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. Method: 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. Conclusion: 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.
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