Until now, CRT systems have been cable-based. However, a new feasibility study shows that the future may be wireless. A combination of the Micra cardiocapsule (a single-chamber pacemaker) and the new WiSE-CRT was tested. The advantage of wireless CRT systems is easier implantation and more effective synchronisation.
Cardiac resynchronisation therapy (CRT) can improve the survival of heart failure patients in whom the heart chambers are not stimulated simultaneously due to a cardiac arrhythmia, often leading to a reduction in ejection fraction (EF). A CRT system provides synchronous stimulation of the right and left ventricles via electrodes inserted into both chambers of the heart, thereby increasing cardiac output.
In a conventional wired CRT system, stimulation of the left ventricle is done via an electrode that runs in the coronary sinus veins. However, in about 8 to 10% of patients, this electrode cannot be implanted due to anatomical peculiarities. An alternative would be a wireless CRT system. There are already wireless single-chamber pacemakers, for example the Micra cardiocapsule, currently the smallest approved pacemaker. It is the size of a vitamin capsule and is inserted into the inner wall of the right ventricle via a heart catheter. So far, however, the Micra cardiocapsule does not have CRT functionality.
The recently available wireless WiSE-CRT system could help here. It consists of an electrode the size of a grain of rice, an ultrasound transmitter and a battery. The electrode is inserted into the inner wall of the left ventricle via a heart catheter. The ultrasound transmitter, which is implanted subcutaneously in the area of the apex of the heart, sends short ultrasound waves to the electrode, which are converted into electric current and lead to stimulation of the left ventricle within two milliseconds. This means that cables are no longer necessary to stimulate the left ventricle.
The special feature: The ultrasound transmitter can be coupled with existing single-chamber pacemakers of the right ventricle, for example the Micra cardiocapsule. In this way, a completely wireless CRT system can be realised. Individual case reports have already been published in which both systems have worked together successfully. However, a larger feasibility study was still pending. A team led by the French cardiologist Adrien Carabelli has therefore initiated a European study in which eight patients were treated with both systems.
All participants suffered from atrial fibrillation, heart failure and showed asynchronous contraction of the left and right ventricles. They had an indication for the Micra cardiocapsule and the WiSE-CRT system, as no conventional CRT system could be implanted due to recurrent inflammation or anatomical peculiarities. The average age of the subjects was 76 years. With the exception of one woman, only men were included in the study. At baseline, the mean EF was 28.4%. The endpoints of the retrospective study were successful implantation of the WiSE-CRT system with functioning detection of pacing from the right ventricle, acute reduction in QRS duration and no adverse events. The selected follow-up time was six months.
After implantation of both pacemakers, the WiSE-CRT system was able to successfully detect stimulation of the right ventricle via the Micra cardiocapsule and synchronously stimulate the left ventricle in all eight patients. In principle, therefore, both systems worked together.
This was also shown by the ECG data. Post-intervention, there was a significant reduction in QRS duration from 204 to 138 milliseconds (p = 0.01). After six months, there was also a significant increase in EF from 28.4% to 39.7% (p = 0.02). In four patients, EF increased by more than 10%. However, there was no evidence of improvement in the New York Heart Association (NYHA) class. One patient did not reach the follow-up date because he died of heart failure after four months. In general, however, no device-associated adverse events were observed in the study.
The data from the small pilot study show that a completely wireless CRT system is no longer a dream of the future and could soon find its way into everyday clinical practice. One advantage of the WiSE-CRT system is the endocardial insertion of the electrode. This distinguishes it from a wired CRT system, whose electrode is inserted epicardially via the cardiac veins of the coronary sinus. The result is a much more effective stimulation of the left ventricle and therefore a better EF, as the WiSE-CRT electrode can be placed more optimally and is not dependent on the course of the coronary sinus. However, the Micra and WiSE-CRT systems are still two different systems that are not perfectly matched. An ideal solution would therefore be to implant another WiSE-CRT electrode in the right ventricle instead of a Micra pacemaker. This second WiSE-CRT electrode could then also receive direct commands from the ultrasound transmitter. Thus, a completely wireless and fully synchronised ventricular action could be achieved via a "one-stop system".
Reference:
Carabelli et al. European experience with a first totally leadless cardiac resynchronisation therapy pacemaker system. EP Europace, Published: 13 December 2020, https://doi.org/10.1093/europace/euaa342