title: Effect of physiological mechanical perturbations on intact human myocardial repolarization.
abstract: OBJECTIVE
  The objective of this study was to investigate the relationship between acute decreases in right ventricular volume during Valsalva strain (with resultant changes in autonomic neural tone) and measures of local endocardial repolarization time independent of heart rate and autonomic neural tone.
  
  
  METHODS
  Patients implanted with a stimulus to T wave (Stim-T) sensing pacemaker specially adapted to output a validate measure of beat to beat local repolarization (n = 9) performed Valsalva manoeuvers (40 mmHg for 15 s) while paced at a cycle length of 500 ms. Stim-T intervals were measured before and after autonomic blockade (Block: 0.03 mg/kg i.v. atropine +/- 0.15 mg/kg propranolol). Right ventricular end diastolic volume was estimated by simultaneous 2D-echocardiography.
  
  
  RESULTS
  Without autonomic blockade, compared to baseline, repolarization significantly prolonged during Valsalva strain (1.1 +/- 0.7%) and shortened during release (-1.4 +/- 1.0%). After block, strain related repolarization prolongation was also observed (1.0 +/- 0.6%), with significantly less release related repolarization shortening (-0.8 +/- 0.8%) compared to pre-block (P < 0.05). Right ventricular end diastolic volume decreased during strain by 11 +/- 10 and 9 +/- 16% from baseline, pre- and post-block respectively (P < 0.05).
  
  
  CONCLUSIONS
  In a chronically instrumented human model, an acute physiologic volume reduction modestly prolongs right ventricular repolarization independent of changes in rate or autonomic tone.
authors.affiliation: Division of Cardiology, St. Michael's Hospital, University of Toronto, Ontario, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Nanthakumar
authors.forename: P
authors.initials: P
authors.lastname: Dorian
authors.forename: M
authors.initials: M
authors.lastname: Paquette
authors.forename: S
authors.initials: S
authors.lastname: Hutchison
authors.forename: J
authors.initials: J
authors.lastname: Andrews
authors.forename: D
authors.initials: D
authors.lastname: Newman
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000368:Aged; D001285:Atropine; D001337:Autonomic Agents; D002304:Cardiac Pacing, Artificial; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D011433:Propranolol; D011446:Prospective Studies; D012804:Sick Sinus Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology; D016037:Single-Blind Method; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000000981:diagnostic imaging / Q000503:physiopathology*; D018667:Tilt-Table Test; D014463:Ultrasonography; D014636:Valsalva Maneuver
chemical_list: D001337:Autonomic Agents; D001285:Atropine; D011433:Propranolol