Acute haemodynamic effects of optimizing the A-V interval with impedance cardiography in dual-chamber stimulation Background: Optimizing the A-V interval in dual-chamber stimulation may improve haemodynamics. Haemodynamic evaluation can be conducted by invasive or non-invasive procedures. One possible method is impedance cardiography, in which changes in cardiac volumes are recorded. The objective of this study was to analyze the acute haemodynamic effects of A-V intervals programmed at different lengths in dual-chamber stimulation, ascertained by determining stroke volume with impedance cardiography. Methods: The study was carried out with 42 patients who had a dual-chamber pacemaker or dual chamber ICD implanted, and the A-V interval was optimized by impedance cardiography. Left-ventricular pump function was determined by echocardiography, and the patients were divided into a group with maintained left-ventricular pump function (EF ≥50%) and another with limited (EF <50%). The criteria for inclusion were: 1. dual-chamber pacemaker or ICD; 2. sinus rhythm, and 3. consent. In all the patients the A-V intervals were programmed from 80-120 ms in steps of 20 ms or at the standard A-V interval (150 ms) and with their own conduction system (VVI 30/min.). For each A-V interval the mean stroke volume was determined in the steady state after 1 minute at the earliest. Results: The 42 patients in the study (33 men, 9 women; average age 66.8 ± 7.7 years, min. 47, max. 84 years) showed values of 45 ± 17 % for the mean ejection fraction (EF) during echocardiography. When the A-V interval was optimized, the stroke volume showed significantly higher values (74 ± 14 p <0001) than at the standard A-V interval (65± 13.5). The least-favourable A-V interval resulted in the significantly lowest stroke volume (least-favourable A-V interval 62.0 ±11.8 ms, optimum A-V interval 74 ± 14 p<0001). On average, the optimized A-V interval was significantly shorter than the least-favourable A-V interval (optimum A-V interval 103 ms ± 25, least-favourable A-V interval 129 ± 28 ms p<0001). In patients with an EF ≥ 50%, the optimized A-V interval was significantly shorter (96 +19.5) than in patients with an EF < 50% (109.5 ± 28 p= 0.048). Conclusions: It is possible to significantly improve the stroke volume acutely, at rest, by optimizing the A-V interval. There is no such thing as a universally optimum A-V interval; it is necessary to optimize it individually, the optimized A-V interval being in the shorter A-V conduction time range in both patients with an EF of ≥ 50% and those with an EF < 50%. Patients with limited LV pump function (EF < 50%) have significantly longer optimized A-V intervals than those whose LV function is not restricted.