title: Effects of afterload on regional left ventricular torsion.
abstract: OBJECTIVE
  To determine if left ventricular torsion, as measured by magnetic resonance tissue tagging, is afterload dependent in a canine isolated heart model in which neurohumoral responses are absent, and preload is constant.
  
  
  METHODS
  In ten isolated, blood perfused, ejecting, canine hearts, three afterloads were studied, while keeping preload constant: low afterload, high afterload (stroke volume reduced by approx. 50% of low afterload), and isovolumic loading (infinite afterload).
  
  
  RESULTS
  There were significant effects of afterload on both torsion (P < 0.05) and circumferential shortening (P < 0.0005). Between low and high afterloads, at the anterior region of the endocardium only, where torsion was maximal, there was a significant reduction in torsion (15.1 +/- 2.2 degrees to 7.8 +/- 1.8 degrees, P < 0.05). Between high afterload and isovolumic loading there was no significant change in torsion (7.8 +/- 1.8 degrees to 6.2 +/- 1.5 degrees, P = NS). Circumferential shortening at the anterior endocardium was significantly reduced both between low and high afterload (-0.19 +/- 0.02 to -0.11 +/- 0.02, P < 0.0005), and also between high afterload and isovolumic loading (-0.11 +/- 0.02 to 0.00 +/- 0.02, P < 0.05). Plots of strains with respect to end-systolic volume demonstrated a reduction in both torsion and shortening with afterload-induced increases in end-systolic volume. Torsion, but not circumferential shortening, persisted at isovolumic loading.
  
  
  CONCLUSIONS
  Maximal regional torsion of the left ventricle is afterload dependent. The afterload response of torsion appears related to the effects of afterload on end-systolic volume.
authors: Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, MD 21224, USA.
authors: G A
authors: GA
authors: MacGowan
authors: D
authors: D
authors: Burkhoff
authors: W J
authors: WJ
authors: Rogers
authors: D
authors: D
authors: Salvador
authors: H
authors: H
authors: Azhari
authors: P S
authors: PS
authors: Hees
authors: J L
authors: JL
authors: Zweier
authors: H R
authors: HR
authors: Halperin
authors: C O
authors: CO
authors: Siu
authors: J A
authors: JA
authors: Lima
authors: J L
authors: JL
authors: Weiss
authors: E P
authors: EP
authors: Shapiro
mesh_terms: D000818:Animals; D003201:Computers; D004285:Dogs; D006321:Heart / Q000033:anatomy & histology / Q000502:physiology*; D006352:Heart Ventricles; D008279:Magnetic Resonance Imaging; D008955:Models, Cardiovascular; D010477:Perfusion; D013318:Stroke Volume / Q000502:physiology*; D014102:Torsion Abnormality