atrial synchronous ventricular pacing (VDD) and ventricular sensing and pacing (VVI) modes and elucidate its relationship with clinical, hemodynamic and electrophysiological variables.Among 35 patients followed up in our pacemaker clinic with pacemakers implanted for CAVB 25 patients were assigned to VDD mode group and 10 patients to VVI mode group. Control group consists of 20 age and gendermatched patients with coronary artery disease and normal AV conduction. Patients of VDD pacing group did not differ by means of HRV from the Control group of patients, while patients of VVI group had significantly higher (p<0.05) values of indices of sympathetic modulation (LFNU) and sympathovagal balance (LF/HF) ratio as compared with Control and VDD groups. Multiple regression analysis demonstrated that HRV indices did not correlate with age, EF, time from implantation of pacemaker but were significantly related with cardiac output and mean PR interval in patients with VDD mode of pacing.Thus, atrial synchronous ventricular pacing normalizes autonomic control of heart rate in patients with CAVB being the same as in patients with normal AV conduction, possibly through preservation of the atrioventricular electrical and hemodynamic sequences, while VVI mode is characterized by higher response of the sinus node to sympathetic modulation. The predictive value of the latter finding needs elucidation. P.2.9 VENTRICULAR PACING THRESHOLDS FOLLOWING HIGH-ENERGY VENTRICULAR DEFIBRILLATION SHOCKS Y. Yamanouchi, H. Urata. Fukuoka University Chikushi Hospital, JapanIncreased ventricular pacing thresholds have been observed following monophasic waveform shocks in implantable cardioverter defibrillators (icds). This study aimed to examine such changes following high-energy biphasic shocks in icds.Method: Ten episodes of VF were induced every 10 minutes in 10 pigs (23.1±3.0 kg). After 10 seconds of VF a 40J biphasic shock (total 10 shocks) was delivered for successful defibrillation in the true-bipolar sensing lead system of the ICD. Ventricular bipolar pacing thresholds before and after these shocks were evaluated at one-minute intervals.Results: The mean pacing threshold before shock delivered was 0.066 ± 0.059 uj. Those of the first, second and third minutes after the first shock were 0.052 ± 0.061 uj、0.044 ± 0.039 uj, respectively; showing that pacing thresholds gradually decreased.

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