title: Load dependence of cardiac output in biventricular pacing: right ventricular volume overload in pigs.
abstract: BACKGROUND
  Previous work from our laboratory has demonstrated that optimization of biventricular pacing is load dependent. During acute pulmonary stenosis and right ventricular pressure overload in swine, cardiac output was maximized by pacing the right ventricle 40 ms before the left ventricle. To extend those studies, this experiment examined biventricular pacing optimization during right ventricular volume overload.
  
  
  METHODS
  After median sternotomy in 6 anesthetized domestic pigs, complete heart block was induced by ethanol ablation. A conduit was grafted from the right ventricle to the right atrium to simulate tricuspid insufficiency. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular-left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, and electrocardiogram were measured at each pacemaker setting with the graft clamped and unclamped.
  
  
  RESULTS
  Atrioventricular and right ventricular-left ventricular delays had no significant effect on cardiac output with the graft clamped. With the graft unclamped, however, there was a statistically significant (P =.003 by mixed modeling repeated measures analysis of variance) trend toward higher cardiac output with left ventricle-first pacing.
  
  
  CONCLUSIONS
  Left ventricle-first biventricular pacing in swine significantly increased cardiac output during acute tricuspid insufficiency but not during the control state. Trials are warranted to develop clinical biventricular pacing for treatment of perioperative right ventricular dysfunction.
authors.affiliation: Department of Surgery, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
authors.forename: David G
authors.initials: DG
authors.lastname: Rabkin
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Curtis
authors.forename: Santos E
authors.initials: SE
authors.lastname: Cabreriza
authors.forename: Alan D
authors.initials: AD
authors.lastname: Weinberg
authors.forename: Henry M
authors.initials: HM
authors.lastname: Spotnitz
mesh_terms: D000818:Animals; D001283:Atrioventricular Node / Q000503:physiopathology / Q000601:surgery; D002302:Cardiac Output / Q000502:physiology*; D002304:Cardiac Pacing, Artificial; D004195:Disease Models, Animal; D006325:Heart Atria / Q000503:physiopathology / Q000601:surgery; D006327:Heart Block / Q000503:physiopathology / Q000628:therapy; D006339:Heart Rate / Q000502:physiology; D006352:Heart Ventricles / Q000503:physiopathology / Q000601:surgery; D008955:Models, Cardiovascular; D013318:Stroke Volume / Q000502:physiology; D034421:Sus scrofa; D016896:Treatment Outcome; D014262:Tricuspid Valve Insufficiency / Q000503:physiopathology / Q000628:therapy; D018497:Ventricular Dysfunction, Right / Q000503:physiopathology / Q000628:therapy