title: Immediate impairment of left ventricular mechanical performance and force-frequency relation by rate-responsive dual-chamber, but not atrial pacing: Implications from intraventricular isovolumic relaxation flow.
abstract: BACKGROUND
  Despite the maintenance of atrioventricular (AV) synchrony, the detrimental effect of left ventricular asynchronization on mechanical performance and intraventricular flow by nonphysiologic right ventricular apical pacing in dual-chamber pacing, with and without rate adaptation, is not clear.
  
  
  METHODS
  Twenty-seven consecutive patients receiving permanent pacemakers for symptomatic bradyarrhythmias (18 with DDD and 9 with AAI mode pacemakers) were evaluated with standard and tissue Doppler echocardiography before and 24 h after pacemaker implantation. The rate-response effect of pacing was studied by programmed rate with increments of 20, from 60 to 100/min.
  
  
  RESULTS
  Color M-mode echocardiography demonstrated that much more DDD patients developed new biphasic intraventricular flow during isovolumic relaxation period than AAI patients (13/18 versus 0/9, P<0.001). In DDD patients, the ventricular relaxation represented by mitral annulus velocity in early diastole significantly attenuated (before vs. after DDDR, 8.5+/-2.8 vs. 5.2+/-1.2 cm/s, P<0.05), and also the mitral flow propagation velocity (33+/-11 vs. 25+/-5 cm/s, P<0.01). The myocardial performance index increased after DDD (0.70+/-0.15 vs. 0.79+/-0.24, P<0.05) but not after AAI (0.61+/-0.1 vs. 0.59+/-0.08, P=NS). For both pacing groups, the accelerated pacing rate prolonged the isovolumic relaxation time and shortened the diastole period (P<0.001). However, only DDD patients had a decreased mitral flow propagation velocity (P=0.026) and an attenuated force-frequency relation in programmed rate acceleration.
  
  
  CONCLUSIONS
  Despite the AV synchrony, right ventricular apical pacing immediately attenuates the left ventricular contraction and relaxation performance, which deteriorated further and suppressed the physiologically positive force-frequency relation after accelerated pacing rate.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital, No. 7, Chung-Shan South Road, Taipei 10016, Taiwan.
authors.forename: Mao-Shin
authors.initials: MS
authors.lastname: Lin
authors.forename: Jiunn-Lee
authors.initials: JL
authors.lastname: Lin
authors.forename: Yen-Bin
authors.initials: YB
authors.lastname: Liu
authors.forename: Chau-Chung
authors.initials: CC
authors.lastname: Wu
authors.forename: Lung-Chun
authors.initials: LC
authors.lastname: Lin
authors.forename: Ming-Fong
authors.initials: MF
authors.lastname: Chen
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D003326:Coronary Circulation; D015150:Echocardiography, Doppler; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction; D016277:Ventricular Function, Left