What are leadless pacemakers?

What are leadless pacemakers?

A pacemaker is a device used to give electrical pulses to the heart when it has slowed down. It is usually implanted underneath the skin of the chest and connected to the heart by insulated cables known as leads introduced through the blood vessels.

Weakest link in the pacemaker system is considered to be its lead, sometimes called it Achilles heel. This is because the lead system is prone for infection, fracture, failure and dislodgement.
The more the number of leads the more the complications, as in sophisticated systems like dual chamber pacemakers and biventricular pacing devices. The incidence is compounded over time with longevity of the device and the recipient. The risk of lead extraction is also significantly high in case it is needed. Hence the need for a leadless pacemaker system.

Micra Transcatheter Pacemaker System is a leadless pacemaker which can be delivered through a small hole in the groin using a delivery system through a leg vein. It is implanted in the right ventricle, the right lower chamber of the heart. The device provides a basic pulse rate at rest which can increase according to the need of the body. This function of increasing the heart rate according to the need is known as rate responsiveness and is based on an accelerometer sensor. The sensor senses movement or acceleration to be precise, and increases heart rate when you are walking or running. You may know that accelerometers are now widely used in mobile phones for apps which show your route and expected time of arrival on the screen.

In a study by Micra Transcatheter Pacing Study Group, the device was successfully implanted in 719 of 725 patients enrolled for a multicenter study. Complication rates were significantly lesser than with regular pacemaker implantations.

The initial generation of leadless pacemakers paced the right ventricle without synchronizing with the contraction of the upper chambers. Later special technology was developed to detect the contractions of the upper chambers and pace the lower chamber in synchrony. In case of conventional pacemakers this is achieved by introducing another lead in the upper chamber which increases the lead related complications. But an additional lead in the upper chamber can also be used to pace the upper chamber, which is not possible with a leadless pacemaker implanted in the right ventricle.

In a compilation of 5 studies, it was noted that leadless Micra pacemaker had 51% lower chance of complications compared with the regular pacemakers with leads. They mentioned that 98.6% of the 1376 patients implanted with Micra had good pacing performance.