Rick Schreurs

64 Chapter 4 achieve a better understanding of the effective right and left-sided AV-delay and 4) to find a better way of predicting the optimal paced AV-delay. METHODS Experiments were performed in seven female landrace pigs weighing 60.8±2.6kg. Animal handling was performed in compliance with the Guide for the Care and Use of Laboratory Animals and in accordance with the European Community recommendations. The protocol was approved by the Dutch National Ethical Committee for Animal Handling. Animal model Animals were pre-medicated with intramuscular Zoletil (5 mg/kg). After induction with intravenous sodium thiopental (5-15 mg/kg), anaesthesia was maintained by continuous infusion of Propofol (10 mg/kg/h), Sufentanyl (5 µg/kg/h) and Rocuronium (0.1 µg/kg/h). Surface electrocardiograms were recorded from the limb lead electrodes. Two pacemaker leads were transvenously inserted in the right atrial (RA) appendage and RV apex. Total AV-block was created by X-ray guided radiofrequency ablation (MarinR, Medtronic, Heerlen, the Netherlands) of the AV-node. After left-sided thoracotomy an epicardial pacemaker lead was placed on the left ventricular (LV) lateral wall. All pacemaker leads were connected to a custom-built pacemaker system. LV and RV pressures and LV volumes were measured using 7F catheter-tip manometer and conductance catheters (CD-Leycom, Zoetermeer, the Netherlands). 4F Millar Mikro-Tip pressure catheters (Millar, Houston, Texas, USA) were used to measure right and left atrial (LA) pressures. A vascular flow probe (Transonic Europe B.V., Elsloo, the Netherlands) was mounted around the ascending aorta to determine stroke volume and (after multiplication with heart rate) cardiac output. Pacing protocol After instrumentation and hemodynamic stabilization, the pacing protocol was performed. Six pacing protocols were performed: BiV, LV lateral wall and RV apex pacing in atrial pace (A-P) and atrial sense (A-S) mode. The AV-interval was programmed between 50 and 250ms in randomized steps of 50ms. Recordings with an AV-delay of 300ms in either A-P or A-S mode were repeated after every step and the average of these measurements was considered the baseline (BL). Data analysis Data analysis was performed using custom-made MATLAB software (MathWorks, Natick, Massachusetts, USA). Hemodynamic data were recorded from the first 20 seconds after switching the AV-delay. Premature beats were excluded from the analysis. PR-interval, P-wave width and QRS duration were measured from the electrocardiogram. LV and RV maximal, end systolic and end diastolic pressures were derived from the pressure curves. LV and RV dP/dt max were defined as the maximal rate of rise of LV and RV pressure. Mean