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Disturbances of the cardiac conduction system causing reentry mechanisms above the atrioventricular (AV) node are induced by at least one accessory pathway with different conducting properties and refractory periods. This work aims to further develop the already existing and continuously expanding Offenburg heart rhythm model to visualise the most common supraventricular reentry tachycardias to provide a better understanding of the cause of the respective reentry mechanism.
The visualization of heart rhythm disturbance and atrial fibrillation therapy allow the optimization of new cardiac catheter ablations. With the simulation software CST (Computer Simulation Technology, Darmstadt) electromagnetic and thermal simulations can be carried out to analyze and optimize different heart rhythm disturbance and cardiac catheters for pulmonary vein isolation. Another form of visualization is provided by haptic, three-dimensional print models. These models can be produced using an additive manufacturing method, such as a 3D printer. The aim of the study was to produce a 3D print of the Offenburg heart rhythm model with a representation of an atrial fibrillation ablation procedure to improve the visualization of simulation of cardiac catheter ablation.
The basis of 3D printing was the Offenburg heart rhythm model and the associated simulation of cryoablation of the pulmonary vein. The thermal simulation shows the pulmonary vein isolation of the left inferior pulmonary vein with the cryoballoon catheter Arctic Front AdvanceTM from Medtronic. After running through the simulation, the thermal propagation during the procedure was shown in the form of different colors. The three-dimensional print models were constructed on the base of the described simulation in a CAD program. Four different 3D printers are available for this purpose in a rapid prototyping laboratory at the University of Applied Science Offenburg. Two different printing processes were used: 1. a binder jetting printer with polymer gypsum and 2. a multi-material printer with photopolymer. A final print model with additional representation of the esophagus and internal esophagus catheter was also prepared for printing.
With the help of the thermal simulation results and the subsequent evaluation, it was possible to make a conclusion about the propagation of the cold emanating from the catheter in the myocardium and the surrounding tissue. It could be measured that already 3 mm from the balloon surface into the myocardium the temperature drops to 25 °C. The simulation model was printed using two 3D printing methods. Both methods as well as the different printing materials offer different advantages and disadvantages. While the first model made of polymer gypsum can be produced quickly and cheaply, the second model made of photopolymer takes five times longer and was twice as expensive. On the other hand, the second model offers significantly better properties and was more durable overall. All relevant parts, especially the balloon catheter and the conduction, are realistically represented. Only the thermal propagation in the form of different colors is not shown on this model.
Three-dimensional heart rhythm models as well as virtual simulations allow a very good visualization of complex cardiac rhythm therapy and atrial fibrillation treatment methods. The printed models can be used for optimization and demonstration of cryoballoon catheter ablation in patients with atrial fibrillation.
In bimodal cochlear implant (CI) / hearing aid (HA) users a constant interaural time delay in the order of several milliseconds occurs due to differences in signal processing of the devices. For MED-EL CI systems in combination with different HA types, we have quantified the respective device delay mismatch (Zirn et al. 2015). In the current study, we investigate the effect of the device delay mismatch in simulated and actual bimodal listeners on sound localization accuracy.
To deal with the device delay mismatch in actual bimodal listeners we delayed the CI stimulation according to the measured HA processing delay and two other values. With all delay values highly significant improvements of the rms error in the localization task were observed compared to the test without the delay. The results help to narrow down the optimal patient-specific delay value.
Introduction: Cardiac resynchronization therapy (CRT) with biventricular (BV) pacing is an established therapy for heart failure (HF) patients with ventricular desynchronization and reduced left ventricular (LV) ejection fraction. The aim of this study was to evaluate electrical ventricular desynchronization with transthoracic and transesophageal signal averaging electrocardiography in HF, to better select patients for CRT.
Methods: 13 HF patients (age 68 ± 10 years; 2 females, 11 males) with New York Heart Association (NYHA) class 2.8 ± 0.5, 28.6 ± 12.6 % LV ejection fraction and 155 ± 24 ms QRS duration (QRSD) were analysed with transthoracic and transesophageal electrocardiogram recording and novel National Intruments LabView 2009 signal averaging software. Esophageal TO Osypka catheter was perorally applied to the esophagus and placed in the position of maximum LV de-flection. The 0.05-Hz high-pass filtered surface electrocardiogram and the 10-Hz high-pass filtered bipolar transesophageal electrocardiogram were recorded with Bard EP-System and 1000-Hz sampling rate.
Results: Transesophageal LV electrogram recording was possible in all HF patients (n=13). Transesophageal interventricular conduction delay (IVCD) was 51 ± 19 ms and measured between the earliest onset of QRS in the 12-channel surface electrocardiogram and the onset of the LV deflection in the transesophageal electrocardiogram. Transesophageal intra-left ventricular delay (LVCD) was 90 ± 16 ms and measured between the onset and offset of the LV deflection in the transesophageal electrocardiogram. QRSD to transesophageal IVCD ratio was 3.43 ± 1.31 ms, QRSD to transesophageal LVCD ratio was 1.75 ± 0.28 ms and QRSD was evaluated between onset and offset of QRS signal in the 12-channel surface electrocardiogram.
Conclusion: Determination of IVCD, LVCD, QRSD-to-IVCD-ratio and QRSD-to-LVCD-ratio by transesophageal LV electrogram recording with LabView 2009 signal averaging technique may be useful parameters of ventricular desynchronisation to improve patient selection for CRT.
