How Pacemakers Function
Pacemakers consist of a pager-sized housing device that contains a battery and the electronic circuitry that runs the device, along with one or two long thin electrical wires that travel from the pacemaker housing device to the heart. The housing device is implanted below the skin in the shoulder area. The thin wires, which can conduct electrical impulses, are then threaded from the housing device through a vein that runs in the chest, to the heart.
In some patients, only one of these long, thin electrical wires, called leads, are implanted into one of the chambers of the heart. Most patients who receive pacemakers have two leads implanted, one going to the right atrium of the heart and one going to the right ventricle of the heart (this is shown in Figure 3).
The pacemaker and leads can be programmed in several complex ways to analyze the heartbeat and then determine if the pacemaker should electrically stimulate the heart to contract.
In the most common type of program, the electrical leads implanted in the right atrium and/or right ventricle can perform two functions. These leads can serve as sensors, detecting if electrical impulses generated by the SA node have occurred and if such electrical impulses have been conducted by the AV node down into the ventricle.
The same electrical leads also can transmit an electrical impulse from the pacemaker's battery down into the right atrium and/or right ventricle. If the lead implanted into the right atrium does not detect that the SA node has fired and created an electrical impulse, the pacemaker sends an electrical impulse to the right atrium, taking over the function of being the heart's "spark plug."
If the lead implanted into the right ventricle does not detect that an electrical impulse has made it through the AV node down into the ventricle, the pacemaker generates an electrical impulse that is conducted via the electrical lead in the right ventricle to the ventricles. In this manner, the pacemaker "supervises" the heart and ensures that it continues to contract at a rate adequate to pump sufficient blood throughout the body.
Pacemaker Implantation Procedure
In most cases, the physician who is to implant the pacemaker meets with the patient before the surgery to discuss the procedure. Pacemaker implantation usually takes about an hour to perform. Although the surgery is a relatively safe procedure, complications do occasionally occur. Complications include bleeding at the site of pacemaker insertion, infection at the insertion site, damage to the blood vessels or lung in the chest, and perforation of one of the chambers of the heart. Death during pacemaker implantation is extremely uncommon.
Patients usually are instructed not to eat or drink anything after midnight on the day of the procedure and should ask their physician about taking medication(s) before undergoing pacemaker implantation. If the procedure is scheduled late in the day, patients may occasionally be permitted to have a very light breakfast.
After the procedure, patients usually are observed in the hospital for a day or so to make sure that bleeding or infection does not occur at the site of pacemaker implantation. In most cases, patients are monitored overnight in an intensive care or intermediate care unit where their heart beat can be continuously monitored. Patients who have a pacemaker inserted may be treated for several days with antibiotics to decrease the risk for infection.