title: Cardiac responses to left ventricular pacing in hearts with normal electrical conduction: beneficial effect of improved filling is counteracted by dyssynchrony.
abstract: Cardiac resynchronization therapy (CRT) has been proposed in heart failure patients with narrow QRS, but the mechanism of a potential beneficial effect is unknown. The present study investigated the hypothesis that left ventricular (LV) pacing increases LV end-diastolic volume (LVEDV) by allowing the LV to start filling before the right ventricle (RV) during narrow QRS in an experimental model. LV and biventricular pacing were studied in six anesthetized dogs before and after the induction of LV failure. Function was evaluated by pressures and dimensions, and dyssynchrony was evaluated by electromyograms and deformation. In the nonfailing heart, LV pacing gave the LV a head start in filling relative to the RV (P < 0.05) and increased LVEDV (P < 0.05). The response was similar during LV failure when RV diastolic pressure was elevated. The pacing-induced increase in LVEDV was attributed to a rightward shift of the septum (P < 0.01) due to an increased left-to-right transseptal pressure gradient (P < 0.05). LV pacing, however, also induced dyssynchrony (P < 0.05) and therefore reduced LV stroke work (P < 0.05) during baseline, and similar results were seen in failing hearts. Biventricular pacing did not change LVEDV, but systolic function was impaired. This effect was less marked than with LV pacing. In conclusion, pacing of the LV lateral wall increased LVEDV by displacing the septum rightward, suggesting a mechanism for a favorable effect of CRT in narrow QRS. The pacing, however, induced dyssynchrony and therefore reduced LV systolic function. These observations suggest that detrimental effects should be considered when applying CRT in patients with narrow QRS.
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway;
authors.forename: Espen
authors.initials: E
authors.lastname: Boe
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Department of Cardiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Center for Cardiological Innovation, Oslo University Hospital, Rikshospitalet, Oslo, Norway; and.
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Russell
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway; KG Jebsen Cardiac Research Center, University of Oslo, Oslo, Norway;
authors.forename: Espen W
authors.initials: EW
authors.lastname: Remme
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Department of Cardiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway;
authors.forename: Ola
authors.initials: O
authors.lastname: Gjesdal
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Department of Cardiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway; KG Jebsen Cardiac Research Center, University of Oslo, Oslo, Norway; Center for Cardiological Innovation, Oslo University Hospital, Rikshospitalet, Oslo, Norway; and Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Oslo, Norway.
authors.forename: Otto A
authors.initials: OA
authors.lastname: Smiseth
authors.affiliation: Institute for Surgical Research, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Department of Cardiology, Oslo University Hospital, Rikshospitalet, Oslo, Norway; Center for Cardiological Innovation, Oslo University Hospital, Rikshospitalet, Oslo, Norway; and helge.skulstad@rikshospitalet.no.
authors.forename: Helge
authors.initials: H
authors.lastname: Skulstad
mesh_terms: D000818:Animals; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D004195:Disease Models, Animal; D004285:Dogs; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D006346:Heart Septum / Q000503:physiopathology; D008297:Male; D013997:Time Factors; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy*; D016277:Ventricular Function, Left; D016278:Ventricular Function, Right; D017725:Ventricular Pressure
keywords: cardiac resynchronization therapy; dyssynchrony; heart failure; hemodynamics; pulmonary hypertension