John P. Higgins, MD
John P. Higgins, MD, MBA, professor of cardiovascular medicine and director of Sports Cardiology at McGovern Medical School UTHealth Houston. He is also a certified personal trainer and exercise specialist.
The concept of a pacemaker began 200 years ago when Luigi Galvani, the Italian physician and biologist, used an electrical current to make a frog’s heart beat. The first pacemaker for humans was introduced in the 1950s. Today, it is estimated that up to 3 million Americans are living with a pacemaker, but pacemakers are not the only implantable electronic heart devices.
Cardiac implantable electronic devices (CIED) restore the natural electrical signals that control the beating of your heart. Conditions that disrupt these signals are called conduction disorders.
A heartbeat starts in the right upper chamber of your heat—the right atrium—in an area called the sinoatrial node (SA node). The signal then travels down a conduction pathway to a node called the atrioventricular node (AV node), which helps controls the rate of your heartbeat. Finally, the signal passes to the main pumping chambers of your heart, called your ventricles.
A pacemaker helps keep your heart rate at a normal level during rest and exercise. A pulse generator implanted under the skin of your chest or abdomen sends electrical pulses through wires, called leads, which are implanted inside one or more of your heart chambers. An electrode at the end of the lead senses your heart’s rhythm and can send an electrical pulse into your heart muscle to control it.
Seventy percent of people living with a pacemaker are over age 65. The main reason for implanting a pacemaker is to control symptoms of a heartbeat that is too slow, called bradycardia. Bradycardia may cause dizziness, weakness, a feeling of passing out called syncope, or actual passing out. When your heart beats too slowly, you may start to feel weak and lightheaded if you try to exercise, called exercise intolerance. A pacemaker may also be used to control a heartbeat that is irregular or too fast.
Conditions that cause slow or abnormal heart rhythms can be caused by disease of the SA or AV node, called heart blocks. Abnormal heart rhythms (arrhythmias) can be caused by age, heart failure, heart attack, congenital heart defects, or enlarged and thickened heart muscle called cardiomyopathy.
The procedure for implanting a pacemaker can be done with local anesthesia and sedation. In some cases, you can go home the same day or the next day. The pulse generator requires a small incision. The leads are passed through blood vessels leading to the heart. Depending on your condition, there may be one or more leads placed.
Since the first pacemaker in 1950, there have been more than 3,000 models. The most recent model is the size of a large pill. This wireless or leadless pacemaker is a small battery-powered self-contained device that is implanted directly into the heart. It does not have the traditional leads. However, the traditional pacemaker generally lasts longer and has more research on its safety and effectiveness.
The main purpose of a pacemaker is to keep your heart’s rate and rhythm normal. The main purpose of an implantable cardioverter defibrillator (ICD) is to prevent sudden cardiac death from a dangerous arrhythmia. The first ICD was approved in 1980.
The procedure for implanting an ICD is very similar to implanting a pacemaker. Like the pacemaker, the ICD has an electric pulse generator, about the size of a pocket watch, that is implanted in the chest wall with a lead connected to the heart that constantly monitors the heart rhythm. If it sees a dangerous or fast arrhythmia, like ventricular tachycardia or ventricular fibrillation, it will attempt to restore the normal rhythm by means of a shock.
Abnormal heart rhythms that start in the ventricles are more dangerous because the ventricles are the main pumping chambers of the heart, and they may stop pumping. When the brain does not get oxygenated blood, a person will suddenly pass out. Unless normal rhythm is quickly restored, death will soon follow.
ICDs are for people who are at risk for a sudden cardiac death, including people with serious heart failure and reduced pumping function (less than 35 percent). Other causes are damage from a previous heart attack, cardiomyopathy, or poor blood supply to the heart (myocardial ischemia).
Like the pacemaker, the technology for ICDs has improved. Today, most ICDs also have a pacemaker function. A subcutaneous ICD is the newest type. The pulse generator is implanted under the skin at the side of the chest below the armpit, but the lead is attached to an electrode that runs along the breastbone. Called an S-ICD, it is larger than a traditional ICD and doesn’t attach to the heart.
The left ventricular assist device (LVAD) is a pump that is implanted for patients whose hearts have become very weak (end-stage heart failure). The first LVAD was approved in 1994 as a way to keep someone with heart failure alive long enough to get a heart transplant. Because of the shortage of heart donors for transplant, LVADs are being used more and more as a bridge to a transplant.
We are now in the third generation of these pumps, and the technology has improved enough that an LVAD may be used to keep people alive who don’t want or can’t get a heart transplant. Recent statistics show that 80 to 85 percent of people living with an LVAD are still alive after one year, and 50 percent are still alive from five to 10 years without a heart transplant.
Unlike implanting a pacemaker or ICD, implanting an LVAD requires open-heart surgery and a stay in intensive care. During this surgery, a pump is placed inside or attached to the outside of the left ventricle. The pump takes over the ventricular pumping function. A tube from the pump comes out through the abdomen to attach to the pump’s control device. A person must wear the pump strapped outside along with a battery and a backup battery to keep the pump going.
The newer LVADs are getting better and better, and some patients have survived up to 13 years. People who do receive a LVAD report improved breathing, the ability to resume the activities of daily living, better sleep, and the ability to enjoy leisure time with loved ones.
People with severe renal, pulmonary, liver, or neurological disease or evidence of advanced metastatic cancer cannot receive an LVAD.
CIED technology is keeping millions of people alive who would not have survived a generation ago. If past is prologue, we can expect to see more improvements and innovations in the coming years.
