Aim: 1) To determine by means of impedance cardiography (ICG) the “optimal” atrioventricular interval (AVI) in accordance with maximal (max) cardiac output (CO). 2) To review whether A00 pacing yields higher CO than D00 pacing does. 3) To review the influence of controlled breathing (CB) on CO.
Patients and methods: In 34 patients (pts), with sick sinus syndrome - SSS, CO was determined by ICG (Task Force Monitor CNSystems, Austria) in lying position during normal breathing (NB) and with CB of 20 breaths per minute. The PM programmed: DDD, 80 ppm (to achieve stable pacing frequency), AVI 75, 100, 120, 140, 160, 180, 250 and 300 ms (AVI programmed in random order). Equalizing phase 2 min, NB 2 min, CB 4 min. In the case of identical max CO in two adjacent AVIs the longer AVI was applied. Retest of one of AVIs was performed in 10 pts.
Results: Max CO in individual AVI (DDD, 80 ppm, n=34) - see the table. Retests confirmed the reproducibility of measured values with a deviation of ±0.1 l.min-1, during both NB and CB.
Discussion: During experimental extension of the AVI in pts with SSS there is a change in atrial contribution to ventricular filling (increase – decrease) and a change in ventricular activation pattern as presented by the QRS shape. Both factors influence CO. Higher CO with A00 vs D00 pacing was not proved. It could be caused by long atrial stimulus-QRS interval (227±51ms, 120-300ms). An unexpected result was the high number of pts with “optimal” short AVI. A proper definition of the “optimal” AVI remains a question.
Conclusion: The values of “optimal” AVI (as that causing max CO) show obvious interindividual variation (in agreement with other methods). Higher CO during A00 pacing in comparison with D00 pacing was not proved. Statistically, CO does not change significantly during CB when compared to NB. (MŠMT – MSM 0021622402)
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