Evagelismos General Hospital of Athens

Despite great technical advances over the last decades, cardiac pacing is still associated with a significant rate of complications mostly ascribed to the pacing leads. Leads are susceptible to mechanical stress, whether transvenous or epicardial, and constitute the pacing component most prone to failure; they are the major contributor to complications, may cause vascular obstruction, and other late complications, such as mechanical failure and infection, whereby extraction is required with its attendant dire consequences. Implantation of a pacemaker in young patients exposes them to high risk of subsequent lead complications, and when failed leads are replaced without extraction, the presence of multiple endocardial leads may cause major vascular morbidity. New devices for biventricular or bifocal pacing to effect cardiac resynchronization therapy (CRT) incorporating 3 leads are associated with even more problems. Hence, there came about a resurge of interest in the technology of leadless pacing. The first totally self-contained leadless pacemaker system was proposed by Spickler back n 1970 using a device powered by mercury-zinc and nuclear power that was successfully tested in animals. Almost 30 years later, Gotto et al 3 tested an automatic power-generating system (AGS) which converts kinetic into electric energy for quartz watches as a power source for cardiac pacemakers. They could demonstrate that the circuit generated pulses of 0.5 ms width at 1 Hz (60 pulses/min). The voltage of the AGS was maintained at 1.6 V while it was being charged by the accelerations. The generator supplied pulses of 0.75 V, 1.47 mA via a 510-ohm load. With fully charged AGS, the generator was also used to pace a mongrel dog's heart at 140 beats/min for 60 min. During pacing, the AGS supplied 420 mJ to the circuit and the cardiac muscle. The AGS was placed on the right ventricular wall of the dog under anesthesia. Energy of 80 mJ is stored in a capacitor by the heart beating at ~ 200 beats/min for 30 min. Thus, the AGS generated 13 microJ per heart beat. This result suggested that the AGS could supply enough energy for use in a cardiac pacemaker. Several years later, Echt at al 4 explored the feasibility and safety of a technology enabling cardiac pacing without leads in an acute porcine model. The system comprised an ultrasound transmitter delivering energy from the chest wall to a receiver-electrode in contact with the myocardium that then converted the ultrasound energy to electrical energy sufficient to pace. In feasibility studies, the receiver-electrodes were attached to the tip of a catheter to facilitate intracardiac positioning at pacing sites. In safety studies, ultrasound energy was transmitted to both chest walls, and histopathologic examinations were performed to evaluate bioeffects due to ultrasound energy transmission. In feasibility studies, direct and ultrasound-mediated electrical pacing was demonstrated at 30 sites in the right atrium, right ventricle EVAGELISMOS GENERAL HOSPITAL OF ATHENS A ́ DEPARTMENT OF CARDIOLOGY