The potential value of ventricular evoked response (VER) evaluation by implantable pacemakers as clinical marker for disease induced hemodynamic changes in the heart, has so far not been explicitly evaluated. We conducted a study to evaluate the reproducibility of the R spike and T wave measurements (R(VER) and T(VER)) under controlled clinical conditions and examine the correlation between VER parameters and standard echocardiographic measurements in the left ventricle. Additionally, the utility of the VER as a marker for NYHA classification and the presence of cardiomyopathy was investigated. The Physios CTM 01 pacemaker capable of recording authentic VER signal morphology, was used with low polarization fractal coated pacing leads to obtain high-fidelity VER recordings in 26 patients with conventional pacing indications (mean age: 69.1 +/- 11.8 years; 20 men). Three patients suffered from dilative cardiomyopathy (DCM), 14 from hyperthropic nonobstructive cardiomyopathy (HNCM), and nine had no myopathy but suffered from coronary artery disease (CAD). Five patients were in NYHA Class IV, 19 in Class III, and two in Class II. Mean R(VER) and T(VER) amplitudes were calculated from one-minute VER recordings. Standard echocardiography parameters were determined during this recording. Two follow-ups at a mean distance of 11.3 +/- 5.7 month were performed. The reproducibility of R(VER) or T(VER) (correlation factors: 0.992 and 0.981, respectively) was superior to the reproducibility of any echocardiographic parameter (correlation factors 0.404-0.943). There was no strong correlation between VER and any echo parameter. Both R(VER) and T(VER) were significantly reduced in NYHA Class IV patients (P < 0.05), and nearly significantly reduced in DCM versus other patients (P = 0.05-0.09). HNCM made no difference to CAD. The investigation shows that analysis of VER parameters bears a promising potential for dynamic monitoring of diseases affecting the hemodynamics, and of therapeutic effects, by means of regular, nonburdening pacemaker follow-up examinations.

Long term right ventricular apical pacing has been known to have adverse effects in cardiac function. The AV hysteresis (AVH) is a feature existing in many dual-chamber cardiac pacemakers that aims to minimize the right ventricular pacing, but its clinical efficacy remains inconclusive due to conflicting evidence from different studies. We have recently developed a novel integrated dual-chamber heart and pacer (IDHP) model, which can simulate various interactions between intrinsic heart activity and extrinsic cardiac pacing. In this study, we use the IDHP model to simulate various atrio-ventricular (AV) conduction pathologies, and to investigate the effects of an AVH algorithm on reducing right ventricular pacing. Our results show that the efficacy of AVH is dependent on the underlying cardiac conditions. While it can preserve intrinsic conduction during minor or moderate first degree AV block, its efficacy is reduced at higher degree AV block conditions. This pilot study further supports using the IDHP model to design and evaluate more advanced pacemaker algorithms for therapeutic interventions.

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.