The heart’s electrical system
Your heart beats about 100 000 times a day. Each beat starts with a tiny electrical impulse from a group of special cells in the right atrium called the sinoatrial node (SA node), the heart’s natural pacemaker. The signal spreads through the heart muscle, making it squeeze and pump blood.
Sometimes this electrical system doesn’t work properly, causing an arrhythmia: a heartbeat that’s too slow, too fast or irregular. A slow heartbeat can make a person dizzy, tired or faint, and can be dangerous.
A pacemaker is a small device that sends electrical pulses to keep the heart beating at a healthy rate.
A Canadian invention
| Year | Event |
|---|---|
| 1950 | John Hopps, an electrical engineer at the National Research Council in Ottawa, working with surgeons Wilfred Bigelow and John Callaghan at the University of Toronto, builds one of the first external cardiac pacemakers |
| 1958 | First fully implanted pacemaker in Sweden (designed by Rune Elmqvist and implanted by Åke Senning); patient Arne Larsson went on to receive about 26 pacemakers and lived to age 86 |
| 1960 | Wilson Greatbatch and William Chardack implant a long-lasting pacemaker in the U.S. |
| 1970s | Lithium batteries extend pacemaker life to many years |
| 2010s | Leadless pacemakers, about the size of a large vitamin, placed directly in the heart |
Hopps’s first pacemaker was about the size of a microwave oven and plugged into a wall outlet. It sent pulses through a wire inserted into a vein to the heart. Hopps himself later needed a pacemaker and lived with one for many years.
How a modern pacemaker works
| Part | Job |
|---|---|
| Pulse generator | A small metal case (about the size of a matchbox or smaller) containing a battery and a tiny computer |
| Leads | Thin insulated wires that run through veins to the heart |
| Electrodes | Tips of the leads that sense the heart’s activity and deliver pulses |
Step by step
- The pacemaker constantly monitors the natural heart rhythm.
- If the heart is beating normally, the pacemaker does nothing.
- If the heart beats too slowly or skips a beat, the pacemaker sends a tiny electrical pulse.
- The pulse makes the heart muscle contract.
- Many pacemakers sense activity and speed up the heart during exercise.
The pacemaker is placed under the skin below the collarbone in a fairly simple surgery, usually with local anaesthetic. The battery lasts about 7–15 years, and then the generator is replaced.
Related devices
| Device | What it does |
|---|---|
| Pacemaker | Corrects slow or irregular heartbeats with small pulses |
| Implantable cardioverter-defibrillator (ICD) | Watches for dangerous fast rhythms and delivers a strong shock if needed |
| Automated external defibrillator (AED) | A portable device in public places; guides anyone to shock a heart in cardiac arrest |
| Cardiac resynchronization therapy | Coordinates the heart’s chambers in heart failure |
AEDs are found in schools, arenas, airports and malls across Canada. They give spoken instructions, so anyone can use one in an emergency.
Living with a pacemaker
Millions of people worldwide live active lives with pacemakers. They can work, exercise, travel and play sports. Some precautions:
- Keep phones and strong magnets a short distance from the device.
- Tell airport security; metal detectors may detect it.
- Some medical procedures, like certain MRI scans, require special pacemakers or precautions.
- Regular check-ups, often done wirelessly from home, monitor the battery and heart.
Engineering and medicine together
The pacemaker is a great example of engineers and doctors working together. It required:
- Electronics: transistors made small, reliable circuits possible
- Batteries: long-lasting lithium batteries
- Materials: biocompatible metals and plastics the body won’t reject
- Biology: understanding the heart’s electrical system
Common mistakes
- Thinking a pacemaker beats for the heart all the time. Most only send pulses when needed.
- Thinking pacemakers and defibrillators are the same. Pacemakers send small pulses; defibrillators deliver strong shocks.
- Thinking only older people get pacemakers. Some children and young adults need them too.
Try it yourself
- Find your pulse at your wrist. Count the beats in 15 seconds and multiply by 4. Is it between 60 and 100?
- Draw the heart and show where the SA node, the leads and the pacemaker generator would be.
- Find out where the nearest AED is in your school or community centre.
Quick recap
- The heart’s SA node sends electrical impulses that start each heartbeat.
- A pacemaker sends pulses when the heart beats too slowly or irregularly.
- Canadian engineer John Hopps built one of the first external pacemakers in 1950.
- Modern pacemakers are small, implanted devices with long-lasting batteries.
- Defibrillators deliver strong shocks for dangerous rhythms.