title: Higher sympathetic nerve activity during ventricular (VVI) than during dual-chamber (DDD) pacing.
abstract: OBJECTIVE
  We determined the short-term effects of single-chamber ventricular pacing and dual-chamber atrioventricular (AV) pacing on directly measured sympathetic nerve activity.
  
  
  BACKGROUND
  Dual-chamber AV cardiac pacing results in greater cardiac output and lower systemic vascular resistance than does single-chamber ventricular pacing. However, it is unclear whether these hemodynamic advantages result in less sympathetic nervous system outflow.
  
  
  METHODS
  In 13 patients with a dual-chamber pacemaker, we recorded the electrocardiogram, noninvasive arterial pressure (Finapres), respiration and muscle sympathetic nerve activity (microneurography) during 3 min of underlying basal heart rate and 3 min of ventricular and AV pacing at rates of 60 and 100 beats/min.
  
  
  RESULTS
  Arterial pressure was lowest and muscle sympathetic nerve activity was highest at the underlying basal heart rate. Arterial pressure increased with cardiac pacing and was greater with AV than with ventricular pacing (change in mean blood pressure +/- SE: 10 +/- 3 vs. 2 +/- 2 mm Hg at 60 beats/min; 21 +/- 5 vs. 14 +/- 2 mm Hg at 100 beats/min; p < 0.05). Sympathetic nerve activity decreased with cardiac pacing and the decline was greater with AV than with ventricular pacing (60 beats/min -40 +/- 11% vs. -17 +/- 7%; 100 beats/min -60 +/- 9% vs. -48 +/- 10%; p < 0.05). Although most patients showed a strong inverse relation between arterial pressure and muscle sympathetic nerve activity, three patients with severe left ventricular dysfunction (ejection fraction < or = 30%) showed no relation between arterial pressure and sympathetic activity.
  
  
  CONCLUSIONS
  Short-term AV pacing results in lower sympathetic nerve activity and higher arterial pressure than does ventricular pacing, indicating that cardiac pacing mode may influence sympathetic outflow simply through arterial baroreflex mechanisms. We speculate that the greater incidence of adverse outcomes in patients treated with single-chamber ventricular rather than dual-chamber pacing may be due in part to increased sympathetic nervous outflow.
authors.affiliation: Department of Medicine, Hunter Holmes McGuire Department of Veterans Affairs Medical Center, Virginia Commonwealth University, Medical College of Virginia, Richmond, USA. ATAYLOR@MAIL.HRCA.HARVARD.EDU
authors.forename: J A
authors.initials: JA
authors.lastname: Taylor
authors.forename: C A
authors.initials: CA
authors.lastname: Morillo
authors.forename: D L
authors.initials: DL
authors.lastname: Eckberg
authors.forename: K A
authors.initials: KA
authors.lastname: Ellenbogen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001794:Blood Pressure; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004562:Electrocardiography; D006327:Heart Block / Q000503:physiopathology / Q000628:therapy; D006339:Heart Rate; D006801:Humans; D007866:Leg; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation; D012119:Respiration; D012804:Sick Sinus Syndrome / Q000503:physiopathology / Q000628:therapy; D013318:Stroke Volume; D013564:Sympathetic Nervous System / Q000503:physiopathology*