Wireless Cardiac Microtubular Pacemaker Implant

Cardiac pacemakers are battery-powered, and the pacing leads can cause valve damage and infection. Furthermore, total pacemaker removal is required for battery replacement. Despite the availability of a wireless bioelectronics device to pace the epicardium, physicians must still implant the device via thoracotomy, an invasive surgical technique that requires wound healing in health care.

Shaolei Wang and a team of researchers from the University of California, Los Angeles developed a biocompatible wireless microelectronics device to build a microtubular pacemaker for intravascular implantation and pacing. Their research was reported in Science Advances.

In a porcine animal model, the pacemaker offered effective pacing to restore cardiac contraction from a non-beating heart. The microtubular pacemaker opens the door to the less invasive implantation of leadless and battery-free microelectronics for health care and heart rhythm restoration.

Advances in vascular surgery

To sustain life, microstimulators can be implanted as cardiac, stomach, neurological, and urological devices. While pacing leads are susceptible to discharge, fracture, and biofilm formation, the effort to develop battery-free leadless pacemakers for minimally invasive implantation remains an unfulfilled challenge in biomedical engineering.

Bioprosthetic valves are among the advances in catheter-based deployment for biomedical implants. Wang and colleagues developed a self-assembled, implantable microtubular pacemaker constructed of lightweight and wireless elements, with the goal of providing high electrical output and operating capacity to permit intravascular myocardial pacing and mechanical coupling.

Forming a self-assembled, microtubular pacemaker

The researchers achieved this by developing a microtubular Cardiac pacemaker to lessen the mechanical stress of pacing-related medical issues. To accept power transmission from an external transmitter, they created a wireless radiofrequency module in a thin, flexible polyimide membrane. They insulated the circuits by encapsulating the polyimide membrane with an elastomer layer and optimized power transfer efficiency to the microtubular cardiac pacemaker by constructing a radiofrequency power transmitter for electrical stimulation.

The scientists proved the ability of the microtubular device to re-energize the non-beating heart, as recorded by cardiac electrocardiograms, to restore myocardial contraction and perform wireless, and leadless myocardial stimulation after implanting the device in the anterior cardiac vein.

Designing the self-assembled microtubular Cardiac pacemaker

The self-assembled microtubular electronics were engineered to fit the circulatory anatomy and electrophysiology enabling wireless and battery-free stimulation.

The team demonstrated a proposal for intravascular implantation in which the flexible printed circuit board membrane featured two antennae, a rectifier circuit, and anode/cathode electrodes to deliver direct current pulses for myocardial stimulation. The smaller electrodes were designed to maintain an optimal current density while consuming less power during cardiac stimulation. Before delivering direct current pulses to the anode and cathode electrodes, the setup stored the direct current energy.

Optimizing the efficiency of the Cardiac pacemaker through magnetic field stimulation

Using the ANSYS program, the scientists optimized the power transfer efficiency from the

transmitter coil to the reception coil via magnetic field stimulation. They discovered that the strongest magnetic field occurs closest to the transmitter coil.

During a cardiac cycle, myocardial contraction normally causes a periodic misalignment around the original position. As a result, the alignment of the transmitter and receiver coils had an effect on the effectiveness of inductive power transfer.

In vitro testing was used to assess the strength of the inductively powered system, with the initiation and termination of radiofrequency pulses coupled to direct current pulses. They compared radiofrequency alternating current, and direct current conversion with a complete bridge rectifier using a two-circuit layout.

Wang and colleagues investigated the electrical impedance and phase of the stimulating electrodes using electrical impedance spectroscopy.

Outlook: Biocompatibility of the microtubular electronics

The researchers used an in vitro incubation experiment to examine the biocompatibility of the materials and incorporated peripheral blood mononuclear cells (PBMCs) to investigate the surface-biocompatibility and inflammatory response of a variety of materials. Granulocytes, monocytes, and lymphocytes were among the PBMC constituents that actively caused inflammation and an immunological response when exposed to a biomaterial.

The bioengineers saw no cell damage or immunological responses after incubating blood cells with materials used in the microtubular pacemaker for up to a week. In the microtubular pacemaker, the creations demonstrated hemocompatibility and immunogenicity.

Thus, the researchers investigated intravascular pacing to reestablish electromechanical coupling and blood circulation. The porcine cardiac models approximated human physiology, making them suitable for clinical translational in vivo research.

As epicardial movements, the researchers detected cardiac contraction in relation to electrical stimulation.

The self-assembled microtubular pacemaker provided an innovative method for intravascular deployment with translational impact in cardiac, gastric, and urological stimulations; eliminating the need for a charge storage unit in bioelectronics; and being suitable for open-chest thoracotomy and accelerating wound healing post-implantation.

For more information: A self-assembled implantable microtubular pacemaker for wireless cardiac electrotherapy, Science Advances (2023).

DOI: 10.1126/sciadv.adj0540