The beating or contraction of the heart is caused by electrical impulses. These impulses are created naturally by the heart's pacemaker cells called the sinoatrial node (SA Node) located at the right atrium of the heart. They regulate the rhythmic beating of the heart (heart rate). The normal heart rate is 60 to 80 beats a minute.
All of the cells within the heart can generate electrical impulses that trigger the heart's contractions but it is the SA Node that initiates the process. This is so because the SA Node generates the impulses faster than the other heart cells that also have this ability.
Artifical Pacemaker
When the sinoatrial node is not fast enough to regulate the heart rate or when the electrical impulses does not stimulate enough for the heart to beat, an artificial pacemaker is surgically inserted to assist in regulating the heart rate.
The pacemaker monitors the heart's natural electrical rhythm and when it does not detect a heartbeat within the normal rate, it stimulates it by emitting its own electrical impulse. The pacemaker constantly monitors this and steps in whenever the beat to beat rate goes under.
The pacemaker is surgically inserted in the left shoulder area below the collar bone (see image). Leads that transmit the impulses are inserted into the heart through the veins. The Right Ventricular lead would be positioned away from the apex (tip) of the right ventricle and up on the inter ventricular septum, below the outflow tract, to prevent deterioration of the strength of the heart.
Video: Pacemaker implantation animation
Most pacemakers are made of titanium and designed so that the body does not reject the device.
The device is hermetically sealed and contains a battery (usually a lithium ion battery) as its power source. Batteries in pacemakers usually lasts 5 to 10 years. Pacemakers with more advanced functions (such as a built-in defibrillator) lasts shorter since it consumes more power. Once the battery has spent all of its electrical energy, the pacemaker is surgically removed and replaced with a new one.
Piezoelectricity Powered Pacemaker
An experimental device converted energy from a beating heart to provide enough electricity to power a pacemaker, in a study (Abstract 15551: Vibration Powered Cardiac Rhythm Devices) presented at the American Heart Association's Scientific Sessions 2012.
The findings suggest that patients could power their pacemakers — eliminating the need for replacements when batteries are spent.
In a preliminary study, researchers tested an energy-harvesting device that uses piezoelectricity — electrical charge generated from motion. The approach is a promising technological solution for pacemakers, because they require only small amounts of power to operate, said M. Amin Karami, Ph.D., lead author of the study and research fellow in the Department of Aerospace Engineering at the University of Michigan in Ann Arbor.
Piezoelectricity might also power other implantable cardiac devices like defibrillators, which also have minimal energy needs, he said.
Today's pacemakers must be replaced every five to seven years when their batteries run out, which is costly and inconvenient, Karami said.
"Many of the patients are children who live with pacemakers for many years," he said. "You can imagine how many operations they are spared if this new technology is implemented."
Researchers measured heartbeat-induced vibrations in the chest. Then, they used a "shaker" to reproduce the vibrations in the laboratory and connected it to a prototype cardiac energy harvester they developed. Measurements of the prototype's performance, based on sets of 100 simulated heartbeats at various heart rates, showed the energy harvester performed as the scientists had predicted — generating more than 10 times the power than modern pacemakers require. The next step will be implanting the energy harvester, which is about half the size of batteries now used in pacemakers, Karami said. Researchers hope to integrate their technology into commercial pacemakers.
Two types of energy harvesters can power a typical pacemaker: linear and nonlinear. Linear harvesters work well only at a specific heart rate, so heart rate changes prevent them from harvesting enough power.
In contrast, a nonlinear harvester — the type used in the study — uses magnets to enhance power production and make the harvester less sensitive to heart rate changes. The nonlinear harvester generated enough power from heartbeats ranging from 20 to 600 beats per minute to continuously power a pacemaker. Devices such as cell phones or microwave ovens would not affect the nonlinear device, Karami said.
RELATED LINKS
Abstract 15551: Vibration Powered Cardiac Rhythm Devices
American Heart Association
University of Michigan Aerospace Engineering
American Heart Association's Scientific Sessions 2012
Artificial cardiac pacemaker
Piezoelectricity: Using Viruses and Nanotechnology To Generate Electricity
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