Pacemakers

A pacemaker is a small device that helps the heart maintain an adequate or normal heart rate. Sometimes hearts best too slowly, and this is known as bradycardia. Bradycardia means the heart is beating too slowly. This could be because the either the heart's innate pacemaker isn't firing fast enough or because there is some sort of abnormal block in the heart's conduction system, which causes the heart to beat too slowly. Classically pacemakers are used to speedup slow heart rates or to speed up heart rates that are bradycardic. Less commonly pacemakers are used to slow down fast heart rates. The medical term for a fast heart rate is tachycardia. Again, this is less common. Most of the time pacemakers are used to speed up slow or bradycadiac hearts. Some pacemakers can even coordinate contractions between two chambers, such as the ventricles. So, the pacemaker would, inserted at the ventricles, contract and sync with each other. Maintaining normal heart rate and making sure the ventricles contract at the same time, that's all working towards maximizing circulation. Because if the heart is going to slowly, it won't circulate blood to the body fast enough. Likewise, if the heart is pumping too quickly, there's not enough time for the ventricles to fill with blood, and therefore the hear won't pump enough blood to the rest of the body. Pacemakers typically consist of two parts. The first part is the pulse generator, which consists of a battery. The battery is what supplies power to the device and supplies the energy for the electrical signal to the heart. The other part is a control center, which is kind of like the brains of the pacemaker. The second main part of the pacemakers are the electrodes. The electrodes are basically wires that run from the pulse generator to the heart. Again, electrodes are wires that run from the pulse generator to the heart. We're gonna talk about four different kinds of pacemakers. The first type is the external pacemaker. Also, known as Transcutaneous. "Trans" means through and "cutaneous" refers to the skin, So this means "through the skin." With an external pacemaker, the pulse generator is on the outside of the body. And the wires are connected to these big pads that stick to the skin. So we have wires are connecting to the sticky pads that are just connecting to the skin. There's nothing on the inside. And the electrical signal goes through the skin, or transcutaneous. External pacers are used in emergency situations, as in code situations when the heart stops. This is because in emergencies you need to act fast, and the fastest way to pace someone is to just stick these two pads onto the skin and pace them. The second pacer we're going to talk about is the temporary Epicardial pacemaker. Epicardial refers to the epicardium, which is the out most layer of the heart. I'm high lighting in green right here. That's the epicardium. In a temporary Epicardial pacemaker you have the pulse generator on the outside of the body, and the wires are actually connected to the epicardium, or the outer most layer of the heart. The wires will have to come out somewhere in the chest wall. So temporary Epicardial pacers are usually placed during heart surgery. Why would you have this placed during heart surgery? Heart surgery is a pretty invasive procedure and the effect will have a lot of trauma at the heart and the tissue around the heart. So you're going to get a lot of inflammation of the tissue at and around the heart. The inflammation can temporarily irritate heart tissue. And this puts people at risk for having an abnormally slow heart rate or bradycardia. So the surgeon, because they might be concerned about the patient having bradycardia can insert a temporary epicardial pacemaker during surgery. Typically these epicardial pacemakers will remain in the heart until several days after the surgery. The next type of pacemaker we're going to talk about is a temporary Endocardial pacer. Endocarial refers to the endocardium, which is the inner most layer of the heart. And I'm outlining that in black here. The endocardial pacer refers to the endocardium, the inner most lining of the heart. In temporary endocardial pacers, the pulse generator is located on the outside of the body. The wires are implanted into the body via a large vein, usually in the neck, such as the subclavian or the right internal jugular. So the wires go through a large vein in the neck and are guided down to either the right atrium or the right ventricle and then from there they'll make contact with the endocardium. Temporary endocarial pacers are also known as trasvenous pacers. "Trans" means through and "venous" refers to the veins, so this pacer goes through the veins and gets down to the heart either through the atrium or the ventricle and then makes contact with the endocardium. When do you use temporary endocardial pacers? You use them in times when there's some sort of temporary heart rate abnormality that should resolve over time. For example, there could be drug induced bradycardia or slow heart rate because of drugs or medications. Or if someone gets whacked on the chest really hard, that can cause some chest trauma and av nodal irritation which can cause the heart to beat at a slow rate. Both of these resolve with time, so you don't need a permanent pacemaker, a temporary one will suffice, until the heart rate comes back to normal. You can also use a temporary endocardial pacer while you're waiting for a permanent pacer. Say somebody comes in at night and needs a permanent pacemaker, but the permanent pacemaker can't be placed until the morning. Well, they can have a temporary pacer placed overnight until morning when they can have the permanent pacemaker placed. Which brings us to the last pacemaker we're going to talk about, the permanent pacemaker. The permanent pacemaker is one where everything is internal. I'm gonna write that here (mumbling) Everything is internal. The pulse generator is usually tucked away underneath subcutaneous tissue or even muscle, and the wires are guided through the venous system into the heart. It looks a lot the temporary endocardial pacer, except the pulse generator is tucked inside the body. Everything is internal. When do you need a permanent pacemaker? In certain cases of heart block. Such as third degree heart block or advanced second degree heart block. Pacers are also indicated for certain people with symptomatic sinus bradycardia. What does that mean? It means, at baseline this patient has a slow heart rate. And the slow heart rate is causing symptoms such as fatigue or lightheadedness or passing out. Does everybody with a slow heart rate need a pacemaker? Not exactly. There's definitely people in the population, such as young athletes, that have a really slow resting heart rate. But they have a strong young heart that can compensate and still perfuse the body, even with a slow heart rate. These permanent pacemakers are good for people who have symptomatic bradcardia. Meaning that they have symptoms accompanying their slow heart rate. And these symptoms indicate that they are not circulating blood adequately to the rest of the body. Which is why they might feel fatigued or ligheaded.