Introduction: In cardiology, ECG-Holter monitoring plays an important role in the diagnosis of arrhythmias. For some purposes the surface ECG does not suffice and invasive intra-cardiac measurements are needed. In patients with pacemakers it would be ideal to use the pacemaker system to collect data. However, pacemaker sample rates and data uplink capacity impedes their use. With the digital Vitatron C- and T-series devices in combination with a dedicated Holter, a platform is available that enables high quality intra-cardiac electrogram (EGM) Holter recordings. In the Intrinsic T Study, this platform is used to collect data for the development of a rate response algorithm based on the intrinsic QT interval. Methods: A dedicated input channel of the pacemaker was configured to measure the ventricular EGM with broadband filtering (0.4 Hz to 280 Hz) without influencing the pacemaker’s functionality. The Holter records 3 sur- face ECG and two intra-cardiac EGM channels uploaded by the pacemaker. It is worn by the patient for up to 24 hours. During this time, signals are recorded during several tests (e.g. exercise test) and during daily activities. Results: Holter recordings of 29 patients were collected. In fig.1 the ECG (VR VL VF) as well as the atrial and ventricular EGM signals are shown. The signal quality permits accurate examination of the Q- and the T-wave morphology from the IEGM. Conclusion: The initial data collected in the Intrinsic T Study shows the quality of this Holter platform. This study proves that the set-up can be used to investigate the morphology of the EGM in detail. High quality, prolonged EGM recordings are feasible, opening a whole new field for research and diagnostic procedures. Fig 1: a) Ventricular paced rhythm. b) Ventricular intrinsic rhythm. P1-72 REDUCTION OF VENTRICULAR PACING IN PATIENTS WITH AV BLOCK AND SINUS NODE DISEASE: INSIGHTS FROM HOLTER ANALYSIS OF A NEW PACING MODE Carsten W. Israel, MD, Giuseppe Boriani, MD, PhD, Johan Brandt, MD, Anne M. Gillis, MD, Myriam Demas, BSc, Todd Sheldon, BSc, Helmut Pu ¨rerfellner, MD and Stefan H. Hohnloser, MD. J. W. Goethe University, Frankfurt, Germany, Universita di Bologna, Bologna, Italy, University Hospital, Lund, Sweden, University of Calgary, Calgary, Alberta, Canada, Medtronic Bakken Research Center, Maastricht, The Netherlands, Medtronic, Inc., Minneapolis, MN and Krankenhaus der Elisabethinen, Linz, Austria. Background: While large trials demonstrated deleterious effects of unneces- sary right ventricular pacing, cardiologists are reluctant to use AAI(R) pacing in patients (pts) with sinus node disease (SND) due to the risk of AV block (AVB). In pts with AVB, DDD pacing usually causes permanent ventricular pacing due to restrictions of AV delay programming. A new algorithm (Man- aged Ventricular Pacing™, MVP) allows AAI(R) pacing with automatic mode change to DDD(R) in case of AVB. The present study analyzed this algorithm by Holter telemetry in pts with AVB and SND. Methods: Pts with a DDDR pacemaker incorporating the MVP algorithm underwent Holter monitoring 1 month after implantation using a system with an antenna for continuous 24 h pacemaker telemetry. Recordings (simulta- neous surface ECGs, electrograms and marker/cycle length annotations) were analyzed with regard to frequency and accuracy of mode switches and the time in AAI(R)/DDD(R) for pts with SND or AVB. Results: In 19 pts (SND=10, AVB=9), 682 switches from AAI(R) to DDD(R) were observed. The occurrence of 1 blocked sinus beats triggered switch to DDD(R) in all instances. Pts with SND were paced in the AAI(R) mode 93% of the time, pts with AVB 48% of the time. In 4 pts with SND (40%), AVB occurred during Holter, in 2 of these due to rate increase during exercise in AAIR mode. In 5 pts with AVB (56%), AAI(R) pacing with intrinsic AV conduction was present for 90% of the recording (see Figure). Conclusion: Ventricular pacing can be minimized by the MVP algorithm for pts with SND. Intermittent AVB was observed in pts with SND rendering ventricular back-up pacing highly useful. In 56% of pts with AVB, MVP maintained AAI(R) mode with intrinsic AV conduction for 90% of the time minimizing right ventricular pacing and its potentially detrimental effects also in this patient group. P1-73 DIFFERENT DEGREE OF VENTRICULAR DYSSYNCRONY INDUCED BY RIGHT APICAL, HISSIAN AND PARA HISSIAN VENTRICULAR PACING Gianni Pastore, MD, Francesco Zanon, MD, Enrico Baracca, MD, S. Aggio, MD, Mariapaola Galasso, MD, M. Carraro, MD, Alessandra Bortolazzi, MD, Tiziana Marotta, MS, Valentina Rizzo, MS and Pietro Zonzin, MD. S. Maria della Misericordia Hospital, Rovigo, Italy and Medtronic Italia, Milano, Italy. Aim of the Study: To compare the degree of ventricular dyssynchrony induced by pacing from different ventricular sites: right ventricular apical pacing (RVAP), direct His Bundle Pacing (D-HBP), para His Bundle Pacing (P-HBP). Methods: We studied 25 pts (18 male, mean age 7410) with normal QRS duration and LV ejection fraction who undergo permanent ventricular pacing at direct his bundle (D-HBP=13 pts) and in the para-hisian area (P-HBP=12 pts). In all pts a back-up pacing lead was added in the apical of RV. Echocardiographic examination and Tissue Doppler Imaging was performed at baseline and after D-HBP, P-HBP and RVAP to evaluate: 1) the mean interval time between the earliest and the latest basal LV wall motion (intra-LV delay); 2) the standard deviation of the basal segment activation time intervals (modified Yu index) 3) the electromechanical latency defined as mean interval time between onset QRS and LV basal segments (EML) movement. Results: The Table summarizes the values at baseline after D-HBP, P-HBP and RVAP. Conclusions: The RVAP induced a major degree of ventricular dyssyn- chrony. The P-HBP did not significantly increase the Intra-LV delay however it produced a similar increase of EML compared with RVAP. Only the D-HBP maintained the normal electrical and mechanical activa- tion of the left ventricle S131 Poster 1