Long-term validation study of a solar powered pacemaker

Contemporary cardiac pacemakers are powered by primary batteries, featuring a limited energy storage. Thus, these devices need to be replaced after a few years due to battery depletion, causing costs and exposing patients to a risk of complications. To overcome this limitation, pacemakers without primary batteries are desirable. We recently introduced a subcoutaneously implantable pacemaker that is powered by solar cells. Although covered by a skin layer, the implanted solar cells generate power, since a significant part of the light penetrates the skin. To investigate the real-life feasibility of such an implant and assess the influence of other factors such as weather or human behaviour, we established a study to determine the solar cell’s power output. A wearable irradiation measurement device that continuously measures the output power of the solar cells (3 cells in series, KXOB22-12X1L, IXYS, USA; active cell area = 3.6 cm^2) was developed. The solar cells are covered by two optical filters to mimic the optical properties of human skin. For 6 months, 32 study participants (13 female, 19 male) wore the device during their daily routine. Predominant weather and activity was described using a questionnaire for every day (608 days in total). The measured mean power was 105 ± 130 μW for summer (July-August), 66 ± 111 μW for autumn (September-October) and 27 ± 49 μW for winter (November-December). No statistically significant difference was observed between males and females. Output power was higher when the people were predominantly outside (mean power over 6 months: 182 μW outside vs. 45 μW inside, p<0.001). For every season, mean power is sufficient to power a pacemaker (power consumption ~10 μW). To increase safety, the implant features a rechargeable battery, which stores the surplus of the generated power. Thus, operation is ensured even during longer periods of darkness

Towards a Leadless Cardiac Multisite Pacemaker System

Introduction Recently, leadless pacemakers have been introduced to overcome the drawbacks associated with pacemaker leads. However, these leadless pacemakers are single-chamber systems, although dual-chamber or even multisite pacing would provide a more physiologic myocardial excitation. We aim at developing a leadless multisite pacemaker system, featuring several single leadless pacemakers (e.g. one in the right atrium and one in the right ventricle) that communicate wirelessly with each other. To retain the pacemakers’ longevity, it is crucial that the communication method is power efficient (modern pacemakers consume only 5-10 µW of power). Method We implemented conductive intra body communication (IBC) into a leadless multisite pacemaker system. IBC makes use of the electrical conductivity of tissue, i.e. uses the myocardium as signal carrier. In a first step, we electrically characterized the myocardium of porcine hearts by performing in-vivo and in-vitro impedance measurements in the frequency range from 10 kHz to 18 MHz. Based on the resulting transfer function, we developed prototypes of communication modules that are optimized for communication via the myocardial tissue. Results The developed leadless communication modules feature multisite pacing and are capable of performing continuous bidirectional communication between the atrium and the ventricle. The functionality of the modules was tested in-vitro and in-vivo on porcine hearts. The lowest damping of the communication signal (15-25 dB) was obtained at frequencies between 500 kHz and 2 MHz. Less than 1 µW of average power was dissipated into the tissue for synchronization. Conclusion We showed the potential of a low-power leadless communication method suitable for leadless pacemakers. By integrating this technique into leadless pacemakers, it may be possible to build a leadless multisite pacemaker system

Endocardial Energy Harvesting by Electromagnetic Induction

Abstract OBJECTIVE: cardiac pacemakers require regular medical follow-ups to ensure proper functioning. However, device replacements due to battery depletion are common and account for ∼25% of all implantation procedures. Furthermore, conventional pacemakers require pacemaker leads which are prone to fractures, dislocations or isolation defects. The ensuing surgical interventions increase risks for the patients and costs that need to be avoided. METHODS: in this study, we present a method to harvest energy from endocardial heart motions. We developed a novel generator, which converts the heart's mechanical into electrical energy by electromagnetic induction. A mathematical model has been introduced to identify design parameters strongly related to the energy conversion efficiency of heart motions and fit the geometrical constraints for a miniaturized transcatheter deployable device. The implemented final design was tested on the bench and in vivo. RESULTS: the mathematical model proved an accurate method to estimate the harvested energy. For three previously recorded heart motions, the model predicted a mean output power of 14.5, 41.9, and 16.9 μW. During an animal experiment, the implanted device harvested a mean output power of 0.78 and 1.7 μW at a heart rate of 84 and 160 bpm, respectively. CONCLUSION: harvesting kinetic energy from endocardial motions seems feasible. Implanted at an energetically favorable location, such systems might become a welcome alternative to extend the lifetime of cardiac implantable electronic device. SIGNIFICANCE: the presented endocardial energy harvesting concept has the potential to turn pacemakers into battery- and leadless systems and thereby eliminate two major drawbacks of contemporary systems

