How Does a Pacemaker Work?

The Heart

This article will address the question of how does a pacemaker work and what it is used for. A companion article addresses the so-called Pacemaker Syndrome.

The heart is the organ responsible for ensuring that oxygenated blood is pumped to all the cells of the body and that carbon dioxide (a biological waste product) is removed from the cells. The deoxygenated (carbon dioxide rich) blood returns to the lungs where carbon dioxide is removed from the body as we breathe out. Fresh oxygen is provided to the blood via the lungs as we inhale and the cycle repeats.

Arrhythmia

If the heart does not beat efficiently, the supply of oxygen to the cells of the body can be compromised, leading to shortness of breath and extreme fatigue. There are three main conditions in which this can happen that can be helped by the implantation of a pacemaker: (a) heart failure; (b) an abnormally slow heartbeat; (c) an abnormally fast heart beat. These three conditions are all examples of arrhythmia.

In a normal, healthy individual, the heart responds to increased or decreased oxygen demand by beating faster (providing more oxygen and energy to cells) or more slowly, e.g. during periods of sleep or relaxation when the body requires less energy and oxygen. The body needs to have a mechanism which can instruct the heart to respond to these needs. The sinus node (or sinoatrial node) is a group of heart cells responsible for generating the electrical impulses which cause the heart to beat and control its frequency, thereby responding to the body’s oxygen supply needs. The normal series of electrical impulses produced by the sinus node is called a sinus rhythm and can be seen on a heart monitor. The electrical signal generated by the sinus node passes from the top of the heart downwards causing the heart muscle to contract, and pump blood, as it does so.

According to the National Institutes for Health [2], a pacemaker can be used to correct the following situations:

“Pacemakers can:

  • Speed up a slow heart rhythm.
  • Help control an abnormal or fast heart rhythm.
  • Make sure the ventricles contract normally if the atria are quivering instead of beating with a normal rhythm (a condition called atrial fibrillation).
  • Coordinate the electrical signalling between the upper and lower chambers of the heart.
  • Coordinate the electrical signalling between the ventricles. Pacemakers that do this are called cardiac resynchronization therapy (CRT) devices. CRT devices are used to treat heart failure.
  • Prevent dangerous arrhythmias caused by a disorder called long QT syndrome”.

The Pacemaker

So, just how does a pacemaker work? The function of the pacemaker is to augment the signal from the sinus node by providing low energy electrical pulses to the heart. Newer heart pacemakers have additional functionalities which permit them to record blood temperature, respiration rate and make adjustments to your heart rate as needed. This information can also be non-invasively retrieved by the physician.

A pacemaker is an electronic device which (if fitted permanently) is usually implanted in the patient’s chest or abdomen. One (or up to three) wires extend from the device and are connected to the heart, such that the electrical signal can be transmitted to the heart muscle. The device includes a battery which acts as the electrical power supply and a computerised generator which produces the signals transmitted to the heart (as needed). The pacemaker works under feedback control with signals being returned from the electrodes to the device. When an arrhythmia is detected, the computer causes the generator to send an impulse to the heart to correct the condition.

References

  1. British Heart Foundation: https://www.bhf.org.uk/living_with_a_heart_condition/treatment/pacemakers-1.aspx
  2. National Institutes of Health, Pacemakers: https://www.nhlbi.nih.gov/health/dci/Diseases/pace/pace_whatis.html