title: Effect of P-wave timing during supraventricular tachycardia on the hemodynamic and sympathetic neural response.
abstract: BACKGROUND
  Previous studies have shown the importance of the timing of atrial and ventricular systole on the hemodynamic response during supraventricular tachycardia (SVT). However, the reflex changes in autonomic tone during SVT remain poorly understood.
  
  
  RESULTS
  Eleven patients with permanent dual-chamber pacemakers were enrolled in the study. Arterial blood pressure (BP), central venous pressure (CVP), and peripheral muscle sympathetic nerve activity (SNA) were recorded during DDD pacing at a rate of 175 bpm (cycle length 343 ms) with an atrioventricular (AV) interval of 30, 200 and 110 ms, simulating tachycardia with near-simultaneous atrial and ventricular systole, short-RP tachycardia (RP<PR), and long-RP tachycardia (RP>PR). Each pacing run was performed for 3 minutes separated by a 5-minute recovery period. All patients demonstrated an abrupt fall in BP, an increase in CVP, and an increase in SNA regardless of the AV interval. The decreases in SBP, DBP, and MAP and the increase in CVP were significantly less during long-RP tachycardia (AV interval 110 ms) than during the other 2 pacing modes (P:<0.05), and the increase in SNA in 7 of the 11 patients was significantly greater during closely coupled atrial and ventricular systole than during long-RP tachycardia (P:<0.05).
  
  
  CONCLUSIONS
  These data suggest that the superior maintenance of hemodynamic stability during long-RP tachycardia is accompanied by reduced sympathoexcitation, which is primarily mediated by the arterial baroreceptors, with a modest cardiopulmonary vasodepressor effect.
authors.affiliation: University of Texas Southwestern Medical Center and Dallas Veterans Affairs Medical Center, Dallas, TX 75216, USA. Hamdan@ryburn.swmed.edu44195
authors.forename: M H
authors.initials: MH
authors.lastname: Hamdan
authors.forename: J D
authors.initials: JD
authors.lastname: Zagrodzky
authors.forename: R L
authors.initials: RL
authors.lastname: Page
authors.forename: S L
authors.initials: SL
authors.lastname: Wasmund
authors.forename: C J
authors.initials: CJ
authors.lastname: Sheehan
authors.forename: M M
authors.initials: MM
authors.lastname: Adamson
authors.forename: J A
authors.initials: JA
authors.lastname: Joglar
authors.forename: M L
authors.initials: ML
authors.lastname: Smith
mesh_terms: D017704:Baroreflex; D001794:Blood Pressure; D002304:Cardiac Pacing, Artificial / Q000379:methods; D004562:Electrocardiography; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D010138:Pacemaker, Artificial; D010543:Peroneal Nerve / Q000503:physiopathology; D012044:Regression Analysis; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013617:Tachycardia, Supraventricular / Q000503:physiopathology*