Leadless cardiac dual-chamber pacing

Background: Recently introduced leadless cardiac pacemakers effectively overcome all lead-related limitations of conventional pacemaker systems. However, these devices only feature single-chamber pacing capability although dual-chamber pacing is highly desirable due to physiologic reasons. Implanting a leadless pacemaker into the right atrium and a second one into the right ventricle would enable leadless dual chamber pacing but requires wireless communication for device synchronization. Conventional radiofrequency telemetry is not suitable for this purpose due to its high energy consumption. Thus, an ultra-low power wireless communication method is crucial to preserve the pacemaker’s longevity (modern pacemakers consume only 5-10 µW of power). Purpose: Dual-chamber pacing capability for leadless pacemakers. Methods: Two pacemakers were developed that feature bidirectional wireless communication. Intra-body communication was implemented as communication method. This method uses the electrical conductivity of blood and tissue: the data from one device is modulated and applied as a small alternating current signal to the myocardial tissue and blood via electrodes. The signal is registered almost simultaneously by the other device. The communication frequency is ~100 kHz and therefore does not influence the heart’s functioning. The pacemakers feature an electrode pair for bipolar stimulation, the communication is performed over the same electrodes. The pacemakers were tested in an acute in-vivo trial on a 60 kg domestic pig. One pacemaker paced the right atrium, the other one the right ventricle. The atrial pacemaker served as master device and dictated the actual pacing rate, the atrioventricular (AV) pacing delay and pacing activity to the ventricular pacemaker in a wireless manner. Results: The pacemakers successfully performed dual-chamber pacing (D00) with wireless intra-body communication using the myocardium and blood as transmission path. No interference with the cardiac function was observed. The ECG sequence in Figure 1 shows the onset of leadless dual-chamber pacing recorded during the in-vivo trial: the atrial (A) and ventricular (V) pacing spikes are indicated by the arrows. The pacing rate was set to 120 bpm and the AV delay to 50 ms. Less than 1 µW average power was applied to the tissue for wireless communication. Conclusion: To our knowledge, this is the first report on successful leadless dual-chamber pacing during an in-vivo trial. Intra-body communication was integrated into a pacemaker system and has proven to be a promising, power-efficient wireless communication method for leadless dual-chamber pacemakers

Towards Batteryless Cardiac Implantable Electronic Devices – The Swiss Way

Energy harvesting devices are widely discussed as an alternative power source for todays active implantable medical devices. Repeated battery replacement procedures can be avoided by extending the implants life span, which is the goal of energy harvesting concepts. This reduces the risk of complications for the patient and may even reduce device size. The continuous and powerful contractions of a human heart ideally qualify as a battery substitute. In particular, devices in close proximity to the heart such as pacemakers, defibrillators or bio signal (ECG) recorders would benefit from this alternative energy source. The clockwork of an automatic wristwatch was used to transform the hearts kinetic energy into electrical energy. In order to qualify as a continuous energy supply for the consuming device, the mechanism needs to demonstrate its harvesting capability under various conditions. Several in-vivo recorded heart motions were used as input of a mathematical model to optimize the clockworks original conversion efficiency with respect to myocardial contractions. The resulting design was implemented and tested during in-vitro and in-vivo experiments, which demonstrated the superior sensitivity of the new design for all tested heart motions

Energy Harvesting by Subcutaneous Solar Cells: A Long-Term Study on Achievable Energy Output

Active electronic implants are powered by primary batteries, which induces the necessity of implant replacement after battery depletion. This causes repeated interventions in a patients’ life, which bears the risk of complications and is costly. By using energy harvesting devices to power the implant, device replacements may be avoided and the device size may be reduced dramatically. Recently, several groups presented prototypes of implants powered by subcutaneous solar cells. However, data about the expected real-life power output of subcutaneously implanted solar cells was lacking so far. In this study, we report the first real-life validation data of energy harvesting by subcutaneous solar cells. Portable light measurement devices that feature solar cells (cell area = 3.6 cm2) and continuously measure a subcutaneous solar cell’s output power were built. The measurement devices were worn by volunteers in their daily routine in summer, autumn and winter. In addition to the measured output power, influences such as season, weather and human activity were analyzed. The obtained mean power over the whole study period was 67 uW (=19 uW cm-2), which is sufficient to power e.g. a cardiac pacemaker