The Artificial Cardiac Pacemaker
The Cardiac Pacemaker also known as the "artificial pacemaker", should not to be confused with the heart’s natural pacemaker. It is a medical device designed to regulate the beating of the heart. The purpose of an artificial pacemaker is to stimulate the heart when either the heart’s native pacemaker is not fast enough or if there are blocks in the heart’s electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart, known as the ventricles.
How is the Artificial Cardiac Pacemaker Used
Artificial pacemakers can be used in order to help with and/or treat these conditions:
- Arrhythmias - an abnormal heartbeat
- Sick sinus syndrome - when the sinoatrial node does not fire properly to contract the heart
Methods of Pacing Used by an Artificial Cardiac Pacemaker
External pacemakers can be used for initial stabilization of a patient, but implantation of a permanent internal pacemaker is usually required for most conditions. External cardiac pacing is typically performed by placing two pacing pads on the chest wall. Usually one pad is placed on the upper portion of the sternum, while the other is placed along the left axilla, near the bottom of the rib cage. When an electrical impulse goes from one pad to the other, it will travel through the tissues between them and stimulate the muscles between them, including the cardiac muscle and the muscles of the chest wall. Electrically stimulating any muscle, including the heart muscle, will make it contract. The stimulation of the muscles of the chest wall will frequently make those muscles twitch at the same rate as the pacemaker is set.
It was first invented by Canadian doctor John Hopps in 1950. He studied as an electrical engineer at the University of Manitoba.
Pacing the heart via external pacing pads should not be relied upon for an extended period of time. If the person is conscious, he or she may feel discomfort due to the frequent stimulation of the muscles of the chest wall. Also, stimulation of the chest wall muscles does not necessarily mean that the heart is being stimulated as well.
Temporary Internal Pacing
An alternative to external pacing is the temporary internal pacing wire. This is a wire that is placed under sterile conditions via a central venous catheter. The distal tip of the wire is placed into either the right atrium or right ventricle. The proximal tip of the wire is attached to the pacemaker generator, outside of the body. Temporary internal pacing is often used as a bridge to permanent pacemaker placement. Under certain conditions, a person may require temporary pacing but would not require permanent pacing. In this case, a temporary pacing wire may be the optimal treatment option.
Permanent Pacemaker Placement
Placement of a permanent pacemaker involves placement of one or more pacing wires within the chambers of the heart. One end of each wire is attached to the muscle of the heart. The other end is screwed into the pacemaker generator. The pacemaker generator is a hermetically sealed device containing a power source and the computer logic for the pacemaker.
Most commonly, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest. However, the placement may vary on a case by case basis.
The outer casing of pacemakers is so designed that it will rarely be rejected by the body’s immune system. It is usually made of titanium, which is very inert in the body.
Basic Functionioning of the Artificial Cardiac Pacemaker
Modern pacemakers all have two functions. They listen to the heart’s native electrical rhythm, and if the device doesn’t sense any electrical activity within a certain time period, the device will stimulate the heart with a set amount of energy, measured in joules.
Bi-Ventricular Pacing (BVP) with an Artificial Cardiac Pacemaker
A bi-ventricular pacemaker, also known as CRT (Cardiac Resynchronization Therapy) is a type of pacemaker that can pace both ventricles (right and left) of the heart. By pacing both sides of the heart, the pacemaker can resynchronize a heart that does not beat in synchrony, which is common in heart failure patients. CRT devices has three leads, one in the Atrium, one in the right ventricle, and the last one is inserted through the coronary sinus to pace the left ventricle. CRT devices are shown to reduce mortality and improve quality of life in groups of heart failure patients.
Advances in Artificial Cardiac Pacemaker Function
When first invented, pacemakers controlled only the rate at which the heart’s two largest chambers, the ventricles, beat.
Many advancements have been made to enhance the control of the pacemaker once implanted. Many of these enhancements have been made possible by the transition to microprocessor controlled pacemakers. acemakers that control not only the ventricles but the atria as well have become common. Pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.
Rate responsive pacing allows the device to sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms.
The DAVID trial have shown that unnecessary pacing of the right ventricle can lead to heart failure. New devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease.
Another advancement in pacemaker technology is left ventricular pacing. A pacemaker wire is placed on the outer surface of the left ventricle, with the goal of more physiological pacing than what is available in standard pacemakers. This extra wire is implanted to improve symptoms in patients with severe heart failure.
Devices with Pacemaker Function
Sometimes devices resembling pacemaker, called ICDs (implantable cardioverter-defibrillators) are implanted. These devices are often used in the treatment of patients at risk for sudden cardiac death. An ICD has the ability to treat many types of heart rhythm disturbances by means of pacing, cardioversion, or defibrillation.