuration is determined by preload. Hence, conventional twist does not reflect how twisted the LV really is. In our model conventional twist underestimated peak twist during caval constriction and overestimated it during loading.