Cardiac pacemakers have been the standard therapy for patients with bradyarrhythmias for several decades. The pacing lead is an integral part of the system, serving as a conduit for the delivery of energy pulses to stimulate the myocardium. However, it is also the Achilles' heel of pacemakers, being the direct cause of most device complications both acutely during implant and chronically years afterwards. Leadless pacing with ultrasound-mediated energy has been demonstrated in animals and humans to be safe and feasible in acute studies. Implantable defibrillators revolutionised the treatment and prevention of sudden cardiac death. Subcutaneous implantable defibrillators have been under development for more than 10 years. A permanent implantable system has been shown to be feasible in treating induced and spontaneous ventricular tachyarrhythmias. These developments and recent advances in pacing and defibrillation will arouse further interest in the research and development of leadless cardiac implantable electronic devices.
All pacing leads are associated with complications such as infection, fracture, failure and dislodgement. Lead extraction is a high-risk procedure. With new device systems that often require implantation of multiple leads and with patients living longer, the incidence of lead complications is becoming compounded over time.1 Therefore, there is a strong demand to develop a pacing system that eliminates the pacing lead as a conduit for energy transfer. Randomised clinical trials on cardiac resynchronisation therapy have demonstrated the clinical benefits of such a system. Access to the left ventricle is achieved with the use of a pacing lead that is advanced into the coronary sinus and positioned in a coronary vein branch. Implantation of this lead is technically demanding and associated with a significant incidence of failure to implant, implantation in a suboptimal location and complications.2,3 Compared with epicardial pacing, endocardial left ventricular stimulation that minimises the conduction delay from the epicardium to the endocardium may be more physiological and therefore may give rise to greater haemodynamic benefits.4,5 Leadless pacing will enable endocardial left ventricular stimulation without the risks of systemic thromboembolism and mitral regurgitation. It will also avoid diaphragmatic stimulation and right ventricular apical pacing, enable multisite pacing and allow almost free choice of stimulation location within the left or right ventricle. It may also address challenges in paediatric pacing and allow the development of a truly magnetic resonance imaging (MRI)-compatible pacing system.
Leadless Pacing with Acoustic Energy
Many concepts have been patented for the development of a leadless pacing system. With a long history and wide application in medical technology, ultrasound energy is considered safe and was chosen to prove the concept of energy transfer. The use of ultrasound-mediated energy to drive a remotely positioned electrode for direct myocardial stimulation is the first to be reported in the medical literature. This new technology uses the mechanical-to-electrical properties of piezoelectric materials for transformation of energy.
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