H.9 Rethinking Design Features of the Leadless Atrial Pacemaker
Pacemakers are commonly implanted in patients who suffer from slow electrical rhythms in the heart. Many thousands of pacemakers are implanted per year in this country. Fundamentally, a pacemaker is comprised of a pacemaker “lead”, which is essentially an electrical cable which is threaded through a vein and screwed into the inside of the heart. The other end of the lead is connected to a pacemaker generator, which is typically placed in the subclavian region around the shoulder. The generator houses the battery and the circuitry of the pacemaker. The lead allows electrical activity in the heart to be sensed by the pacemaker and it also allows electrical current to be delivered to the heart to stimulate it, if slow heart rhythms are detected by the pacemaker.
The pacemaker lead is the Achilles heel of the system. The lead is prone to electrical and mechanical failure because of the mechanical stresses which are imposed on it. Additionally, pacemaker leads can become infected, if infections enter the bloodstream. Leads, particularly if multiple leads are present in the heart, can also lead to problems with occlusion of veins which may impede blood return to the heart.
Because of these challenges, there has been great interest in developing “leadless” pacemakers. One leadless pacemaker is commercially available (Micra, Medtronic) and another is close to approval (Nanostim, Abbott). Both designs are similar – they include a pacemaker which is shape like a pellet and affixed to the heart using either tines or a screw. The leadless pacemaker is delivered to the heart via a delivery catheter which is inserted through the femoral vein in the leg. Once the leadless pacemaker is embedded in the heart, the delivery catheter can be removed. The entire pacemaker then sits permanently inside the heart, without any leads.
[Note for students: your project can focus on any one of these challenges mentioned below. You would not be not expected to “make a leadless pacemaker”. And your project would not have to address all of these challenges below]
Current leadless pacemaker designs are well-suited to function in the right ventricle (lower chamber of the heart). However, many patients have slow electrical rhythms in the upper chamber of the heart (atrium) and current leadless designs are not well-suited for placement in the atrium. Several major challenges exist with leadless pacemakers in the atrium. First, most current designs for leadless atrial pacing have sought to place the leadless device in the right atrial appendage, which is a lobe of the right atrium. However, there are concerns about the device protruding out from the appendage into the main body of the atrium. Additionally, the atrium is relatively thin-walled compared to the ventricle and fixating the leadless device in the atrium with either a screw or tines is challenging. There are concerns of the screw or tines perforating the thin-walled atrium and causing bleeding around the heart. New approaches to fixation are needed. Lastly, the right atrial appendage is anatomically easier to approach from above (i.e. through the superior vena cava and other veins which drain blood from the upper part of the body). However, the delivery catheter for leadless pacemakers is quite large and easier to introduce into the body from below (i.e. through the inferior vena cava and femoral veins which drain the lower part of the body). The delivery catheter designs need to be reevaluated.
This proposal is intended to fundamentally rethink approaches to leadless pacemaker therapy in the atrium. Successful designs have major commercial relevance. The market for leadless pacemakers is potentially in the many billions of dollars given the large need for pacemaker therapy.