Simulation of AV hysteresis pacing using an integrated dual chamber heart and pacer model.

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.

Ventricular evoked response as clinical marker for hemodynamic changes in dilative cardiomyopathy.

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.