Modulation Scheme Analysis for Low-Power Leadless Pacemaker Synchronization Based on Conductive Intracardiac Communication

Conductive intracardiac communication (CIC) has been demonstrated as a promising concept for the synchronization of multi-chamber leadless cardiac pacemakers (LLPMs). To meet the 2–5 μ W power budget of a LLPM, highly specialized CIC-transceivers, which make optimal use of the cardiac communication channel, need to be developed. However, a detailed investigation of the optimal communication parameters for CIC-based LLPM synchronization is missing so far. This work analyzes the intracardiac communication performance of two low-power modulation techniques, namely On-Off-Keying (OOK) and Manchester-encoded baseband transmission (BB-MAN), as a function of the transmitted bit-energy. The bit error rate (BER) of a prototype dual-chamber LLPM was determined both in simulation and in-vitro experiments on porcine hearts. A BER of 1e − 4 was achieved with a median bit-energy in the range of 3-16 pJ (interquartile range: 4-15 pJ) for data rates from 75-500 kbps and a receiver input noise density of 7 nV/ √Hz . Both modulation schemes showed comparable performance, with BB-MAN having a slight bit-energy advantage (1-2 dB at 150-500 kbps) under equalized transceiver characteristics. This study demonstrates that reliable CIC-based LLPM synchronization is feasible at transmitted power levels < 10 nW under realistic channel conditions and receiver noise performance. Therefore, modulation techniques such, as BB-MAN or OOK, are preferable over recently proposed alternatives, such as pulse position modulation or conductive impulse signaling, since they can be realized with fewer hardware resources and smaller bandwidth requirements. Ultimately, a baseband communication approach might be favored over OOK, due to the more efficient cardiac signal transmission and reduced transceiver complexity

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

Fundamental characterization of conductive intracardiac communication for leadless multisite pacemaker systems

Objective: A new generation of leadless cardiac pacemakers effectively overcomes the main limitations of conventional devices, but only offer single-chamber pacing, although dual-chamber or multisite pacing is highly desirable for most patients. The combination of several leadless pacemakers could facilitate a leadless multisite pacemaker but requires an energy-efficient wireless communication for device synchronization. This work investigates the characteristics of conductive intracardiac communication between leadless pacemakers to provide a basis for future designs of leadless multisite pacemaker systems. Methods: Signal propagation and impedance behavior of blood and heart tissue were examined by in vitro and in vivo measurements on domestic pig hearts and by finite-element simulations in the frequency range of 1 kHz-1 MHz. Results: A better signal transmission was obtained for frequencies higher than 10 kHz. The influence of a variety of practical parameters on signal transmission could be identified. A larger distance between pacemakers increases signal attenuation. A better signal transmission is obtained through larger inter-electrode distances and a larger electrode surface area. Furthermore, the influence of pacemaker encapsulation and relative device orientation was assessed. Conclusion: This study suggests that conductive intracardiac communication is well suited to be incorporated in leadless pacemakers. It potentially offers very low power consumption using low communication frequencies. Significance: The presented technique enables highly desired leadless multisite pacing in near future

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