Introduction: Cardiac resynchronization therapy (CRT) with biventricular (BV) pacing is an established therapy for heart failure (HF) patients with ventricular desynchronisation and reduced left ventricular (LV) function. The aim of this study was to evaluate preejection period (PEP) and left ventricular ejection time (LVET) with transthoracic signal averaging impedance and electrocardiography in HF patients with and without BV pacing.
Methods: 10 HF patients (age 68.9 ± 8 years; 2 females, 9 males) with New York Heart Association (NYHA) class 2,9 ± 0.5, 30.9 ± 10.5 % LV ejection fraction and 159.4 ± 22.9 ms QRS duration were analysed with transthoracic impedance and electrocardiography (Cardioscreen Medis, Ilmenau, Germany) and novel National Intruments LabView 2009 signal averaging software. One day after BV pacing device implantation, AV and VV delays were optimized by transthoracic impedance cardiography and stroke volume (SV) and cardiac output (CO) were gained by Cardioscreen.
Results: Transthoracic impedance and electrocardiography AV and VV delay opimization was possible in all HF patients with BV pacing devices (n= 10). PEP was 154 ± 24ms without BV pacing and measured between onset of QRS in the surface electrocardiogram and onset of ventricular deflection in the impedance cardiogram. LVET was 342 ± 65ms without BV pacing and measured between onset and offset of ventricular deflection in the impedance cardiogram. The use of optimal AV and VV delay BV pacing resulted in improvement of SV from 64.1 ± 26.5 ml to 94.1 ± 33.96 ml (P < 0.05) and CO from 4.05 ± 1.36 l/min to 6.44 ± 1.56 l/min (P < 0.05).
Conclusion: PEP and LVET may be useful parameters of ventricular Desynchronisation. AV and VV delay optimized BV pacing improve SV and CO. Impedance and electrocardiography with LabView 2009 signal averaging may be a simple and useful technique to optimize CRT.
BiCI users’ sensitivity to interaural phase differences for single- and multi-channel stimulation
(2016)
Biological in situ methanation: Gassing concept and feeding strategy for enhanced performance
(2017)
The expansion of fluctuating renewable electricity production from wind and solar energy requires huge storage capacities. Power-to-gas (PtG) can contribute to tackle that issue via a two-step process, the electrolytic production of hydrogen and a subsequent methanation step (with additional CO2). The resulting fully grid compatible methane, also known as synthetic natural gas (SNG), can be both stored and transported in the vast existing natural gas infrastructure.
To overcome current major drawbacks of PtG, the relatively low efficiency and the high costs, we developed an improved method for the methanation step. In our approach we use a further development of the biological in situ methanation of hydrogen in biogas plants. Because this strategy uses directly internal residual CO2 from the biogas process in the biogas plant, you neither need additional external CO2 nor special reactors. Thus, PtG is combined with the production of an upgraded highly methane rich raw biogas.
However, the low solubility of hydrogen in aqueous solutions and the exploitation of the maximum biological production rates are still an engineering challenge for high performance biological in situ methanation.
In our experiments a setup with membrane gassing turned out to be most promising to ensure a sufficient gas liquid mass transfer of the hydrogen. The monitoring of hydrogenotrophic and aceticlastic archaea showed some adaption of these microbial subgroups to the hydrogen feed.
In order to achieve high methane concentrations of more than 90 % in the raw biogas a CO2-controlled hydrogen feed flow rate is suggested. For methane concentrations lower than 90 % simple current controlled hydrogen supply can be applied.
Introduction: To simplify AV delay (AVD) optimization in cardiac resynchronization therapy (CRT), we reported that the hemodynamically optimal AVD for VDD and DDD mode CRT pacing can be approximated by individually measuring implant-related interatrial conduction intervals (IACT) in oesophageal electrogram (LAE) and adding about 50ms. The programmer-based St Jude QuickOpt algorithm is utilizing this finding. By automatically measuring IACT in VDD operation, it predicts the sensed AVD by adding either 30ms or 60ms. Paced AVD is strictly 50ms longer than sensed AVD. As consequence of those variations, several studies identified distinct inaccuracies of QuickOpt. Therefore, we aimed to seek for better approaches to automate AVD optimization.
Methods: In a study of 35 heart failure patients (27m, 8f, age: 67±8y) with Insync III Marquis CRT-D systems we recorded telemetric electrograms between left ventricular electrode and superior vena cava shock coil (LVtip/SVC = LVCE) simultaneously with LAE. By LVCE we measured intervals As-Pe in VDD and Ap-Pe in DDD operation between right atrial sense-event (As) or atrial stimulus (Ap), resp., and end of the atrial activity (Pe). As-Pe and Ap-Pe were compared with As-LA an Ap-LA in LAE, respectively.
Results: End of the left atrial activity in LVCE could clearly be recognized in 35/35 patients in VDD and 29/35 patients in DDD operation. We found mean intervals As-LA of 40.2±24.5ms and Ap-LA of 124.3±20.6ms. As-Pe was 94.8±24.1ms and Ap-Pe was 181.1±17.8ms. Analyzing the sums of As-LA + 50ms with duration of As-Pe and Ap-LA + 50ms with duration of Ap-Pe, the differences were 4.7±9.2ms and 4.2±8.6ms, resp., only. Thus, hemodynamically optimal timing of the ventricular stimulus can be triggered by automatically detecting Pe in LVCE.
Conclusion: Based on minimal deviations between LAE and LVCE approach, we proposed companies to utilize the LVCE in order to automate individual AVD optimization in CRT pacing.