Impact of AV Sequential Pacemakers on Cardiac Hemodynamics

AV sequential cardiac pacemakers, still being used as most physiological approach on purpose, may have inadvertent effects on cardiac mechanics, mainly causing asynchronous contraction and relaxation (asnchrony). To scrutinize the issue, 15 elective coronary angiography subjects of whom 5 were deprived of any cardiac disorder that might induce asynchrony, and 10 were chronic coronary patients without prior myocardial infarction, were enrolled into the study. Mcthods: Asynchrony was assesscd on contrast left ventriculograms taken twice in 30° RAO with 50 f/sec speed and simultaneous pressure recordings, as pacing the right heart in AOO mode first (spontaneous asynchrony), and in DOO mode of same rate and possible longest AV delay next (pacemaker induced asnchrony). During a cardiac cycle, figures of each frames were divided in 8 segments by long axid and 3 semi-axes. The sum of discrepancy areas between global and 8 regional volume-time (v-t) curves, after being normalized by stroke volume and cycle length, was calculated as asnchrony index (AI), and standard deviation of times to minimal volumes of 8 segments was found as temporal asnchrony index (Alt). Diastolic filling was evaluated by atrial filling fraction (AFF), peak early filling rate (PEFR) which were derived from global v-t curves and pressure at mitral opening (Pmo), white the possible impact of intrinsic factors on asnchrony was appraised with chamber stiffness (a) and elasticity constant (k) which were obtained from volume,pressure curves. Left ventricular maximal systolic and end-diastolic pressures and volumes, dP/dt max and dP/dt min, TAU were measured as hemodynamical parameters. Pacing rates were similar between groups. DOO pacing changed none of the aforementioned values significantly in healthy group. In coronary patients, AFF increased and PEFR decreased significantly with DOO pacing (p<05, <.04, respectively). Although AI, Alt and a, k were higher compared to control group at AOO pacing, only the formers and TAU elevated significantly during DOO pacing (p<05). Moreover, changes of diastolic filling parameters had a strong correlation with only Pmo and AI (AFF-Pmo: r=.72, p<.03, PEFR-Pmo: r=.68, p<.05, AI-AFF: r=94, p<.001). Multiple regression analysis of determinants (AI, Pmo. TAU, a) indicated that AI changes had correlated only with those of TAU in each group (Control group: AI-TAU: r=.94, p<.01, coronary group: AI-TAU: r=.78, p<0.02) So it is concluded that A-V sequential pacemakers may induce significant asynchrony which may have a detrimental effect primarily on relaxation and early diasıolic filling. Spontaneous asynchrony, however, determines to what extent this will occur.