Ask Dr. K: Pacemakers have become smaller, more reliable

The normal heart beats about 60 to 80 times a minute, with a regular rhythm. This happens because of special cells in your heart that generate electrical signals. In other words, every heart comes with its own natural “pacemaker.” When that natural pacemaker fails, a little electrical machine is placed inside you as a substitute.

The pacemaker basically does two things. First, it senses what your natural pacemaker is doing. Then, if it senses your natural pacemaker is not sending proper signals, it substitutes for your natural pacemaker and sends the signals instead. Those electrical signals are painless, and they trigger a heartbeat.

Pacemakers are programmed to meet the needs of your heart, whether it beats too fast, too slow or with an irregular rhythm.

The programmable part of the pacemaker, the little box, is called the pulse generator. It often weighs less than 1 ounce and is encased in titanium. The wires from the pulse generator to the heart are called leads. At the ends of the leads are tiny metal plates (electrodes) that attach to the inner surface of your heart. These electrodes pick up your heart’s natural electric signals and send them to the pulse generator. When the pulse generator determines that it needs to send your heart an electrical nudge, that signal travels back along the leads to your heart muscle.

During your surgery, a patch of skin on your chest, near your collarbone, will be shaved, cleaned and numbed with a local anesthetic. A 2- to 3-inch incision will be made, which provides access to a very large vein. Your doctor will thread the pacemaker leads through this vein into your heart. There, the tips of the electrodes will attach to the heart wall.

Once the electrodes are inside your heart, a type of X-ray called fluoroscopy will confirm that the electrodes are in the correct place. Your doctor will test the leads electronically to ensure they are operating properly. Then your doctor will connect the pacemaker leads to the pulse generator.

The pulse generator is usually placed below the left or right collarbone. Your doctor will create a small pocket in the skin under the collarbone incision and insert the pulse generator into this pocket. Finally, the doctor will close the incision with stitches. The entire procedure usually takes about one hour.

(I’ve put an illustration on my website, AskDoctorK.com, showing where the components of the pacemaker will be placed.)

The original pacemakers appeared in the 1960s. Since then, as the miniaturization of electronics has exploded, they have become much smaller, more reliable and capable of treating more electrical problems of the heart.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.