Bradycardia, Heart Block
There are many types of pacemaker with some helping assist the sinus node by pacing the heart’s top chambers referred to as atria, some assisting by pacing in the bottom chambers called the ventricles, and some that have three wires and can pace atria as well as both ventricles. The type selected will depend on if the main issue is with the heart’s sinus node, AV node, or both. The three wire systems, referred to as biventricular pacemakers, can help assist with sinus node, AV node, and help improve heart efficiency and ejection fraction in patients with a weakened heart (cardiomyopathy). The leadless pacemakers have no wires and are contained in a small bullet size unit. As there are no wires, there are fewer components to fail and less likelihood of infection. At the present time, these can only perform ventricular pacing. For patients who only require ventricular pacing, this is a nice option with less risk of infection, less components to fail, and with quicker recovery time as the arm restrictions that must typically be observed for a month after traditional pacemaker implant do not apply. After a traditional chest wall pacemaker implant, the patient is often advised not to do heavy lifting or extreme motions with their arm. After a leadless pacemaker, the only restriction is to avoid heavy lifting for a few days. Leadless pacemakers aren’t for everyone and may not be suitable for those who require pacing in the atria.
Pacemakers are electronic devices that help stimulate the heart to increase heart rates. The first pacemakers were made in the 1920s. These were large machines that were powered with a hand-crank. In the early 1950s, pacemakers were still very large and were powered by plugging into an outlet. It was in 1957 that the first battery powered pacemaker was produced. Early battery powered pacemakers were external with the device outside the body connected to wires in the heart. Devices evolved to pacemakers that were implantable, but were often placed in the abdomen due to their large size. As devices became smaller, they are now implanted on the chest wall through a small incision with wires placed in the heart through a small hole made in the blood vessels in the chest. The newest generation of pacemakers have no wires and are self contained. These are implanted through a small hole made in the blood vessel in the groin (femoral vein).
Bradycardia, Heart Block
The ancient Greeks called the heart beat or pulse the “sphygmos.” It was around 1580 when Geronimo Mercuriale put together the idea that passing out and low heart rates were related. Bradycardia (slow heart rate) can be due to issues with the sinus node (the natural pacemaker of the heart) or the AV node (the “wire” that connects the top and bottom chambers of the heart). If the heart rate is inappropriately slow, it can cause fatigue, dizziness, and exercise intolerance. If there is no heart rate due to complete failure, it can results in asystole (no pulse) resulting in death. Assessing slow heart rates can be through an electrocardiogram (EKG or ECG) or heart monitor (Holter monitor, hospital telemetry monitor, or extended cardiac monitor). Sometimes, an exercise treadmill test is used to assess adequacy of heart rate response to exercise.
Medtronic currently makes the only FDA approved leadless pacemakers (Micra and Micra AV). The Medtronic leadless pacemaker is implanted through the femoral vein. A small hole is made in the femoral vein (near the
groin) and a catheter (a thin tube) is advanced to the heart. Through this thin tube, the leadless pacemaker is placed in the ventricle and held in place by tines (thin wires) that embed into the heart muscle. The pacemaker is then checked using a wireless bluetooth connection and the tube is removed. There is no incision on the chest to place the pacemaker. As there are no wires and no chest incision, there are no arm activity restrictions. The main restriction is no heavy lifting for one week before resuming all usual activities.