Rick Schreurs

ABSTRACT Introduction In pacemaker therapie the atrioventricular (AV) delay is an important determinant of ventricular filling, and therefore hemodynamic function. However, the actual AV-delay for a ventricle depends on the site of ventricular pacing and whether the right atrium is paced or sensed. Aim of this study was to examine the role of interatrial delay (IAD) and ventricular pacing site on biventricular pump function and how to assess the AV-delay that results in the best overall cardiac pump function. Methods Experiments were performed in 7 pigs with complete AV-block. Intracardiac pressures were measured in the right (RA) and left atrium (LA) and left (LV) and right ventricle (RV). Cardiac output was measured using an aortic flow probe. IAD was determined as time difference between RA and LA dP/dt max . AV-delay optimization protocols were performed during LV, RV and biventricular (BiV) pacing during both atrial sensing (A-S) and atrial pacing (A-P). The optimal AV-delay was defined as the AV-delay with the largest increase in cardiac output compared to AV-delay 300ms. Left and right effective AV-delay were defined as the time interval between LA and LV dP/dt max and between RA and RV dP/dt max , respectively. Mean effective AV-delay was calculated as the average of right and left effective AV-delay. Results The optimal AV-delay did not differ between the 6 pacing settings. Cardiac output increased due to a combination of increased forward flow and decreased diastolic mitral regurgitation. For all ventricular pacing sites combined, P-wave width and IAD were ~40ms and 10-15ms larger during A-P compared to A-S, respectively. Optimal right (194±53ms), left (172±57ms) and mean effective AV-delay (183±54ms) were significantly longer than the optimal AV-delay as programmed by the pacemaker (155±47ms). The mean effective AV-delay corrected for heart rate was 27±7% and had the lowest coefficient of variance (0.27) to predict the optimal AV-delay over a wide variety of pacing modes. Conclusion This experimental porcine study demonstrates that IAD and interventricular dyssynchrony influence the optimal AV-delay: the optimal AV-delay increases with larger IAD (or RA pre- excitation) and with LV pre-excitation. Calculation of the mean effective AV-delay allows estimation of the optimal AV-delay, regardless of atrial pacing, atrial sensing or ventricular pacing site(s).